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Damping ring kickers

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Minimum damping ring circumference depends on minimum realizable bunch spacing ... 6 ns kicker 6 km circumference (Fermilab small ring) ... – PowerPoint PPT presentation

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Title: Damping ring kickers


1
Damping ring kickers
  • George Gollin
  • University of Illinois at Urbana-Champaign
  • and
  • Fermi National Accelerator Laboratory

2
Outline
  • The problem
  • The specs
  • Current ideas
  • Opinions from the speaker
  • Illinois/Fermilab efforts
  • ILC-America ILC-global near term goals

3
The problem
  • Linac beam (TESLA TDR)
  • 2820 bunches, 340 nsec spacing ( 300 kilometers)
  • Cool an entire pulse in the damping rings before
    linac injection
  • ILC damping ring beam
  • 2820 bunches, closely spaced
  • Eject every nth bunch into linac (leave adjacent
    bunches undisturbed)
  • Minimum damping ring circumference depends on
    minimum realizable bunch spacing (kicker speed
    and instability issues)
  • Kicker
  • 20 ns kicker ? 17 km circumference (TESLA dog
    bone)
  • 6 ns kicker ? 6 km circumference (Fermilab small
    ring)

4
What an interesting problem!
Theres significant global interest in tackling
the challenges posed by the damping ring and
kicker. We have already started an informal,
global conversation see Andy Wolskis site at
http//awolski.lbl.gov/ILCDR/. for a partial list
of who has made contact. There are physicists
from ANL, CERN, Cornell, Daresbury, DESY.
Fermilab, Frascati, Harvard, Illinois, KEK, LBNL,
Minnesota, SLAC, Tokyo so far.
5
What we have to work with
  • Injection
  • already-orbiting bunches have not damped
    appreciably, have large transverse sizes (2 cm)
  • kicker must inject new bunches into damping ring
    acceptance without losing already-orbiting
    bunches.
  • Extraction
  • damping is finished, bunches are small (a few
    microns in diameter)
  • kicker must preserve beam emittance for
    still-orbiting bunches as well as the kicked
    bunch.
  • Performance demands on kicker are different for
    injection/extraction. Should we consider separate
    designs for injection and extraction?

6
The specs
  • Kicker specs depend, in part, on beam dynamics
    phase space volume occupied by a just-kicked
    bunch must be well separated from that of an
    unkicked bunch.
  • Dog bone (TESLA TDR) kicker specs
  • impulse 100 G-m (3 MeV/c) 0.07 G-m (2 keV/c)
  • residual (off) impulse 0 0.07 G-m (2 keV/c)
  • rise/fall time lt 20 ns
  • Perhaps larger (but less precise) impulse at
    injection, smaller (but more precise) impulse at
    extraction will be desirable.
  • Small ring kicker rise, fall times can be
    asymmetric
  • leading edge lt 6 ns, trailing edge lt 60 ns

7
The ideas (1) strip line kicker modules
  • Fast switches dump high voltage pulses into a
    series of strip line structures.
  • Electromagnetic pulse applies transverse kick to
    one bunch, but is absorbed in a load in each
    strip line module before next bunch arrives.
  • switch speed, on-resistance, and stability are
    concerns
  • adequate precision of strip line termination is
    challenging
  • TESLA and SLAC are thinking about this

8
The ideas (2) longitudinal kick dispersion
Separate the beam so that it travels along
multiple paths. Demands on kicker are less
severe it only sees every 4th bunch. The system
needs to be studied in detail how to do it, what
happens when it is installed in a damping
ring. Cornell, Frascati are thinking along these
lines.
9
The ideas (3) Fourier engineering
  • Instead of a pulsed kicker, construct a kicking
    pulse from a sum of its Fourier components.
  • Most interesting (to me) idea now combine this
    with a pulse compression system to drive a small
    number of low-Q cavities.
  • what are stability requirements on RF components?
  • how robust to bunch arrival time errors can the
    system be made?
  • Illinois, Fermilab, Cornell are involved.

10
The speakers opinions (1)
The kicker has the potential to be a
show-stopper. Damping ring architecture (bunch
timing structure, injection/extraction optics,
etc.) is strongly tied to details of the
kicker. A fast pulsed kicker might be simplest to
operate BUT switch speed and stability are
challenging issues. Significant proof of the
feasibility of at least one design is needed
before a choice of damping ring design (big ring
vs. small ring) will be possible.
11
The speakers opinions (2)
  • Fermilab small ring studies incorporate
  • damping ring bunch trains with 60 ns inter-train
    gaps
  • long straight section to allow installation of
    as-yet unspecified kicker
  • Perhaps these features should be included in all
    damping ring designs?
  • There are three distinct stages in damping
    process
  • injection and assembly of bunch trains
  • damping
  • disassembly of bunch trains and extraction
  • Beam is very different in each of these stages.
    Should there be distinct subsystems (including
    different kickers) for each of them?

12
Separating injection, damping, extraction
functions
  • Large acceptance injection ring
  • (340 6) 334 ns circumference
  • assemble a single bunch train by injecting
    successive bunches into this ring at the tail of
    the train already orbiting the injection ring
  • transfer entire bunch train into the damping ring
    in one orbit
  • Large acceptance damping ring (6 ns bunch
    spacing)
  • Small acceptance extraction ring
  • (340 6) 346 ns circumference
  • transfer one entire bunch train from the damping
    ring
  • extract by kicking the last bunch in the train on
    successive orbits

13
Separating injection, damping, extraction
functions
Injection and extraction rings differ in
circumference by two bunch spacings to allow
injection/extraction to/from tail of bunch train.
14
Fermilab/Illinois activities
  • Initial studies use Fermilab A0 photoinjector
    beam (16 MeV electrons) for studies
  • build a fast, simple strip line kicker
  • use the kicker to study the timing/stability
    properties of the A0 beam
  • build a single-module pulse compression kicker
  • study its behavior at A0
  • perform more detailed studies in a higher energy,
    low emittance beam (ATF??)

15
A0 photoinjector beam
16 MeV electron beam, good spot size,
emittance. EOI submitted to A0 group last
spring. Space in beamline will be available
January 2005
16
Simple kicker for initial tests
Start with a simple kicker whose properties are
calculable and can be measured independently of
its effects on the A0 electron beam. Most
important how well can we measure a devices
amplitude and timing stability with the A0 beam?
Fermilab is currently designing this. Probably
ready by January 2005.
17
UIUC/FNAL, longer term plans
  • Design, then build one module using existing
    components.
  • Fermilab RF group is involved
  • UIUC HEP electronics design groups chief is too.
  • So were starting to make progress.
  • Goals
  • install strip line kicker in A0 by January, 2005
  • understand A0 by spring, 2005
  • install small pulse compression kicker at A0 by
    summer, 2005

18
ILC-America ILC-global near-term goals
  • Possible goals and timelines
  • pre-KEK discuss tentative plans for kicker RD
    with our colleagues in America, Asia, and Europe
    to have a sense of who would like to do what.
  • at KEK rough-out an RD plan aimed at choosing a
    kicker technology in 2 years
  • at Snowmass (August, 2005) kicker workshop with
    international participation to assess how well
    weve gotten started, and what we have learned

19
End notes
  • The kicker and damping ring scare the daylights
    out of me.
  • We must build one and make it work before the ILC
    main linac is completed.
  • More information
  • Studies Pertaining to a Small Damping Ring for
    the International Linear Collider,
    FERMILAB-TM-2272-AD-TD
  • ILC Damping Rings web site http//awolski.lbl.gov
    /ILCDR/
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