POSITRON PRODUCTION FROM MONOCRYSTALLINE TARGETS AT THE KEKB INJECTOR LINAC

1
POSITRON PRODUCTION FROM MONOCRYSTALLINE TARGETS
AT THE KEKB INJECTOR LINAC

• Masao KURIKI for Tsuyoshi Suwada
• Accelerator Laboratory, KEK,
• 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

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Collaboration

• Tsuyoshi Suwada, Kazuro Furukawa, Takuya
  Kamitani,
• Masanori Satoh, Takashi Sugimura,
• Accelerator Laboratory, KEK
• Hideki Okuno,
• Institute of Particle and Nuclear Studies, KEK
• Kensei Umemori,
• Institute of Materials Structure Science, KEK
• Takeshi Haruna, Yuhsuke Kanamaru, Ryosuke
  Hamatsu,
• Department of Physics, Tokyo Metropolitan
  University
• Katsuhide Yoshida,
• Saga Light Source
• Alexander P.Potylitsyn, Igor S.Tropin,
• Nuclear Physics Institute, Tomsk Polytechnic
  University
• Robert Chehab,
• LAL, IN2P3-CNRS, Universite de Paris-Sud

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Motivation

• High-intensity positron sources are required for
  next-generation ee- linear colliders and
  high-luminosity B-factories.
• Conventional methods using amorphous heavy metals
  limit to increase the intensity of primary
  electron beams due to the heat load on the
  target.
• New method using the processes of coherent
  bremsstrahlung (CB) and channeling radiation (CR)
  is one of the bright schemes for high-intensity
  e production.

Ref R. Chehab, et al., Proc. the 1989 IEEE
Particle Accelerator Conf. (PAC89 ), Chicago,
IL, USA, March 1989, p.283.
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Channeling Radiation Coherent Bremsstrahlung
Processes
Channeling Photon Spectrum
2GeV e-
Crystal W
Amorphous W
20GeV e-
Crystal W
Amorphous W
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Experimental Setup
e targets tested Tungsten crystal(Wc) Diamond
crystal(C)
4 GeV e-
target configuration for Wc
e momentum acceptance ?P/P2.4
(FWHM) Geometrical acceptance ??????1msr at
Pe20MeV/c.
8 GeV e-
target configuration for Diamond
Beam charge 0.1/bunch
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Experimental Results Rocking-curve
Tungsten Crystal axis lt111gt
Diamond Crystal axis lt110gt
on-axis
on-axis
Diamond alone
off-axis
off-axis
The peak widths were obtained to be 40 mrad and
1.6 mrad (FWHM) for the W crystal and the
diamond, respectively. Their widths are clearly
larger than each critical angle for axial
channeling.
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Experimental Results e production enhancement
Tungsten Crystal
Diamond Crystal
The enhancement of the W crystal changes from 1
to 3.4 depending on the crystal thickness, while
for the 7.25-mm-thick diamond alone it is about
29. The results indicate that although for the
thinner thickness the enhancements of the crystal
targets are higher than that of amorphous W
targets.
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Experimental Results e production efficiency
Tungsten Crystal
Diamond Crystal
The positron-production from the 9-mm-thick W
crystal and 7.25-mm-thick diamond target with a
9-mm-thick amorphous W plate are 25 and 12,
respectively, larger than that from amorphous W
at each maximum positron yield at 20 MeV/c. The
shower-max is clearly reduced and the radiation
length is effectively reduced by crystal effect.
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Positron production station of the KEKB Injector
Linac
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Positron production at KEKB Injector
Previous experiment
This experiment at the KEKB e station
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Positron production at KEKB Injector
Previous experiment
This experiment at the KEKB e station
In Operation Now
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Summary

• A series of the e production experiments with a
  W crystals and diamonds have been successfully
  performed.
• A large positron-yield enhancement was observed
  for thinner crystal targets.
• The positron-production efficiencies are 25 and
  12 for the 9-mm-thick W crystal and the
  7.25-mm-thick diamond target with a 9-mm-thick W
  plate, respectively.
• 10.5 mm thick crystal W was installed into the
  positron station of KEKB injector linac and it is
  in operation with the same enhancement.

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Back Up Slides
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Summary

• A series of the positron-production experiments
  by 4- and 8-GeV channeling electrons hitting an
  axially-oriented tungsten crystals (lt111gt axis)
  and diamonds (lt110gt axis) have been successfully
  performed at the KEKB injector linac.
• The positron-production efficiencies from the
  crystal targets were measured as a function of
  the target thickness and as a function of the
  positron momentum in the momentum range of less
  than 30 MeV/c.
• The results show that when the crystal axis was
  aligned along the incident beam direction, a
  large positron-yield enhancement was observed for
  thinner crystal targets.
• The enhancement factor decreases as the target
  thickness increases and no clear dependence of
  the positron-yield enhancement with the momentum
  was observed in the measured region for both the
  crystal targets.
• The positron-production efficiencies are 25 and
  12 for the 9-mm-thick tungsten crystal and the
  7.25-mm-thick diamond target combined with a
  9-mm-thick amorphous tungsten plate,
  respectively, at the momentum of 20 MeV/c.

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Experimental Conditions

• Primary Electron Beam
• Beam Energy 4 (8) GeV
• Angular Spread 5 (10) ?rad (H, HWHM), 4 (26)
  ?rad (V, HWHM)
• Transverse Beam Size 2mm (FWHM) in diameter
• Beam Charge 0.1 nC/bunch
• Bunch Length (Single Bunch) 7.7 ps (FWHM)
• Beam Repetition 25Hz
• Angular Spread of the Electron Beam at the
  Positron Target
• ? 55-60 ?rad lt ?c (? beam divergence due to
  multiple scattering at an beam-extraction vacuum
  window (30?m-thick SUS))
• Critical Angle for the Channeling Condition at
  the Positron Target
• Linhard Crytical Angles (?c (2U/E)1/2 ,
  UPotential depth of atomic field)
• ?c 610?rad _at_4 GeV for Tungsten Crystal
• ?c 130?rad _at_8 GeV for Diamond Crystal

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Photo Picture of Experimental Setup
Positron Spectrometer
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Layout of the KEKB e-/e Injector Linac
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Geometrical and Momentum Acceptance of the
Positron Spectrometer

• Geometrical and momentum acceptance were
  estimated based on the GEANT3 simulations

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Present Positron Source at the e-/e KEKB
Injector Linac
e W Target Pulse Coil
DC solenoids Accelerating sections
e beam
Primary e- beam
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Layout of the KEKB e-/e Injector Linac
Pulse coil
e W Target
Bridge coil
e beam
e- beam