1. Development of The Klystrons for J-PARC Project
Kenichi Hayashi and Osamu Yushiro
Toshiba Electron Tubes & Devices Co., LTD.

2. Contents Outline of the J-PARC project
What kinds of klystron are used?
What are the klystrons like?
324 - MHz, 3 - MW Klystron: E3740A
Design
Test results
Some of problems
972 - MHz, 3 - MW Klystron: E3766
We are now developing this tube.
Brief on design and test results
Summary

3. J-PARC at JAERI Tokai site Linac (350 m)
Nuclear and Particle Physics Facility
Materials Life Science Facility
3 GeV Rapid Cycling Synchrotron (350 m)
Linac (350 m)
50 GeV Synchrotron (1600 m)
Accelerator-Driven Transmutation Experimental Facility
Neutrino Experimental Facility

4. E3740A E3766 The 400 MeV Linac of J-PARC
The linac requires two types of klystron.
20 of the 324-MHz klystron, E3740A are used at DTL.
23 of the 972-MHz klystron, E3766 are used at ACS.
To 3 GeV RCS
To ADS
E3740A
E3766

5. Specs & Design Parameters of the Klystrons
Triode-type electron gun for anode modulating

6. 324-MHz Klystron E3740A: Overall Design
Aim of designing (against growing in size due to low operating frequency)
To reduce size and trim weight
By unifying the tube with the focusing solenoid to provide adequate mechanical strength.
By trimming each component.
Limitation of the building and easy handling
By placing the tube horizontally.
about 65% lighter than the same-size tube we have developed.

7. E3740A: Klystron & Klystron Assembly
Output waveguide
Electron gun
Interaction cavities
Collector
Output window
~ 5 m
~3,200 kg with oil
Focusing solenoid
Oil tank
Klystron
Stand

8. The photo of the E3740A Focusing solenoid Interaction cavities
Electron gun
Oil tank
Output window & waveguide
Collector

9. E3740A: Design of the electron gun
To reduce the surface gradient by optimizing the electrode configuration.
To assure long life and stable emission by adopting metal-coated cathode.
Cathode terminal
Anode terminal
Body
Beam trajectory from EGUN
Beam diameter 30 mm
Beam ripple < 3%
Surface gradient 65 kV/cm
94 kV
Anode
Cathode
110 kV

10. E3740A: Design of the interaction circuit
To shorten the tube length by ~25% using the 2nd harmonic cavity
Efficiency (%)
Input power (W)
Gun side
Collector side
Optimizing the parameters using FCI (Field Charge Interaction 2+1/2 PIC code)

11. The simulation was done using HFSS code:Model and result.
E3740A: Design of the output circuit
T-bar structrure : To simplify the coaxial-to-rectangular conversion section.
Qext ~ 13
wave
wave
T bar
Output cavity
WR2300
Window ( TiN coated Al2O3)
The simulation was done using HFSS code:Model and result.

12. E3740A: Test Results 1 (a) (b) Transfer characteristics
Output power (MW)
Input power (W)
(a)
(b)
Anode voltage
Anode current
Beam voltage
Output power
Input power
Beam current
t: 0.1 ms/div
Transfer characteristics
Traces of the beam & wave parameters
(a) Beam voltage: 110 kV, Anode voltage: 91.7 kV, Beam current: 48.2 A
(b) Beam voltage: 104 kV, Anode voltage: 86.5 kV, Beam current: 43.5 A

13. E3740A: Summary of Operation

14. E3740A: Problem 1, Oscillation
Oscillation at the main frequency
We observed oscillation at 324 MHz at the beam voltage above 90 kV for the first tube.
Power level of the oscillation reached up to 300 kW.
We found from various experiments and analyses that
The oscillation occurred in the input cavity.
Due to reflected electrons from the collector.
Measures:
Enlarging the collector to decrease the reflected electron.
Lowering the external Q factor of the input cavity.

15. E3740A: Change in collector size
The first tube
The second tube
The final tube
f100
f70
0.07%
0.34%
0.18%
Ratio of reflected electron to incident beam

16. Confined slow ions and electrons
E3740A: Magnetic field distribution
f100
f70
First
Final
We observed during the test of the second tube that the output power sometimes failed at random.
Inner diameter of drift tube: f70 to f100
Magnetic field (mT)
First
Final
Confined slow ions and electrons

17. 972-MHz Klystron E3766: Overall Design
The tube has the same beam parameters as the E3740A to use the common power supply system.
6 cavities for broad bandwidth 10 MHz (-3 dB).
Collector
Output window
2.93 m
Interaction cavities
Electron gun

18. E3766: Test results
We are now testing the tube and we have confirmed that:
an output power of up to 2 MW was obtained at a beam voltage of 97 kV with an efficiency of 52%.
We intend to achieve 3-MW output by this September.

19. Summary
The 324-MHz, 3-MW, long-pulse klystron E3740A has been developed in collaboration with KEK and JAERI.
We have confirmed :
The maximum power of 3.03 MW.
Stable operation with efficiencies above 56%.
The tube is put into commercial production:
We have already produced 13 sets, and we intend to produce 20 sets in total by this September.

21. E3740A: Test Results 2 Saturation characteristics Efficiency Gain
Output power (MW)
Beam current (A)
Efficiency (%) & Gain (dB)
Gain
Efficiency
Output power
Saturation characteristics

22. E3766: Design of the electron gun
Same design principles as the E3740A
To reduce the surface gradient by optimizing the electrode configuration
To assure long life and stable emission by adopting metal-coated cathode
Beam diameter 21 mm
Drift-tube diameter 30 mm
Beam ripple < 2%
Surface gradient 65 kV/cm at 120 kV
Beam trajectory from EGUN

23. The simulation was done using HFSS code:Model and result.
E3766: Design of the output circuit
To shorten the output circuit by using step-waveguide structure.
A single-gap re-entrant cavity with an iris is used.
Qext ~ 16
wave
WR975
Pillbox window ( TiN coated Al2O3)
Output cavity
The simulation was done using HFSS code:Model and result.