Development of The Klystrons for J-PARC Project

Kenichi Hayashi and Osamu Yushiro

Toshiba Electron Tubes & Devices Co., LTD.

Contents

1. Outline of the J-PARC project

• What kinds of klystron are used?

• What are the klystrons like?

2. 324 - MHz, 3 - MW Klystron: E3740A

• Design

• Test results

• Some of problems

3. 972 - MHz, 3 - MW Klystron: E3766

• We are now developing this tube.

• Brief on design and test results

4. Summary

Accelerator-Driven Transmutation Experimental Facility

Linac (350 m)

3 GeV Rapid Cycling Synchrotron (350 m)

50 GeV Synchrotron (1600 m)

Materials Life Science Facility

Neutrino Experimental Facility

Nuclear and Particle Physics Facility

J-PARC at JAERI Tokai site

To 3 GeV RCS

To ADS

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.

E3740A E3766

E3740A E3766Frequency (MHz) 324 972Output Power (MW)Efficiency (%)Gain (dB)RF Pulse Length (ms)Beam Pulse Length (ms)Repetition Rate (Hz)Beam Voltage (kV)Anode Voltage (kV)Beam Perveance (I/ V1.5)No. of cavities 5 6Window Coaxial PillboxOutput Flange WR-2300 WR-975Tube Length (m) 4.55 2.93

35055

0.62

1.37× 10- 6

0.75011094

Specs & Design Parameters of the Klystrons

Triode-type electron gun for anode modulating

324-MHz Klystron E3740A: Overall Design

Aim of designing (against growing in size due to low operating frequency)

1. To reduce size and trim weight

• By unifying the tube with the focusing solenoid to provide adequate mechanical strength.

• By trimming each component.

2. Limitation of the building and easy handling

• By placing the tube horizontally.

about 65% lighter than the same-size tube we have developed.

E3740A: Klystron & Klystron Assembly

Output waveguide

Electron gun Interaction cavities Collector

Output window

Focusing solenoidOil tank

Stand

Klystron

~ 5 m~3,200 kg with oil

Focusing solenoid

Interaction cavitiesElectron gun

Oil tank

Output window & waveguide

Collector

The photo of the E3740A

94 kV

110 kV

E3740A: Design of the electron gun

Anode terminal

Body

Cathode terminal

Anode

Cathode

Beam trajectory from EGUN

•Beam diameter 30 mm

•Beam ripple < 3%

•Surface gradient 65 kV/cm

1. To reduce the surface gradient by optimizing the electrode configuration.

2. To assure long life and stable emission by adopting metal-coated cathode.

0

10

20

30

40

50

60

70

0 5 10 15　 Pd　[W]入力電力

　η　[%]

効率

epyb=110kVepyb=100kV　epyb=90kV

Effi

cie

ncy

(%

)

Input power (W) 　Gun side

E3740A: Design of the interaction circuit

Collector side

Optimizing the parameters using FCI (Field Charge Interaction 2+1/2 PIC code)

To shorten the tube length by ~25% using the 2nd harmonic cavity

wave

waveT bar

Output cavity

Window ( TiN coated Al2O3) WR2300

T-bar structrure : To simplify the coaxial-to-rectangular conversion section.

Qext ~ 13

E3740A: Design of the output circuit

The simulation was done using HFSS code:Model and result.

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 5 10 15　　　pd　[W]励振電力

　　　po　[MW]

出力

電力

① epyb=110.0[kV]　,　epya=91.7[kV]　,　ik=48.2[A]：② epyb=104.0[kV]　,　epya=86.5[kV]　,　ik=43.5[A]：

①

②

epyb: 　 epya 　 ikビーム電圧 ：アノード電圧 ：ビーム電流

Ou

tpu

t po

we

r (M

W)

Input power (W)

(a)

(b)

E3740A: Test Results 1

(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

ビーム電圧

ビーム電流アノード電圧

アノード電流

励振電力

出力電力

測定点

ビーム電圧

ビーム電流アノード電圧

アノード電流

励振電力

出力電力

測定点

Anode voltage

Anode current

Beam voltage

Output power

Input power

Beam current

Traces of the beam & wave parameterst: 0.1 ms/div

Transfer characteristics

E3740A: Summary of Operation

Nominal MaximumFrequency (MHz)Beam Voltage (kV) 104 110Anode Voltage (kV) 86.5 91.7Beam Current (A) 43.5 48.2Output Power (MW) 2.53 3.03Efficiency (%) 55.9 57.3Saturation Gain (dB) 53.9 56.3RF Pulse Length (ms)Beam Pulse Length (ms)Repetition Rate (pps)

324

50

0.620.7

1. 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.

E3740A: Problem 1, Oscillation

100 100 70

E3740A: Change in collector size

0.34% 0.18% 0.07%The first tube The second tube The final tube

Ratio of reflected electron to incident beam

100

70

First

Final

70

0

10

20

30

40

50

-500 0 500 1000 1500 2000 2500 3000

[mT]

磁界

強度

Mag

netic

fiel

d (m

T)

First Final

E3740A: Magnetic field distribution

Inner diameter of drift tube: 70 to 100

2. We observed during the test of the second tube that the output power sometimes failed at random.

Confined slow ions and electrons

972-MHz Klystron E3766: Overall Design

　

Frequency (MHz) 972Output Power (MW) 3Efficiency (%) 50Gain (dB) 55RF Pulse Length (ms) 0.65Beam Pulse Length (ms) 0.7Repetition Rate (pps) 50Beam Voltage (kV) 110Anode Voltage (kV) 94Beam Perveance (I/ V1.5) 1.37No. of cavities 6Window PillboxOutput Flange WR-975Tube Length (m) 2.93

•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).

Interaction cavities

Electron gun

Collector

Output window

2.93

m

E3766: Test results

1. 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%.

2. We intend to achieve 3-MW output by this September.

Summary

The 324-MHz, 3-MW, long-pulse klystron E3740A has been developed in collaboration with KEK and JAERI.

1. We have confirmed :

• The maximum power of 3.03 MW.

• Stable operation with efficiencies above 56%.

2. 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.

0

10

20

30

40

50

60

70

60 70 80 90 100 110 120　　　epyb　[kV]ビーム電圧

　　　η　[%

]効

率 　　　Gp　[dB]

利得

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

　　　po　[M

W]

出力

電力

ηGppo

Ou

tpu

t po

we

r (M

W)

Beam current (A)

Effi

cie

ncy

(%

) &

Ga

in (

dB)

Gain

Efficiency

Output power

E3740A: Test Results 2

Saturation characteristics

E3766: Design of the electron gun

　

1. To reduce the surface gradient by optimizing the electrode configuration

2. To assure long life and stable emission by adopting metal-coated cathode

Same design principles as the E3740A

Beam trajectory from EGUN

Beam diameter 21 mm

Drift-tube diameter 30 mm

Beam ripple < 2%

Surface gradient 65 kV/cm at 120 kV

　wave

Output cavity

WR975

Pillbox window ( TiN coated Al2O3)

1. To shorten the output circuit by using step-waveguide structure.

2. A single-gap re-entrant cavity with an iris is used.

The simulation was done using HFSS code:Model and result.

E3766: Design of the output circuit

Qext ~ 16