CERN modulator R&D Pulsed High Power Modulators

1. CERN modulator R&DPulsed High Power Modulators 09/03/2010 CERN Pulsed Power Modulators

2. Summary Day1 • General • PV: Clarify functions for optimisation of topology/design • DA: RF team needs to be included in design process • PV: How to make a system study to assess best solution CERN Pulsed Power Modulators

3. Definition of a voltage pulse Klystron: Energy deposited in case of quench <10J ‘pre-beam energy consumption’ PC + LLRF stabilisation time Fall time Beam time Rise time Droop (1 – 5% nominal) Klystron: -20% of nominal (max) time ‘Flat-top’ Pulse width Reset time Min repetition period CERN Pulsed Power Modulators

4. Summary Day1 • Topologies • Measurement/characterisation of klystron arc voltage • Visit of klystron manufacturer to clarify klystron characteristics (eg during L4 contract discussions) • Is a klystron max reverse voltage 20%, <20% or <<20%? • Flat top droop v klystron efficiency ? CERN Pulsed Power Modulators

5. Summary Day1 • Topologies • Classic Bouncer used by Fermilab and Desy (XFEL) • Marx still not in final version at SLAC after 10yrs (proto2 in progress) • Many switches (5 x 3 x 16), with single switch failure = klystron failure • What about HF component in waveform? CERN Pulsed Power Modulators

6. Summary Day1 • Topologies • SNS failures due to loss of soft switching • Generally good approach to design (HF resonant link) • Does the RF feedforward fully compensate the switching ripple? • Karlsrue Modulator used SMES – could be good idea if large cryo installation already available… • RAL (DTi) • Single switch reliability? No other manufacturer likely to be interested in such a switch. 5% droop. • What price did RAL pay for system? CERN Pulsed Power Modulators

7. 2e- DTI (Direct Switch) topology 110 kV, 45A, 2ms, 50 Hz (9.8 MWpk, 940 kWav) • Voltage droop is 5%; • All components in oil (difficult to access for repair); • Reliability in arc protection?; • Compact (no transformers); • 100kV IGBT technology is single source and pattented; • - Needs to be checked further Study of Large Average Power Pulsed Klystron Modulators Carlos Martins – IST / CIEEE

8. Summary Day1 • RF – HF Ripple • Does the RF feedforward fully compensate the switching ripple? • What is the acceptable RF phase ripple? • RF CL bandwidth ~10kHz • L4 states total budget is ±0.5deg in cavity; • 1% ripple = 8 deg; • Implies feedforward compensation for total ripple = equivalent of 0.01% above 10kHz • Simulations with RF in progress CERN Pulsed Power Modulators

9. Summary Day1 • RF - CLIC • Requires 0.02 deg phase stability • Can feedback due to 20km transport delay to give 0.2deg • Openloop klystron performance gives RF quality (<200us pulse) • Feedforward can correct systematic errors • Implies non-systematic ripple must be <0.001%... CERN Pulsed Power Modulators

10. CLIC Layout CERN Pulsed Power Modulators

11. Summary Day 1 • 50Hz, >100kW (average) topologies seriously considered: • Extrapolation of monolithic bouncer design? • Interleaved bouncer design • Resonant HF link • Interleaved systems will have problems with reproducibility (sub harmonics change with environment variables such as temperature, etc) CERN Pulsed Power Modulators

12. 3- New topologies oriented for large average power a) – Pulse transformer based • Main challenges: • - Pulse transformer design and construction; • Availability of the main solid state switch; • Droop compensation system; Modulator Study of Large Average Power Pulsed Klystron Modulators Carlos Martins – IST / CIEEE

13. 3- New topologies oriented for large average power Potential applications ( My View) V Rise time Fall time time Flat-top Pulse width Study of Large Average Power Pulsed Klystron Modulators Carlos Martins – IST / CIEEE

14. 3- New topologies oriented for large average power b) – Pulse transformer based, modular and interleaved • Main challenges: • - Pulse transformer design and construction; • Availability of the main solid state switches; • Droop compensation system; • HV decoupling diodes; • Pulse-to-pulse reproducibility Capacitor charger #2 Capacitor charger #n Capacitor charger #1 Droop comp. #1 Droop comp. #2 Droop comp #n + - + - + - Klystron Klystron voltage time Study of Large Average Power Pulsed Klystron Modulators Carlos Martins – IST / CIEEE

15. 3- New topologies oriented for large average power + + + AC AC AC DC DC DC - - - c) – Modular resonant ZCS/ZVS • Main challenges: • HF transformers design and construction; • Design of H-bridge and IGBT drivers guaranteeing soft-switching in ZCS-ZVS • Mitigate sub-harmonics due to unbalancing of the modules; Study of Large Average Power Pulsed Klystron Modulators Carlos Martins – IST / CIEEE

16. Key Unknowns • Technology • What is the best topology for a given application/pulse width? • What are the technology limitations (magnetics, switches, etc)? • Efficiency • How to get the best efficiency for usable output power? • Minimise rise times and system power losses? • Size (+ weight + layout) • What infrastructure is required? Can the system be split? Underground installation? • Cost • Initially first order cost is sufficient, with improving estimates as design is refined CERN Pulsed Power Modulators

17. Summary Day1 • Comparison of topologies: • Table (graph?) needed with all main topologies at a given pulse power, with size, cost, efficiency, ripple • Two tables • SPL parameters • CLIC drive beam parameters • Include commercial offerings (TT, Scandinova) CERN Pulsed Power Modulators

18. Selected long-pulse modulators CERN Pulsed Power Modulators