HAPPEXIII, PVDIS, PREx targets - PowerPoint PPT Presentation

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HAPPEXIII, PVDIS, PREx targets

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ASME issues seemed to have calmed down... 20 cm 'race-track' style (existing HAPPEX-II/H cell) ... ASME issues seemed to have calmed down (non-trivial! ... – PowerPoint PPT presentation

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Title: HAPPEXIII, PVDIS, PREx targets


1
HAPPEX-III, PVDIS, PREx targets
D.S. Armstrong April 17 09
  • Cryotargets
  • what we requested new 25 cm racetrack
    cells
  • status
  • 2) Solid Targets for HAPPEX-III/PVDIS
  • plan
  • 3) Solid Targets for PREx (from ROM)

2
Cryotargets for HAPPEX-III/PVDIS
  • HAPPEX-II used 20 cm racetrack cell (design
    Dimitri Margaziotis, Cal State LA)
  • transverse-flow design
  • Excellent boiling performance
  • Geometry no problem using
  • at HAPPEX-III/PVDIS angles with
  • up to ?4 mm raster
  • (vertical acceptance is issue)
  • - PVDIS asked for 25 cm version

3
New Cell Block Design
from Dave Meekins (this is for 10 cm cell)
4
Cell length for HAPPEX-III
  • 25 cm cell also?
  • Advantages
  • Swap-compatible with PVDIS cell (mutual spares)
  • Ratio of Al (windows) to lH2 smaller by ?0.8
  • - reduced QE background
  • - perhaps reduced boiling (if film boiling at
    window dominates)
  • somewhat reduced acceptance (?10-15) at detector
    for Al windows
  • Luminosity (assuming cryogen load can be
    delivered)
  • Disadvantages
  • Increase radiative tail losses 15-20 increase
    in radiative effects, taking into account Al
    windows and, they are the worst kind (before
    scattering vertex, reduces asymmetry)
  • Perhaps a bit harder to manufacture
  • Maybe boiling performance worse, if
    bulk-dominated We know 20 cm was good.

5
Cryotargets request
  • Requested identical 25 cm cells for PVDIS,
    HAPPEX-III
  • act as mutual spares in case of leaks
    changeover of lH2 to lD2 on a
    loop is a couple of shifts much
    better than replacing entire cell block on
    target ladder..
  • Can have three cells on cryotarget ladder now
    (was not the case for HAPPEx-II)
  • Have one working 20 cm cell (hydrogen
    thin-walled) from HAPPEx-II
  • Requested
  • For new (25 cm) cells
  • - Side walls thickness aim for ?7 mils.
  • - Entrance and exit windows aim for ? 5
    mils.
  • - Important to have good measurement of
    window thicknesses, particularly
  • in 1cm x 1cm region around the nominal
    central ray
  • (allowing for ?4 mm raster and a ?5 mm offset of
    the beam axis)
  • ASME issues seemed to have calmed down

6
Aluminum window thickness
  • HAPPEX-1 15 cm beer can cell
  • HAPPEX-II 20 cm racetrack cell

Al background (1.4 ? 0.1)
Al background (0.91 ? 0.12) (2004)
(0.76 ? 0.25) (2005)
Machining and measurement tolerances chatter of
bit Need integrating mode data with variable
density gas (target warming) to scale xt
factor
7
Cryotargets status
  • ASME issues seemed to have calmed down
    (non-trivial!)
  • Mike Seely resigned from Targets group (December
    2008)
  • I was late getting all specs to Targets group
  • getting info to Kees to justify
    (mea culpa)
  • Dave Meekins has been busy with other targets
    (SANE, Qweak)
  • Cells not yet made, but still have adequate time
  • a few weeks needed for machining a few
    weeks for testing
  • Dave M. time is not yet a problem

8
Solid Targets HAPPEx-III PVDIS
  • - H2O cell (pointing angle measurement)
  • - BeO viewer
  • - Al dummy foils, located 25 cm apart (at the
    windows of the long
  • racetrack cells) with 1.00 mm thickness
  • - Standard C multi-foil optics target as we
    used in 2005
  • - Carbon single foil target
  • - Ta foil target (pointing angle
    measurement)
  • - empty position
  • Cant run H2O cell when cryotarget cold
    (duuh)
  • Run optics/pointing measurements first with
    H2O cell installed, then break vacuum (all
    running at low current to this point), remove H2O
    cell, cool target. Estimate 2-day turnaround.
    Note point angle measurement done at 1-pass
    beam energy, so there is also parallel overhead
    to restore 3- pass beam.

9
Solid Targets PREx
Top of stack (closest to cooling) one cryoloop
only
  • Start with warm target water cell truncated
    target ladder (BeO, Ta, empty?)
  • Break vacuum, remove water cell (no high current
    on Pb yet)
  • Run with cold target and full solid target ladder.

10
Backup Slides (point angle details)

11
Pointing Angle Measurement
  • Important for Q2 measurement
  • Use nuclear recoil technique as was done for
    HAPPEX-II/HAPPEX-He
  • Need targets with different recoil (i.e.
    different mass) to maximize precision
  • Can use elastic scattering (MM) or inelastic
    to nuclear excited states (M?M)
  • At 1.18 GeV, 13.8
  • E E
  • ¹H 41.3 MeV
  • 9Be 4.4 MeV
  • 16O 2.5 MeV
  • 181Ta 0.2 MeV


Thus H2O target gives close to optimal
performance BeO possible, much less lever arm in
E E, TiH has engineering problems. Dave
Meekins designed water cell 5 mm H2O, 2 ?1-mil
thick steel windows. Note cannot run with
cryotargets need to de-install water cell to
install cryotargets (roughly 2-3 day
turnaround)
12
Water cell results from HAPPEX-II
Determined ? to ?0.01 in 2005
Note Compared to 6, ?Q2/?? is 42 as
large at 13 and 24 as large at 20 scattering
angles
13
Water cell for HAPPEX-III
Will H2O target work at HAPPEX-III, PVDIS
kinematics? H-II E 2.76 GeV ?6.1
Q2 0.085 GeV2 q1.47 fm-1 H-III E
3.46 GeV ?13.8 Q2 0.625 GeV2 q4.0 fm-1
H-III (2-pass) E 2.32 GeV ?13.8 Q2
0.290 GeV2 q2.7 fm-1

(not feasible) H-III (1-pass) E 1.18
GeV ?13.8 Q2 0.077 GeV2 q1.41 fm-1 ?
go to 1-pass beam for HAPPEX-III
pointing measurement (cross sections about
30 of HAPPEX-II values)
1-pass
2-pass
McCarthy and Sick, Nucl. Phys. A 150(1970)63
14
Water cell excited 16O states
test
1-pass
2-pass
T.N. Buti, PhD thesis (MIT, 1984) T.N. Buti
et al. Phys. Rev. C 33(1986)755
15
Water cell for PVDIS
PVDIS (1-pass) E 1.2 GeV ?12.9 q1.36
fm-1 (no problem)
?20 q2.11 fm-1 (more
of a challenge) at 20 hydrogen elastic
cross section down by factor 30 vs. H-II
ratio of elastic 16O/hydrogen similar to
H-II 16O excited states down relative
to hydrogen elastic by factors of 5
(31-), 8 (11-) and 20 (21) Conclusion Doable,
but fits will have to rely on 16O elastic and the
31- (6.13 MeV) state entirely (I have not looked
into 56Fe peaks, dont expect to see them)
16
Summary pointing angle measurement
  • Water cell is best choice, if one can tolerate
    the changeover time (scheduling)
  • Could use BeO, Ta, as less-invasive
    alternates to water cell
  • Need to go to 1-pass beam for both HAPPEX-III and
    PVDIS ? measurements.
  • PVDIS ? measurement at 20 with water cell more
    challenging, but precision demands reduced.
    However PVDIS proposal goal is a Q2 contribution
    to error budget of 0.12 at ?20 which means
    ?0.2 mrad (?0.01), which matches HAPPEX-II
    precision
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