The HERMES Polarized H

1
The HERMES Polarized HD Gas Target 10 Years of
Operation
Erhard Steffens University of Erlangen-Nürnberg an
d HERMES Collaboration (DESY-Hamburg)

• Introduction and history
• Polarized gas targets in a high energy storage
  ring
• Overview of HERMES HD target
• Summary of runs 1996 to 2005 (H, D H-)
• Conclusions

2
The Clue to High Density Storage Cells

• Ballistic flow from Atomic Beam Source (H, D)
• Flow driven by pressure gradient
  Laser Driven Sources (H, D, 3He)

• Storage Cell proposed by W. Haeberli
• Proc. Karlsruhe 1965, p. 64
• Proc. Workshop IUCF 1984, AIP Conf. Proc.128,
  p.251

Polarized atoms from source
Target areal density given by t L ro with ro
It / Ctot and Ctot S Ci Note Conductance of
tube proportional to d3/L
T-shaped storage cell
Density gain compared to Jet of same intensity
can be up to several hundred!
3
1st Test of a Storage Cell in a 2 GeV Electron
Storage Ring VEPP-3 at BINP

• Storage cell surface is coated to inhibit
  recombination and depolarization
• Coatings like Teflon or Drifilm are sensitive to
  Synchrotron Radiation ( hard X-rays)
• First test of storage cell (uncooled, Drifilm
  coating) performed by BINP-ANL collaboration in
  1988 R.A. Gilman et al, PRL 65 (1990) 1733
• Results show that the coating is stable on the
  time scale of ½ year!

Aymmetry for electro-disintegration of the
deuteron as function of running time for a
polarized deuterium storage cell target in the
VEPP-3 storage ring at BINP
Found later In the cooled HERMES storage cell (T
100 K) a water surface is formed with superior
quality
4
Expectations Paris 1990
Talk on Experiments with Dense Polarized
Internal Targets
I
5
Expectations Paris 1990
II
6
Past History FILTEX

• Goal spin filtering of antiprotons (proposal
  1985)
• Tool dense polarized H target in p_bar storage
  ring LEAR (CERN)
• Test experiment with protons in the Heidelberg
  test storage ring TSR 1992

7
Past History FILTEX
8
Past History FILTEX
W. Korsch, F. Rathmann, K. Zapfe, P. Schiemenz
1014/cm2 demon- strated!
High polari- zation in weak field!

• View into the FILTEX target chamber
• rear last 6-pole (SmCo)
• center T-shaped storage cell
• right cryopump with hole for beam

9
The HERMES Experiment

• HERMES experiment proposed for the HERA 30 GeV
  polarized electron ring
• - Letter of Intent 1988
• - Proposal 1990
• - Technical Design Report 1993
• - First Operation in April 1995 (with pol. 3He
  target)

Physics see talk by E. Aschenauer (Wedn.)

• Requirements on the target
• - Areal density t 1014/cm2 in two
  substates OK
• - Sampling polarimeter with DP/P 3 ?
• - Coating stable wrt synchrotron
  radiation (OK?)
• - Suppression of Wake Fields in the
  target Simulations OK
• - Suppression of beam-induced (rf)
  depolarization

Several open questions left...
10
HERMES Target- Overview
Target chamber
11
HERMES Target 1996
H-Target installed in early 1996
Erlangen Liverpool Madison Marburg Munich Yerevan
F. Stock B. Braun G. Graw G. Court T. Wise et al
12
Atomic Beam Source (ABS)
Heidelberg-Marburg-Munich-Madison

• Collimated cold atomic beams produced by
  disso-ciator with cold nozzle (100K) and
  differential pumping system (SSi 104 l/s)
• Spin-dependent focussing of H and D atomic beams
  by 6-pole magnets mJ 1/2
• Nuclear polarization Pz, Pzz produced by means of
  rf transitions with 100 effi-cieny rapid
  switching enabled

Bc 50.7 mT
13
Design of Target Chamber
G. Court Liverpool T. Wise Madison
HD
Collimator C2
e
Target Cell 400mm
Wake Field Suppr.
SC Coils
14
Storage Cell Design
Liverpool-Madison-Ferrara

• Cell optimized for operation in an electron
  storage ring
• Conducting surface with smooth variation of cross
  section excitation of wake fields!
• System of W collimators for protection against
  beam and SR
• Cooled via cooling rails by cold He gas to
  60-100K
• 75mm Al walls with Drifilm coating - Radiation
  damage visible!
• But Very effective wall coating due to ice layer
  maintained by small fraction of water in the
  atomic beam !

15
Diagnostics
B. Braun, Ch. Baumgarten, P. Lenisa, et al

• Target gas analyzer (TGA)
• - measures degree of dissociation a to 1 in few
  minutes
• - molecules (with polarization fraction b)
  dilute nuclear polarization
• - enters the final values of target polarization

Sketch of the TGA
16
Diagnostics

• Target gas analyzer (TGA)
• - measures degree of dissociation a to 1 in few
  minutes
• - molecules (with polarization fraction b)
  dilute nuclear polarization
• - enters the final values of target polarization

Temperature scan on new cell (hydrogen 1997)
17
Diagnostics

• Target gas analyzer (TGA)
• - measures degree of dissociation a to 1 in few
  minutes

Temperature scan on used cell (deuterium 2000)
after formation of water layer
no T-dependence visible no recombination in the
cell!
18
Diagnostics

• Target gas analyzer (TGA)

At T 100 K stable water layer, suppresses
recombination (a 1) At T 260 K water layer
partly removed!
19
Diagnostics

• Sampling polarimeter (BRP)
• - measures substate population ni of sample beam
  to Dn/n 1 in few minutes
• - BRP polarizations Pe (electrons) and Pz , Pzz
  (nuclei) calculated
• - Sampling corrections applied to calculate
  PTarget seen by the beam!

Erlangen-Heidelberg-Munich-Ferrara-Yerevan
D. Braun, Ch. Baumgarten, G. Graw, D.
Reggiani, P. Lenisa et al
Detector
Sample Beam
Schematic view of Sampling Polarimeter
20
Diagnostics

• Sampling polarimeter (BRP)
• - measures substate population ni of
  sample beam to Dn/n 1 in few minutes

Hydrogen hfs-population as function of holding
field
Detector
Sample Beam
B. Braun Thesis, Munich 1995
21
Diagnostics

• Sampling polarimeter (BRP)
• - measures substate population ni of sample beam
  to Dn/n 1 in few minutes
• - BRP polarizations Pe (electrons) and Pz , Pzz
  (nuclei) calculated

BRP polarization for the deuterium run 2000 top
vector pol. Pz bottom tensor pol. Pzz
22
Beam-induced Depolarization

• HERA-e
• Bunch frequency nBunch 10.4 MHz
• Bunch length st 38 ps

Harmonics nn nnB up to very high harmonics!
(nmax 103 corr. to 10 GHz)
hnn
Resonance condition DE(Bn) hnn ?
resonant guide fields Bn exist!
Bn
23
Beam-induced Depolarization

• blue p resonances (DmF 1)
• red s resonances (DmF 0) narrow-spaced!
  
• 
  Transverse target only

s24
p34
24
Beam-induced Depolarization
Ferrara-Erlangen-Peking
BRP used to detect the resonances induced by
harmonics of the bunch field! Shown the widely
spaced p resonances

• HERA-e
• Bunch frequency nBunch 10.4 MHz
• Bunch length st 38 ps

Harmonics nn nnB up to very high harmonics!
(nmax 103 corr. to 10 GHz)
Resonance condition DE(Bn) hnn ?
resonant guide field Bn exists!
p 3-4
p 1-2
B-scan of p-resonances
25
Beam-induced Depolarization
Ferrara-Erlangen-Peking
BRP used to detect the resonances induced by
harmonics of the bunch field! Shown the narrow s
resonances

• HERA-e
• Bunch frequency nBunch 10.4 MHz
• Bunch length st 38 ps

Harmonics nn nnB up to very high harmonics!
(nmax 103 corr. to 10 GHz)
Correction coil
For optimum setting of correction current Small
change of BRP detector current by the bunch field
? Beam-induced depolarization is low!
No beam
B-scan of s-resonances
26
Target Performance
recombination
spin exchange
wall depol.
beam induced
calculated target polarization ?
target areal density ?
Figure Of Merrit
27
Conclusions

• Polarized HD target successfully operated over
  10 years in a HE electron storage ring more or
  less continuesly
• Several problems solved during commissioning
  phase(s) thanks to many enthousiastic
  collaborators impossible to name them all!
• Nature was kind to us (no show-stopper) ?
• Technology ready to be used for other projects!

www.fz-juelich.de/ikp/pax