Title: HAPPEXIII, PVDIS, PREx targets
1HAPPEX-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)
-
2Cryotargets 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
3New Cell Block Design
from Dave Meekins (this is for 10 cm cell)
4Cell 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.
5Cryotargets 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
6Aluminum 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
7Cryotargets 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
8Solid 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.
9Solid 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.
10Backup Slides (point angle details)
11Pointing 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)
12Water 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
13Water 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
14Water 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
15Water 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)
16Summary 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 -