1. Application of moderate (5 MW) X-band power sources for the CLIC accelerating structures testing program and other projects
I. Syratchev, CERN

2. To date, the most remarkable results with CLIC accelerating structure and PETS were achieved at SLAC and KEK. Due to their heroic efforts we are pretty convinced now that CLIC two-beam acceleration with 100 MV/m is feasible!
GHz
GHz
12 GHz
12 GHz

3. CLIC accelerating structure program. Overall strategy

4. We need a lot more of testing capabilities!
But an inconvenient truth is:

5. Some numbers
In 2010 altogether one PETS and 3 CLIC-type accelerating structures have been tested (successfully !!!).
Our medium term (until 2016) modest plans require about 100 testing slots. This includes accelerating structures, PETS, waveguide components and certain number of very long (in terms of number of pulses) statistical runs. From our experience, the single testing slot takes hours at 50 Hz rep. rate, or more realistically ~ 2 month in average.
Assuming that single 50 MW klystron + pulse compressor can operate 2 structures in parallel, we will need about 8 klystron based reliable power stations, and we will need it now! We hope that SLAC and KEK X-band sources will continue and bring an important contribution to the program.
Such a program certainly requires 50 MW klystron industrialization efforts (both funding and time). Life time of klystron becomes an issue.

6. Could the testing period be reduced by increasing the repetition rate?
50 MW klystron. The XL-4 klystron was tested at 120 Hz and reduced pulse length ns. To make it to operate reliably at a full spec some modification of the RF window and collector will be needed?
Accelerating structure cooling circuit is designed for 50 Hz, increasing average power by factor 2-3 ( Hz) is feasible (under investigation).
Operation. Currently the processing is conducted at ~ BRD trip rate. With 2 structures running in parallel the after-BRD down time will slow down processing progress. Longer term tests (at a low BRD trip rate) will profit from the higher repetition rate.
1 min after-BRD-down-time was assumed
Processing zone
With a single source, the repetition rate and processing time are not correlated linearly
Running: BDR TR ~10-6
Processing: BDR TR ~10-5

7. Can we go even higher (above 100 Hz) in a repetition rate?
40 MW x few hundred ns, X-band klystrons cluster power station
Peak power vs. pulse length 1 2 V1 V2
PhM AM
To structures ~ 40 MW
Tin=3.2s, =4.75
2x5.5 MW
400 Hz
Load
PC, Q0=1.8x105
Example: Tin=3.2s, Tout=300 ns
Pin=2 x 5.5 MW, Pout=38 MW
=4.75
Increasing input pulse length, the extra 2 MW /+1s can be approximately gained.
Structures
Combining the two stations we get an accesses to 80 MW peak power kHz range test facility!
Drawback: The efficiency goes down to ~ 14% for 240 ns pulses.
Power, norm.
Load
Time, ns

8. High power 4 port commutation with phase manipulation
12 GHz (5.5 MW x 4.6 sec x 400 Hz) x 4
/2
PhM
PhM
/2 AM AM
Pav/Kl.=10 kW
100 Hz x 4
/2
-/2
133 Hz x 3 
82 MW x 240 ns
(61 MW x 400 ns)
200 Hz x 2
-/2
400 Hz x 1
-/2
Single klystron failure
By RF phase manipulation of 3 individual klystron (0- ) at 200 Hz, we can established 4 testing slots running at 100 Hz each. In the case of a single/few structure/s breakdown/s, the missing pulse can be send to any other testing channel, thus maintaining the overall repetition rate available for the tests.
x0.25
x0.25 x4
x2.25
x0.25
-/2
/2 -

9. The two configurations provide similar number of testing slots
4 x (5.5 MW x 3.0 sec x 400 Hz)
2 x (50 MW x 1.6 sec x 100 Hz)
PhM
PhM
PhM
PhM AM AM
Pav/Kl.=6.4 kW
Pav/Kl.=8 kW
To single structure (x100 Hz)
To single structure (x 100 Hz)
240 ns
240 ns

10. Single klystron parameters (for 78 MW x 240ns compressed pulse)
Single klystron peak power issues
5.5MW-6.5MW peak power klystron looks like an optimal choice to provide efficient generation of the pulses for CLIC accelerating structures testing. Such tubes are available at 9.3 GHz from different vendors.
Reducing peak power below 5 MW will require extension of the cluster: 4x5.5MW = 4x(2x2.75MW). This will soon hit psychological barrier, but certainly it needs to be studied to compare the price (+few klystrons/modulator?), performance (+modulator voltage?), reliability (+circulators?) and efficiency of the two layouts.
+20% for RF components losses
Single klystron parameters (for 78 MW x 240ns compressed pulse)
Time, ns
Power, MW
400 Hz/Kl. example
Operation issues:
After breakdown, the accelerating structure needs to be re-processed. This is normally do by gradual increasing both the peak power and pulse length. In our case it can be done in a simple way by changing only the klystron pulse length without re-programming klystron phase modulation.
In a similar way the peak power can be balanced between the channels

11. (As specified)
Demonstrated:
With 3.2s, 5.4 MW pulses and 6 kW average,
The repetition rate was 350 Hz.

12. VKX-8253A
The VKX-8253A is a solenoid focused 9.3 GHz klystron has demonstrated 5.4 MW peak at 18 kW average, and achieved 6 MW peak at 6 kW average. The unit is designed to achieve 20 kW average at 5 MW peak but operation is currently limited by test station availability.

13. Layout of the multipurpose 12 GHz RF power station
12 GHz (5.5 MW x 4.6 sec x 400 Hz) x 8 klystrons
PhM
PhM
PhM
PhM AM AM AM AM
Pav/Kl.=10 kW
Pav/Kl.=10 kW
82 MWx3x100Hz
82 MWx3x100Hz
Super power
channels
164 MWx2x50 Hz
(82 MW x2 100 Hz)

14. Compact SLED-type X-band pulse compressor.
Design & components by F. Peauger, CEA.
H01 Mode Converter F36mm
Short circuit + pumping port
H Cavity
H01 Circular Taper (F36mm→ F50mm)
Iris
Hybrid
To Accelerating Structure
From Klystron
SLAC-type Double height 3 dB hybrid
H01M ‘rugby’ cavity
Mode: H0,1,31
Length: 420mm
Max. : 110 mm
Q0: 1.82x105 (HFSS)
H01 tapers (36->50)
KEK-type compact H10-H01 mode converter
The mode converters are used to pre-fabricate H01 mode in a circular waveguide ( 50 m). The coupling iris and tuning piston are also placed in the same diameter to avoid diffraction coupling to the modes with higher radial number (H0,N>1,M).
The cavity shape is optimized to provide required Q0 (1.8x105). The internal tapers are designed to minimize modes conversions of the operating mode.
The fixed tuning pistons will be used as a separate (not the part of vacuum system) pieces to balance the cavities frequencies. Final frequency tuning will be done with the cooling water temperature control.
These components were designed and fabricated by CEA as a French in-kind contribution to the 12 GHz klystron station waveguide network at CERN

15. Other applications
The new collaboration between CLIC/CERN and KVI/GRONINGEN (Netherlands) has been recently established. The subject is the development of high gradient electron linac based on CLIC (12 GHz) accelerating structure technology capable to operate at ~1 kHz repetition rate.
X-band linac module
The moderate peak power klystron cluster plus pulse compressor is the most economic way to deliver high peak RF power and high repetition rate.

16. The ~50 MW x 300 ns X-band pulsed power sources are the crucial elements of the CLIC accelerating structures development program
Currently we are preparing the order for fabrication of few 50 MW XL-5 klystrons. Together with pulse compression systems they will allow for testing of two RF devices per klystron in parallel at a nominal CLIC RF peak power level.
Development of clustered sources based on moderate (5-6 MW) peak power tubes is considered to be a complimentary effort, which will increase the CLIC structures testing capacity.
We are looking now for the business partners, who can develop and build such a tube operating at 12 GHz. Ideally, we would like to receive complete unit, including klystrons, HV modulators, waveguide network and even pulse compressors!
Being available, such clustered source can be a working horse in many projects, where high gradient and high repetition rate are required (FEL’s, medical machines…).