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Carlos DE ALMEIDA MARTINS ( CERN – Accelerators & Beams Department Power Converters Group )

Current development of [120kV, 40A, 1.5ms, 2hz] klystron modulators for CERN Linac 4 (A review of the state of the art in solid state technology). Carlos DE ALMEIDA MARTINS ( CERN – Accelerators & Beams Department Power Converters Group ). Collector (GND). On the electrical “side”,

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Carlos DE ALMEIDA MARTINS ( CERN – Accelerators & Beams Department Power Converters Group )

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  1. Current development of[120kV, 40A, 1.5ms, 2hz]klystron modulators for CERN Linac 4(A review of the state of the art in solid state technology) Carlos DE ALMEIDA MARTINS ( CERN – Accelerators & Beams Department Power Converters Group ) Development of klystron modulators for CERN Linac 4

  2. Collector (GND) On the electrical “side”, behaves like a transistor ~ hundreds kV -15 V + + Emitter - - V Anode mod (grid) (or DC) Base Collector Filament (source) (or DC) GND Cathode (-) It’s an Electrical to RF power converter !!! What is a Klystron? Development of klystron modulators for CERN Linac 4

  3. Icathode Collector Cathode 1/R A resistor … variable Vcathode Klystron arcing and protection Arc: Behaves like a short circuit (arc voltage ~ 50V); Maximum allowed energy in the arc: ~20 J (Power supply has to be quiclky switched off or bypassed) Normal operation Klystron as an electrical load Development of klystron modulators for CERN Linac 4

  4. RF PO 100 kV crowbar (Thyratron) Klystron 100 kV, 40A, DC (CW) power converter for LHC klystrons Past experience in klystron supply from Power Converters group at CERN. Thyratron CROWBAR Development of klystron modulators for CERN Linac 4

  5. Two main approaches, depending on the klystron type: Methods for klystron powering in pulsed mode Klystrons with Anode Mod terminal Klystrons without Anode Mod terminal • Limitations: • Klystrons are more expensive and less reliable; • Cathode voltage permanently applied - > insulation stress • Challange: • Development of the “pulser” power supply; • Power supply (converter) = klystron modulator Development of klystron modulators for CERN Linac 4

  6. With Anode mode terminal Klystron supply in pulsed mode.J-PARC, GSI topologies Ex: at J-PARC, Japan Ex: at GSI, Germany Development of klystron modulators for CERN Linac 4

  7. Without Anode Mod terminal (Thyratron + PFN based topology) Klystron supply in pulsed mode.Traditional topologies Ex: Linac 2, CTF3 at CERN • Limitations: • Use of cathodic tubes (thyratrons, ignitrons); •  Limited lifetime with increased maintenance; • Bulky and expensive system (PFN’s with increasing number of cells for large pulse widths; • Possible periodic PFN tuning required to compensate for ageing effects; Development of klystron modulators for CERN Linac 4

  8. The TESLA type modulator, H. Pfeffer, D. Wolff, and Al., FERMILAB Simplified electrical schematic, with pulse transformer Klystron supply in pulsed mode.Some recent solid state topologies 120 kV, 140A, 1.6ms, 5 Hz (Without pulse transformer) Development of klystron modulators for CERN Linac 4

  9. The Oak Ridge Nat Lab (SNS) type modulator, Bill Reass and Al. Los Alamos Lab Klystron supply in pulsed mode.Some recent solid state topologies 140 kV, 70A, 1.6ms, 60 Hz Development of klystron modulators for CERN Linac 4

  10. The SLACtype modulator, G. Leyh, R. Cassel and Al, SLAC 115 kV, 135A, 1.5 ms, 5 Hz Klystron supply in pulsed mode.Some recent solid state topologies Development of klystron modulators for CERN Linac 4

  11. 45 3 MeV Test Stand ( end 2007) 1 klystron modulator 3 MeV Test Stand – Phase I (2007, 2008) CERN 3 MeV Test Stand project(Linac 4 Front End) Due to the pulsed nature of the Linac, a pulsed solution was chosen for the klystron modulator Development of klystron modulators for CERN Linac 4

  12. Klystron modulator parameters for the 3 MeV Test Stand (LEP CW klystron) Rise time fall time time Flat-top Pulse width • Cathodes power supply • Pulse width: 0.8 ms • Flat-top duration 0.6 ms • Precision at flat-top: < 1% • HF ripple at flat-top: < 0.1% • Repetition rate: 2 Hz • Nominal voltage: 100kV • Nominal current: 20A • Rise/fall times: 150µs • Cooling: Air (natural and forced) • Maximum energy in case of arc: < 20 J • Anode Mode polarization power supplies • Stability at flat-top: < 1% • HF ripple at flat-top: < 0.1% • Nominal voltage to cathode : 40..60 kV • Nominal current: 5 mA • Filament heater power supplies • Stability and ripple: < 1% • Nominal voltage: 30V • Nominal current: 35A • Floating withstand voltage to ground: 180kVdc for 1 min. Development of klystron modulators for CERN Linac 4

  13. Proposed topology (to be used in the 3 MeV Test Stand and Linac 4) • Description • Capacitor bank charged via a standard commercial power converter, PS1; • Pulses formed by solid state medium-voltage switches; • Step-up pulse transformer with oil insulation; • Droop compensation system, PS2; • Commercial anode and filament power converters, PS3 and PS4, possibly with dry insulation; • No CROWBAR needed in the HV line for klystron protection Ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Simplified schematics CERN prototype of solid state pulsed klystron modulator. Development of klystron modulators for CERN Linac 4

  14. Some new technological improvements Switch mode filament heater power converter, PS4 CERN prototype of solid state pulsed klystron modulator. Droop compensation system, PS2 • Today, still a “passive bouncer”, but plans for active one: • Switch mode type; • Standard semi-conductor components; • Air insulation; • Fast closed loop feedback control Development of klystron modulators for CERN Linac 4

  15. CERN prototype of solid state pulsed klystron modulator. Main Components Pulse transformer • From STANGENES • Oil insulation; • 10kV / 100kV; • 200A / 20A; • 800µs / 2 Hz HV Main Solid state switch • From ABB – Lenzburg; • IGCT technology; • 5 (+2 redundant) IGCT in series; • 12 kV / 300A; • 1.5 ms / 2 Hz Development of klystron modulators for CERN Linac 4

  16. CERN prototype of solid state pulsed klystron modulator. Main Components Filament Heater Power Converter (HV oil tank shown) • From FUG; • Oil (or Dry Siligal) insulation; • 35V / 30A, DC; • Floating at 120kV HV plug-in connectors High-Frequency 180kVdc isolation transformer Diode rectifier bridge and filter box HV output connectors Development of klystron modulators for CERN Linac 4

  17. CERN prototype of solid state pulsed klystron modulator. Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms A global klystron supply solution: (Cathode, Anode, Filament) in one system Development of klystron modulators for CERN Linac 4

  18. Cathode voltage Thyratron Firing 200µs Earc (65kV)=0.44J Earc (100kV)~1J Cathode Current (4A/div) Cathode voltage (zoom at flat-top) Cathode Voltage (20kV/div) Without bouncer < 1% With bouncer Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Normal Operation Arc protection (short circuit with Thyratron) Test of the prototype in a dummy load Development of klystron modulators for CERN Linac 4 18

  19. Test of the prototype with the LEP klystron Ch2: Cathode Voltage to ground (20 kV/div) Ch2: Cathode Voltage to ground (2 kV/div) < 1% Ch3: Cathode Current (4A/div) Ch3: Cathode Current (0.8A/div) 1% 1.2% Ch4: Anode Voltage to ground (10 kV/div) Ch4: Anode Voltage to ground (1 kV/div) Cathode ratings: 100 kV, 20A, pulsed 2 Hz, flat-top: 600 ms Normal Operation at nominal Zoom at flat-tops Development of klystron modulators for CERN Linac 4 19

  20. Surface building for klystrons and modulators Low-duty SPL (2016 ?) Linac4 (2013) PS2 (2016 ?) ~ 100m LINAC 4 Tunnel Linac 4 – Phase II (~ end 2012) Linac 4 16 klystron modulators The CERN Linac 4 project 1st stage: Linac4 injects into the old PSB  increased brightness for LHC 2nd stage: Linac4 into SPL (and PS2)  renewed and improved LHC injection Development of klystron modulators for CERN Linac 4

  21. Klystron modulator parameters for Linac 4 (LEP CW klystrons + new pulsed klystrons) Rise time fall time time Flat-top Pulse width • Cathodes power supply • Pulse width: 1.5ms • Flat-top duration 1.2 ms • Precision at flat-top: < 1% • HF ripple at flat-top: < 0.1% • Repetition rate: 2 Hz • Nominal voltage: 120kV (*) • Nominal current: 2x20A (*) • Rise/fall times: 150µs • Cooling: Air (natural or forced) • Maximum energy in case of arc: < 20 J • Anode Mode polarization power supplies • Stability at flat-top: < 1% • HF ripple at flat-top: < 0.1% • Nominal voltage to cathode : 60 kV (*) • Nominal current: 5 mA (*) • Filament heater power supplies • Stability and ripple: < 1% • Nominal voltage: 30V (*) • Nominal current: 35A (*) • Floating withstand voltage to ground: 180kVdc for 1 min. (*) to be confirmed, taking the new klystrons design into consideration Development of klystron modulators for CERN Linac 4

  22. Klystron modulator for Linac 4Choice of topology Ratings: 120 kV, 40A, pulsed 2 Hz, flat-top: 1.2 ms Proposed topology: Identical to the prototype one • Modifications • Active droop compensation based on a fast switch-mode power converter (closed loop); • HV part of the filament heater power converter placed in the klystron oil tank (saves 2 HV cables/connectors and one oil tank); • One modulator will be able to supply one or two klystrons in parallel; Development of klystron modulators for CERN Linac 4

  23. + AC - DC 140 kV, 70A, 0.6ms?, 50 Hz Capacitor charger: In surface building Pulse former: In the tunnel A possible klystron modulator topology for large average power (Full SPL at 50 Hz). The dual topology of the LHC switch-mode converters (QF, QD): LHC magnets : High current / Low voltage -> several modules in parallel SPL klystrons: High voltage / Low current -> several modules in series Development of klystron modulators for CERN Linac 4

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