INJECTION PAINTING, FOIL

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INJECTION PAINTING, FOIL TARGET DISTRIBUTION
SNS ASAC Review

• Joanne Beebe-Wang
• BNL, Upton, NY 11973, USA

September 13, 2000
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Introduction

• What is injection painting
• It is an injection with a controlled phase space
  offset between the centroid of injected beam and
  the closed orbit in the ring to achieve a
  different particle distribution from the injected
  beam.
• Why injection painting for SNS
• to satisfy target requirements
• to reduce beam losses due to space charge
• to reduce foil hits (foil life-time, beam
  loss at foil)

Joanne Beebe-Wang
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Basic Painting Schemes
Correlated painting Anti-correlated painting
Joanne Beebe-Wang
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Analytical Expression
It is a 4-D problem (x, x, y, y). But, if 1)
distribution of injected beam can be expressed
as n(x,x,y,y)nx(x,x) ny(y,y) 2) the
bump in (x, x) phase space moves independently
from (y, y), it becomes a 2-D by 2-D problem.
In normalized x, px phase space, if -
changes slow compare to betatron
oscillation, particles injected at P paint the
same phase space as particles injected at P1 .
Maximum ?x is determined by the particles
injected at Q.
Joanne Beebe-Wang
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Analytical Expression (continued)
Particle distribution due to transverse phase
space painting for a single particle If the
distribution of injected beam is Gaussian with
?0x and ?0y where where I0(z) is the
modified Bessel function of order zero, and
center offset ( ?x0(t), ?x0(t))
Joanne Beebe-Wang
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Analytical Expression (continued)

• From the analytical expression of particle
  distribution we can find out
• Very high local density at the center of the
  beam if ?x(t)?y(t)0. So, one should not
  have zero offset in 4-D phase space any time.
• Correlated painting will give a rectangular
  shaped beam distribution with high density along
  the diagonal line, and low density on the x- and
  y-axis.
• If ?0x ltlt ? x(t) and ?0y ltlt ? y(t),
  anti-correlated painting with offsets ? x(t) A
  t1/2 , ? y(t) B (tinj -t)1/2 will give a
  KV-like particle distribution at time tinj .

Joanne Beebe-Wang
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Basic Painting Schemes
Correlated painting with/without space
charge ?x5.82 ?y4.80 ?inj,x4.93m
?inj,y7.24m ? inj,x0.11 ?inj,y0.07 inj.
?RMS,Nor0.5?mm-mr Final ?120 ?mm-mr
Joanne Beebe-Wang
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Basic Painting Schemes
Anti-correlated painting with/without space
charge ?x5.82 ?y4.80 ?inj,x4.93m
?inj,y7.24m ? inj,x0.11 ?inj,y0.07 inj.
?RMS,Nor0.5?mm-mr Final ?120 ?mm-mr
Joanne Beebe-Wang
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Basic Painting Schemes
painting scenarios correlated anti-correlated B
eam shape without SC Rectangular Oval Beam
emittance evolution Small to large
constant Final emit. ?x?y(?mm-mr) 120120 160
Foil-hit rate (11 linac dist.) 6.1 ? 8.3 8.0
? 10.5 Max foil temp. (K) (11 linac dist.)
2113 ? 2273 2248 ? 2376 Horizontal aperture (?H
) 11 11 Vertical aperture (?V
) 11 11.5 Susceptible to coupling
Yes No Capable for KV painting No Yes Paint
over halo Yes No Horizontal
halo/tail Normal Normal Vertical
halo/tail Normal Large Satisfy target
requirements Likely Not likely Bump function
Square root Square root candidates
exp(-t/0.3ms) exp(t/0.6ms) for
optimization Combination Sinusoidal
Joanne Beebe-Wang
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Injection Bump Optimization
Joanne Beebe-Wang
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Foil Heating Foil Miss
Injected Beam Distribution Foil Temperature
K
Joanne Beebe-Wang
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Foil Heating Foil Miss (continue)
Injected Beam Distribution Foil Temperature
K
Joanne Beebe-Wang
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End to End Simulation
Foil Miss, Foil Hit Foil Temperature
Joanne Beebe-Wang
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Foil Lifetime Tests on BNL linac

• Same beam size, same energy deposition/pulse
• Lifetime 5-80hrs on BNL linac depending on
  foil thickness, fabrication and mounting methods
• SNS repetition rate 9 BNL linac repetition
  rate
• Maximum 24 foils on the foil changing chain

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Foil Heating Scattering
Joanne Beebe-Wang
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Foil Hits Beam Loss

• Beam loss as a consequence of foil traversal
  through the following mechanism
• (1GeV proton, foil300?g/cm2, foil traversal
  rate7hits/particle)
• Nuclear Scattering
• estimated fractional loss3x10-5
• Particle loss in gap due to energy straggling
• estimated fractional loss3x10-6
• Transverse emittance growth due to multiple
  Scattering
• estimated ??4x10-2 ?mm-mr

Joanne Beebe-Wang
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Radiation due to Nuclear Scattering
Particle Loss (Fraction) Radiation at
Injection Area
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Injection Beam Loss
Beam loss caused by injection errors

• Major sources of beam loss that go to the
  injection dump
• Foil Inefficiency (FI)
• Foil 400?200?g/cm2
• FI 2?10
• Foil miss (FM)
• (see figures)
• Injection dump limit
• FM FI ? 10

Transverse position Linac
emittance error error ?c at injection
???inj-0.5 ?mm-mr
Joanne Beebe-Wang
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Injection Errors caused by Injection Mismatch

• There could be three kinds injection errors
  caused by injection mismatch. They cause
  emittance growth in the circulating beam.
• Current design ?UN120?mm-mr, ?inj,y7.24m,
  ?inj,y0.042, ?p/p0.25
• Steering Mismatch Expected ?x 0.2 mm,
  ?x 0.2 mrad ??RMS,UN 0.9 ?mm-mr
• Dispersion Mismatch
• Designed ?D 7 cm, expected ?D 0.02
• ??RMS,UN 0.004 ?mm-mr
• ? ?-function Mismatch
• Expected ??/?M ??/?M 0.025
• ??RMS,UN 0.02 ?mm-mr
• The impact on circulating beam emittance growth
  is negligible.

Joanne Beebe-Wang
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Target Distribution
Beam requirements at the target
Joanne Beebe-Wang
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Conclusions

• Simulation shows that correlated painting has
  better chance to meet the target requirement and
  may minimize halo. Anti-correlated painting
  causes excessive halo at full intensity.
• Halo/tail driven by space charge and magnet
  errors can be reduced by splitting tunes.
• Injection error increases foil-miss rate which
  causes increased dump load and decreased beam
  power. Its impact on beam emittance growth is
  negligible.
• Injection ?, ?-function mismatch can reduce foil
  heating. It can also be used to reduce the foil
  traversal rate for increased linac emittance.

Joanne Beebe-Wang