Klystron Power Supply

Transcription

1 Klystron Power Supply Mitsuo Akemoto KEK Joint US-CERN-Japan-Russia International Accelerator School 2017-RF Technologies- Oct , Hayama, Japan 1

2 Contents 1. Klystrons -Klystron characteristics 2. Basic Pulse Circuits -Line-type Modulator -Direct Switch Modulator -Chopper circuit -Marx circuit 4. Modulator Improvements and Power Devices 5. Long Pulse Modulator Example : ILC Modulator 3. Short Pulse Modulator Example : KEKB Linac Modulator The pulsed high voltage generator for klystron are called modulators. 2

3 Various types of Klystrons 3

4 Peak power(mw) Overview of Pulsed Klystron Modulators LCLS 360kV,5.84µs SACLA 350kV,4.2µs PAL-XFEL 400kV,8µs KEKB 300kV,5.6µs SNS 140kV,1200µs XFEL 12kV, 1700µs ILC 120kV,1700µs ESS 100kV, 3400µs ,000 10,000 Pulse width(µs) 4

5 Typical Klystron Parameters Klystron type Klystron voltage RF output power CW ~100 kvdc ~1.2 MW Long pulse(~ 1 ms) ~130 kv ~10 MW Sort pulse(~ 1 µs) ~500 kv ~200 MW 5

6 Klystron Characteristics Klystron beam current I k Child's law Anode I k PV k 3/ 2 I k V k P=microperveance, I k =klystron current, V k =klystron voltage Klystron power P k P k I k V k PV k 5/ 2 η=klystron efficiency Klystron impedance Z k Z k V k I k 1 P V k and power variation P k P k 5 2 V k V k Cathode Z k Klystron model Equivalent circuit 6

7 Modulator Requirements Compact High-Efficiency High-Reliability Low-Cost 7

8 Basic Pulse circuit Hard-tube (Direct switch) Line-type Suitabe for long pulse Suitable for short pulse 8

9 Line-type Modulator PFL or PFN Advantages Electronics is simple. Short current is 2 times operating load current. Disadvantages Pulse width is fixed. Matched impedance is load impedance. Pulse shape is depend on load impedance. PFN needs to be tuned for flat pulse. Output voltage is half input voltage Basic line-type modulator 9

10 Pulse-Forming Line Line impedance Z Z Propagation velocity of the line u Output pulse width T cable u Limitation 1 T cable 2L u 2 r r c L: line length µ r : relative permeability ε r : relative permittivity c : light velocity Polyethylen ε r =2.3 T cable =1µs at 100 m RG58-U(Z=50Ω, C=100pF/m, L=250nH/m), Tcable=10ns/m To get a pulse width of 10µs, need a long line of 1 km. 10

11 Pulse Forming Network(PFN) Pulse Forming Network 20 sections, L=1.3 µh, C=0.015 µf, Z=9.3 Ω Characteristics impedance Pulse width(n stages) Pulse rise time 11

12 PFN Simulation Load impedance =PFN impedance Output voltage waveform Each Capcitor voltage of PFN PFN: 20 sections 12

13 Direct switch Modulator Advantages Pulse width is controllable. Pulse shape is good. Impedance matching is wide range. Output voltage is input voltage Disadvantages High stored energy. Short current is large current. (crowbar circuit is used for klystron protection.) Basic direct switch modulator 13

14 Direct Switch Modulator Topology Klystron: Vk=350 kv, Ik=310 A Pw=4.2µs Direct Switch Modulator Hybrid Modulator High voltage SW(350 kv,310a) Induction Adder Modulator Marx Modulator Middle voltage SW(50kV,2200A)+PT(1:7) Low-voltage SW(6kV,310A)+PT(1:1) x 59 stages Low-voltage SW(6kV,310A)x59 stages 14

15 Buck Converter(1) Buck converter circuit diagram Buck converter is DC/DC power converter which steps down voltage from its input to its output. V L L di dt During steady state V L 1 T T V L dt 0 0 The voltages and currents with time in an ideal buck converter during steady state. 15

16 Buck Converter(1) Buck converter circuit diagram ON Buck converter is DC/DC power converter which steps down voltage from its input to its output. V L L di dt During steady state V L 1 T T V L dt 0 0 The voltages and currents with time in an ideal buck converter during steady state. 16

17 Buck Converter(1) Buck converter circuit diagram OFF Buck converter is DC/DC power converter which steps down voltage from its input to its output. V L L di dt During steady state V L 1 T T V L dt 0 0 The voltages and currents with time in an ideal buck converter during steady state. 17

18 Buck Converter(2) Output voltage V c Duty Factor <1 Buck converter is DC/DC power converter which steps down voltage from its input to its output. Output voltage ripple Pulse Width Modulation Maximum value at α=0.5 18

19 Boost Converter Boost converter circuit diagram ON Boost converter is DC/DC power converter which steps down voltage from its input to its output. Duty factor The voltages and currents with time in an ideal boost converter during steady state. 19

20 Boost Converter Boost converter circuit diagram OFF Boost converter is DC/DC power converter which steps up voltage from its input to its output. Duty factor <1 The voltages and currents with time in an ideal boost converter during steady state. 20

21 Marx Generator Marx circuit(erwin Marx invented in 1924) +V R C Gap Switch Charging resistor V out stage NV in N stages Multi-stage is achieved by charging the capacitors in parallel and discharging in series. The capacitors are charged to V through the charging resistors while the switches are open. The switches close and the capacitors are connected in series, producing high voltage. The circuit generates a high-voltage pulse by charging a number of capacitors in parallel 21

22 Solid State Marx Modulator V out =V Solid state Marx circuit +V Stage 1 Stage 2 Stage Discharging Switch(DS) Charging Switch(CS) The capacitors are charged in parallel and discharged in series. Discharge switches can be independently controlled. The output is controlled by sold-state elements, diode and IGBT switches. V out Stage # DS DS DS 1 ON OFF OFF 2 OFF ON OFF 3 OFF OFF ON V out =3V Stage # DS 1 ON 2 ON 3 ON 22

23 KEKB Klystron Modulator (Line-Type) 23

24 KEKB Klystron and Modulator Klystron Specifications Output Power 46 MW RF Pulse Width 4.0 µs Efficiency 45 % Perveance 2.1 µa/v 3/2 Beam Voltage 298 kv Repetition Rate 50Hz Modulator Specifications Pulse Modulator SLED Max. Peak Output Power 108 MW Max. Average Output Power 30 kw Pulse Transformer Ratio 1:13.5 Primary Output Voltage 22.5 kv Primary Output Current 4.8 ka Total PFN Capacitance 0.6 µf Pulse Rise time(10-90%) 0.8 µs Pulse Flatness(P-P) 0.3 % Pulse Width 5.6 µs Thyratron Anode Voltage 45 kv Thyratron Anode Current 4.8 ka Thyratron Average Anode Current 1.3 A Repetition Rate 50 Hz Pulse Transformer Tank Klystron 24

25 Circuit Diagram of KEKB Modulator PFN-type modulator LC resonant charging De-Qing Single thyratorn switch 25

26 Vc Charging Circuit of KEKB Modulator LC Resonant charging I 0 2E I de-q Es E 0 Time(10ms/div.) 26

27 PFN Voltage(xVdc) PFN Charging Voltage Stability 2.5 V PFN V 0 C DC C DC C PFN 1 cos t V 0 1 cos t 2 Normal V PFN 25% voltage increase V PFN 1 L c C PFN T 2 L c C PFN 1.5 System delay V PFN V PFN a b 1 a a Normal PFN Voltage a=pfn regulation(5%) b=ac line deviation(5%) τ=system delay time(50µs) Charging time=50ms(50hz) wt(dgrees) Stability V PFN V PFN 0.15% 27

28 Circuit Diagram of KEKB Modulator PFN-type modulator LC resonant charging De-Qing Single thyratorn switch 28

29 PFN of KEKB Modulator PFN circuit diagram PFN Design Inductance of the tuning Inductor > 1µH 2 pallel, 20 section L=1.3µH, C=0.015µF Z=9.2Ω/2=4.7Ω 29

30 PFN Capacitor Energy Density of Capacitor No-Healing W V 1 2 r 0 E 2 W: Stored energy (J) V : Volume of capacitor (m 3 ) r : Relative permittivity 0 : Permittivity of a vacuum (8.85x10-12 F/m) E : Field strength (V/m) (J/m 3 ) Metallicon Self-Healing(SH) Metallicon Dielectric film Thin metal ~7µm Dielectric film Evaporated thin film Few hundreds angstrom Dielectric material:capacitor thin papaer(ε r ~4.5) plastic film(ε r =2.0~2.3) 50~100V/µm Dielectric film ~200V/µm 30

31 Electric field strength(v/µm) Life Test of SH Capacitor Accelerated Life Test Electric field strength vs Lifetime SH NH Ref(n=20.8) L L 0 n V V 0 Capacitor Volume 1/4 Test Capacitor Test Results Breakdown capacitor inside Lifetime(Shots) 50pps X 7,000H X 8 Years Cross section of dielectric/electrode Configulation(not to scale) Group No. Sample No. Structure Dielectric strength (V/µm) lifetime (Hours) S S S S S S S Breakdown Capacitor 31 Element Lifetime : 8 Hours( 0.72 M shots)

32 Thyratron Switch 45 kv, 5 ka, 6 µs, 50 Hz Switching Anode Gradient Grid Litton EEV ITT L4888B CX2410K F-241 Specification of Thyratron F-241 Heater voltage Heater current Reservoir voltage Reservoir current Peak anode voltage Peak anode current 6.3 V 70 A(Max.) 2.5~6.0 V 20 A(Max.) 45 kv (Max. 50 kv) 4.8 ka(max. 10 kv) Average anode current 1.3 A(Max.8 A) Rate of rise of anode current Peak control grid voltage Control grid pulse width 5 ka/µs(max. 10kA/µs) 1.0~4.0 kv 2 µs(at 70% value) Inside structure of Thyratron F Control Grid(G2) Auxiliary Grid(G1) Cathode Heater Reservoir tank

33 Thyratron Switch Breakdown voltage vs. Gas Pressure Thyratron circuit Paschen Curve for Hydrogen Thyratron operation region Driver circuit Keep alive has ~250 ma dc current at 100 V 33

34 Example of Thyratrons History Example of Ranging(Reservoir Adjustment) Example of Ranging Tube Type: CX2410K Keep-alive Failure Lower Limit Optimized Value Upper Limit S/N: 68(95) : 5-2 取り付け : HV-ON 時で Ikeep(H,L)ITL : HV-ON 時で Ikeep(H,L)ITL : 運転時 Ikeep 流れない S/N: 55(95) : 5-1 取り付け : HV-ON 時で Ikeep 流れない S/N: 69(95) : 3-4 取り付け : HV-ON 時でIkeep(H,L)ITL : Ikeep 流れない 34

35 Number of Tubes Status of KEKB Thyratron Lifetime Profile Failure Modes Distribution Operation period ( Sep Feb.2008) : No. of Thyratrons= CX2410K F241 L4888B Reservoir Failure Others High voltage Break Down Time(kHours) G1 discharge Keep alive Failure Thyratron Quality? 35

36 Maintenance activity for Thyratrons Thyratron MTTF : 34,00 hours (as of 2011) To maximum lifetime, and to minimize cost. Acceptance Test Break down rate < 0.05/ hour after operating for 100 hours. Switching Jitter < 10 ns Anode delay time Exchange new thyratron in advance Most Important modulators ( such as buncher section) at intervals of two years(~14,000 hours), Exchanged one is reused. Checking and adjustment Reservoir current, keep-alive current, if necessary, adjust or exchange. Regular maintenance Ranging(reservoir voltage adjustment) check of jitter and pulse timing at intervals of one year 36

37 Klystron waveforms Klystron voltage, current, RF waveforms 37

38 Operation Statistics of KEKB Modulator Linac failure distribution(2007) Total operation time : 6322 Hours Machine failure time : 114 Hours Modulator failure distribution Modulator failure time = 17.6 Hours 53% of RF failure Reliabilty of an RF system is directly linked to the linac availability. Keep-alive current tuning Thyratron failure Air cooling fan Modulator availability=

39 Modulator Improvements By Power Devices Example : Charging Power Supply High-Power Solid-State Switch 39

40 PFN Charging Power Supply LC Resonant Charging(f=50 Hz) HV transformer : very Large Switching Power Supply(f=30 khz) HV transformer : very Small Transformer core size S V P N p f V p : Primary voltage N p : Number of primary turns S : Core cross section f : AC frequency N s N p S Transformer core 40

41 Charging Current(A) PFN Voltage(kV) Charging Current(A) Switching PS (DC-AC-DC Converter) DC AC(33kHz) DC Input Power Section Inverter section High Voltage Section Es= 45 kv, fr=50 pps Time(ms) µs 30µs(33 khz) Modulator Control System Block Diagram of Inverter Power Supply System(Toshiba) Time(ms) Expanded pulse top trace of the charging current 41

42 Down-sizing of KEKB Modulator LC Resonant Charging(f=50 Hz) ー > Switching Power Supply(f=30 khz) Original modulator Compact modulator 4.7m 1.8m Reduce the modulator size by one-third of the existing modulator. Switching power supply technology is essential to reduce modulator size. 42

43 Switching Power Supply Two type inverter power supplies have been developed at KEK. Design parameters Item Main Sub Charging voltage Vc((kV) Average charging current Iav(A) PFN capacitor C(µF) AC frequency f(khz) Voltage stability(%) Sub Power Supply Main Power Supply Charging time(ms) 17 - Charging power(kj/s) 34 5 Charging voltage stability V V I av V C f V : Charging voltage I av : Average charging current C : Capacitance f : AC frequency T C C V c I av 43

44 PFN Voltage Stability Measurement (Main power supply) 112.9V Voltage stability=112.9v/43kv=0.26%(p-p) for 10K times 44

45 PFN Voltage Stability Measurement Main + Sub power supplies 12.3V Voltage stability=12.3v/43kv=0.029%(p-p) for 10K times 45

46 Thyratron Replacement Switch Thyratron Short life time(~34khoures) Reservoir voltage Tuning(Ranging) Solid-State Switch Long life time(?) No tuning No heater & reservoir PSs 46

47 Thyratron Replacement Switch Many companies and Laboratories are currently developing various semiconductor switches to replace the thyratrons. Semiconductor Switches Technical Approach Series connection for high-voltage Parallel connection for high-current Array of semiconductor devices 47

48 APP Thyristor Switch(SLAC) 41cmx41cmx86cm(H) 2Px16S C. Burkhart, et. al, Development of a solid state thyratron replacement for the LCLS klystron modulator Pulsed Power Conference,

49 25kV SI-Thyristor Switch(PPJ) 25 kv, 5kA, 10µs, 10 Hz 6Px10S SI-Thyristors Switch Size : 300(W)x150(D)x500mm(H) F. Kamitsukasa, et. al, Development of a High-Power Solid-State Switch for a Klystron Annual Meeting of Particle 49 Accelerator Society of Japan 2013.

50 45kV 6kA Solid-State Switch KEK has evaluated Turn-on characteristics of SI-thyristor and has designed and built a 45 kv solid-state switch and successfully operated for 57 hours( 5 M shots). 50

51 SI Thyristor Structure of SI Thyristor SI Thyristor (Cathode) Diode for Inverse Current Isolation Band Gate Electrode Buried Gate Gate Cathode ne P ++ Channel n - SI Thyristor 92 mm Wafer Anode P e Current Flow Diagram of the on-state SI thyristor Voltage Turn off current RMS current di/dt 4.0 kv 600A 600A 150kA/µs Normally-on type device Vg=-20V 51

52 Tune-on Test SI-Thyristor and Gate driver circuit Low Inductance Test Circuit Capacitor Low-inductance Coaxial structure Diodes Equivalent circuit Photography of the test circuit Circuit inductance(~136nh) Gate driver circuit and SI-thyristor 52

53 Turn-on characteristics of SI-Thyristors Anode voltage and current waveforms Test Results - Peak current 10kA - Peak di/dt 110kA/µs - Switching time(90-10%) 128ns Peak anode voltage and Peak di/dt vs. Applied voltage Anode current di/dt waveform 53

54 15 SI-Thyristors connected in series 45kV 6kA Semi-Conductor Switch Hold-off voltage 45 kv Peak current 6,000 A Pulse width 6 µs Repetition rates 50 pps Device SI-Thyristor[NGK :RS1600PA40T1(4kV)] Connection 15 devices in series Insulation Oil Cooling Forced oil cooling 700 mm Switch assembly Basic circuit diagram Gate driver circuit and SI-thyristor 54

55 High-Power Test Circuit Performance test at ATF Operation Parameters Peak output power 136 MW Hold-off voltage 45 kv Peak current 6 ka Pulse width 6 µs Repetition rates 25 pps di/dt 10 ka/µs 55

56 Dead-Short Circuit Test 56

57 Switching Waveforms Normal operation Klystron Arc-down 57

58 Thyratorn vs. Solid-State Switch Switching Current Switching Voltage Thyratron : EEV CX1536 Thyratron Switching Time(90-10%): 40 ns Solid-State Switching Time(90-10%): 208 ns 58

59 Switch Losses of Solid-State Switch Switch losses were measured by calorimetry. PFN PFN Switch Details of switch losses Voltage (kv) Stored energy (J/pulse) Losses (J/pulse) Balance resisters Gate Circuits Devices (J/pulse) (J/pulse) (J/pulse) (5.8%) 0.98(10.5%) 0.8(8.5%) 7.6(81.0%) (5.8%) 1.92(9.0%) 0.8 (3.8%) 18.6(87.2%) (5.1%) 2.77(8.5%) 0.8 (2.4%) 29.2(89.1%) (5.0%) 3.10(7.4%) 0.8 (2.4%) 37.2(90.7%) Total switch loss is 41J/pulse. Main loss is devices(91%) 130 W/ C Oil cooling system 59

60 Long Pulse Modulator Example : ILC Modulator 60

61 ILC Modulator Specification Parameter Pulse Voltage Voltage Regulation Pulse Current Pulse Length(flat-top) Total Pulse Energy Repetition Rate Average Output Power Value 120 kv 1%(p-p) 140A 1.6 ms 27 kj 5 Hz 135 kw 61

62 Capacitance of Direct-switch Modulator Capacitor Size vs. Droop C R D r Capacitor Storage Energy (W C ) Output pulse Energy (W P ) Droop(D) Switch C R Droop(%) W c /W p Ratio Droop 62

63 Waveform function of Droop Compensation Load waveform The electric charge of Capacitor q(t), the circuit equation is given by Solve the equation at initial condition t=0, V 0, q(t) is Droop compensation circuit Calculating from the equation, in the condition q(0)=c V 0 at t=0 i(t) is given by In the condition i(t)=v 0 /R, V B (0)=0, V B (t) is given by 63

64 Bouncer Circuit LC resonant circuit V V R V OUT V Bounc 0 er t 64

65 Design Parameters of STF Modulator#2,3 Peak Output Power 16.8(12.0) MW Secondary Output Voltage 120(130) kv Secondary Output Current 140(92) A Pulse width 1.7 ms Flat-top width > 1.5 ms Rise time(10-90%) ~ 0.1 ms Flatness < ±0.5% Repetition Rate 5 pps Pulse Transformer Ratio 1:15 Capacitor Bank 2000 µf<20%droop> Energy deposit in klystron from gun spark < 20 J Main Switch Voltage 8.8(9.5) kv Current 2100(1380) A ( )=5MW Klystron 65

66 STF#2 Modulator Circuit Compact Switching PS IGBT Main Switch IGBT 1600V,600A 20S4P STF#3 IEGT Switch C 420V 3ø 50 kj/s Switching PS 100 µh Capacitor Bank 2 mf IGBT Main Switch 20S4P C 2mF Klystron L 0.3 mh LC Bouncer Circuit Main Cabinet Self-healing-type capacitor Pulse Transformer 1:15 Compact pulse transformer 66

67 Overview of STF Modulator #2 Storage Capacitor Bouncer Circuit IGBT Switch Klystron 50kW Switching PS Pulse Transformer Main cabinet is 4.2m wide x 2.2m deep x 2.2m high 3.8m(STF#3) 67

68 IEGT Switch for STF#3 Modulator Switch 9 kv, 2100A, 1.7 ms, 5Hz Redundancy of one-series Detect a short circuit fault for each IEGT device Gate Driver 6 stack IEGTs Snubber Circuit Comparison of IEGT and IGCT IEGT IGCT Device ST2100GXH24A (toshiba) 5SHY35L4511 (ABB) Voltage 4.5kV 4.5kV Turn-Off 5500A 3800A Current RMS 2100A 2200A Current di/dt 5000A/μs 1000A/μs Outline φ125mm post 26.5mm t φ85mm post 26.5mm t Gate Voltage Drive 20W Power Current Drive 100W Power IEGT(Injection Enhanced Gate Transistor) Transformer for gate driver PS IEGT Switch Assembly Size:900 mm W x 920 mm D x 685 mm H 68

69 Pulse Transformer Core size is optimized by rise-time of ~100µs Cross section of Core(A) Pulse Rise time(t r ) L l (Leakage inductance) N p 120kV A A V s N s B N s 1.7ms ~2T(dc-bias) t r 2.2 L l R L l 1 2 H 2 2 dv N s L l t r R s Klystron Resistance R=120kV/140A =857Ω 39mH 69

70 Pulse Transformer(2) STF#1Specifications of Pulse Transformer Primary voltage 21.7 kv Primary current 588 A Primary impedance 36.8Ω Secondary voltage 130 kv Secondary current 98 kv Secondary impedance 1327 Ω Flat-top pulse width 1.5 ms Rise-time(10-90%) 40µs Pulse droop < 3% Step-up ratio 1:6 Pulse repetition rate 5pps Design Feature DC bias Auto winding Heater transformer is isolation transformer type. Core assembly Cores 25 Cores used for JHF pulse transformer were reused in total number of 39 cores for cost saving. Material is 0.22mm thick silicon steal ribbon. 4.4 tons in weight 70

71 Pulse Transformer(3) 1255mm Design Values(Secondary side) Primary inductance : 60 H Leakage inductance : 20 mh Distributed capacitance : 570 pf 167T L l =28 mh@abb 65T 65T 1 65T 4 158T 1710mm 660mm 3 2 巻き線方式 Pulse Transformer assembly Main Pulse Transformer:4.8t Tank:1.84t Oil:2.5t Total weight:9.14t 71

72 Klystron Voltage Waveforms(STF#2) Bouncer trigger optimization Es=7.0 kv, Pw=1.7 ms, fr=5 pps 72

73 5 MW Klystron Operation(STF#2) Es=9.6 kv, Pw=1.70 ms, fr=5 pps Td=456 µs Rise-time(10-90%)=0.92 µs 73

74 Klystron Voltage Flat-top Waveform(STF#2) Es=9.6 kv, Pw=1.70 ms, fr=5 pps Td=456 µs 74

75 Klystron waveforms at Breakdown(STF#2) Energy deposit in klystron from gun spark Arc voltage=100 V W 100V W=2.0 J < design value I k dt Es=9.0 kv, Pw=1.7 ms, fr= 5 pps 75

76 P2 Marx Modulator(SLAC) RF System Overview P2 Marx Design Considerations Compatibility with two-tunnel design High availability Low-cost Ease of maintenance Portability of design to future applications 32 Cells 3.75 kv Nominal Cell Voltage N+2 Redundancy (4 kv Max) 350 µf Cell Capacitance One-cell 20% Droop Compensation Active, closed-loop control regulates output voltage Air Cooling/Insulating(No oil) Independent Charging Supplies FPGA-based Diagnostic/Control Module 76

77 P2 Marx Modulator(SLAC) Correction Scheme SLAC P2 Marx Cell Cell Output Current Cell Output Voltage Main IGBT V ce PWM Inductor Current Ripple Cancelation Droop compensation circuit 2 cells switching in phase 77 2 cells switching 180 o out of phase

78 P2 Marx Modulator(SLAC) Layout 283 cm H 168 cm D 347 cm W Oil-free Easy access 78 Marx cell : 22.7 Kg

79 P2 Marx Modulator(SLAC) Performance 79

80 P2 Marx Modulator(SLAC) 電力効率 (TDR) Arc-down test at full output power by a self-break oil gap across the load. Assuming a 200 V arc, we calculate a deposit of less than 10J. 80

81 Marx-type Modulators 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 81

82 10.00K 0.00K K K K MARX80ver2.CIR K 0.00m 0.40m 0.80m 1.20m 1.60m 2.00m v(r340) (V) t (Secs) 420 V 50 Hz 3φ 10kW Inverter Charging PS 10kW Inverter Charging PS 10kW Inverter Charging PS 10kW Inverter Charging PS Inverter Charging System 620 V 20 khz KEK Marx Modulator Isolation Step-up Transformer 2.0 k V 20kHz System Block Diagram Marx Unit #20 Marx Unit #19 Marx Unit #02 Marx Unit # kv DC -6.4 k V 140 A 1.7 ms 5Hz Klystron -120 k V 140 A 1.7 ms 5Hz 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 Simulated output voltage waveform 82

83 KEK Marx Modulator View 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) 83 is available.

84 Marx Unit 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 Output voltage 2.0 kv -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) 84

85 Marx Cell Marx cell parameters Marx Cell Parameter Value Input voltage -2.0 kv Output voltage -1.6 kv Capacitor voltage droop 20% PWM frequency 50 khz SiC 充電経路 FET 3P2S Storage capacitor C Filter L Filter C SiC SBD 2S IGBT 48uH SiC FET 3P2S IGBT 1.33uF SiC SBD 2S 550Ω Circuit diagram of Marx cell 0.133uF Opt.i/F Opt.i/F 400mm 300mm 75mm(H) SiC power devices(1.2 kv FET, SBD) were selected because of its higher breakdown voltage, low onresistance and fast switching speed. Energy conversion efficiency is about 93%. 85

86 SiC Power Device(Si vs. SiC) Reduce chopper switching loss by one-third comparing with Si device ON Si IGBT:IXGK75N V, 75A SiC FET:SCH2080KE 1200V, 40A 2S3P Frequency:50 khz Duty cycle :75% Charging voltage :1 kv Switching loss(1 cycle) 86

87 Charging and Pulsing in Marx unit Charging Pulsing -6.4kV Pulse DC -2kV (input) DC -2kV (input) Charging switch Chopping switch 87

88 Droop Compensation Output voltage droop of Marx cell Droop ratio: 20% PWM duty cycle is increased from 76% to 95% in proportion to time. Output droop can be compensated by PWM control. 88

89 Ripple Cancelation 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 Repetition Frequency -Order =5Hz CHG 2us PWM Frequency Duty_Start PWM Frequency Duty_Stop 10us PWM1 CELL Stage1 Dis-Charge PWM2 CELL Stage2 Dis-Charge PWM3 CELL Stage3 Dis-Charge PWM4 CELL Stage4 Dis-Charge Pulse Width=1.7ms 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. 89

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

91 Thank you for your attention! 91