Injection and Extraction intoout of Accelerators

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Injection and Extraction into/out of Accelerators

• Neil Marks,
• ASTeC, U. of Liverpool.
• Daresbury Laboratory,
• Warrington WA4 4AD,
• U.K.
• Tel (44) (0)1925 603191
• Fax (44) (0)1925 603192

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The Injection/Extraction problem.

• Single turn injection/extraction
• a magnetic element inflects beam into the ring
  and turn-off before the beam completes the first
  turn (extraction is the reverse).
• Multi-turn injection/extraction
• the system must inflect the beam into
• the ring with an existing beam circulating
• without producing excessive disturbance
• or loss to the circulating beam.
• Accumulation in a storage ring
• A special case of multi-turn injection -
  continues over many turns
• (with the aim of minimal disturbance to the
  stored beam).

straight section
magnetic element
injected beam
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Single turn simple solution

• A kicker magnet with fast turn-off (injection)
  or turn-on (extraction) can be used for single
  turn injection.

B
t
injection fast fall
extraction fast rise
Problems i) rise or fall will always be non-zero
? loss of beam ii) single turn inject does not
allow the accumulation of high current iii) in
small accelerators revolution times can be ltlt 1
ms. iv) magnets are inductive ? fast rise (fall)
means (very) high voltage.
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Multi-turn injection solutions

• Beam can be injected by phase-space manipulation
• a) Inject into an unoccupied outer region of
  phase space with non-integer tune which ensures
  many turns before the injected beam re-occupies
  the same region (electrons and protons)
• eg Horizontal phase space at Q ¼ integer

septum
0 field deflect. field
turn 2
turn 3
turn 1 first injection
turn 4 last injection
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Multi-turn injection solutions

• b) Inject into outer region of phase space -
  damping coalesces beam into the central region
  before re-injecting (leptons only)

c) inject negative ions through a bending magnet
and then strip to produce a p after injection
(H- to p only).
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Multi-turn extraction solution

• Shave particles from edge of beam into an
  extraction channel whilst the beam is moved
  across the aperture

septum

• Points
• some beam loss on the septum cannot be prevented
• efficiency can be improved by blowing up on
  1/3rd or 1/4th integer resonance.

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Magnet for injection and extraction (i).

• i) Kicker magnets needed to deflect the
  circulating beam for a very short time (a small
  number of turns) they need
• pulsed waveform
• rapid rise or fall times (usually ltlt 1 ms)
• flat-top for uniform beam deflection.
• Usually achieved with a
• window frame design

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A typical kicker magnet (EMMA)
Because of the high frequency waveform, the
magnet yoke is assembled from high frequency
ferrite. Work performed by Kiril Marinov (ASTeC)
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Magnet for injection and extraction (ii).

• Septum magnets needed to deflect (strongly) the
  injected or extracted beam without deflecting the
  circulating beam.
• pulsed or d.c. waveform
• spatial separation into two regions
• one region of high field (for injection
  deflection)
• one region of very low (ideally 0) field for
  existing beam
• septum to be as
• thin
• as possible to
• limit beam loss.

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Septum Magnets classic design.

Often (not always) located inside the vacuum and
used to deflect part of the beam for injection or
extraction

• The thin 'septum' coil on the front face gives
• high field within the gap,
• low field externally
• Problems
• The thickness of the septum must be minimised to
  limit beam loss
• the front septum has very high current density
  and major heating problems

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Septum Magnet eddy current design.

• uses a pulsed current through a backleg coil
  (usually a poor design feature) to generate the
  field
• the front eddy current shield must be, at the
  septum, a number of skin depths thick elsewhere
  at least ten skin depths
• high eddy currents are induced in the front
  screen but this is at earth potential and bonded
  to the base plate heat is conducted out to the
  base plate
• field outside the septum are usually 1 of
  field in the gap.

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A modern septum design (EMMA)
Work performed by Kiril Marinov (ASTeC)
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Comparison of the two types.

Classical Eddy current Excitation d.c or
low frequency pulse pulse at gt 10
kHz Coil single turn including single or
multi-turn on front septum backleg, room
for large cross section Cooling complex-
water spirals heat generated in in thermal
contact with shield is conducted to
septum base plate Yoke conventional
steel high frequency material (ferrite
or radio metal).
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Kicker power supplies - distributed

Standard (CERN) delay line magnet and power
supply
? Power Supply ? Thyratron? Magnet
?Resistor The power supply and interconnecting
cables are matched to the surge impedance of the
delay line magnet
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Kicker Power supplies lumped.

• The magnet is (mainly) inductive - no added
  distributed capacitance
• the magnet must be very close to the supply
  (minimises inductance).

I (V/R) (1 exp (- R t /L)
i.e. the same waveform as distributed power
supply, lumped magnet systems..
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Improvement on above

The extra capacitor C improves the pulse
substantially.
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Resulting Waveform

Example calculated for the following parameters
mag inductance L 1 mH rise time t 0.2
ms resistor R 10 W trim capacitor C
4,000 pF. The impedance in the lumped circuit is
twice that needed in the distributed! The voltage
to produce a given peak current is the same in
both cases.
Performance at t 0.1 ms, current amplitude
0.777 of peak at t 0.2 ms, current
amplitude 1.01 of peak. The maximum
overswing is 2.5. This is much simpler and
cheaper than the distributed systems.