Improved beam line for Hall A

1
Improved beam line for Hall A

• layouts, present and proposed
• optics in altered region
• benefits of proposed layout
• costs of proposed layout
• conclusions

2
layouts present and proposed
ep not possible after Moller scattering (per Kees)
1m of 10cm tube with H/V corr, 3 BPM, switch to
2.5cm tube, quad, 2m fast raster, BPM, H/V
correctors
4.5m available where ep is shown, not 5m
3
Optics plots altered region (combined optics)
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Optics plots 2 (combined optics)
p extent
BPM
PIVOT
BPM
TargetRaster
Moller raster
MOLLER Target
PIVOT
5
Smaller spot at target
Betas (top) and beam envelopes (bottom) with
minima 5m upstream of pivot. Is this better or
worse for beam spot size stability give slow
0.05 changes in quads?
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Benefits

• fast raster after all quads so its always what
  you set
• quads after Compton may be set for target beam
  size and BPM phase advance
• better control of beam size due to new quad
  locations
• more correctors and BPMs to eliminate scraping
  and improve orbit locks
• better control of orbit through raster and eP due
  to new BPMs and correctors
• fewer ion chamber trips
• double raster length eases engineering for 11 GeV
• 4.5m drift before diagnostic girder allows for
  either eP system or MOLLER target insertion
• high current Moller polarimetry feasible via
  combined optics

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Costs

• Existing fast raster system mounted on leg of
  Compton before the electron detector as Moller
  raster. -250 microns at electron detector, 5K
• Single QR or QA-pair inserted between 1C18 A/B
  harps on French bench. 45K
• GEANT simulations to determine effects of
  elements on 1 beam pipe after Moller
  spectrometer dipole and the shielding changes
  needed as a result. We need to keep S/N up in
  Moller polarimeter detectors.
• ME design 100K
• Two girder extrusions and two stands, one
  extending inverted girder 20K
• Three additional BPMs and electronics 36K
• S/H cards for new BPMs 30K??
• Three additional H/V corrector sets and power
  supplies 24K
• New fast raster system 100K??
• If eP not retained, yet another BPM/corrector
  pair in that drift, 20K
• 1H00 harp omitted. May fit immediately after
  IBC/IUN/IBC as its mounted there now I need
  more accurate dimensions. Can it be moved next
  to IPM1P03A? This allows better optics control
  at the Compton electron-laser interaction point.
  New vacuum vessel will be needed for this region
  as the middle Compton dipoles move up 8 cm. Add
  NEG pumps to improve vacuum near electron
  detector.
• quad upgrades not in 12 GeV project two 20A
  power supplies

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Further work needed

• Layout to pin down locations to centimeters
  (Accelerator and Engineering)
• 11 GeV raster design 40 longer coil and power
  supply with twice the voltage, 40 more current.
  If the pair of coils of the same plane must be
  driven in series, four times the voltage and 1.4
  times the current. (TBD)
• Moller polarimeter dipole and detector S/N
  modeling shielding design with BPMs, correctors
  and rasters where 4 pipe now exists. Primary
  beam through Moller dipole what corrector
  strength is needed? (Hall A collaboration)
• Combined optics must be implemented to allow high
  current Moller polarimetry. This requires one
  quad between the Moller dipole and the fast
  raster, increasing design problem of the latter.
  It will also constrain either beam size or phase
  advance in 7m before target. (Physics and
  Accelerator)

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Conclusions (1)

• A rearrangement of the Hall A line is proposed
  which removes a severe optics constraint, raster
  performance
• Beam quality will be improved for all
  experiments, especially 11 GeV parity experiments
  including MOLLER.
• Ion chamber trips will be reduced, improving
  availability and reducing irritation in MCC and
  the other halls
• Cost of order 0.8M design, procurements,
  installation

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ep system

• The ep system is not functional.
• It is very difficult to steer in the Compton with
  the ep ion chambers set to trip at low values.
• Compton optics matching will take several hours
  and disrupt the other halls unless one hour mask
  durations may be applied to Compton and ep ion
  chambers during optics data acquisition using
  harps.
• Do any of the remaining 6 GeV experiments require
  the ep system? Will the system be of any use at
  higher energy?
• Might the system be easier to repair if removed
  from the hall during January 2010? Replace with
  10 cm beam tube for vacuum conductance.

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UVa Polarized target chicane

• 2007 design for g2p requires removal of Moller
  polarimeter shielding, inverted quad girder, and
  final diagnostic girder for vertical chicane.
  Moller polarimeter will be non-functional.
• Proposed design has room for vertical chicane
  after final correctors, in space designated for
  ep and final diagnostic girder. Moller
  polarimeter intact.
• Space for second fast raster in proposed design
  may be occupied by slow raster.
• Tungsten calorimeter can substitute for Unser and
  second BCM as on next slide.

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Beamline Chicane
EP
Moller
Target center
Chicane Design Jay Benesch (JLab CASA) Two
upstream Dipoles, one with vertical degree of
freedom. Reuse the dipoles from the HKS
experiment. Utilize open space upstream of
target. Minimal interference with existing
beamline equipment.
Major Installation
UVA/Jlab 5 T Polarized Target Upstream Chicane
and supports Slow raster and Basel
SEM. Instrumentation for 50-100 nA beam. Local
beam dump. Hall A Septa.
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layouts g2p and this proposal
1m of 10cm tube with H/V corr, 3 BPM, switch to
2.5cm tube, quad, 2m fast raster, BPM, H/V
correctors
4.5m available where ep is shown, not 5m
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The Experiment
E0(GeV) µ(deg) Days
1.1 6 1.0
1.7 6 1.5
2.2 6 1.6
3.3 6 2.9
4.4 6 2.7
4.4 9 6.0
Data Taking 15.7
Qweak has polarization control for g2p _at_ 2.2, 3.3
and 4.4 GeV
Overhead 8.4
Total Days 24.1
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Conclusions (2)

• The ep system should be removed from the hall
  ASAP. Repair offline if the collaboration
  wishes.
• The proposed Hall A line is more compatible with
  the vertical chicane needed for the UVa polarized
  target and g2p than is the present line.
• If mechanical design begins in January 2010 and
  labor is available it should be possible to
  install the new line and g2p in the six month
  2011 down.
• BTW I hope youve got the He3 needed for the
  dilution refrigerator. DHS has exhausted the
  supply.