S&AC-TN-75-13 August 1975

INSTRUCTION BOOK FOR THE 6575 MODULATOR

Carl Olson

Stanford Linear Accelerator Center

TABLE OF CONTENTS

Section Page

Safety Precautions Equipment Specification Theory of Operation

General Information PFN Charging Circuit Pulse Forming Networks K&d of Line Clipper Hydrogen Thyratron Switch Tube Thyratron Trigger Chassis No. 1, AD 730-616

Thyratron Trigger Chassis No. 2, AD 730-617

De-Q'ing Chassis No. 1 and 2 Keep Alive Power Supply Pulse Transformer Tank Assembly and Klystron

Filament Power Supply Turn-On and Turn-Off Procedures Modulator Adjustments

Tbratron Ranging Pulse Forming Network Tuning Pulse Transformer Tank Maintenance Procedure Calibration Information

Preventive Maintenance Component Specifications List Schematics

1 4

5 8

10 11 12 16

19 22

25

26

28

30

34

39

43 44

t I 1

SAFETY PRECAUTIONS

The voltage levels present in this equipment are exceedingly dangerous. Body contact will most likely result in instant death. Since one mistake could be fatal, extreme caution should be exer- cised when working on the modulator. Interlocks and warnings signs on doors and panels should not be depended on for protection.

The safety precautions listed below must, as a minimum, be fol- lowed and strictly adhered to:

Only qualified personnel, completely familiar with the potent- ially dangerous areas should work on this equipment. Anytime doors are opened or panels removed at least one additional man must be pre- sent as a safety standby.

To gain access to the interior of the modulator first shut off and lock the high voltage breaker located on the upper left front panel. This will disconnect the 600~ AC input from the power supply trans- former.

Next remove the key from the breaker lock and use the attached door key to open the rear left-hand door of the cabinet, thereby closing a spring-loaded, two section high voltage shorting switch and discharging voltages of 20kV and 4OkV on filter and PFN capacitors, respectively. Detach the grounding stick from the doorframe and visually check continuity of the braid connection between the metal hook and the cabinet. To avoid serious injuries in case of shorting switch or series limiting resistor failure, bring the stick in con- tact with the PFN inductors, the thyratron (switch tube) anode and grid and the power supply terminal of charging choke L12. Leave the grounding hook in metal contact with the thyratron anode lead when working on the unit with the power removed. Be certain to replace the stick to its normal location prior to closing the door.

The key that opens the remaining five doors is located in a key- lock inside the cabinet on the modulator support post separating the

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left-hand rear and middle doors. Its removal opens the interlock

chain, thereby preventing turn-on of the equipment. Once access is made to the front compartment the person working

on the unit should observe certain safety precautions. The grounding

hook attached to the door must be used to ground the filter capaci- tors. It should be left in contact with the capacitors while working on the unit. Three phase, 600 volts, ac line voltage will be present

at the line side of the high voltage breaker. The modulator is equipped

with a special plexiglass shield that protects against accidental body contact with the 600 volt live potential. Personnel are warned not to remove this shield unless the external circuit breaker located at the WS distribution panel, that supplies power to the modulator

being worked on, is placed in the "Off" position and locked in this

position. The single phase 117V ac enters the modulator through two line

filters. These filters are located on the ceiling of the modulator in the front compartment. The load terminals of these filters are

exposed and could present a possible hazard should personnel be stand- ing on an object that raises him to this height. When working at this

height within the modulator, place the external single phase ac dis- tribution breaker, that supplies power to the modulator being worked on, to the "Off" position.

Working personnel are warned that the door interlock system does not remove the single phase 117'V ac from a number of components, such as fans, trigger chassis, etc. Before working on any component the circuit breaker that feeds power to this unit should be placed in the "Off" position. The single phase circuit breakers are located at the bottom of the control panel.

Trigger Chassis No. 2, AD 730-617, commonly called "5kV Driver Chassis", has lethal voltage within its confines and the utmost in caution should be observed when working on this unit. The power supply feeding the trigger PFN is rated at 5 kV and the P.FN capacitor can be charged to 10 kV. Before working on the trigger chassis, the filter capacitor C7 and PFN should be shorted to remove any possible charge.

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The control panel is mounted on a hinge and by removing its

fastening screws it,can be swung open to allow servicing the components mounted on its surface and those mounted on the relay panel imme- diately behind.

Since opening the control panel does not de-energize protective interlocks, the modulator can remain in the "On" mode with this panel open. A protective plexiglass shield has been added behind the con- trol panel to prevent personnel from accidentally getting too close to the high potential terminals present in the modulator. There is an opening around the side of the shield and personnel are warned never to inadvertently reach into the interior of the modulator through this opening since immediately behind the shield there is a potential

of 20 kV. Personnel power present in the the energized mode.

should also be cautious of the 117V ac control control and relay panels when working on them in

Remember These General Safety Rules:

1) Never touch any-thing inside the modulator cabinet unless the main breaker is shut off and the terminals and cases of all energy storing components are grounded.

2) Never work on the energized equipment with a door open unless at least one other qualified person is present as a safety back-

up*

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EQUIPMENT SPECIFICATIONS

Pulse Voltage

Pulse Current

Pulse Power

Pulse Width (meas. at 9% level)

Pulse Rise Time (meas. between the 1 and 9% level)

Pulse Fall Time (meas. between the 1 and 99$ level)

Pulse Flatness

Pulse Jitter

Pulse Amplitude Drift (with 2 5s line voltage variation)

Long Term

Short Term

250 kV (ITISX.)

256 amperes

64 megawatts (max.)

2.5 ps (min.)

0.7 ps (max.)

1.0 ps (max.)

+ 0.25% (ITBX.)

2 10 nanoseconds (max.)

+ - 1.5s per hour

2 0.25% per 5 min. period

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GENERAL INFOBMATION

The sole purpose of the SLAC 6575 Modulator is to furnish the

beam pulse via a pulse transformer to the high powered klystron. This beam pulse (modulator's output pulse) has a peak power rating of 64

megawatts, duration of 2.5 microseconds, and a maximum repetition rate of 360 pulses per second. The output level and repetition rate can be varied remotely at Central Control by adjusting the three phase input de-Q'ing reference voltage and the trigger rate to the modulator. The pulse duration and its shape are preadjusted by tuning the inductors in the modulator's pulse forming network.

The SLAC 6575 Modulator is called a "Line Type Modulator". It is so named in that it uses a capacitance - inductance network (pulse

forming network) so constructed as to electrically simulate a trans- mission line. A simplified diagram of the modulator is shown in Fig. 1. The main pulse and charging circuits have been drawn in schematic form to aid in the explanation of these circuits.

After each and every output pulse the pulse forming network (PFN) capacitors charge to twice the dc power supply voltage due to the dc resonance charging characteristics of the charging transactor and the total PFN capacity. The charging current flows from power supply ground, through the primary of the pulse transformer, the PFN inductors, the charging diodes, and transactor, to the positive side of the dc power

suPPlY* Because of the low value of inductances of the pulse trans- former primary and the PFN inductors at the charging rate they have negligible effect on the charging cycle.

The PFN capacitor retains the voltage level of twice the dc power supply voltage until the hydrogen switch tube is triggered. Once this occurs the PFN capacitors discharge through the primary of the pulse transformer, the switch tube, and the PFN inductors. Since the re- flected impedance of the klystron into the pulse transformer primary is approximately equal to the characteristic impedance of the PFN, half of the voltage on the PFN capacitors is delivered to the pulse transformer

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and half is dropped across the PFN. The time for complete discharge of the PFN to occur is approximately 3.5 microseconds. Once the discharge is complete the positive plate voltage on the hydrogen thyratron extinguishes and conduction ceases.

In addition to the main pulse and charging circuits described above there are additional supporting circuits as shown in Fig. 1. Trigger Chassis No. 1 and 2 receive the input trigger pulse and shape and amplify it to the value required to trigger the hydrogen thy- ratron switch tube.

The de-Q'ing chassis in conjunction with the SCR switch and charging transactor regulates the value of the charge placed on the PFN. Should this charge vary, the subsequent output pulse to the klystron would in turn be affected. Without some form of regulation any short term three phase line variations would show up as changes in the out- put of the dc supply which would cause the network charge to vary accordingly.

The de-Q'ing circuitry regulates as follows: The PFN voltage is reduced to a usable level by means of the voltage divider, and fed to the comparator with a dc reference voltage. (The dc reference voltage is also fed to the Variable Voltage Substation where it sets the level of the ac voltage fed to the modulators.) When the sampled PF'N voltage exceeds the dc reference voltage, the comparator generates an output pulse which is conditioned by the driver to trigger the SCR. The energy left in the charging transactor at that time is dissipated in the secondary load resistor. The PFN is left at the voltage it had prior to the time the de-Q'ing circuit fired by the reverse blocking action of the charging diode.

The de-Q'ing circuit is normally adjusted to dissipated a few percent of the charge in each cycle. It can, on a pulse-to-pulse and long term basis, regulate the,PFN voltage to O.l$.

A klystron filament power supply and a pulse transformer core bias supply are also included within the confines of the modulator. The output of both can be adjusted by controls and monitored by meters at the modulator's control panel.

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“a ’ 2

L-4 ---

-l /q

j ---------

\I$$ ,j I

1

T-

-----m

--

a.

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PFN CHARGING CIRCUIT

The PFN Charging Circuit consists of charging choke L12, Charging Diode Assembly ~~168 through CR317, and the DC Power Supply which is made up of Rectifier Transformer T20, Filter Choke, Lll, and Filter Capacitors ~62~ and ~62~.

On the charging cycle, when the thyratron is not firing and repre- sents an open circuit, the circuit can be simplified as shown below.

The.equivalent charging circuit consists of the charging choke, charging diode, a PFN, and primary winding of the pulse transformer - all in series. The pulse-forming network portion is simplified by showing only the total capacitance since-the inductance of the PFN coil and that of the pulse transformer is negligible compared to the induct- ance of the charging reactor. As can be observed, this circuit is essentially a series LC resonance circuit. The PFN capacitance will charge to approximate twice the DC power supply voltage in a time equal to half the period of circuit oscillation. Let us assume that the PFN capacitance has just discharged completely to the load and its charge and voltage is zero. The capacitor will now be charged in a sinusoidal manner as shown in the sketch below:

v. . ; Itage Pulse

DC Power Supply Level -

ov

2;rre r.t Pulse

When the voltage on the PF'N capacitors reaches the dc power supply voltage (approximately 20.8 kV), current through the charging choke ceases to increase and the surrounding magnetic field starts to collapse. This collapsing field induces a potential of approximately 20.8 kV across the transactor primary with a polarity that is series aiding with the dc power supply. This is equivalent to having the Pulse Forming Network Capacitance connected across a 41.6 kV power supply. If it were not for the Charging Diode Assembly CR168 through CR317,

this excess charge on the PFN capacitance would discharge back into the power supply at the natural series resonance frequency of the charging choke and PFN capacity. Since the excess charge cannot return to the power supply, the 41.6 kV remains on the PFN until the hydrogen thyratron is triggered.

L13 is called the despiking coil. Its name is functionally de- scriptive in that its purpose is to help to filter out transient voltage spikes from feeding back from the load into the charging diodes, charging choke and de-Q'ing circuitry.

The dc power supply consists of a delta-wye or delta-delta rect- ifier transformer that feeds a three-phase double-way solid-state rectifier followed by a choke input filter.

Filter choke Lll and filter capacitor ~62~ and B provide filtering for the 360 cps power supply ripple.

Capacitor ~61 and resistors ~263 through R268 across the secondary of T20, and ~58 through ~60 and resistors R260 through ~262 across the primary windings, help to protect the rectifier diode assembly CR10 from being damaged by transients caused by the collapse of the transf- ormer magnetizing field due to abrupt ac line disruptions.

PULSE FOFMING NETWORKS

From the previous discussion on the klystron and pulse trans- former we found that the modulator is required to provide a beam pulse of 20,800 volts at 3000 amperes for a duration of approximately 3.5 ps into the primary of the pulse transformer.

To provide such a pulse a two terminal device, called a pulse forming network (PFN), is used. The PFN simulates by the use of lumped constants of capacity and inductance the characteristics of a trans- mission line. The 6575 modulator's PFN consists of variable inductors L14 through L33 and fixed capacitors C66 through ~85. In the schematic diagram, SD 730-600, there are two separate PFN's connected in parallel shown with their associated switch tube V5.

The 6575 modulator's PFN can be separated into two sections and used with two hydrogen thyratrons or combined into one unit and used with a single large hydrogen thyratron. The pulse magnitude and duration into the primary of the pulse transformer will be the same in either case.

The PFN stores energy in the capacitors at a slow rate and discharges this energy rapidly in the form of a rectangular pulse of short duration when the hydrogen thyratron(s) is triggered. The ability of the pulse to approach a rectangular pulse and its duration depends on the circuit constants of the PFN.

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END OF LINE CLIPPER

The function of the end-of-line clipper is to remove any negative voltage that may be present on the PFN capacitors because of a momentary shorted or low impedance load. If this negative

voltage was not removed the PFN capacitors would be charged to a higher voltage during the next charging cycle. If the short re- mained this condition would get progressively worse until the modulator was shut down by the high current overload interlock.

The figure below illustrates what would happen if the load shorted, which often occurs with a klystron load, without an end-of- line clipper.

0

Overshoot I& Load snort

The components that make up the end-of-line clipper are the diode assembly, CR12 through ~~61, voltage dropping resistors, R395 through R544 and thyrite resistors ~568 through R591.

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HYDROGENTHYRATRONSWITCHTUBE _

The hydrogen thyratron V5 performs the function of an electronic switch that prevents the PFN from discharging through the pulse transformer - until the modulator is commanded to do so by an external trigger pulse applied through appropriate pulse conditioning electronics to the con- trol grid of the hydrogen thyratron.

The SLAC modulator is adapted to use two medium power or one large high power hydrogen thyratron.

The modulator is equipped with a thyratron mounting plate that will accept one large or two smaller tubes. Ample filament power is available for the single tube or the dual tube arrangement. Two reservoir supplies are also available. Early in the operation of the accelerator dual tubes were replaced with one large single one and shortly thereafter the two reservoir transformer secondaries were connected in series to provide extra voltage which is required to keep older thyratrons running.

The single and dual tubes have similar electrodes with one ex- ception. The single tube is equipped with an additional electrode called the pretrigger grid. A brief description of the thyratron physical construction and function of each of its electrodes will be given below.

The cathode is a rugged oxide coated structure heated by a filament. It is designed to furnish the required large pulse currents, 2400 amperes for the dual tubes, and 4000 amperes for the single tube.

The cathode heater voltage may be adjusted by powerstat TlO. The control grid is a far more massive affair than is found in

vacuum tubes, since it has to withstand recombination heating and bombardment of electrons and ions without a rise in temperature suf-

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ficient to cause primary grid emission. The apertures of the grid may consist of perforations of various shapes and sizes depending on the

particular tube's design. The control grid, during quiescent conditions,

is maintained at dc ground potential. At this level it effectively shields the cathode from the gradient grid and anode positive po- tentials. The tube is triggered when the control grid is driven positive 2 kV to 2.5 kV.

The gradient grid is a large structure, much like the control grid. Its function is to enable the tube to hold off greater voltages than is possible with a single grid tube. The gradient grid is connected to the mid-point tap of voltage divider, ~38 through ~138. Its voltage

is half that of the anode. As a consequence the high voltage gradient of the anode terminates on the gradient grid and is effectively shielded from the cathode.

The anode is another very large electrode. It is made large for the same reason the grids were, that is, to provide sufficient mass to dissipate the heat generated by the high pulse currents. The anode is connected directly to the positive terminal of the PF!N.

The reservoir, or hydrogen replenisher, is incorporated within the tube to provide a source of hydrogen to replace the gas lost because of gas cleanup. The reservoir consists essentially of a controlled weight of (usually) titanium hydride which is maintained at a relatively constant temperature within the tube envelope. Under these conditions titanium, hydrogen and the hydride are in thermal equilibrium and any variation of the amount of hydrogen within the tube envelope causes an adjustment of the equilibrium conditions. By this means the pressure within the envelope is maintained relatively constant. The hydride is usually contained in a metal cylinder which may be closed at one or both ends depending on the cylinder material. The capsule is heated by a separate supply. The supply is adjustable

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and its setting is critical for proper operation of the tube. Before making the reservoir voltage adjustment the operator should refer to the adjustment procedure in the "Thyratron Ranging" section of this document. This is extremely important because if it is not adjusted properly a very expensive switch tube may be destroyed.

.

The single tube has an additional electrode called the pre-trig- ger grid. This electrode is located near the cathode and is connected

to the keep-alive power supply. The pre-trigger electrode, in con- junction with the keep-alive power supply maintains a constant current of approximately 325 mA between it and the cathode. This current creates an ionized region in the proximity of the cathode. The addition of the pre-trigger electrode and the subsequent localized region of ionization improves the tube's anode delay time and anode delay time drift.

A brief discussion will now be given to summarize the operations of the hydrogen thyratron switch tube(s).

Let us assume that the PFN is charged to its maximum voltage of 41.6 kV. Since the anode is connected to the positive terminal of the PFN its potential is also 41.6 kV. The electrons leaving the ca- thode are prevented from reaching the control grid/gradient grid space by the ground potential barrier of the control grid. When the control grid is driven positive more than approximately 1 kV, it attracts electrons from the cathode which make collisions with gas atoms. Some electrons are also attracted to the gradient grid and anode, and when the electron current flow reaches sufficient energy and sufficient collisions with gas atoms occur, cumulative ionization takes place and the tube fires through. The voltage across the tube decreases to a value of 400 volts (maximum). The current passed is then largely determined by the external circuitry.

During breakdown the control grid becomes surrounded with posi- tive ions which prevent the grid from regaining control. The tube will return to its nonconducting state after removal of the anode voltage or with the application of a negative voltage for a sufficient

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time (known as the recovery time) to allow the charged particles, electrons and positive ions to recombine. The control grid poten- tial then returns to its original value, and positive voltage can be reapplied to the gradient grid and anode as the PFN charges with- out conduction taking place. The tube thereby acts as an elect- ronic switch which may be closed by the application of a positive signal to the control grid, but which can only be opened by the re- moval or reversing of anode voltage for a definite time interval.

It was mentioned earlier in the discussion of the PFN that the klystron load reflected to the pulse transformer primary is slightly larger than the PFN characteristic impedance. Such a condition creates a "positive" mismatch. This was intentionally done to pre- vent the anode from receiving a negative reflected voltage pulse from the PF'N immediately after the main output pulse. If a fairly high negative pulse did appear on the anode during the time the tube was still ionized, conduction could occur from anode to cathode which would cause damage to the cathode.

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THYRATRON TRIGGER CHASSIS NO. 1, AD 730-616

The thyratron trigger chassis AD 730-616, is comprised of a 300 volt plate power supply, a 150 volt bias power supply, a driven blocking oscillator, a cathode follower output stage, and a fault interlock and gating circuit.

The plate and bias power supplies are solid state, full wave bridge supplies. The plate supply is unregulated while the bias supply is regulated by Vl, VR150 regulator tube and R14, voltage dropping resistor.

The trigger circuit proper consists of a driven blocking os- cillator V2 and a cathode follower output stage V3. The first triode section of V2 serves the function of a pulse amplifier and buffer stage. This stage improves the pulse rise time and isolates the blocking oscillator from the external trigger supply. The second triode of V2 with its associated components performs the function of a blocking oscillator. The cathode follower output stage, V3, provides a low impedance driving source for the following stage. (Trigger Chassis No. 2).

The theory of operation of the trigger unit will now be given in greater detail: A typical trigger pulse as shown in the sche- matic diagram, SD 730-616, is applied across R18 and R20 via trigger input jack 54. This pulse should have an amplitude of 50 volts with a rise time of 50 nanoseconds. Reference to the waveforms shows that the input pulse is partially differentiated by the parallel resistance of R21 and R22 and capacitor Cy. The grid of the driver triode section of V2 is biased to -20 volts (cut off bias). The input pulse drives the grid from the -20 volt level to approximately 14 volts positive. The resultant increase of plate current flows through the primary winding of pulse transformer T17. Terminal 3 of T17 secondary winding goes positive, as the current and the ensuing magnetic flux in 1117 primary increases. This positive potential is applied to pin No. 7, grid, and drives the grid from the -26.8 volts in the positive direction. When the grid

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voltage exceeds the cutoff bias (approximately 20 volts) plate current

commences to flow. This increase of plate current through T17 primary creates additional flux to link with its secondary and output ter- tiary winding. The grid voltage rises in the positive direction in- creasing the plate current still more. This regenerative action occurs very rapidly until the tube is in saturation (the time from off to the full on state, rise time of the pulse, is dependent on the distributed capacity and leakage inductance of T17). When the grid has become positive by a few tenths of a volt, the grid im- pedance becomes of the order of a few hundred ohms imposing a heavy resistive load upon the transformer. Eventually the power dissi- pated in the grid circuit, in internal losses, and in the output tertiary winding become equal to that which can be supplied by the plate circuit. A state of temporary equilibrium is reached in which the grid voltage is held constant by a linearly changing magnetizing current in the transformer. (The flux generated by grid current flowing through the secondary winding and load current through the tertiary winding in direct opposition to the primary cancels some of the primary flux, thereby lowering the primary reactance which results in increased plate current.) During the time the grid was drawing current, capacitor Cl1 was being charged with its plate near-

est grid No. 7 going negatively. When the voltage across capacitor Cl1 exceeds the positive voltage supplied by the transformer secon- dary the grid voltage starts to decrease. As the grid drops, plate current correspondingly decreases; a further decrease in grid potential results, and regeneration again takes place until the grid is driven beyond cut-off. Because of the collapsing magnetic field and the discharge of Cl1 the grid swings negative approxi- mately 250 volts, simultaneously the plate swings positive by approximately 500 volts. The grid potential then returns to -26.8

volts and the plate to + 300 volts. The output pulse from the tertiary winding of T17 is applied across

R30 to the grids of V3 (pins 1 and 4). The grids are biased below

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cut-off (-20 volts) to -25.6 volts by voltage divider R29 and R30. The input pulse raises the grid voltage from -25.6 volts to approxi- mately 210 volts positive. The resulting turn on of plate current through cathode resistor R31 raises the cathode potential from 0 volt to 210 volts when the output 58 is loaded with a 1OK resis- tive dummy load. When the normal load (Trigger Chassis No. 2, AD 730-617) is connected to 58, the output waveform takes a diff- erent shape as shown. The output of cathode follower, V3, normally works into a 10K ohm resistor, across the grid to cathode of the KC 71A hydrogen thyratron, V4, in Trigger Chassis No. 2. V4 is a switch tube in series with a pulse forming network and a pulse transformer. The pulse forming network is charged to a potential of approximately 10 kV. When the hydrogen thyratron, V4, grid is driven positive by the output of V3 (Cathode Follower) the tube goes into conduc- tion.

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THYRATRON TRIGGER CHASSIS NO. 2, AD 730-617

The function of Thyratron Trigger Chassis No. 2, AD 730-617,

commonly called 5 kV driver, is to furnish the grid drive pulse to the high powered hydrogen thyratron switch tube V5 used to discharge the main PFN. The drive pulse is a 2 to 2.5 kV pulse of 0.2 to 0.3 microsecond rise time (10 to 70.7% level), and a pulse duration of 2 microseconds (measured at 70.7$ level).

The circuit selected to provide the output pulse described above is a scaled down version of the main high-powered pulse supply. Specifically, the circuit consists of a dc power supply, charging choke L5, charging diode CR8, pulse forming network (Zl), pulse transformer T18, hydrogen thyratron switch V4, by-pass diode CRY, and other supporting components.

The essential parts of the trigger chassis are drawn below to aid in the following discussion.

lx Paver %lpply

Charging Charging Choke Diode

v4 l Hydrogen

Thyratron

\-L

Pulse Forming Network

By-Pass Diode

Pulse Transf.

-1y-

Cn the charging cycle, when the thyratron is not firing and represents an open circuit, the circuit can be simplified as shown below.

B+

DC Power SUPPlY

Charging Charging Choke Diode

opsptip~ ,Pu& ~~~F~~~work

T Circuit Resistance

The equivalent charging circuit consists of the charging choke, charging diode, PFN, and primary winding of the pulse transformer - all in series. The pulse-forming network portion is simplified by showing only the total capacitance since the air core inductance of the coil in the network is negligible compared to the inductance of the charging reactor. As can be observed this circuit is essentially a series LC resonance circuit. The capacitor will charge to approxi- mately twice the dc power supply voltage in a time equal to half the period of the circuit oscillation. Let us assume that the PFN capacitance has just discharged completely to the load and its charge and voltage is zero. The capacitor will now be charged in a sinu- soidal manner as shown in the sketches below:

DC Power Supply Level

ov I /

Voltage Pulse

C Di Current Pulse

I

-2-

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When the voltage on the PFN capacitor reaches the dc Power Supply voltage (approximately 5 kV), current through the charging choke ceases to increase and the surrounding magnetic field starts to collapse. This collapsing field induces a potential of approxi- mately 5 kV across the charging choke with a polarity that is in series aiding with the dc power supply. This is equivalent to having the pulse forming network capacitance connected across a 10 kV power supply. If it were not for the charging diode this ex- cess charge on the PF'N capacitance would discharge back into the power supply at the natural series resonance frequency of the charg- ing choke and PFN capacity. Since the excess charge cannot return to the power supply, the 10 kV remains on the PFN until the hydrogen thyratron is triggered.

The trigger circuit is redrawn below to show the components involved when the PF'N is discharged through the load and the hydro- gen thyratron switch tube.

Hydrogen Thyratron Dl-=ms Conduction

On the discharge cycle the network approximates a charged transmission line, and circuit behavior can best be understood on this basis.

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DE-Q'ING CHASSIS NO. 1 AND 2

Before going into a description of the circuitry of the de-Q'ing Chassis 1 and 2 it would be appropriate at this time to review the function of the entire de-Q'ing system and the reason for its existence in the modulator.

The de-Q'ing system consists of de-Q'ing Chassis 1 and 2, the de-Q'ing SCR switch assembly, PS 730-567, and charging transactor, L12. The function of these components is to regulate the charge placed on the PFN capacitors. Should this charge vary, the subsequent output pulse to the klystron would in turn be affected. Without some form of regulation any short term three-phase line variations would show up as changes in the output of. the dc supply which would cause the network charge to vary accordingly.

The de-Q'ing system regulates as follows: The PFN voltage is reduced to a usable level by means of the voltage divider, ~289 through R389-C403, and fed to the comparator with a dc reference voltage. (The dc reference voltage is also fed to the Variable Voltage Sub- station where it sets the level of the ac voltage supplied to the modulators.) When the sampled PFN voltage exceeds the dc reference voltage, the comparator generates an output pulse which is conditioned by the driver electronics to trigger the SCR. The energy left in the charging transactor, L12, at that time is dissipated in the sec- ondary load resistors, ~281 through l3288. The PF'N is left at the voltage it had prior to the time the de-Q'ing circuit fired by the reverse blocking action of the charging diode.

The de-Q'ing circuit is normally adjusted to dissipate a few percent of the charge in each cycle. It can, on a pulse-to-pulse and long term basis, regulate the PFN voltage to 0.1%.

An explanation of the de-Q'ing Chassis 1 and 2 will be given below. The reader should refer to schematics SD730-704 and SD730-725. These prints, in addition to showing the circuitry, provide voltage

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levels and waveforms which will be referred to in the description below.

De-Q'ing Chassis 1 is shown on schematic SD730-704. Transistors Ql and Q2 make up the voltage comparator. A sample of the dc reference voltage that is fed to the Variable Voltage Substation enters at 525 and the sampled PFN voltage at 532. With zero voltage from the voltage divider at 532 and Q2 base, Ql remains in the conductive mode. Ql's emitter current flowing through ~560 places a reverse bias on Q2. When the sample voltage from the voltage divider on Q2 base reaches a positive voltage greater than its emitter voltage, Q2 conducts. When Q2 conducts its collector drops from approximately 15 volts to 5 volts (emitter voltage).

The collector voltage increases as shown in waveform 2 in direct relation with the increasing voltage of the test signal on Q2 base as shown in waveform 1. During the conduction period of $2, the discharge current of C240 reverse biases Q3 to cut-off. &3's collector voltage increases to approximately 15 volts and remains at this level until Q2 goes into the non-conductive mode.

The RC combination of R563, C242 and R565 differentiates the positive collector pulse of Q3. The ensuing positive pulse developed across R565 triggers Q4. The combination of Q4 and Q5 forms a com- plimentary monostable multivibrator. The positive pulse on the base of Q4 allows this transistor to conduct. It's collector current flowing through R567 drops the voltage at the base of Q5 below its emitter voltage. Q5 conducts and its collector current flowing through ~764 develops the output pulse as shown on waveform No. 5.

This positive pulse is fed back to the base of Q4 and maintains conduction of Q4 until capacitor C400 becomes charged.

When this occurs conduction through Q4 ceases, it collector current drops to practically zero, the base of Q5 raises to the emitter potentiali Q5 is turned off, and the output pulse drops to zero.

-23-

The output pulse is supplied to de-Q'ing Chassis No. 2 located on the rear wall of the modulator above the SCR Assembly. A description of de-Q'ing Chassis No. 2 will be given below. The reader should refer to schematic SD730-725.

The input stage of de-Q'ing Chassis No. 2 consists of a com- plimentary monostable multivibrator practically identical to the output stage of de-Q'ing Chassis No. 1 described above. The output pulse of the multivibrator Q6 and Q7 is fed to an emitter follower stage consisting of four transistors Q8 through Qll connected in parallel. This emitter follower stage provides the low impedance driving source required to trigger the SCR switch. The output pulse is shown in Fig. 11. Its rise time is approximately 40 nanoseconds.

The output impedance of de-Q'ing Chassis No. 2 is approximately 5.5 ohms at 60 pps and 6.8 ohms at 360 pps.

Resistor R779 was included in the circuitry to allow the unit to be checked without the necessity of having a load connected.

A unique feature of the de-Q'ing system that deserves some com- ment here is that the de-Q'ing system will not be overloaded should there be loss of dc reference voltage because of some external fault. One would naturally think that since the comparator in de-Q'ing Chassis No. 1 is triggered as soon as the sampled voltage from the divider goes positive without the presence of the dc reference voltage that this would lead to excessive dissipation in the SCR switch. This does not occur because even though a positive pulse is applied to the gate of the SCR its anode potential is still negative and hasn't reached the positive potential required for conduction to occur.

-24-

KEEP ALIVE POWER SUPPLY

The function of the Keep Alive Power Supply, AD-730-719, is to furnish essentially constant current in the neighborhood of 325 milliamperes to the pre-trigger electrode of the single tube hydrogen thyratron switch tube. (NOTE: The dual tubes are not equipped with a pre-trigger electrode.) This current, flowing between the pre- trigger electrode and the cathode, provides a localized ionization region when the switch tube is in its quiescent state. This ioni- zation region helps considerably to decrease the single switch tube anode delay time and anode delay time variation.

The Keep Alive Power Supply consists of a current limiting trans- former !E!5, a solid state bridge rectifier CR330, thyrector diode transient suppressors CR329 and CR331, filter capacitor C513, current limiting resistors R759 and ~760, Zener diode CR332, by-pass capa- citor C514, transient protectors thyrite resistors ~761 and ~762,

and spark gap SG-2. The constant current feature of this power supply is obtained by

using a current limiting transformer and heavil.y loading its secon- dary so that it approaches the short circuit condition. A typical curve of a current limiting transformer showing output voltage versus current is shown below:

-25-

PULSE TRANSFORMERTANKASSEMBLY AND KLYSTRON FILAMENT POWER SUPPLY

The pulse transformer tank which is mounted on the bottom of the klystron contains a pulse transformer, filament transformer, klystron socket, capacitive voltage divider, and assorted bypass capacitors.

The purpose of the pulse transformer is to step up the output voltage pulse of the modulator by a factor of 12 and to feed filament power to the klystron filament transformer via its two independent (bifilar) secondary windings. These pulse transformers are biased core type in which a D.C. current is fed through the primary winding in such a direction as to allow full use of the hysteresis curve during pulsing. The source of bias current is the core bias power supply consisting of T3, T4, CRIA, CRlB, Ll, ClA, ClB, ~506, and

c507. The core bias current is read on front panel meter M5 and is adjusted to 15 amperes by means of T3. There is a special stop (nylon screw) mounted on T3 to prevent reducing bias current below 12 amperes. K 19-l relay shuts the modulator off in case of loss of core bias current. If the pulse transformer is run at less than 12 amperes of core bias current: excessive heating occurs in the core which will result in failure of the pulse transformer.

The capacitive voltage divider divides the output pulse voltage (klystron cathode voltage) by a factor of 5000 for viewing and moni- toring purposes. Normally, this divider is loaded by a small pulse transformer in the M-K package in the fiat rack which causes distor- tion of the output pulse from the capacitive voltage divider. In order to accurately view the modulator output pulse, one should use 21 feet of RG 58/u cable from the pulse transformer tank and the oscilloscope input with no termination on the end of the RG 58/u

cable.

-26-

Klystron filament voltage is adjusted by means of Tl on the modulator front panel, read on meters M3 and Mb. ~18-1 is an under- current relay which turns off the modulator in the event of an open in the klystron filament circuit or unusually-low klystron filament current. Transformer T2 is specially designed to limit the maxi- mum inrush current to a cold (low resistance) klystron filament when starting up.

-27-

,“.

TURN-ON ANIYTURN-OFF PROCEDURES

In the discussion that follows we will assume initially that all circuit breakers are in the off position and all access doors are open. We will also assume that all of the various adjustments such as klystron filament, thyratron filament and thyratron reser- voir voltage, etc., have been made and the modulator previously, before this turn-on, was performing satisfactorily.

Prior to turning on the modulator the operator should receive proper clearance from the responsible individual(s). Next, each and every door should be closed and locked. The operator should observe that all grounding hooks are placed in their respective holders and not inadvertently left in contact with a hot terminal. After all doors are closed, except the rear left one, the key used to close the five doors shall be inserted into the key interlock located on the rear of the door separator between the left-hand rear and middle doors and turned to the on position. The rear left-hand door shall then be closed and locked. The key for this door is attached to the main breaker key which should now be inserted into the breaker key lock located on the upper left front panel and turned to the breaker unlocked position.

The operator shall now check to see if the j-phase and single phase ac service is connected by noting if their respective indi- cator lamps are lit. If these are off, the distribution circuit breakers feeding the modulator should be turned on after the operator has received proper clearance. Next, the main j-phase circuit breaker, and the 6, single phase, circuit breakers located on the control panel (lower front of modulator) should be turned on. The Control Power Off indicator lamp, DSl, located on the control panel should light. The Control Power On push button should now be depressed. The Control Off lamp, DSl, should go out and the Filament Time Delay lamp, DS5, should go on. After approximately 15 minutes the klystron

-28-

time delay relay should close and Ds5, Klystron Time Delay indicator lamp should go out and the green Ready lamp, DS18, should light. If

'the Ready lamp fails to light while some other lamp in the interlock chain lights up, trouble exists in the particular circuit indicated by the illuminated lamp and corrective action should be taken. After the Ready lamp lights, the high voltage may be turned on by actuating the High Voltage On push button ~18. The green Ready lamp, ~~18,

should extinguish and the red High Voltage On lamp, DSly, and if an external.trigger is applied the blue Klystron Current lamp, DS20, should light. The modulator will now deliver an output to its load. The DC Current meter, M8, and the DC Voltmeter, MYi', will indicate the average current and voltage delivered by the modulator's power supply to the PF'N and then to the load.

In addition to the protective interlocks, a special fault re- cycler circuit is incorporated. This circuit protects the modulator when certain overloads occur by momentarily interrupting the three- phase line supply to the high voltage rectifier for an adjustable time (200 milliseconds to 1 minute) and then automatically turns the modulator back on. If the fault clears itself during the momen- tary off period, the modulator will continue to operate. If, how- ever, the fault does not clear, the fault recycler will continue to interrupt the three phase line supply until a predetermined number of cycles (1 to 15) is reached. If the preset number of faults, 10 for example, do not occur within a preset time limit, 2.2 to 55 minutes, the recycler stepping switch is automatically returned to position one and the modulator continues running. Should the preset number of allowable faults occur before the allotted reset time, the modulator will be shut off and the operator will have to actuate first the Reset push button and then the HV ON push button to get the modulator back in operation. Each and every time a fault occurs, one of the four fault lamps will light during the momentary off period. Should a fault continue to exist, remedial action should be taken.

-2g-

THYRATRON RANGING

The large thyratrons in these modulators should be ranged every 100 hours, or less, during the first 500 hours of their operation and at least every 500 hours thereafter. This is because their reservoir operating point (center range) changes with time. If these tubes are run at, or below, their low reservoir point for more than a few seconds, excessive tube heating results which will cause failure of a very expensive tube. Therefore, these tubes should only be ranged by experienced electronic technicians. However, for the sake of completeness, the method is as follows: _ Plasma Detector

The Plasma Detector is connected to the antenna in the modulator by the use of an RG58 A/U cable and an RF' attenuator. The Plasma Detector is plugged into a 115V AC outlet and allowed to warm up for ten minutes. When the detector has warmed up and is sufficiently stable the button marked BALANCE should be pushed and held in. THE BALANCE ADJUST knob is then turned to bring the pointer on the meter to the red line marked RAL.

The controls marked RF GAIN and DIFF. GAIN are normally set l/4 to l/2 turn from their extreme counterclockwise position. This setting in most cases is correct in order to keep the RF from the thyratron from saturating the detector. Should those controls be set too high the amplifier saturates causing the peak of the reservoir curve to be difficult to determine accurately.

The REP. VOLTS knob should then be turned in the proper direction to bring the pointer to center scale on the meter. The detector at this point should be ready for thyratron ranging.

With the modulator operating at 180, or 360 pps, and above 15kV on the power supply meter the thyratron reservoir voltage is increased in 0.1 volt increments spaced 2 minutes apart while watching the meter pointer. During this time, depending upon the initial setting of the

-3o-

reservoir voltage, the pointer will either slowly rise to a peak and drop, or continue to drop from its initial value. It may be necessary occasionally to readjust the RED' VOLTS knob to keep the pointer on scale. As this process continues, a point will be reached at which the modulator will "kick off" frequently and nothing short of reducing reservoir voltage will allow it to run. That point is called high limit. Turn off the high voltage and reduce the reservoir 0.2 volts and wait several minutes before turning high voltage on again. The reservoir voltage is now decreased in 0.1 volt steps 2 minutes apart and the meter pointer should continue to rise until a peak is reached, which is the center reservoir point. Again it may be necessary to readjust the REF. VOLTS control to keep the pointer on scale. After passing the center reservoir point the pointer will drop as reservoir voltage is decreased. Low limit is reached when the reservoir voltage has been reduced 0.3 or 0.4 volt from the center reservoir point and is evidenced by a slight rise in the pointer. Further reduction of reservoir voltage will produce another curve like the one we just witnessed but it may damage the thyratron because operation is below low limit. That -e- second curve may confuse you because it appears to be like the proper one so be sure to find high limit first and look for center reser- voir 0.3 to 0.5 volt lower. Low limit should be found 0.6 to 0.9 volt below high limit. A typical curve would appear as follows:

The reservoir voltage should be returned to the center reser- voir point (as determined earlier) which is the proper operating point, until the next ranging operation.

If the center reservoir point as determined by the Plasma Detector is more than 0.2 volts from the center reservoir point determined during the previous ranging operation, the ranging opera- tion is suspect and another method is to be used, called Hot Ranging Technique.

Hot Ranging Technique

With the modulator operating 180 pps, or higher, and above 15kV on the power supply meter, raise the reservoir voltage 0.1 volt every two minutes until a reservoir voltage is reached at which the modulator will not keep operating without "kicking out". Note this voltage; it is high limit. Reduce the reservoir voltage 0.2 volt and wait a few minutes before turning HV back on. Reduce reservoir voltage in 0.1 volt steps every two minutes while observing the thyratron grid voltage waveform on an oscilloscope. A point will be reached where the waveform looks "hairy" with many small voltage spikes on it. Shut the modulator off immediately. Note this voltage; it is low limit. Set the reservoir voltage midway between these two limits; it is the operating point (and should correspond to the point (2 O.lV) as determined by the Plasma Detector, if it is operating properly).

Note : Another technique may be used to determine high limit which does not result in the modulator "kicking off" with resultant disruption of beam operation in the accelerator.

Using this technique, one views the charging waveform at the ENC jack on the front panel marked PFN VOIXAGE on an oscilloscope with a Z or W plug-in and adjusts the scope so as to observe only the part of the waveform where the rising portion turns into the flat top. As the reservoir voltage is slowly increased, as described above, a little peak will be observed to grow at the above mentioned point.

-32-

Immediately upon observing the peak note reservoir voltage and drop

it because the modulator will "kick off" within seconds. That

point is high limit and the center reservoir point will be found

about 0.3 volt lower.

-33-

PULSE FORMING NETWORK TUNING

The modulator output pulse can be adjusted to + 0.25% for at least 2.5 microseconds on the pulse top at any voltage between 150 and 250 kv. At voltages other than that at which it was tuned, the pulse top will take on a slope due to load changes. This slope can amount to as much as 2s. The klystron looks like a diode load as far as the modulator is concerned, and therefore its impedance varies with voltage in accordance with the "three halves power law." Also, klystron impedance at a given voltage will vary from klystron to klystron in accordance with perveance. As a given klystron ages, its perveance will decrease slowly because the cathode wears out. Thus the load on the modulator varies from klystron to klystron, with voltage, and with age of a particular klystron.

The tuning of the PFN should only be done by experienced elect- ronics personnel and then only with the permission of the control room operators. When the accelerator is operating with a beam, the modulator may be tuned on the "housekeeping' trigger pulse. The voltages within the modulator are lethal. If the tuning is not done properly, the klystron can be over-voltaged and ruined.

A protective screen door must be installed in place of the door in front of the PFN when the regular door is left open. This protective door must have a Lucite sheet over the screen to protect the worker from flying porcelain should a capacitor bushing blow. The worker must use safety glasses. A special tuning wand made of

Lucite rod with a metalic section mounted in it which in turn is grounded to the modulator cabinet through a piece of wire braid and an alligator clip shall be used to operate the tuning cylinders.

Set the A.C. voltage fed to the modulator at 436 V 2 2 V, set the de-Q'ing reference voltage to 90 V $ 0.1 V; use 180 or 360 pps repetition rate. View the klystron voltage pulse on a properly calibrated and adjusted 545 Tektronix Oscilloscope with a "ZI' or

-34-

"W" preamplifier (also properly adjusted and calibrated). Use a 21 foot RG 58/u cable between the scope and the pulse transformer tank viewing jack. Use 0.5 V/cm sensitivity on the scope. Adjust the de-Q'ing current by means of "de-Q'ing bias" pot on the front panel. Observe pulse width at the 99.5% level of the 250 kV pulse. If the pulse width is less than 2.5 psec, pull out PF'N inductor tuning cylinders with the tuning tool. If the pulse width is greater than 2.8 psec push in the PF'N inductor tuning cylinders until it is within 2.5 and 2.8 psec. NOTE: It may be necessary to change the taps on the PFN coils if the tuning cylinders don't give enough inductance shift. In all cases, always open the thyratron compartment door and install the ground hook on the network before attempting to remove the PF'N protective screen. Check to make sure the ground connection on the ground lead is in good order. Continue to flatten the pulse at 250 kV by use of the tuning cylinders and/or taps and increasing the scope sensitivity in steps to 0.1 V/cm. The 250 kV tune-up point was chosen because it is the most likely operating voltage for these klystrons. Always start at the front end of the network and work toward the rear. It should be possible to contain all the pulse top ripple within 2 cm or 0.2 V. Turn off de-Q'ing and check to see that the MK-package overvoltage trip functions. Adjust the taps on the HV plate transformer to obtain 18-36 amperes on the de-Q'ing meter.

-35-

TYPICAL KLYSTRON VOLTAGE PULSE

Top Pulse:

200 KV 2 psec/cm Approx. 15% positive match

Bottom Pulse:

200 KV - 500 V/cm .5 psec/cm Approx. 2.5 ,usec pulse width

-36-

TYPICAL PULSE FORMING NETWORK TAP SETTINGS and

SLUG POSITIONS

COIL NO.

FROM TOP OF COIL TO TAP

FROM TOP OF SLUG COIL TO TAP INSERTION

-37-

-

120 140 160 180 200 220 240 260

KLYSTRON VOLTAGE - KV 589-l-A ’

TYPICAL KLYSTRON VOLTAGE vs De-Q’ING REFERENCE VOLTAGE

-38-

PULSETFfANSFORME!RTANK MAINTENANCE PROCEDURE

When a klystron-pulse tank assembly is returned for servicing, the following procedures are to be carried out.

1. Before removing the klystron-magnet assembly, pinch off the tygon tube leading,from the tank body to the oil reservoir. Suitable tube clamps are available for this purpose.

2. Remove the bolts holding the klystron-magnet assembly to the cooling spool. (NOTE: Use non-magnetic tools when working around the magnet.) The oil reser- voir must be independently supported until the klystron is removed, after which it may be rebolted to the cooling spool.

3. Lift the klystron-magnet assembly straight up until it is clear of the pulse tank assembly. Check the "0" ring (magnet to cooling spool seal) and discard if it shows signs of flattening.

CAUTION: Never attempt to remove the klystron from its magnet while the magnet is still resting on the pulse tank. Any foreign material such as water, dirt, etc. that may be trapped in the space between the magnet and the klystron tube will fall into the pulse tank and contaminate the oil.

4. Before removing the oil from the tank assembly, check its dielectric strength. If it tests above 25 kV rms (standard test cup and 30 second hold), save for reuse.

-39-

6.

7.

8.

9.

If it tests less than 25 kV, either discard or save for future processing.

Remove the cooling spool and reservoir tank from the tank body. Check the large "0" ring and discard if it shows signs of permanent flattening.

Remove the pulse transformer secondary leads from the klystron socket and remove the socket assembly and its support brackets frcan the tank. Wash all parts in solvent and inspect carefully. Look for arc marks and tracking or treeing in the epoxy supports.

Disconnect the pulse transformer primary wiring and remove the triaxial socket. Wash and inspect carefully for evidence of arcing, pitting, etc. Renew "0" ring if necessary.

Remove the pulse transformer base plate sub assembly from the tank. Wash the entire assembly in the solvent tank. Inspect the pulse transformer and capacity voltage divider for evidence of arcing or tracking. Replace any defective item. Check the date code on the filament by pass capacitors, C 173A, C173B, C175,

~176~ and ~176~. Replace all that are 2 or more years old.

Install the sub assembly in the modulator test tank and check the following:

a. Pulse transformer peak magnetizing current. Raise modulator output voltage until pulse transformer output voltage reaches 270 kV + 2yi.l

1 The salt water load should be between 1050 and 1150 ohms for this test.

-4o-

With the core bias set to 12 amps, note the peak

magnetizing current. 2 (This peak should occur @ 3.2 -f: 0.1 microseconds. If it does not, retune mod- ulator PFN as required.) Note the peak current. If it is greater than 120 amps, replace the pulse transformer. Reduce the core bias to 9 amps. If the peak current increases by more than lO$ or rises above 120 amps, replace the transformer. Record

the peak magnetizing current on the tank card.

b. Check the capacity voltage divider ratio by comparing its output to that of the standard calibrated divider that is in the test tank. Calculate the division ratio (it should be 5OOO:l 2 5%) and record on the tank card and also on the capacity divider file card.

c. If either the pulse transformer or capacity divider are suspected or waveform distortion, they should be tested according to PS-730-513-R7 (Pulse Transformer) or PS-730-564-Rl (Capacity Voltage Divider).

10. Wash the tank body and dry thoroughly.

11. Reassemble in the reverse order. Be sure to set the height

of the klystron socket properly. (See Drawing No.

AD-730-691~Rl.)

2 Magnetizing current is measured by observing the difference between the pulse transformer primary and secondary currents. A Tectronix "W" type head operated in the A-B mode is used for this measure- ment. The primary current must be divided by 12, by means of suitable attenuator in order to compare primary and secondary currents directly.

-4l-

12. Check all wiring for routing and proper clearances. (See Drawing No. AD-730-691-m.)

13. Check the klystron filament circuit as follows: Clip a 1+ 5% ohm, 300 watt resistor between the klystron socket cup and the center contact. (1 ohm includes the resistor loads.) With 100 V rms applied between pins A and B of the cannon plug, the voltage across the 1 ohm dummy load should be 17 volts + 10%.

14. Check the continuity of the core bias circuit with an ohmeter. The resistance from pin E of the cannon connector to the center conductor terminal of the triaxial socket should be less than one ohm.

15. Check the resistance between pin A of the cannon connector and ground (the tank body). The resistance should be 1000 ohms + g$.

16. Seal the top of the cooling spool with a plexiglass plate and evacuate the pulse tank assembly to 100 microns. Valve off and check the pressure rise. It should not be greater than 5 microns per minute.

-42-

1.

2.

3.

4.

5.

6.

7.

a.

9.

10.

11.

12.

13.

14.

CALIBRATION INPORMATION

klystron (~18)

Set to actuate at 1.75 amperes as read on a clip-on ammeter clipped over the lead feeding its coil. Thyratron Filament Undercurrent Relay (K22) Set to actuate at 40 amperes as read on a clip-on ammeter clipped over a thyratron filament lead. Thyratron Filament Adjust (TlO) Set to 6.3 V as read at the thyratron filament leads. Thyratron Reservoir Undercurrent Relay (K21) (KU275C or CHI191) Set to actuate at 10 amperes on a clip-on ammeter clipped over the reservoir (GL789O's) ditto except 5 amperes. Filament Time Delay Relay Set to 15 minutes Core Bias Undercurrent Relay Set to actuate at 13 amperes. Cabinet Temperature Thermoswitch Set to open at 175'F. Time Delay Relay K14 Set to operate in 1.5 seconds. Undervoltage Relay K25

Set to close at 200 V. Klystron Current Relay K30

as read lead.

Set to close between 12 and 17 ma by means of R743. End-of-Line Cli-oner Interlock Set R790 so that SCR Qg operates at + 15 V signal. Thyratrcn Trigger Overcurrent Relay IQ3

Set R750 so that K23 actuates at 80 ma.

Trigger Chassis H.V. Power Supply Adjust T15 for 3.8 kV output. * Keep Alive Power Supply Output Current Should be approximately 300 ma.

-43-

PREVENTIVEMAINTENANCE

Once a month:

1. Replace filters.

2. Clean insulators.

3. Clean and lubricate ratchet wheel on K13 (Use G.C. "no-noise" solvent).

-44-

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