high efficiency x-band klystrons development at cern · 2019. 2. 8. · clic ws, january 2019, cern...

I. Syratchev, J. CaiCLIC WS, January 2019, CERN

High efficiency X-band klystrons development at CERN

Igor Syratchev and Jinchi Cai, CERN


The new klystron bunching technologies have been established and evaluated. The computer code KlyC/2D and special scaling procedures have been developed and implemented. A number of high efficiency klystrons has been designed and few were communicated to industry.

High efficiency klystron development at CERN

S-band/IndustryCPI50 MW

X-Canon6 MW

X-CLIC8 MW

X-CLIC50 MW

L-FCC1.3 MW UHF-LHC

0.4 MW

X-CanonPPM, 50 MW

L-MBK ILC10 MW

L-MBK CLIC20 MW

UHF-LHC0.3 MW

Designed at CERN

Industrial tubes for science

S-Canon6 MW

X-BVERI50 MW

High Efficiency industrial prototypes


As of 01.11.2018

6 MW X-band klystron available from industry

Operates at repetition rate of 400 Hz

E37113


Objectives of the 6 MW klystron retrofit development at CERN.

Design of the COM klystron with improved (60%+) efficiency, thus increasing the peak power from 6 MW to 8-9 MW without modifications of the modulator and the tube cathode (fixed perveance).

Development of new computer tool (KlyC module) capable of the fast and reliable optimisation of the multi-gap output RF circuit.

Establishment of the complete compute simulation cycle (A-Z) including gun, solenoid and collector using PIC code CST/3D.

Deign of the new RF window (TW in ceramic) with higher RF power capacity than in existing device.

Providing the company with details of design study and fabrication of the prototype.


The 8MW X-band klystron design sequence flowchart.

1. KlyC 1D optimisation with artificial single cell output cavity (73%)

2. KlyC 2D with artificial output cavity (67%)

3. KlyC 2D The multi-cell output coupler (60.8%)

Optimal coupler topology choice: 4 cells

4. KlyC 2D full tube optimisation with additional gain cavity (62.8%, Pin=80W)

CST/3D benchmark, 60.5%Excessive E surf. (100 MV/m)

5. Output coupler re-optimisation, E surf. ~70MV/m, 60.8% (CST, 58%)

6. Solenoidal field optimisation to avoid the beam interception: 0.38T (KlyC:60.2%;CST 59.8%)

RF circuit design summary

Pin=800W

7. Solenoid design (CST). Scaled from existing Canon magnet.

8. Collector design. CST TRK. P <150 kW/cm2 in diode mode.

9. CST PIC simulations of the tube + solenoid + collector (59%)

10. Original Canon cathode + bucking coil + solenoid tuning in CST.

11. Technical design of the single feed input/output couplers and RF cavities.

12. Final KlyC 2D optimisation with beam parameters imported from CST gun simulation (59.5%)

13. Full (A-Z) tube simulation in CST (58.1%)


12. Final KlyC 2D optimisation with beam parameters imported from CST gun simulation (59.5%)


100W 8MW

15

4kV

,90

A

Eff.=58.1%

Bz field imported from solenoid system

Emax=80MV/m

13. Full (A-Z) tube simulation in CST (58.1%)

22 millions mesh cells2 millions particles in simulated volume


60MHz at-1dB

KlyC2D

The tube performance summary

KlyC2D

KlyC2D KlyC2D vs. CST 3D


E37113 tube window Compact (32 mm long) window with travelling wave in ceramic


As of 01.11.2018

50 MW X-band klystrons available from industry


Frequency

Peak power

Repetition rate

Pulse width

Power Gain

Efficiency

-3dB bandwidth

Beam voltage

beam current

Focusing

11.424GHz

50.4MW

10Hz

1.5μs

50.9dB

60.4%

36MHz

446kV

187A

Solenoid

The first HE (60%) commercial prototype of the 50 MW COM X-band klystron.BVERI, Beijing, China


53 MW X-band klystron design activity at CERN.

Parameter Target value

Frequency, GHz 11.994

Voltage, kV 400

Current, A 190

Perveance, µAV-3/2 0.75

Efficiency, % ~70

Power, MW 53

Surface E field, MV/m ≤ 100

Pulse length, ns 2000

Power gain, dB > 55

Cathode loading, A/cm2 < 5


Multi-cell klystron output circuit simulation. New module in KlyC.

1. Introduce cell by cell the geometries of the individual cells into KlyC EM module. Specify their frequencies and loaded Q-factor of the coupler cell. The arbitrary coupler topology (tapered aperture and/or cells length) is supported.

- KlyC will simulate the eigen-fields and eigen-frequencies for each cell.- Calculate the coupling matrix and generate eigen-field and complex eigen-

frequencies of entire geometry.

2. Use the idealized bunched beam (internal KlyC option) as a power source. Specify bunch frequency, length and congregation (normalised amplitude of the intra- bunch velocity spread).3. Optimise the coupler’s individual cells frequencies using KlyC optimiser (and/or manually)

4. ‘Glue’ the bunching circuit and proceed with optimisation of the entire tube.


The coupler performance optimised by KlyCCoupler topology: constant aperture/impedance 6 cells structure with ‘long’ last coupler cell.


The coupler performance benchmark with CST/3D

In this comparison, the idealized bunches parameters are identical for both codes.

E max ~ 100 MV/m

Bunch length /3, monochromatic bunch

Bunch length /3, bunch congregation 0.25‘cold’ measurements

‘frozen’ beam, congregated bunches

Eff. = 74% at 11.994 GHz

Eff. = 73.% at 11.994 GHz

Bz=0.38T, congregated bunches

No beam interception


First design option with 8 cavities circuit optimised in KlyC.

Output circuit zoom in

Output circuit with ideal bunch


430 KV, 190A cathode design

A. Krasnykh J. Neilson

CERN-SLAC collaboration on the 50 MW HEX tube


The 50 MW HEX klystron progress summary

90 MHz at -1dB

Parameter Target value

KlyC/2D

Frequency, GHz 11.994 11.994

Voltage, kV 400 400

Current, A 190 190

Perveance, µAV-3/2 0.75 0.75

Efficiency, % ~70 70.2

Power, MW 53 53.4

Surface E field, MV/m ≤ 100 <100

Pulse length, ns 2000 2000

Power gain, dB > 55 58.8

Cathode loading, A/cm2 < 5 4.74

The design is not yet finalized. The perveance and/or bunching circuit topology can be modified.


The tube design migration to CST/3D.

Coming next

• Coupler post optimisation in CST. The direct interface between KlyC and CST is developed and tested. It allows for the local and fast optimisation in CST using the bunched beam information from KlyC.

• Gun simulation in CST and final tube optimisation in KlyC.• Collector design• Full tube simulation in CST.

The full design shall be completed in three month (by March 2019). Start looking for the partners for the prototype fabrication, anticipating the first

testing at the end of 2020. Optimised design and fabrication of HTSC solenoid (0.38T; 320 K?) for HEX

klystron (end of 2020).

Complimentary studies (CST/3D) of PPM and reversed PM focusing solenoids options for 8MW and 50MW HEX tubes.


http://cds.cern.ch/record/2649486/files/

…Converts the klystron design work into a pleasant journey…

high efficiency x-band klystrons development at cern · 2019. 2. 8. · clic ws, january 2019, cern...

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