Tetrodes are efficient !

EnEfficient RF Sources workshop 2014, Cockcroft InstituteEric Montesinos, CERN-RF

TETRODES ARE EFFICIENT !

Eric Montesinos, CERN-RF 2EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue

OutlineFrequency & Power range of tetrodes & diacrodes

Theoretical and measured efficiency

Availability vs Efficiency, an example with a YL1530 tetrode operated in the CERN SPS

Imposed parameters and their impact to efficiencyOverheadCirculatorsHigh Voltage Power SupplyFundamental Power Coupler

Granularity

Conclusion: Tetrodes are very efficient

Eric Montesinos, CERN-RF 3

0 50 100 150 200 250 300 350 400 450 50010

100

1000

10000Tetrodes & Diacrodes available from

industry

CW

Frequency MHz

Pow

er k

W p

er s

ingl

e tu

be

EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue

Frequency & Power range of tetrodes


0 50 100 150 200 250 300 350 400 450 50010

100

1000


industry

peak < 1 ms

Frequency MHz

Pow

er k

W p

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ingl

e tu

be




0 50 100 150 200 250 300 350 400 450 50010

100

1000


industrypeak < 1 msCW

Frequency MHz

Pow

er k

W p

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ingl

e tu

be




Theoretical efficiency

RF power in

DC power in

Heat out

RF power out

PRFin + PDCin = PRFout + Heat

As with tetrodes Gain is usually > 13-16 dB


CBABA


Amplifier class

InputSignal

OutputSignal

Operative curve

Class A

InputSignal

OutputSignal

Operative curve

Class B

Unsusedarea

InputSignal

Output SignalLess than 180⁰

Operative curve

Class C

Unsusedarea

360⁰2

270⁰3

180⁰ 90⁰Conduction Angle

0⁰0

A AB B C0%25%50%75%100%Efficiency

Amplifier Class Description

Class-A Full cycle 360⁰ of conduction

Class-AB More than 180⁰ of conduction

Class-B Half cycle 180⁰ of conduction

Class-C Less than 180⁰ of conduction


Theoretical Class B efficiencyDC power isPdc = Vdc Idc

Assuming the tube is linear whilst it is conducting, the dc anode current is found by Fourier analysis of the current waveform and is Idc = Ipk/πIrf = Ipk/2 = Idc π/2And ideal class B, Vrf = VdcSo, RF power isPrf = ½ Vrf IrfPrf = ½ Vdc Idc π/2 = π/4 Vdc Idc

Theoretical efficiencyη = Prf/Pdc = ¼ Vdc Ipk / Vdc Idcη = 78.5 % Vdc

Class B

Ipk


Class B efficiency in practiceTwo reasons for not achieving this impressive number1. tube is not fully linear whilst

it is conducting2. Anode voltage must be

higher than G2 voltage, VG2 being ~ 10% Vdc

This leads intoPdc = Vdc Idc = Vdc 1.05 Ipk/πPrf = ½ Vrf Irf = ¼ 0.9 Vdc IpkTheoretical efficiency in practiceη = Prf/Pdc = ¼ 0.9 Vdc Ipk / 1.05 Vdc Ipk/πη = 67 %

Class B

UG

2

Ipk

Vdc


Measurement on a YL1530 tube

0 5 10 15 20 25 30 35 40 45010203040506070

YL1530 @ 200 MHz (Filament – 7.5%)

CW output power [kW]

Effici

ency

RF/

DC Operating point

RF/DC efficiency = 66.4 %


Overall YL1530 efficiency @ 35 kWOperating conditions for 35 kWGain = 16 dB, PRFin = 0.88 kWPG1 & PG2 = 50 WPfilament = 1.3 kWIpk = 19 AVDC = 10 kVIDC = 1.05 Ipk/π = 6.4 AVRF = 8.5 kVIRF = Ipk/2 = 9.5 A

61 %

Class B

UG

2

Ipk

Vdc


CERN SPS

SPS1976 (7

km)


CERN SPS YL1530 Power plantsTwo amplifiers, 64 YL1530 tubes

Frequency 200.2 MHz

One amplifier delivers650 kW with 32 YL1530

-0.2 dB for combiningplant (-4.7 % power)

Each single tube is operated 21.2 kW

Overall Efficiency = 48 %


Overall YL1530 efficiency @ 21 kWOperating conditions for 21 kW with settings for 21 kWGain = 16 dB, PRFin = 0.58 kWPG1 & PG2 = 50 WPfilament = 1.3 kW de-rated to 1.2 kWIpk = 13 AVDC = 10 kVIDC = 1.03 Ipk/π = 4.3 AVRF = 6.5 kVIRF = Ipk/2 = 6.5 A

48.2 %

Class B

UG

2

Ipk35

Vdc

Ipk21


SPS Supercycle

SPS1976 (7

km)

North Area

CNGS2006

LHC2008 (27

km)


North Area CNGS LHC


SPS SupercycleDuring 2012

Supercycle 48 seconds

19.25 seconds / 650 kW9.6 seconds / 488 kW19.15 seconds / 0 kW

For 7000 hours of operation 2.5 GWh

SPS1976 (7

km)

North Area

CNGS2006

LHC2008 (27

km)


Operating with ‘OFF Line’ TubesIn normal operation, one tube delivers a maximum power of650 kW + 4.7 % / 32 = 21.2 kW

Systems have been designed (1980) to deliver full voltage into the cavity even with only 24/32 tubes

In case of 8 tubes ‘OFF Line’, remaining tubes shall deliver23 kW x (32/24)^2 = 37.8 kW

32 x 21.2 kW = 18 x 37.8 kW = 680 kW

YL1530 tubes are rated 37.5 kW

32P 18P


1 y 2 y 3 y >= 4 y0

20406080

100120140160180200 YL1530 SPS 200 MHz, 2 x 32 tubes in

parallel(Filament – 7.5 % & 21 kW instead of

35kW)

# years of operation before failure of the tube

# tu

bes


Tubes statistics

Total 1980-2013 : 254 tubes

Average lifetime : 32’000 hours

Tubes with > 28’000 hours : 78 %(also true for tubes stored 20 years !)

19EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue Eric Montesinos, CERN-RF

Amplifiers statistics

Loss of

emission39%

Input re-

flec-tions38%

Un-known

8%

Over temp8%

Arcing7% Reason of

fault# of

faults% of

faultsLoss of emission 99 39

Input reflections 97 38

Unknown 20 8Over Temp 20 8Arcing 18 7We lose 14-16 tubes per year,

that we exchange during Technical Stops 3-4 times a yearUnpredictable : 23 % (equivalent to 4 tubes)Graceful degradation : 77 % (possible to monitor and predict)

YL1530 SPS 200 MHz, 2 x 32 tubes in parallel


Availability of the CERN SPSWith these operating conditions• - 7.5 % Ufilament → +37.5 %

lifetime• Off Line tubes for the

unpredictable faults• Overall efficiency 48 % during

cavity maximum voltage• Supercycle average power 390

kW

Over 7000 hours of operation in 2012, these two RF Power plants have been responsible for only 16 hours of down time !

2003 2008 20130

1

2

% S

PS d

own

tim

e


Availability of the CERN SPSAvailability of an Injector is the key parameter

CERN’s total annual electricity consumption is 1.3 TWh, for an operation of almost 7000 hours per year

When SPS is down, electrical bill without physics, costs 4500 CHF / h (minimum, only electricity cost based on 60 CHF / MWh)

20 % for LHC cryogenics + cooling and ventilation10 % for LHC experiments7 % for the North area experiments(http://cds.cern.ch/record/1324541?ln=en)

http://cds.cern.ch/record/1324541?ln=en




Availability of the CERN SPSWe can improve the efficiency from 48 % to 61 % of the RF Power source by• Increasing the filament to the

nominal value (- 37.5% lifetime)

• Reducing the number of tubes in operation(2 x 20 tubes operated 34 kW)

• no additional down time with ‘off line’ operation BUT reduced beam intensity(OR Three hours stop for a tube exchange

Savings 66,000 CHFMoney (electrical bill savings)2.5 GWh at 60 CHF/MWh with

48 % efficiency costs 312,000 CHF61 % efficiency costs 246,000 CHF

Costs 273,000 CHF(money, not taking into account impact to physics)14 additional tube exchanges,42 hours physics lost & electrical bill due to LHC & experiments infrastructure costs


Availability of the CERN SPSWe can improve the efficiency from 48 % to 61 % of the RF Power source by• Increasing the filament to the

nominal value (- 37.5% lifetime)

• Reducing the number of tubes in operation(2 x 20 tubes operated 34 kW)

• no additional down time with ‘off line’ operation BUT reduced beam intensity(OR Three hours stop for a tube exchange

Savings 66,000 CHFMoney (electrical bill savings)2.5 GWh at 60 CHF/MWh with

48 % efficiency costs 312,000 CHF61 % efficiency costs 246,000 CHF

Costs 186,000 CHF(money, not taking into account impact to physics)14 additional tube exchanges,42 hours physics lost & electrical bill due to LHC & experiments infrastructure costs


Availability of the CERN SPSWith respect to this CERN SPS example, applicable to all RF plants with smaller energy consumption compare to ‘other’ energy consumers in the machine,

being more efficient with RF power plant with an overall efficiency increased from 48 % → 61 %, and no margin in the RF power plant,

for the same beam qualityWill induce more accelerator stopsCost more electricity at the endEven worse if the kWh cost increases in the coming

years…


Overhead

0 500 1000 1500 2000 2500 3000 3500 4000 4500 50000

10

20

30

40

50

60

70YL1530, 35 kW @ 200 MHz

Input power W

Out

put p

ower

kW 1 s (x1.4)100 µs (x1.5)

10 µs (x1.7)

CW (x1.2)

35 kWnominal

CourtesyWolfgang Höfle


Overhead

0 0.5 1 1.5 2 2.5 3 3.5 40

0.20.40.60.8

11.21.41.6

Tetrodes, Klystrons, SSPA

Tetrode

Input power / nominal Input power

Out

put p

ower

/ no

min

al

Out

put p

ower

RF Pulse

Overhead needed for LLRF

operation

klystrons


HVPS

For tetrodes (and gridded tubes more generally) HVPS is very simpleNo RF -> idle current (can be zero in class B or class C)

Even if HV is drooping, the LLRF will impose output power, and tetrode remains able to deliver requested Power

RF Pulse RF Pulse

time

PdcHV10-20 % tolerant

HVless tolerant

Griddedtubes

klystrons

0 2 4 6 8 10 120

102030405060708090

100RS2004 tetrode

Unominal (8.5 kV)- 10 % U nom-inal-20 % Unominal

Pin kW

Pout

kW


CirculatorIf the reflected power is not too long, Tetrodes do NOT need a circulator

With a good reflected power protection, Tetrodes can sustain full reflection

We operate the SPS since 1976-1980 without a single failure due to reflected power

Our protection is made with old relays, few milliseconds


Fundamental power couplerEven if we can imagine cavities able to receive a large amount of power

In the frequency range, Fundamental Power Coupler will limit the maximum power that can be delivered to the cavity

The limit will be~ 1.0 MW peak power~ 0.5 MW average

power(for a stable operation 10-20 years lifetime of a coupler)


GranularityIn the frequency range, Tetrodes power limit is close to FPC power limit

One (or few) tube per cavity

Redundancy ensured by a small additional number of tubes/cavities

This will ensure to operate with a high efficiency, still having availability

FPC

FPC

FPC

FPC

FPC


GranularitySingle higher power source

Need a circulator to protect the tube

More losses in circulator & splitting system

No individual control of the cavities

Limited to the weakest cavity

Will lose a large number of cavities in case of source failure

Not easy to have a few spares

FPC

FPC

FPC

FPC

FPC


GranularityMulti lower power sources

Need a circulator to protect the sources

More losses due to combining system- 0.1 dB is - 2.5 % in PowerAt 352 MHz or 400 MHz

A simple N connector is - 0.01 dB

If redundancy is made by increased number of modules, not anymore the best operating point, efficiency is reduced

If at the efficient operating point, same number of few additional cavities as with tetrodes

FPC

FPC

FPC

FPC

FPC


Granularity‘New’ way of making the storage of spares

One tube is in ‘stand-by’ mode and can possibly replace any faulty tube within few minutes with a‘OFF line – ON line’ matrix

All four tubes in operation will be operated at their best efficiency point

Still have robustness thanks to the fifth tube

2 MW

2 MW

New SPS power plants: 2 x 2 MW @200 MHz

Four + one diacrodes option scheme


Conclusion (I/II)Regarding the frequency range & regarding the power range

If AVAILABILITY of the machine is the key criteriaTetrodes are a good choice

Single (few) tubes per cavity with good efficiency & redundancy with few additional cavities (on hold)Multi tubes solution for redundancy operated at a lower power, lower efficiency with nevertheless a very correct final overall cost

If EFFICIENCY is the key criteriaRegarding the arrangement choices, Tetrodes can be operated 60-70 % overall efficiency in operation


Conclusion (II/II)

If within the frequency & power range

Never neglect a tetrode (diacrode) option

Carefully look at it, and you will see they are very good !

Thank you for your attention

EnEfficient RF Sources workshop, 03-04 June 2014, Cockcroft Institue Eric Montesinos, CERN-RF 36


Theoretical Class B efficiencyDC power isPdc = Vdc Idc

Assuming the tube is linear whilst it is conducting, the dc anode current is found by Fourier analysis of the current waveform and is Idc = Ipk/πIrf = Ipk/2 = Idc π/2And ideal class B, Vrf = VdcSo, RF power isPrf = ½ Vrf IrfPrf = ½ Vdc Idc π/2 = π/4 Vdc Idc

Theoretical efficiencyη = Prf/Pdc = ¼ Vdc Ipk / Vdc Idcη = 78.5 % Vdc

Class A

Class B

Class C

Ipk


Tubes costs in the CERN SPS7000 hours operation per year2 x 32 tubes operation

Filament, nominal -7.5 %Lifetime 32000 hoursReduced thermal lossesBroken tubes per year 14Cost 350,000 CHF

Overall efficiency 48 %Electricity 2.5 GWh, 0.125 CHF/kWhCost = 0.06 2.5/0.48Cost = 312,000 CHF

2 x 20 tubes operation

Filament, nominalLifetime 20000 hours (-37.5%)Increased Thermal lossesBroken tubes per year 14Cost 350,000 CHF

Overall efficiency 61 %Electricity 2.5 GWh, 0.06 CHF/kWhCost = 0.06 2.5/0.61Cost = 246,000 CHF


Pulsed machineOperating frequency 352 MHzPulse duration 3.5 msRepetition rate 14 HzNumber of cavities 26RF Power 400 kWTotal RF peak power 10.4 MWTotal RF average power 510 kW

Redundancy by number of cavities (operation still possible with one/two cavity OFF)Operated at maximum powerSame tetrode being driverPre-driver SSA ~ 600 W

Tetrodes TH595Operating conditions for 200 kWGain = 15 dB, PRFin = 6.3 kWPG1 & PG2 = 500 WPfilament = 1.35 kWIpk = 56 AVDC = 16 kVIDC = 1.05 Ipk/π = 18.7 AVRF = 14.5 kVIRF = Ipk/2 = 28 A

66 %


Pulsed machineOperating frequency 352 MHzPulse duration 3.5 msRepetition rate 14 HzNumber of cavities 26RF Power 400 kWTotal RF peak power 10.4 MWTotal RF average power 510 kW

Redundancy by number of cavities (operation still possible with one/two cavity OFF)Operated at maximum powerSame tetrode being driverPre-driver SSA ~ 600 W

HVPS

Tetrodes are efficient !

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