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

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

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

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

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) 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.

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

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

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

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)

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.

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

E3740A: Summary of Operation

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.

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

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

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

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.

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.

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

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

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.