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A solid state long pulse klystron modulator development of a prototype

A solid state long pulse klystron modulator development of a prototype. by Carlos DE ALMEIDA MARTINS (CERN - AB/PO). Pulsed power modulators in traditional technology; Solid state long pulse power modulators: - A state of the art by different HEP laboratories;

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A solid state long pulse klystron modulator development of a prototype

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  1. A solid state long pulse klystron modulatordevelopment of a prototype by Carlos DE ALMEIDA MARTINS (CERN - AB/PO) 2nd Meeting LINAC4 Technical Design Commitee

  2. Pulsed power modulators in traditional technology; Solid state long pulse power modulators: - A state of the art by different HEP laboratories; CERN solid state long pulse modulator: - prototype specifications; Proposed topology; Estimated cost breakdown and time planning; Possible future improvements; Topics of the presentation 2nd Meeting LINAC4 Technical Design Commitee

  3. 1. Pulsed power modulators in traditional technology • Limitations: • Use of cathodic tubes (thyratrons, ignitrons); • Limited lifetime and increased maintenance; • Bulky and expensive system; • Periodic PFN tuning required to compensate ageing effects; • PFN’s with increasing too much cells for large pulse widths; 2nd Meeting LINAC4 Technical Design Commitee

  4. 2. Solid state long pulse power modulators • Developed during the 90’s; • Replacement of cathodic tubes by solid state HV semi-conductor switches; • Different HEP laboratories, including CERN for short pulses, have developed and constructed prototypes based on different topologies; • In this presentation: • Brief review of the state of the art in long pulse applications (>100 µs); • CERN (AB/PO, AB/RF) proposal for a solid state long pulse modulator prototype: • - gain expertise in this technical domain; - design the modulator as a power converter; • - develop a prototype before series production of similar modulators in view of LINAC 4; 2nd Meeting LINAC4 Technical Design Commitee

  5. 2. State of the art by different HEP laboratories Two main approaches, depending on the klystron type: Klystrons with Anode Mod terminal Klystrons without Anode Mod terminal • Advantages and Drawbacks • DC power supply as a commercial product; • Simple and low cost solution; • Cathode terminal permanently connected to HV •  Increased degradation of klystron insulation; • Minimum cathode current may be required between pulses (dead zone) to stabilize the klystron; •  Increase the power of the DC power supply; • Advantages and Drawbacks • Klystron is supplied only during the pulse (useful period); • Zero current on the cathode between pulses • Minimizes electrical consumption; • Invest on the design and construction of the “pulser” part 2nd Meeting LINAC4 Technical Design Commitee

  6. 2.1. Topologies for pulse anode modulation The GSI type modulator • Description • Cathode terminal is fed by a non-floating commercial DC power supply, PS1; • Use of a switch mode power converter for droop compensation, PS2; • Anode terminal is fed by a floating “pulser” composed by a DC power supply, standard solid state switches and a HF transformer; 2nd Meeting LINAC4 Technical Design Commitee

  7. 2.1. Topologies for pulse anode modulation The J-PARC type modulator • Description • Cathode terminal is fed by a set of HV AC/AC and AC/DC power converters; • No droop compensation system; • Anode modulation terminal supply is derived from the cathode DC-link line using a cathodic tube “pulser” • Drawbacks (GSI and J-PARC modul) • High voltage permanently applied to the cathode terminal; • Minimum cathode current may be required between pulses for stabilization; • Capacitor bank has to be considerably increased to reduce voltage droop; • HV CROWBAR on the DC-link line is required for protection in case of arcing • Advantages (GSI and J-PARC modul) • Direct supply of the cathode terminal with a standard power supply; • No need for intermediate step-up devices; • Simple and reliable; 2nd Meeting LINAC4 Technical Design Commitee

  8. 2.2. Topologies for pulse cathode modulation • Description • Medium voltage capacitor bank charged via a SCR rectifier; • DC-link bus feeds 3 independent IGBT H bridge inverters • Each H-bridge inverter feeds a HF step-up transformer with secondary windings connected in star, forming a 3-phase system; • Capacitors in parallel with secondary windings allowing for resonance soft switching techniques; • The HV line is obtained from a 3-phase diode rectifier The Oak Ridge Nat Lab (SNS) type modulator • Advantages • Pulse generator and droop compensation integrated in a all-in-one system; • Topology compatible with any pulse width specification; • HF transformers with high watt-per-kilo ratio; • Minimal stored magnetic energy in the transformer because of AC 3-phase operation. Avoids CROWBAR in HV line; • No controlled active devices in the HV line. • Drawbacks • Very complex topology. Impacts on cost, reliability maintenance, component availability; • Very complex control algorithms; • Soft switching techniques on the H-bridge unavoidable for large pulse widths. •  Further increasing complexity. 2nd Meeting LINAC4 Technical Design Commitee

  9. 2.2. Topologies for pulse cathode modulation The FERMILAB/DESY (TESLA) type modulator • Description • A capacitor bank is charged to medium voltage by a standard power supply; • Capacitor bank is discharged in the primary winding of a pulse transformer by a solid state switch stack; • The voltage is increased by the step-up transformer and applied to the cathode; • A “bouncer circuit” is connected in series with the primary winding for voltage droop compensation • Advantages • Simple, reliable and of relatively low cost; • No active devices in the HV side; • All electronic devices and components can operate with dry-type insulation; • No need for CROWBAR system in the HV line. Stored energy in the transformer and stray capacitances will be dissipated in the undershoot network, in case of arcing. • Drawbacks • Pulse transformer (DC component) may be too much bulky in extra long pulse applications; • The “bouncer circuit” is still an open loop compensation system. Limitations on the pulse flatness. 2nd Meeting LINAC4 Technical Design Commitee

  10. 3. CERN solid state long pulse modulator specifications (i.e. 3 MeV test stand) 4. Proposed topology • Identical to the FERMILAB/DESY modulator; • With an improved closed loop voltage droop compensation system, based on a high frequency switch mode power converter 2nd Meeting LINAC4 Technical Design Commitee

  11. 4.1. Proposed topology:- Power part schematics • Description • Capacitor bank charged via a standard commercial power supply, PS1; • “Pulser” formed by solid state medium-voltage switches; • Step-up pulse transformer with oil insulation; • Active closed loop droop compensation power converter, PS2; • Commercial floating anode and filament power supplies, PS3 and PS4, with oil insulation in the output stage; • Installation of a thyratron CROWBAR in the HV line for klystron protection during the test campaign Simplified schematics 2nd Meeting LINAC4 Technical Design Commitee

  12. 4.1. Proposed topology:- Waveforms 2nd Meeting LINAC4 Technical Design Commitee

  13. 4.1. Proposed topology:- Commercial power converters Commercial power converters, PS1, PS3, PS4 • From FUG or Heinzinger, switch mode; • Price offers received; • Dry insulation technology for PS1; • Traditional, well proved oil insulation technology (PS3 and PS4); • Technical visit to these companies on the 4th and 5th May 2006; High Voltage stage Low Voltage stage High Voltage stage Low Voltage stage High Frequency transformer 2nd Meeting LINAC4 Technical Design Commitee

  14. 4.1. Proposed topology:- Droop compensation Droop compensation power converter, PS2 • CERN (AB/PO) made, switch mode type; • Standard semi-conductor components; • Air insulation; • Fast closed loop feedback control 2nd Meeting LINAC4 Technical Design Commitee

  15. 4.1. Proposed topology:- Pulse transformer Pulse transformer • From STANGENES (world leader in design and production of high voltage pulse transformers); • Price offer received; • Oil insulation (possibility for dry-type in a later stage); • Technical visit to this company in July 2006; 2nd Meeting LINAC4 Technical Design Commitee

  16. 4.1. Proposed topology:- Main solid state switch Main solid state switch • From BEHLKE, Germany; • Price offer received, for a 14 kV, 600Apk device; • Dry-type insulation; • Integrated driver; • Technical visit to this company in the 16th May 2006 2nd Meeting LINAC4 Technical Design Commitee

  17. 8.5 cm 4.1. Proposed topology:- 100 kV connectors and cables LEP type connectors and cables re-used for the prototype Connectors and cables for future developments in dry-type technology 2nd Meeting LINAC4 Technical Design Commitee

  18. 5. Estimated cost break-down and time planning Cost break-down • Tentative time schedule • Prototype construction in Autumn 2006; • First pulses by the end of 2006; • without droop compensation power converter; • with a resistive passive load simulating the Klystron; 2nd Meeting LINAC4 Technical Design Commitee

  19. 6. Possible future improvements • Use of dry-type insulated pulse transformers; • Use of dry-type commercial power supplies; • Use of dry-type insulated Klystrons ??; • Select better suited HV cables and connectors; • Optimization for production in series; For further details, please consult the Functional Specification EDMS no. 707883: https://edms.cern.ch/document/707883/1 2nd Meeting LINAC4 Technical Design Commitee

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