1. Towards high power klystrons with RF power conversion efficiency in the order of 90%.
Syratchev(CERN) on behalf of
High Efficiency International Klystron Activity
HEIKA

2. Future large scale accelerators
circular
FCC
linear
0.5 TeV
ILC e+e-: Pulsed, 1.3 GHz, PRF total= 88 MW
3.0 TeV
FCC ee: CW, 0.8 GHz, PRF total= 110 MW
CLIC e+e-: Pulsed, 1.0 GHz, PRF total= 180 MW

3. Motivation for HEIKA
The increase in efficiency of RF power generation for the future large accelerators such as CLIC, ILC, ESS, FCC and others is considered a high priority issue.
Only a few klystrons available on the market are capable of operating with 65% efficiency or above. Over decades of high power klystron development, approaching the highest peak/average RF power was more important for the scientific community and thus was targeted by the klystron developers rather than providing high efficiency.
The deeper understanding of the klystron physics, new ideas and massive application of the modern computation resources are the key ingredients to deign the klystron with RF power production efficiency at a level of 90% and above.
The coordinated efforts of the experts in the Labs and Universities with a strong involvement of industrial partners worldwide is the most efficient way to reach the target … thus HEIKA.

4. CLIC Multi-beam (6/10 beams) pulsed klystron power balance diagram.
Thales TH1803
20 MW, 50 Hz, 150 sec
150 kW
180 kV
Modulator (=0.9)
HV transformer
Energy storage
Total = 0.62
switch
Cathode
RF circuit (=0.7)
Collector
60 KW
Lower (<60kV) voltage:
mini-cathodes
No oil tank (cost)
Shorter tube (cost)
Faster switching (efficiency/cost)
Gated mini-cathode:
No switches (cost)
Modulator efficiency ~1.0
(+) Improved stability
New klystron RF circuit (=0.9)
(+) Reduced Collector dissipation (16 kW)
150 kW + 88 kW
Solenoid 4 KW
Permanent Magnets:
- No power consumption
- Potential cost reduction
Vs. SC solenoid:
- More expensive solution
Can we do
better?
Total = 0.9
CLIC requires about 800 klystrons. Successful implementation of all the actions above could save 60MW and reduce the power plant cost by ~15%.

5. ‘’Classical” bunching
The new bunching technology shows a potential to boost klystron efficiency to the 90% level.
Link:
CLIC MBK preliminary optimisation
‘’Classical” bunching
Electrons velocities distributions prior entering the output cavity 2
RF=78.0%
Bunch phase
Normalised velocity
Useful RF phase
Output cavity
New bunching with core oscillations (COM)
RF period, rad 2
RF=89.6%
Normalised velocity
Bunch phase
Normalised velocity
Output cavity
RF period, rad

6. Comparison of the two bunching methods (CLIC MBK).
20 MW CLIC
‘Classical’
20 MW CLIC
10 MW ILC
N beams = 8
V = 180 kV
I total = 128 A
RF extraction efficiency: 89.6%;

7. Tube parameters: FCC ee CW, 0.8 GHz, 1.5 MW MBK klystron (HEKCW)
HEIKA/HEKCW working team:
I. Syratchev (CERN)
C. Lingwood (Lancaster)
D. Constable (Lancaster)
V. Hill (Lancaster)
R. Marchesin (Thales)
Q. Vuillemin (Thales/CERN)
A. Baikov (MUFA)
I. Guzilov (VDBT)
C. Marrelli (ESS)
R. Kowalczyk (L-3com)
T. Habermann (CPI)
A. Jensen (SLAC)
Tube parameters:
Voltage: 40 kV
Total current: 42A
N beams: 16
µK/beamx106 : 0.33
N cavities: 8
Bunching method #1: COM
HEKCW
16 beams MBK cavity
R/Q = 22 Ohm/beam

8. 79.8% 83.3% 86% Evolution of the HEKCW klystron (PIC simulations)
Original 8_01 design. Saturated bunch.
8_04. The new design of ‘gentle’ buncher reduced significantly radial bunch stratification.
83.3%
8_H02. Hollow beam configuration with optimal geometry made bunch nearly perfect.
86%

13. BAC MBK factory tests results

14. Full scale tests at CERN will start on June 20.

15. TULIP- high gradient compact proton linac for cancer therapy