BINP kicker design proposal for ATF2

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BINP kicker design proposal for ATF2

• Boris Grishanov, Fedor Podgorny (BINP, Russia),
  Andrei Seryi (SLAC)
• ATF2 Workshop
• January 5, 2004

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Background

• Extraction of ILC-like train from ATF, within the
  conventional strategy, appears to be a complex
  and expensive task
• Realization of this task is at the limit of the
  technical capabilities of the element base
  available at present time
• In order to solve this task and build a very
  reliable system, it seems appropriate to share
  the difficulties with the adjacent systems

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Difficulties of ILC train extraction

• Need to form the packet of powerful high-voltage
  pulses with short rise time (1-2 ns) high rep
  rate (gt 2 MHz)
• Stringent requirements on time and amplitude
  accuracy and stability
• Absence of suitable switches
• In principle, the power-supply system can be
  built on the basis of the ultra-high-speed
  transistor switches produced by
  however, the single power of such switches is
  small
• Therefore this system will be bulky, expensive,
  and not sufficiently reliable
• Nevertheless, there are no other more suitable
  switches available

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Extraction concept

• Is based on the fact that the transverse beam
  size before the extraction is very small
• Therefore,
• there is no need to form the field of the kicker
  in the entire geometric aperture of the vacuum
  chamber
• there is no need to ensure the full-aperture
  throw of the beam only due to the impact of the
  kicker
• Taking this into account, one can significantly
  simplify the extraction system and the ILC-like
  train
• At the same time, one could reduce the number of
  kicker modules, high power switches and all the
  associated elements, lowering the cost and
  increasing the reliability

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Four parts of the concept

• Use low-aperture kicker located at the edge of
  the vacuum chamber
• Use local orbit bump which slowly drives the beam
  into the kicker and closer to septum at the end
  of the damping cycle before the extraction
• Use two groups of kickers to halve the rep rate
  of individual kickers
• Even optimistically, Behlke switches could not
  work with rep rate needed for ATF extraction.
  Solution the ensemble of kickers will consist of
  two groups moreover, the modules of kickers from
  the different groups are located alternatively.
  Each module is fed from its own pulsed power
  supply with a repetition frequency of about 1
  MHz, and the entire system works with twice
  higher frequency.
• Correct the drift length oscillation with RF
  corrector
• In this geometry the effective center of the kick
  become alternately shifted for the adjacent
  bunches by the length of one kicker module.
  Accordingly, the drift length will oscillate for
  the different bunches. If this difference exceeds
  the allowed value, the situation can be mitigated
  with the aid of the RF-corrector in the
  extraction line (or special power supply of one
  of the kickers).

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Extraction with low aperture kicker slow orbit
bump
built-in low aperture kicker
cross-section of the vacuum chamber
damping ring working aperture
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Schematics of the low-aperture kicker
Detail of the drawing low aperture kicker One of
the plates is split so that the beam could be
slowly moved into the kicker.
Ø 5 mm
1mm
Note Wakes in the 1mm gap during multi-turn
orbit bump need to be studied
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Field map in the kicker
Dimensions of the plates and of the bus are
chosen to provide 50 Ohm impedance
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Kicker pulse shape
Kicker pulse shape with fixed amplitude of the
traveling wave pulse and for various length of
the kicker (15, 20, 25, 30, 40, 60 cm).
Calculated for quasi-square pulse with 2.5ns FWHM
duration and with raise/fall (with sin2 shape)
duration of 1.5ns. This picture shows that the
length of the kicker should not be longer than
20cm.
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Two groups of kickers to double rep rate
Difference of drift length
Pair of kicker modules from neighboring groups,
for doubling the rep rate Each module works with
rep rate of about 1 MHz Angle, provided by a
single 20cm module working in the traveling wave
regime, is up to 0.5 mrad Difference in drift
length is canceled by an RF-corrector in
extraction line
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Blue and yellow kickers are working on odd and
even turns.
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Septum

• The present ATF septum has 22mm knife thickness
• Narrower (3-4mm) knife septum is possible
• It is very beneficial (or even necessary) to
  rebuild the septum, to reduce the required kick

extraction chamber
main chamber
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Septum of SR source Siberia-2

• Next page shows drawings of vacuum chamber of
  Siberia-2 storage ring (made by BINP for
  Kurchatov Institute) near the septum magnet.
  Developed by V.Kiselev, V.Korchuganov, V.Ushakov,
  A.Filipchenko. Field of septum 2 ?, knife
  thickness about 2.5 mm, aperture 1014 mm2,
  powered by sin-half-wave with duration about 100
  ms. The beam size is about 1mm, the nominal orbit
  is located about 3mm from the wall of the knife.
  The knife is copper with magnetic screan.

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Siberia-2 septum
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Another septum example

• Photo of septum with copper bus, knife 3mm,
  aperture 84mm2, field 3 ?, powered similar as
  previous.

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Kicker location optimization

• In present configuration and with 22mm septum
  knife the required kick is 5mrad
• That would require 20 modules gt x0.2m 4m 1m
  5m which is 2-3 times longer than available
  space
• Optimizing the kicker location and reducing the
  needed kick by modifying the septum would be
  needed

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Tentative parameters
The number of modules depend on the possibility
to provide orbit correction and modify the septum
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Conclusion further work needed

• The proposed concept can make it possible to form
  the ILC-like bunch train at ATF on the basis of
  contemporary element base with the reasonable
  cost and good reliability
• Further work is needed, in particular
• Evaluation of the possibility to modify septum
• Estimate impact of wakes
• Optimize orbit correction bump
• Define needed number of kicker modules
• Detailed design of kicker module
• Prototype, test and final construction