transverse 1turn injection

1
Injection and Extraction

• transverse 1-turn injection
• multi-turn injection
• H- charge exchange injection
• resonant continuous injection
• envelope matching
• fast extraction
• kickers septa
• slow extraction resonance islands
• beam separation
• crystal extraction

MCCPB, Chapter 9
2
The LHC injector chain
LINAC ? PSB ? PS ? SPS ? LHC

• Each proton has to pass four circular machines

3

• beam transfer between accelerators
• beam removal and beam delivery

injection minimum beam loss minimum
emittance dilution 1-turn
injection or multi-turn
injection for accumulation new or more
exotic techniques to control and improve
beam properties extraction reverse process,
usually at higher beam energy
space-charge effects less important
hardware more challenging
extraction efficiency (minimize activation
and maximum performance)
procedure depends on application
fast 1-turn extraction, slow
extraction spill novel
extraction schemes (e.g., bent crystals)

4
1-turn injection

• the beam is brought onto the central orbit
• using septum magnet and fast kicker

magnet arrangement
rms closed-orbit variation
rms beam sizes
momentum error
septum thickness
5
injected beam must at the center of the aperture
when it reaches the kicker
determines the correlation between xsep and xsep
needed at the exit of the septum
can be adjusted by changing the strength of the
septum slope of beam at the kicker is
6
to position the injected beam on the design orbit
the kicker must apply the opposite angular
deflection
a large value of bkic reduces the kicker
strength a large value of bsep reduces the
relative contribution to qkic which arises from
the septum thickness dsep
in case of FODO lattice, septum and kicker are
best placed downstream of focusing quadrupole,
where b is maximum
7
septum dc magnet, dc electrostatic wires stray
or leakage fields (nonlinear) can affect stored
beam may be reduced by magnetic shielding
kicker(s) fast gap between bunches or bunch
trains 50-100 ns time constants 80 kV, 5000 A,
500 G typical numbers ferrites for field
containment ceramic chamber with conducting layer
on the inside reduces impedance seen by the beam
and heating of the ferrite (conducting layer can
be much thinner than skin depth)
8
other injection issues transient beam loading of
rf cavities phase-space matching (Dx,y bx,y,
sz/drms, must be matched to ring optics in
longitudinal phase space possibly bunch rotation,
bunch compression, energy compression, etc.
9
multi-turn injection
e.g., convert a current-limited cw beam from
injector into a pulsed beam of higher intensity
transverse multi-turn injection ramped orbit bump
in the vicinity of the septum instead of a
kicker - different for e- and protons for e-
radiation damping is utilized inject 1 bunch,
reduce bump after few turns, bunch shrinks due
to damping, increase bump again, inject next
bunch into the same rf bucket similar for
e-cooled protons, or stochastically cooled
p-bars (but here usually in longitudinal phase
space)
10
for protons or heavy ions orbit bump is varied
slowly, bunches are injected into different
regions of phase space early bunches in the
center of the acceptance
some emittance dilution is inherent to this
scheme for N-turn injection
11
other possibility two kickers, powered in
parallel by the same pulser only second
kicker deflects the injected beam both kickers
act on the stored beam advantage kicker rise
and fall times do not need to be smaller than the
bunch spacing, but can be of order of the
revolution time requirements on the kicker can
be further alleviated by a dc orbit bump which
brings the stored beam closer to the septum prior
to injection
12
double-kicker injection
13
example injection process for PEP-II
note PEP-II peculiarity injected beam is smaller!
(Courtesy M. Donald, 2002)
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longitudinaltransverse multi-turn injection as
before ramped local orbit bump with varying
amplitude but at the same time the injector linac
energy is ramped such that at the injection
septum the distance to the closed orbit
corresponding to the instantaneous linac energy
remains constant
smaller transverse emittance, increased energy
spread
injection b oscillation
injection bd oscillation
15
10 turns after start of purely transverse
injection
20 turns after start of combined transverselongit
udinal inject.
simulated horizontal phase space for multiturn
injection into LEAR each bunch represented by
three ellipses with slightly different momentum
deviations, the two vertical lines on the right
represent thickness of the septum
(Courtesy Ch. Carli, 2002)
16
improved optics with larger b at e- cooler
combined transverse longitudinal injection
purely transverse injection
Effective turns stored in LEAR vs injected
turns
17
longitudinal multi-turn injection if for e- ring
time between injections is shorter than damping
time, multiturn transverse injections become
difficult solution longitudinal
injection circulating beam is brought close to
the septum by ac bump injected beam has negative
energy offset so that DDd equals physical
distance xsep between stored and injected
beam injected bunches execute slow synchrotron
oscillations
no b oscillation
18
double injection into the same rf bucket at
LEP here also the stored bunch is offset in
energy so that Dx2DDd time between injections
is half a synchrotron period (similarly, one
could inject every Ts/4 period) advantage
factor 2 faster radiation damping than in
transverse plane possible disadvantage time
between injections constrained by
synchrotron frequency
19
phase-space painting protons or ions many small
linac bunches are injected into different spots
of the 2-D or 6-D phase space aim approximately
uniform distribution reduced space-charge
effects avoid instabilities which
blow up e in uncontrolled way simplest case
painting done by synchrotron oscillations injected
beam position can also be moved
adiabatically examples horizontal-longitudi
nal injection in LEAR (above)
horizontal-vertical injection at RAL
injected phase-space density P and projection p
are related by
radial increment between successive bunches
desired p(x) P(r)
R maximum radius at which bunches are injected,
Ninj total no. of injections
20
combined vertical/horizontal painting at
RAL vary vertical steering magnet in injection
line, while the guide field in the ring is
decreased initially small x oscillation
large y oscillation later large x
oscillation small y oscillation also
a vertical or horizontal orbit bump (or both) in
the ring could be employed
21
H- exchange injection
Novosibirsk 1963 Budker Dimov H- accelerated by
linac stripped to protons when they traverse a
thin foil at injection into the
ring Liouvilles theorem does not apply, in
principle very high phase-space densities
possible however, usually painting and uniform
distribution preferred to avoid space-charge
effects heating limits foil thickness to 50-200
mg cm-2 (lt1 mm) stripping efficiency 98 for 50
MeV protons materials polyparaxylene, carbon,
aluminimum oxide
22
scattering Qrms0.2 mrad for single traversal
Qtot N1/2 Qrms for N
traversals stacking in betatron synchrotron
phase space reduces traversals
schematic of H- injection with stripping foil
23
following lattice parameters at foil are
considered advantageous
transverse acceptance
momentum acceptance
location between two symmetric focusing
quadrupoles
unstripped H-
beam evelope
quadrupole assists in deflecting unstripped H-
foil
H-
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other uses of foils heavy ions they
can be fully stripped (depends on thickness
of foil and energy) extracting H0 or p from
H- storage ring alternatives gas jet, laser e-
are also stripped in strong magnetic fields
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novel H- stripping scheme under study for SNS
uses laserdipoles
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other scheme resonant injection bumper magnets
with dipole, quadrupole and octupole
fields produce separatrix with two stable
islands (sketch) afterwards fields are adjusted
so that islands merge opposite process is now
studied at the CERN Ps for clean extraction
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continuous injection
beam continually replenished, beam current
constant then average luminosity peak
luminosity steady-state operation for
light sources (e.g., SNS) no fill-to-fill
variations, no transients quasi-static
conditions if at some beam-beam limit tbeame-L
const ? i.e., lifetime decreases exponentially
with L gain in peak luminosity
28
example PEP-II continuous injection could
increase luminosity by factor of 5! each bunch
can be replenished every Dt2.1 s 67-ns bump
would move injected bunches to about 4s from
stored-beam core for unobstructed passage through
the detector minimum supportable lifetime
tN/DN Dt N nominal bunch population DN
injected bunch increment Dt time between
injections into same bucket N1.2x1011, DN109,
Dt2.1 s yields t4.2 min.
29
injection envelope matching (Michiko)
turn-by-turn profiles after injection into
the SLC damping ring
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D mismatch?
before b matching
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after b matching
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fast extraction

• similar to 1-turn injection
• orbit bump move beam close to septum
• fast kicker deflects beam into extraction
  channel
• kicker rise time lt time separation between
  successive
• bunches or bunch trains
• kicker-pulse length fall time depend on
  bunches
• to be extracted and fill pattern

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minimum deflection angle required
kicker just upstream of focusing
quadrupole, septum 1 cell downstream, maximum
value for b
kicker
septum
m
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reduced jitter of extracted beam with
double-kicker system (ATF)
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kicker septa
kicker (1) current loop inside vacuum (2)
terminated transmission line inside
vacuum (3) ferrite magnet outside
vacuum (4) multicell transmission
lines with ferrite flux
returns typical time constants 50-150 ns (rise
and fall times) SLC,NLC 60 ns PEP-II 120 ns
36
fast horizontal kicker with ferrite
yokes t(lw)/g i.e., length x width/vertical
gap shorter time constant by dividing magnet
into shorter segments kicker pulsers thyratron
discharges, with filters, capacitors to shape
pulses solid-state FET -gt potentially shorter
time constants
37
PEP-II kickers kicker magnet cross
section pulsing circuit with FET switch
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very fast travelling-wave kicker protoype for
TESLA layout
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very fast travelling-wave kicker prototype for
TESLA measured output rf pulse
6 ns total pulse length demonstrated deflection
angle 24 mrad at 3.3 GeV
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schematic of beam-beam kicker 2 ns pulse length
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schematic of another beam-beam kicker
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Fourier series kicker
G. Gollin U Illinois
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• septa small thickness desired
• -gt weaker kicker, larger extraction
• efficiency
• electro-static wire septa, e.g., at Tevatron,
• 2 354 cm long sections, 75W255Rh wires
• of 0.002 inch diameter and 0.1 inch spacing,
• field 83 kV/cm
• more widely used
• (b) Lambertson iron septum dipoles
• (c) current-carrying septum dipoles
• Bm0 J d , if d is small pulsed operation

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schematic of Lambertson septum iron magnet c
circulating beam e extracted beam
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cross section of current-sheet septum
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slow extraction
tune ripple causes uneven spill -gt active
filters on power supplies, feedforward
slow spill can be controlled by tune and
chromaticity
47
extraction via resonance islands
illustration of conventional scheme
for extracting beam from PS to SPS
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tune variation for proposed resonant extraction
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simulated phase space during resonant extraction
50
beam separation at collision point
example e-e- separation for a VLLC
51
crystal extraction from stored proton/ion beam
Dubna, Protvino, CERN SPS Tevatron
52
channeling condition angle of incidence lt
Lindhard critical angle 5 mrad (Z/p
TeV/c)1/2 thermal vibrations, discreteness of
lattice, electrons -gt dechanneling (exponentiall
decrease of channeled protons) dechanneling
length L00.9 m pTeV/c cooling of crystal
increases L0 minimum bending radius for
channeling Rc0.4 p TeV/c meter single-pass
extraction, multi-pass extraction up to 18
efficiency demonstrated for p 10 was achieved
with fully stripped Pb ions
53
Summary
1-turn injection fast extraction kicker
septum to control x, x multi-turn injection in
1 plane only or in various plane-combinations hori
zontal or longitudinal accumulation,
painting programmed orbit bumps slow extraction
(resonant extraction) crystal extraction H-
charge exchange issues rise fall times of
kickers, continuous injection, tolerances, and
how to relieve them injection envelope
matching extraction via resonance islands beam
separation