Commercial high-power X-band experience: klystron/modulators,

and waveguide vacuum flanges

CLIC Workshop January 2016

G. McMonagle

(on behalf of Xbox team)

• Klystrons

• Modulators

• Klystron Drivers

• Flanges

2008-2010

SLAC CollaborationXL4 to XL5

KLYSTRON

XL4 USA frequency 11.4 GHz only high power X band tube in operationNo commercial optionLong experience at SLAC in building and using these tubesCollaboration between CERN and SLAC to build 12 GHz design (XL5)PSI and Trieste joined collaboration5 tubes ordered“Best efforts” collaboration, no guarantees1st tube installed at CERN in 2010

KLYSTRON

Parameters Specifications units

RF Frequency 11.9942 GHz

Peak RF power 50 MW

RF pulse length 1.5 µs

Pulse repetition rate 50 (100) Hz

Klystron voltage 410-470 kV

Micro perveance 1.15E-6

KLYSTRON

Good collaborationBut some problems needed extra payments due to best efforts

NO GUARANTEE

2008-2010

SLAC CollaborationXL4 to XL5

KLYSTRON

2010-2014

Call for Tender for commercial solutionLimited repliesContract to CPI

CPI VKX-8311ASame specification as XL5Ordered 2 new tubes plus option of buying a 3rd

1st tube successfully tested at SLACDelivered to CERN and installed in XBox1Tube has been performing fine since installation

2nd tube also successfully tested at SLACDelivered to CERN and installed in Xbox 2

During SAT tests problems arose with tube performance

KLYSTRON

KLYSTRON

First diode tests (no RF) of CPI#2 tube showed that 0.7 GHz gun oscillations starts at about 240 kV and even generate RF power from the input cavity:

Fortunately, going higher in voltage, the instability zone moves towards the rise/fall time, so the plat top can be used now.

No margin to reduceKlystron operation voltageRun at nominal even whenlow power required to avoid oscillations on RF

Why were oscillations not visible in SLAC tests ?Consultation between CERN and CPI concluded it must be due to geometry in the high voltage tank, CERN took reservation on warranty of tube performance.CPI manufactured pieces for 3 different solutions to try and resolve the problem1. Special plates with ferrites to be mounted on walls of modulator tank :-

Improvement but did not get rid of all oscillations but could run at a lower voltage with good flat top

2. Plates to change geometry (reduce volume and mimic shape) to match Xbox1 modulator :- No improvement

3. Solution 2 with ferrites :- Slightly better than 2 but 1 was best.

Lost 3 weeks of operations with these manipulations, CPI wanted to investigate more but we decided option 1 is sufficient to allow us to run

KLYSTRON

Are there any oscillations on 1st tube?

Yes but at within a small voltage at around 200kV and on falling edgeAbove and below these voltages tube is fine.

3rd tube has been ordered and will be tested in a new Scandinova modulator in CPI factory (not at SLAC) FAT next week

First indications from CPI are that there are no oscillations like 2nd

tube but may have similar issue to 1st, will find out more next week !

KLYSTRON

2008-2010

SLAC CollaborationXL4 to XL5

KLYSTRON

2010-2014

Call for Tender for commercial solutionLimited repliesContract to CPI

2013-2015

Xbox 3Combination of lower peak power klystron with high average power, turnkey contract awarded to Toshiba for 4 klystron modulators

KLYSTRON

Toshiba E37113 Peak power: 6 MWBeam Voltage: 150 kVBeam current: 90 AAverage power: 12.4 kWEfficiency: 47.5% RF pulse width 5µsRep rate 400Hz

All 4 tubes have been successfully installed in the modulators at CERN in October 2015

All have pulsed to nominal parameters in diode mode

First tube has also been operating with RF

Waiting for delivery of RF waveguide components, LLRF and klystron drivers

RF commissioning hopefully starting March 2016

KLYSTRON

2010

Xbox 1

MODULATORS

MODULATORSXbox 1 modulator

CEA Saclay collaboration financed modulatorArea chosen for modulator installation had limited footprintTherefore size of modulator was critical and CEA also decided to go for solid state technology

Contract awarded to Scandinova

ScandiNova solid-state modulator (Ser. #1)for powering the XL5 klystron

- Designed for 400kV, 300A, 3.25us HV pulse width FWHM, 1.5us RF pulse width at 50Hz repetition rate

- Max. 450kV, 350A, 3.5us, 50Hz- Specified 0.25% HV ripple and 0.1% HV

repeatability- Compact design (3x2m2) including HV oil

tank and klystron- Primary voltage 1400V max.- Integrated control and interlock system- Integrated vacuum and solenoid power

supplies for klystron

MODULATORS

Factory test done into dummy load (no klystron available)

Normally modulator delivered to client in fully assembled unit (as in factory) but due to space restrictions had to be disassembled the remounted at CERN

SAT tests with dummy load no klystron available

Did not achieve nominal parameters until 2015 with CPI klystron installed (arcing in SLAC klystron gun)

MODULATORS

Issues with 1st modulator

Calibration measurements.In factory no problem into resistive load (so we thought)

In SAT, modulator was commissioned with dummy load again as klystron was not delivered yet.

When klystron arrived was difficult to correlate measurements from SLAC to measurements at CERN, indications were that the perveance of tube was not correct.

Eventually found that SLAC measurements were erroneous by 10% (confirmed by Trieste during their acceptance of tube #3)

External Water

Cooling System

Filament

DCPS 0-

30A

Core

Bias

DCPS

HVPS

#1 - N

Control System Unit

P

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w

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r

D

i

s

tr

i

b

u

ti

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n

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it

L

1L

2L

3GN

D

Water Cooling Distribution

S

W

#3

S

W

#1

S

W

#2

S

W

#n

RF-

Source

RF-

Amplifie

r

Solenoid

PS #1-3

Ion

Pump

PS 5X

Modulator

>45 L/min

Collector

>120

L/minBody

>10

L/min

Solenoid

>10

L/min

Tri

gIpuls

eUpul

seRemote

RS232

12GH

z

400VAC

50Hz

Safety

Interface

3-

phase

480VA

C

1-phase

120VAC

Local RS232

K2 Solid

State

Modulator

Pulse

Transform

er Oil Tank

RF 3GHz

3x18

5A

C

T

CVD

Water Flow

Interlocks

Vacuum

Interlock

Current Interlock

Waveguide

pressure Int., Arc

Int, VSWR Int.

L

1NGN

D

230VAC

50Hz

MODULATOR AND RF SYSTEM, OVERVIEW

MODULATORS

Current measurements on low side of pulse transformer secondaryNot ideal due to stray capacitance giving overshoot on measurementDifficult especially when starting up in short pulse to say where real peak is situated

Need a CT on high sideFor future modulators

Initially only SN built HT measurementLater commercial calibrated solution installed

MODULATORS

GUI interface was not very user friendly

No real time and date stamp on interlock occurrences

Some switch failure and reliability problemsMay have been due to many tube arcs in the XL5 tube

Flat top on voltage difficult to achieve many iterations on changing tuning elements on each switchFlat top only really perfect at nominal voltage

Had some issues with switch units when at nominal voltageBeware if you have to increase charging voltage to keep performanceSome switch units may not be triggering and overloading the others (no indication of non triggering switches)

When in operation the modulator performance is very good

2010

Xbox 1

MODULATORS

2012

Xbox 2

MODULATORSXbox 2 modulator competitive tender from CERN

Scandinova awarded contract

Measurement requests implemented into new unit (Calibrated CVD, CT on high side), but not real time and date stamp for intelocks

New design of switch unit (unfortunately not backward compatible with 1st unit)Different spares needed.

3 charging power supplies integrated (2 in first)

Unfortunately we decided to commission this modulator with the XL5 as there was pressure to put CPI tube #1 in Xbox1.Resulted in getting modulator to work correctly but not at full pulse width due to tube limitations.

Waited for CPI #2 to arrive before full commissioning and tuning of pulse shape

Apart from a few teething problems and of course tube oscillations system running very well

MODULATORS

Xbox in building 150 More space, overhead crane availableManipulation and operation a lot easier than Xbox1

2010

Xbox 1

MODULATORS

2012

Xbox 2

Xbox 3

2014

MODULATORS

Lessons learnt from previous two projects

Price enquiry to klystron manufacturers for turnkey solution

Klystron contract awarded to Toshiba who subcontracted modulators to Scandinova

Tube and modulators arrived at CERN after full SAT test with klystron

Very quick and successful integration at CERN

MODULATORS

Modified K1 ScandiNova modulatorThe illustration of new 2 cabinet concept that will be adopted for 6 MW Toshiba klystrons.

Doubled width oil tank. To facilitate installation of the Toshiba klystron which has rather wide (0.7 m) solenoid.

Additional cabinet (comes for free). It can be used for Klystron RF driver amplifier, Solenoid PS, Ion Pump PS etc.

New Control System that will simplify integration of external parts and offer a lot of new features.

Flexible design (klystrons positioning) to minimize the length of RF waveguide circuit:Modulator parameters (max.)

for 6 MW Toshiba klystron

Peak RF power: 8.0 MWPulsed voltage: 175 kVPulse current: 115 AAverage power: 50 kWPulse length (flat): 5secRep. rate: 400 HZ

1.6 m

1.3

m

MODULATORS

Xbox 3 in building 150

Please sign up for visits later in the workshop

MODULATORS

New improved performance in modulators due to new control system and GUI

FPGA programming of switch triggers and charging power supplies allows easier tuning of flat top by delaying triggersAlso allows flat top to be tuned at lower voltages of operation not just at nominal

New GUI an excellent improvementReal time and date stamp for interlocks and eventsInterlock levels and settings a lot more user friendly

MODULATORS

Final words on modulator performance, measurements made on new S band K2 at SNSame performance on Xbox modulators

K2-SYSTEM PULSE FLATNESS <0.4%DC-LEVEL STABILITY K2-SYSTEM

USING PRECISION MULTIMETER

<0.002%

K2-SYSTEM PULSE-PULSE STABILITY <0.04%

USING OSCILLOSCOPE

Klystron Drivers

For Xbox 1 and 2 Using TWT 3kW pulsed driver to provide power to Xbox 1 and 2~ 700w needed but allows tube to placed considerable distance away from klystron

Non member stateExpensiveProtected technology , end user statements needed

Designed for high duty factor (high pulse rep)Using at 50 Hz peak power drops off after few thousand hours operationRecycling at high prf necessary to recondition tubeRecently seeing glitches in pulses causing problems in pulse compressionFinite lifetime of tubes, whole unit needs to be sent back for change (long and expensive)

Klystron Drivers

Xbox 3Development of solid state driver with a member state companyPrototype built achieved 310W output power (initial goal >400W)

Tested on Xbox3 ARMS phase and amplitude stability is very good with 0.17 degrees and 0.14% respectively

Peak power limited due insertion loss by coaxial combination and isolator inside unit.

4 new units ordered with waveguide combination and output>1.1dB extra gain expected to achieve >400W output (delivery February 2016)

If successful two units can be combine to power klystrons in Xbox 1 and 2Still cheaper than USA TWT

FLANGES

Xbox 1 and Xbox 2

Using SLAC type male/female type flange

Expensive to manufacture flanges and gaskets

Attention to detail on integration of “directional” components needed when choosing flanges.

Experience in Xbox 1 shows copper plating on flanges is necessary to reduce RF losses and RF heating

FLANGESNew sexless flange manufactured for Xbox3(design agreed between laboratories that use x band technology)

Initial problem with copper plating, now resolved with new technique at CERN(for more info see Serge Lebet)

When mounting it was found difficult to align flanges and keep the flange gasket in place.New mounting jig developed prototype ready this week

FLANGE

GASKET

Initial testing of flange at SLAC

Summary

• New technology, fast learning curve for CERN– And manufacturers

• Good collaboration between laboratories and commercial suppliers allowing fast development in the field

• Other competitors coming on market especially in solid state modulators e.g. Ampegon (SwissFEL) and Jema (University of Valencia)

2010

2016

Xbox operations at CERNXFEL’S?Medical apps?University test stands?Xbox3 technology in industry?

Thank you for your attention