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HK: Hadronen und Kerne

HK 3: Instrumentation I, Ion Sources, Targets

HK 3.6: Talk

Monday, March 16, 1998, 15:30–15:45, A

The HERMES Polarized Hydrogen Target — •B. Braun on behalf of the HERMES collaboration — Phys. Inst., Univ. Erlangen-N"urnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen

The polarized internal gas target was operated during 1996 and 1997 parallel to the collider experiments in the HERA electron ring at DESY to study the spin structure of the proton by scattering of longitudinally polarized leptons from longitudinally polarized protons. A high target areal density is obtained by using a cold thin-walled storage cell placed on the axis of the electron beam. The storage cell is supplied with polarized hydrogen atoms by a highly intense atomic beam source, which is based on Stern-Gerlach separation in sextupole magnets and adiabatic high frequency transitions. A sample of the target gas in the cell is analyzed using a Breit-Rabi polarimeter, to continuously measure the atom polarization, and a target gas analyzer to determine the fraction of molecules. The resonant interaction of the the bunched 27.6 GeV electron beam with the polarized atoms has been studied in detail. At an operating holding field value of 335 mT no depolarization is detectable. Luminosities up to 1.7· 10³¹ cm⁻²s⁻¹ were obtained in the course of the run. In total the target was operated in-beam for about 16 months at an atomic polarization above 0.9 and molecular fraction typically below 10 %.

Supported in part by the BMBF, Germany,
contract number 057ER12P(2) and 056MU22I(1).