ilc damping ring kickers presenter: josef frisch dec 7, 2004
TRANSCRIPT
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ILC Damping Ring Kickers
Presenter: Josef Frisch
Dec 7, 2004
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Basic kicker types
• Conventional pulser (Remainder of this presentation).– High voltage pulse driving (probably) strip line kicker– Simple, minimal impedance problems (screen electrodes)– May require exotic pulser.
• RF kicker– Pulsed RF source driving low Q deflection structure. – Makes use of available high power, broadband RF sources– Possible impedance issues
• Resonant deflection system– Uses multiple resonant cavities driven with a set of frequencies
to select bunches– Multiple designs – too varied to discuss here– Quasi-CW RF eliminates ringing, provides good stability– Impedance, RF kicks within bunches, etc need to be understood.
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Approximate requirements for pulsed kicker
• Deflection angle 0.6 mrad (0.01 T-M) for TESLA ring design
• If we allow 10 Meter total kicker length– Need 50 Amp kicker drive
• Length of each kicker << bunch spacing (assuming speed of light kicker).– For 3 nanosecond, need ~20 Kickers
• Stripline kicker impedance probably ~100 Ohms (assuming speed of light kicker)
• Pulsers: 5Kv, 50Amp, 20 units, 2nanosecond rise and fall time .– Just for scale: Actual specifications depend on detailed ring
design• Un-kicked bunches must not be disturbed by more than
7x10-4 of kicked bunch.
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Basic Extraction Scheme
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Comments on Basic Scheme
• Shortest ring for given current– No unused bunches, or gaps (except ion clearing).
• Tight requirements on kicker stability and fall time– Need to not disturb neighboring bunches by more
than 7x10-4 of kicked bunch
• Falling edge of a pulse typically more difficult to control than rising edge. – Ringing from impedance mismatches, stray
inductance etc.
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Buffer pulse scheme
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Comments on buffer pulse scheme
• “Buffer” pulses are not needed for luminosity– Can probably kick by 10-2 of main kick– Allows longer settling time to 7x10-4.
• Need to replace buffer pulses– May be tricky with positrons if bunches are generated
by main electron beam: Might need to waste a machine cycle.
• Slightly longer ring for same average current.
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Kicker Gap Scheme
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Comments on Kicker Gap Scheme
• Gap allows extraction kicker with fast rise, but unrestricted settling for next pulse, settle to 7x10-4 after gap
• Injection kicker (larger pulse) only needs 1% interference with preceding bunch, and 1% after gap.
• Scheme does not work if positrons generated by luminosity generating electron beam– Works if you have a pre-damping ring.
• Scheme requires that ring empty, then re-fill in 2 milliseconds – might cause ring stability problems.
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Kicker Gap Extraction & Injection
Injection and extraction with fast rise slow fall if DR size is not determined by kicker rise time
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Comments on Kicker Gap Scheme
• Average ring current constant
• Allows use of slow fall time kicker
• Requires 2X ring length for same bunch spacing.
• Beam current harmonic content changes– DR physics question
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Kicker Driver Requirements
• 20 Units• ~5KV, 50Amps
– Depends on damping ring design, kicker length, etc– 250KW peak power– 2.5KW, average power, 1 millisecond– 25 Watt long term average
• Few nanosecond rise and fall, with settling to <7x10-4 for preceding and following pulses.
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Snap / Step Diodes
• <50 picoseconds to 20V. • sub-nanosecond to 300V, 6 Amps.
(1800W peak). • High power devices from Institute of
Electrophysics– 600 picosecond to 1000 Amps (?? Voltage)– 5 nanosecond to 400KV. – Repetition rates to few KHz.
• Power dissipation probably limits rep rate.
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Step recovery diode pulses
Very fast high voltage pulsesRepetition rate limited to ~KHz(for these devices).
Institute of Electrophysics
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Avalanche Transistors• Avalanche Transistors
– <200 picoseconds to 200V, ~50 Amps (10KW)
– Arrays (tapered transmission lines) demonstrated to 40KV, 800A, 200ps. (Kentech)
– Recovery time too long except in liquid nitrogen (50nsec reported)
– Average power limited to ~1W / device.
– Combining may lead to ringing.
• Low Repetition Rate
40 KV in 200ps rise time (Kentech)
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MOSFETs• Individual devices to ~1Kv, ~50Amps, ~3ns rise and fall
times. • Variety of combining schemes to high power, medium
fast rise. – DARHT-2 kicker: 20KV, 10ns rise / fall, 1.6MHz burst ( 4 pulses)– Belkhe / TESLA: 7.5Kv, 72A, 5.3ns, 1MHz (200 pulses). (fall
time slower)– Belkhe – datasheet 3Kv, 80A, 2ns, 1 MHz (MAX) burst. (10
pulses). – Kentech: 10Kv, 2ns – could operate at high rate.
• Relatively low impedance – (~10 Ohms), stray inductance ringing can be a problem– Gate drive is very low impedance <<1 Ohm.
• Probably OK for ~10 nsec rise / fall times. (maybe faster)• May be used as driver for additional stage / compressor
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MOSFET Pulses
4MHz pulses, but with 18ns risetime
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More MOSFET pulses (Kentech)
5 channels
Lower voltage2.5MHz pulser
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MOSFET pulser comments
• Very likely to use MOSFET technology in pulser – maybe with shock line for compression.
• Some designs (Belkhe) are very fast but have limited repetition rate. Problem is not thermal – but design in proprietary.
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Shock Lines - Ferromagnetic• Nonlinear transmission line: Wave velocity increases with pulse voltage• “Sharpens” front end of pulse• Ferromagnetic (most common): (used for SLAC Kicker (Cassel)• 95KV, 380 Picoseconds rise (Seddon et al, 1987), Ferroxcube B2 ferrite
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Shock Lines – Ferromagnetic (SLAC)
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Ferromagnetic Shock Lines, Falling edge
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Shock Lines - others
• Ferroelectric– 20KV, 400 Picosecond (Oxford – Web report)
• Diode loaded line– Monolithic (Allen, 1994 thesis), 4V at <700
Femtoseconds! (expect <170 fsec in future)
• Vacuum Magnetron line: – At high voltages, magnetic field insulates line– Probably only applicable at higher power than
we require.
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Shock Lines - comments
• Most work in shock lines has been to obtain very fast, very high power pulses – well beyond our requirements
• Typically operated at low repetition rates.• Need to eliminate (typical) slow tail from release of
energy stored in non-linear material. • For ILC high repetition rate may lead to heating
problems (need low loss nonlinear material). • Ferromagnetic and ferroelectric materials tend to also
have magnetostrictive / piezoelectric effect– For millisecond pulse burst could lead to stability problems.
• Many non-linear materials have strong temperature sensitivity – may lead to stability problems.
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Hard Tube Switches
• Pulser based on Eimac Y-690 tube used for Pockels Cell drive at SLAC (M. Browne, D. Brown). – 6KV, 30 Amps, <1.5ns rise time.– Driven by avalanche transistors – not appropriate for
high repetition rate– Would need to parallel 2 tubes for ILC kicker (easy)
• Nonlinearity of tubes helps with settling time. • Average power “not unreasonable” but would
need to check. (grid dissipation)
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Hard Tube Pulser
Note, tail on pulse believed to be due to output Transformer (not needed for ILC kicker)
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Custom Tube Pulser
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Custom tube Comments
• Single beam switched between multiple (~20) Anodes.
• Tube parameters comparable to other big power tubes (klystrons).
• Something of this sort would very likely work, but would require a large development effort.
• Only consider if conventional pulsers will not work.
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Kicker Magnet
• Probably need speed of light kicker• Kicker fill time + pulse rise time -> effective rise
time– Need short (< 1 Meter) kickers.
• Need to avoid reflections / ringing– Must be designed as a RF component– Full E+M simulation / optimization
• Possibly shield beamline with thin screen (to block beam wakefields (~10GHz), but transmit kicker fields (~300 MHz).
• Want optimized design to minimize kicker power
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Stability / Settling time issues
• Multiplicity of kickers helps with random noise
• Reproducible and small settling time problems can be fixed with additional kicker driven by AWG and power amplifier.
• Probably want feed forward from beam position / angle out of ring to kicker in main beam line– Assumes turn-around after damping ring
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Correction Scheme
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Correction Scheme - variant
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Correction scheme / layout issues.
• The 7x10-4 stability specification is Heroic!– Difficult to measure without a beam line
(ATF?)
• The kicker driver will likely have pulse – pulse feedback to flatten the waveforms
• Would like a beamline arrangement which allows feed-forward from output beam
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Ongoing Work
• ATF Damping Ring in Japan: Proposal to build a single pulse extraction system– Good test bed for kickers, and stabilization– Provide ILC – like test beam (~200 bunches)– Requires higher Kicker drive power than ILC
• Working on kicker / optics design to reduce
• DHART FET pulser -> shock line– Test high repetition rate shock lines
• DESY working on paralleling Belkhe pulsers to increase repetition rate.
• SLAC to obtain Belkhe pulser for testing shock lines.
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Overall Comments
• Can probably build a kicker to meet any likely damping ring requirements, for a small fraction of the damping ring cost– Optimize the ring design, see what is needed.
• Best guess: MOSFETs driving Ferromagnetic shock line. – Hard tubes an option.
• Custom tube can probably solve the problem, but expensive to develop – leave as a backup plan.
• Want technology demonstration prototypes soon, to allow selection of technology, and system development.
• Kicker parameters (voltage, current, etc) depend on details of ring design.