KEK Marx-Modulator R&D Accelerator Laboratory KEK Marx-Modulator R&D Mitsuo Akemoto KEK LCWS2016 December 6, 2016

Marx Modulator Group KEK M. Akemoto, M. Nakajima, M. Kawamura Accelerator Laboratory KEK M. Akemoto, M. Nakajima, M. Kawamura Nagaoka University of Technology W. Jiang, R. Suzuki, T. Hayashi Pulsed Power Japan Laboratory Ltd. A. Tokuchi, Y. Sawamura

Marx-type Modulators Accelerator Laboratory Marx Topology : Charge in parallel, discharge in series Features: Modularity, Electrostatic Adding, Independent module control 　　　and Low-voltage sub-units Marx-type modulator is expected to have high availability and low-cost. DTI Marx Modulator for ILC SLAC P2 Marx Modulator for ILC Ampegon Pulse Step Modulator for XFEL

ILC Modulator Specification Accelerator Laboratory Parameter Value Pulse Voltage 120 kV Voltage Regulation 1%(p-p) Pulse Current 140A Pulse Length(flat-top) 1.6 ms Total Pulse Energy 27 kJ Repetition Rate 5 Hz Average Output Power 135 kW

KEK Marx Modulator Marx Unit: Charging system: System: Accelerator Laboratory Marx Unit: 6.4 kV output pulser with four Marx cells at -2 kV each Marx Cell has a step-down converter with a switching frequency of 50 kHz Flat pulse voltage is formed with a PWM modulation Charging system: Independent unit charging through 20 kHz isolation step-up transformer Each unit is charged up to -2kV and the input voltage of the Marx unit is regulated. System: N+1 redundancy Air insulatated, water cooled, No oil 10kW Inverter Charging PS Marx Unit #20 -120 k V 140 A 1.7 ms 5Hz 10kW Inverter Charging PS Marx Unit #19 Isolation Step-up Transformer Klystron 10kW Inverter Charging PS Marx Unit #02 10kW Inverter Charging PS Marx Unit #01 -6.4 k V 140 A 1.7 ms 5Hz 620 V 20 kHz 2.0 k V 20kHz -2.0 kV DC Inverter Charging System 420 V 50 Hz 3φ System Block Diagram Simulated output voltage waveform

KEK Marx Modulator View Accelerator Laboratory Marx Unit Charging system Size 1.6 m(D) x 3.3 m(W) x 2.3m(H) Tests with a dummy load were ready at end of this March. Quarter of the modulator full charging power(50kW) is available.

Marx Unit Accelerator Laboratory Marx unit is the semiconductor Marx generator and consists of four Marx cells and a control circuit board with FPGA to control the each cell. Marx cell is a step-down converter. Marx unit parameters Parameter Value Input voltage 2.0 kV Output voltage -6.4 kV Capacitor droop 20% Number of Marx cell 4 Marx cell (Step-down converter) Block diagram of Marx unit 455mm×650mm×382mm(H)

Marx Cell 充電経路 Parameter Value Input voltage -2.0 kV Output voltage Accelerator Laboratory 400mm×300mm×75mm(H) 充電経路 SiC FET 3P2S Opt.i/F IGBT Filter L Filter C Storage capacitor C Marx Cell SiC SBD 2S Marx cell parameters Parameter Value Input voltage -2.0 kV Output voltage -1.6 kV Capacitor voltage droop 20% PWM frequency 50 kHz SiC FET 3P2S SiC SBD 2S IGBT 1.33uF 550Ω 0.133uF 48uH SiC power devices(1.2 kV FET, SBD) were selected because of its higher breakdown voltage, low on-resistance and fast switching speed. Energy conversion efficiency is about 93%. Circuit diagram of Marx cell

SiC Power Device(Si vs. SiC) Accelerator Laboratory Reduce chopper switching loss by one-third comparing with Si device ON Si IGBT：IXGK75N250 2500V, 75A SiC FET：SCH2080KE 1200V, 40A 2S3P Switching loss(1 cycle) Frequency：50 kHz、Duty cycle :75%、Charging voltage :1 kV

Charging and Pulsing in Marx unit Accelerator Laboratory Charging Pulsing -6.4kV Pulse DC -2kV (input) DC -2kV (input) Charging switch Chopping switch

Droop Compensation Output voltage droop of Marx cell Accelerator Laboratory Output voltage droop of Marx cell PWM duty cycle is increased from 76% to 95% in proportion to time. Droop ratio: 20% Output droop can be compensated by PWM control.

Ripple Cancelation Accelerator Laboratory The output ripple of the unit can be reduced by cell phase shift control. Output voltage ripple of Marx unit Timing chart of four-cell gate signal Ripple ratio : 52%  6%(for Marx unit) Each cell gate signal is shifted by 90 degrees. In the same way, modulator output ripple can be reduced by unit phase shift control.

High voltage Test at Dummy Load Accelerator Laboratory Charging voltage=1300 V, Vp=80 kV, Ip=90 A, Pw=1.7 ms, Ripple=0.6%(p-p)

Present status Accelerator Laboratory In the single unit test on the dummy load, a 6.4kV, 140A, 1.7ms pulse is successfully generated at 5Hz. In the 20 unit full test, chopping FET switch(FET rated voltage : 1.2kV , Switch : 2 series and 3 parallel connection) has reached a peak voltage of 2.2kV at a charging voltage of 1.3kV. The voltage margin is not enough to operate at a full charging voltage of 2kV. This constrains the modulator output voltage. The switch and diode should be changed to new SiC 3.3 kV devices to operate at a full charging voltage of 2kV.

Future Plans 2016(this fiscal year) Accelerator Laboratory 2016(this fiscal year) To check the modulator system at a charging voltage of 1.3kV, the high power tests at 80kV, 45A, 1.7ms, 5Hz with a klystron load will be performed. 2017 New unit using 3.3 kV devices will be tested at a charging voltage of 2 kV. After confirming the performance of new unit, all units will be improved. 2018 Now, quarter of the modulator full charging power(5 charging power supplies, 50kW) is available. The remaining 15 charging power supplies will be added to complete the charging system. Full power tests with a 10MW MBK klystron will be performed.