Positron Source Positron Target Working Plan

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Positron Source Positron Target Working Plan
The conventional e source (ZDR) appears to be
unworkableAn RF multiplexed e source system is
being adopted.Many issues to be worked out
optics (isochronicity), combiner (aperture,
trajectory spread), selective losses
(photocathode gun?)
e targets
RF Separater
RF Combiner
250 MeV e
6.2 GeV e-
3 out of 4 target system scheme
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Positron Source Positron Target Strength Analysis

• LLNL Calculations
• Show for NLC stresses strength of material
• LANL Analysis of SLC target
• Experience with irradiated W-Re
• Severe loss of mechanical strength with radiation
  dose (p) SLC exposure
• How does strength degrade as dose increases?
• Indication is that the NLC design is marginal at
  best, and will worsen with use.

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Positron Source Positron Target Working Plan

• 4 targets 3 operating, 1spare/repair
• Access and 5m shielding between vaults sets scale
• Timing need to arrange the e- train to make the
  e train

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Positron Source Coupon Tests

• Small samples of possible target materials to
  study properties and benchmark simulations
• At FFTB, 5 20 ?m spot sizes, 2x109 to 2x1010
  e-/bunch, 30 GeV
• Samples
• W-25Re
• Ta
• Ni
• Cu
• Ti
• W
• Glidcop

W-25Re 420 J/g deposition
W-25Re 2101 J/g deposition
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Positron Source SLC Target Dissection at LANL

• The damage to the SLC positron target is being
  analyzed at LANL.
• The target has been cut into pieces and
  metalographic studies are beginning.
• Examining level of deterioration of material
  properties due to radiation exposure.

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Positron Source Schedule

• Ongoing
• Develop multiplexed target scheme.
• SLC target dissection and materials analysis
  (LANL).
• Shock dynamic stress analysis (LLNL).
• Coupon tests of materials.
• 1/01
• Mini-workshop on the SLC target failure.
• Participants from at least LANL, LLNL, SLAC.
• 6/01
• Is there another way (eg. Hybrid targets)?
• Select a path for the positron system.
• 4/02
• Beam tests of the target design at SLAC.

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Polarized Positron Source Laser based (LLNL)
(also under study at KEK ATF)

• Method
• Compton backscattered gammas retain the laser
  helicity, e polarization can be changed randomly
  at 120 hz.
• Laser system is demanding.
• The Complex
• 2-8 GeV e- accelerator, similar to existing
  plan.
• Sizable laser facility with significant power
  and cooling reqs.
• Gamma drift line (100m 1km)
• Positron target and collection facilities
  (ZDR-like)
• Conventional e source probable needed for
  commissioning.

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Polarized Positron Source Undulator based
(SLAC) (As for TESLA, using a wiggler)

• Method
• Helical undulator magnet makes circularly
  polarized gammas.
• A more conventional technology, undulator
  placement an issue.
• Randomization of e helicity more difficult
• The Complex
• Requires ?150 GeV low ? electron beam
• 100m long undulator, superconducting?
• Gamma drift line (1 2 km)
• Positron target and collection facilities
  (ZDR-like)
• Conventional e source probable needed for
  commissioning.

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Polarized Positron Source

• Plan
• Simulation (common to both) of collection yield,
  polarization retention
• Look at gamma production options at LLNL and at
  SLAC
• Look at testing polarized e production.
• Collaborate? (Omori _at_ ATF, Floetmann _at_ ?)