ILC Damping Ring Kickers

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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 ltlt 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
  lt7x10-4 for preceding and following pulses.

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Snap / Step Diodes

• lt50 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 pulses Repetition rate
limited to KHz (for these devices). Institute
of Electrophysics
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Avalanche Transistors

• Avalanche Transistors
• lt200 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 ltlt1 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 voltage 2.5MHz 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 lt700
  Femtoseconds! (expect lt170 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, lt1.5ns 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 -gt effective
  rise time
• Need short (lt 1 Meter) kickers.
• Need to avoid reflections / ringing
• Must be designed as a RF component
• Full EM 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 -gt 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.