Linac Marx Modulator Update

Trevor Butler7/22/2015

Linac Marx Modulator Update

Present Status• 28 Cell Assembled (100%) – Problem w/ clamp ckt• 28 Cell Testing– (100%)

– Gate Circuit Testing– B-Dot Coil Gate Clamp Testing– Short Circuit Testing– 300 Amp pulse with short circuit

• 28 Cell Mechanical Structure ~ 80% complete• Built Control System Relay Rack (100%)• Qualified Charging Power supplies by full load testing

in Linac Test Cage (100%)• Building Charging Supply Rack (50%)

– Design & Build Internal Controls– Building Control Interface Box

• Waveform Feed forward/Learning (~75%)– Completed Feed forward & Learning on Ramp Section– Completed Feed forward on Beam step, but was unable

to complete beam learning on multiple length beams.– Unable to test Feedback with present setup

• Components for 54 cells have arrived (100%)• Cabinet for the 54 cell is being design (~50%)

– Designed with windows can absorb spark energy

• Will use the 28 cell controls relay rack/ charging supply to run the 54 cell design at reduced rep rate.

Charging Power Supply To Do List• Finish PS Interface Chassis (50%)• Build Current Summing Plate with LEM’s & Ross

Relays (0%)• Install LOTO Clips & Ground Stick (0%)• Design and Build Front pate with 480 AC indicator /

Verification / Temperature (25%)• Build PS Mounting Plate (0%)• Modify PS Chassis Supports (0%)• Install 120 VAC Dual Quad Boxes (0%)• Mount Fans on Relay Rack (0%)• Mount Kirk Keys (0%)• Mount Disconnect Switch (0%)• Build Copper Ground Bus (0%)• Fabricate Top Plate for Ref, Inhibit, and Contacts

(0%)• Mount rear door locks (0%)• Build and Install 9 of the 15 pin connectors (0%)• Install Air Flow Interlocks (50%)• Order addition charging Supply (0%)• Complete internal wirings (10%)• Install cooling fans & power strips (25%)

Linac Marx Modulator Update

Mechanical Structure To Do ListFinish Assembly of Mechanical Structure• Determine optional place for testing

– Need cooling water for 15 Hz testing, which is not available until the end of the shutdown if we use our dummy load

– Limited to only a few Hz operation without this dummy load

– Plan to take over location next to present assembly area for testing

– Waiting finish Marx assembly until this location is cleared.

• Modify top plate too include connects for PWM Filter then send back for plating (10%)

• Install cooling fans (0%)• Install 120 VAC power strips (0%)• Install cool air intake fans (0%)• Modify special cell to accommodate different

charging voltage (25%)• Install all 28 cells (50%)

Miscellaneous To Do List• Create and install ~100 fiber optic links (0%)• Install stripline parts & coaxial output line (50%)• Test Charging Power Supplies under full load (0%)• Calibrate the delay of each Marx cell for ripple

optimization to compensate for cabling (0%)

Test in development area• Test system for corona (0%)• Test for temp. rise & cooling efficiency (0%)• Test Control system (0%)• Test Charging Power Supply system (0%)• Test into dummy load (0%)

– Start of at low repetition rate– Finish at high rep rate.

• Test into Short Circuit (0%)– Test with turn on into short– Test with short at high voltage

• Test for maximum step size before clamp cicuit activates (0%)

• Test for maximum dv/dt and PWM slew rate (0%)

Linac Marx Modulator Update

LRF1 Installation• Goal: install system in LRF1 by end of shutdown• Move system from development area• Rewire all power, HV, controls, and fiber optic

components• Move the water filter to accommodate cabinet

– Need to find and procure non-conductive 2.5” cooling hose– May need to modify all 7835 sockets dependent on position

• Power (480 3phase, and 120 single phase)– Decided to power system from electrical panel placed

upstairs power from temporary breaker panel located in lower level

– Will power Charging Relay Rack, Controls Relay Rack, and Marx Cabinet with extra 120 VA power available upstairs

• Dual Operation– Power placement will enable the system to run

independently of the present modulator– Switching between system will require removal of the

switch tube surge resistors, bypassing Mod Compete Relay, Installing new HV on interlock, installing new interlock module

• Need to have controls coded in to FPGA to replace waveform generator module, which includes the driver start, driver stop, crowbar compare pulses to interface new modulator to old driver system

Challenges• Will the 28 cell version it pass the spark test?• Can we achieve the required waveform stability on

LRF1? System will require feedback, which has not been tested since it needs 28 cell modulator as load

• Presently, control system can only create a ramp up and ramp down pulse, without any feed-forward, learning, or feedback

• First goal of testing in LRF1 will be to see the response of the modulator into varying impedance load, which will then determine the best way to program cells, which will take substantial investment from Kevin Martin and Matt Kufer once the system in tested into LRF1

• Good news is that since system will be able to be switched back and forth within perhaps a 1-2 hour time frame, the testing of code could be done in future study times.

• Largest Challenges– Can system run into 7835 tube load impedance– Can 54 system pass spark test and hold off high voltage

without corona or component damage (Some could be checked using a dummy load)

Marx ModulatorCabinet Assembly

ChargingPower Supply

New Location Idea

Extra Slides

28 Cell Version Pictures

Location, Location, Location

A5A7 A5A3Power

WaterCooling

Modulator

ModulatorDeck

Capacitor Bank

Marx

Hallway

Buncher

Mar

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Mar

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ontr

ols

MarxChargingPS

Charging Supply Testing• Testing for 15 Hz operation• Running close to full rated power rating

of the supplies• Supplies create power for <$1 per watt,

comparted to almost $2 Watt for the Lambda supplies

Controls Learning Studies• Implemented both Feed-forward & Learning• Determined there was a large amplifier gain change after spark, undermining the

feed-forward calculation, which assumes a fixed gain• Added spark detection to clear learning after spark• Future studies involve testing beam learning

Different cavity gradient regulation schemesDirect Gradient Analog Feedback• Presently used to regulate our vacuum tube modulators• Op-Amp feedback loop with adjustable proportional gain• Advantages

– Simple in design, and robust in operation– Direct feedback cancels out any pulse to pulse variations as it noticed significantly on LRF1

• Disadvantages– Lack of real time tuning and optimization via ACNET.– Interfacing with existing LLRF Learning Algorithm can be problematic and require frequency

tuning

Feed-Forward Operation (often confused with Learning)• Uses a system model of the load (the 7835 triode, accelerating cavity, and beam

intensity) to predict the required amount of voltage to get the desired gradient level• Advantages

– Can act as a first guess before implement any learning or feedback• Disadvantages

– Almost impossible to get perfect model.– Even if you could, it could drift over time, requiring constant tuning to stabilize gradients

Different cavity gradient regulation schemesLearning Operation• Learns the waveform error from pulse to pulse, placing correction on next pulse• If the Learning Operation is used on top of the Feed-Forward loop, then the system

would have less error to correct• Advantages

– Able to learn out slow process (Aging of tube, drifting of cavity frequency, • Disadvantages

– Unable to regulate voltage within the pulse.

Real-Time Feedback• Realtime operating system, like the SoC FGPA topology• Error between the cavity fields is calculated in realtime and the error is sent to the

PWM for correction within the pulse• Advantages

– Able to Control cavity fields within the pulse, accounting for pulse to pulse variations• Disadvantages

– Complex to design– Long development time