october 3, 2006e. steffens – spin 2006 1 the hermes polarized h&d gas target: 10 years of...

October 3, 2006 E. Steffens – Spin 20061

The HERMES Polarized H&D Gas Target: 10 Years

of Operation

Erhard Steffens

University of Erlangen-Nürnbergand

HERMES Collaboration (DESY-Hamburg)

• Introduction and history

• Polarized gas targets in a high energy storage ring

• Overview of HERMES H&D target

• Summary of runs 1996 to 2005 (H║, D║ H┴)

• Conclusions


The Clue to High Density: The Clue to High Density: Storage CellsStorage Cells

Polarized atoms from source

Target areal density given by

t = L o

with o = It / Ctot and Ctot = S Ci

Note: Conductance of tube proportional to d3/L

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

• 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

Density gain compared to Jet of

same intensity can be up to several hundred!

T-shaped storage cell


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


Expectations Paris 1990

Talk on:

‚Experiments with Dense Polarized Internal Targets‘

I


Expectations Paris 1990

II


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



View into the FILTEX target chamber

- rear: last 6-pole (SmCo)

- center: T-shaped storage cell

- right: cryopump with hole for beam

1014/cm2

demon-

strated!

High

polari-

zation

in weak

field!

W. Korsch, F. Rathmann, K. Zapfe, P. Schiemenz †


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 P/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...


HERMES Target- Overview

Target chamber


HERMES Target 1996H-Target installed in early 1996

Erlangen

Liverpool

Madison

Marburg

Munich

Yerevan

F. Stock

B. Braun

G. Graw

G. Court

T. Wise et al


Atomic Beam Source (ABS)

Atomic Beam Source (ABS)

• Collimated cold atomic beams produced by disso-ciator with cold nozzle (100K) and differential pumping system (Si ~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

Heidelberg-Marburg-Munich-Madison


Design of Target Chamber

H&D

e±

Collimator C2

SC Coils

Wake Field Suppr.

G. Court – Liverpool

T. Wise – Madison

Target Cell 400mm


Storage Cell Design Storage Cell Design

• 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

• 75m 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 !

Liverpool-Madison-Ferrara


Diagnostics

• Target gas analyzer (TGA)

- measures degree of dissociation to 1% in few minutes

- molecules (with polarization fraction ) dilute nuclear polarization

- enters the final values of target polarization

Sketch of the TGA:

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


Diagnostics



- molecules (with polarization fraction ) dilute nuclear polarization

- enters the final values of target polarization

Temperature scan on new cell (hydrogen 1997)


Diagnostics



Temperature scan on used cell (deuterium 2000) after formation of water layer

no T-dependence visible

no recombination in the cell!


Diagnostics

• Sampling polarimeter (BRP)

- measures substate population ni of sample beam to n/n = 1% in few minutes

- BRP polarizations Pe (electrons) and Pz , Pzz (nuclei) calculated

- Sampling corrections applied to calculate PTarget seen by the beam!

Sample Beam

Detector

Schematic view of Sampling Polarimeter

Erlangen-Heidelberg-Munich-Ferrara-Yerevan

D. Braun,

Ch. Baumgarten,

G. Graw,

D. Reggiani,

P. Lenisa et al


Diagnostics

• Sampling polarimeter (BRP)

- measures substate population ni of sample beam to n/n = 1% in few minutes

Sample Beam

Detector

Hydrogen hfs-population as function of holding field

B. Braun

Thesis, Munich 1995


Diagnostics

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

- BRP polarizations Pe (electrons) and Pz , Pzz (nuclei) calculated

BRP polarization for the deuterium run 2000top: vector pol. Pz

bottom: tensor pol. Pzz


Beam-induced Depolarization

HERA-e:

• Bunch frequency Bunch = 10.4 MHz

• Bunch length t = 38 ps

Harmonics n = n·B up to very high harmonics! (nmax ≈ 103 corr. to 10 GHz)

Resonance condition:

E(Bn) = h·n

→ resonant guide fields Bn exist!

h·n

Bn



24

- blue: resonances (mF = ± 1)

-red: resonances (mF = 0) narrow-spaced!

Transverse target only

34



HERA-e:




Resonance condition:

E(Bn) = h·n

→ resonant guide field Bn exists!

B-scan of -resonances

3-4 1-2

BRP used to detect the resonances induced by harmonics of the bunch field!

Shown: the widely spaced resonances

Ferrara-Erlangen-Peking



HERA-e:




B-scan of -resonances

BRP used to detect the resonances induced by harmonics of the bunch field!

Shown: the narrow resonances

No beam

Correction coil

For optimum setting of correction current:

Small change of BRP detector current by the bunch field

→ Beam-induced depolarization is low!

Ferrara-Erlangen-Peking


Target Performance

Target/year H║ (1997) D║ (2000) H┴ (2003)

r 0.055 0.003 0.004

PSE 0.035 ≤0.001 0.055

PWD 0.02 ≤0.01 0.055

PBI absent absent 0.015

PT 0.851±0.033 0.845±0.028 0.795±0.033

t (1014 nucl./cm2)

0.7 2.1 1.1

FOM

(PT2·t)

0.5 1.5 0.7

recombination

spin exchange

wall depol.

beam induced

calculated target polarization →

target areal density →

Figure Of Figure Of MerritMerrit


Conclusions

• Polarized H&D 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

october 3, 2006e. steffens – spin 2006 1 the hermes polarized h&d gas target: 10 years of...

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