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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 modulatordevelopment of a prototype by Carlos DE ALMEIDA MARTINS (CERN - AB/PO) 2nd Meeting LINAC4 Technical Design Commitee
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
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
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
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
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
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
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
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
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
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
4.1. Proposed topology:- Waveforms 2nd Meeting LINAC4 Technical Design Commitee
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
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
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
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
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
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
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