Performance of a hydrogen/deuterium polarized gas target in a storage ring

The performance of a high-density polarized hydrogen/deuterium gas target internal to a medium-energy electron storage ring is presented. Compared to our previous electron scattering experiments with tensor-polarized deuterium at NIKHEF (Zhou et al., Nucl. Instr. and Meth. A 378 (1996) 40; Ferro-Luzzi et al., Phys. Rev. Lett. 77 (1996) 2630; Van den Brand et al., Phys. Rev. Lett. 78 (1997) 1235; Bouwhuis et al., Phys. Rev. Lett. 82 (1999) 687; Zhou et al., Phys. Rev. Lett. 82 (1999) 687) the target figure of merit, (polarization)(2) x luminosity, was improved by more than an order of magnitude. The target density was increased by upgrading the flux of nuclear-polarized atoms injected into the storage cell and by using a longer (60 cm) and colder (similar to 70 K) storage cell. A maximal target thickness of 1.2 (1.1) +/- 0.1 x 10(14) nuclei/cm(2) was achieved with deuterium (hydrogen). With typical beam currents of 110 mA, this corresponds to a luminosity of about 8.4 (7.8) +/- 0.8 x 10(31) e(-) nuclei cm(-2) s(-1). By reducing the molecular background and using a stronger target guide field, a higher polarization was achieved. The target was used in combination with a 720 MeV polarized electron beam stored in the AmPS ring (NIKHEF) to measure spin observables in electron-proton and electron-deuteron scattering. Scattered electrons were detected in a large acceptance magnetic spectrometer. Ejected hadrons were detected in a single time-of-flight scintillator array. The product of beam and target vector polarization, PePt, was determined from the known spin-correlation parameters of e''p quasi-elastic (or elastic) scattering. With the deuterium (hydrogen) target, values up to PePt = 0.49 +/- 0.03 (0.32 +/- 0.03) were obtained with an electron beam polarization of P-e = 0.62 +/- 0.04 (0.56 +/- 0.03) as measured with a Compton backscattering polarimeter (Passchier et al., Nucl. Instr. and Meth. A 414 (1998) 4988). From this, we deduce a cell-averaged target polarization of P-t = 0.78 +/- 0.07 (0.58 +/- 0.07), including the dilution by unpolarized molecules. (C) 2001 Elsevier Science B.V. All rights reserved.