R.S. Kowalczyk

The HERMES dual-radiator ring imaging Cherenkov detector

Abstract The construction and use of a dual radiator Ring Imaging Cherenkov (RICH) detector is described. This instrument was developed for the HERMES experiment at DESY which emphasises measurements of semi-inclusive deep-inelastic scattering. It provides particle identification for pions, kaons, and protons in the momentum range from 2 to 15 GeV , which is essential to these studies. The instrument uses two radiators, C 4 F 10 , a heavy fluorocarbon gas, and a wall of silica aerogel tiles. The use of aerogel in a RICH detector has only recently become possible with the development of clear, large, homogeneous and hydrophobic aerogel. A lightweight mirror was constructed using a newly perfected technique to make resin-coated carbon-fiber surfaces of optical quality. The photon detector consists of 1934 photomultiplier tubes (PMT) for each detector half, held in a soft steel matrix to provide shielding against the residual field of the main spectrometer magnet.

Silane coatings for laser-driven polarized hydrogen sources and targets

It is necessary to use special coatings on the surfaces of volumes containing polarized atoms in order to minimize depolarizing spin interactions during wall collisions. We are studying coatings of organosilicon compounds that preserve hydrogen and potassium polarizations and prevent molecular recombination of hydrogen during wall collisions in a laser-driven polarized hydrogen source. Continuing problems with coatings for these sources has been the reproducibility of high-quality surfaces and reliable assessment of surface quality before installation of coated parts in the laser-driven source. We have used an atomic force microscope to scan surfaces coated with different organosilicon compounds with the goal of assessing surface quality and determining a method of preparing reproducible surfaces that do not degrade with time. Here we show AFM scans of the different coatings, discuss the quality of coatings made with different chemicals and application procedures, and present the results of coating stability tests as a function of temperature and exposure to potassium. We find that a simple organosilicon afterwash gives a significantly improved surface.

A polarized gas internal target using a storage cell in an electron storage ring

Abstract The first experiment using a storage cell to increase the thickness of an internal polarized gas target in an electron beam storage ring was performed at the VEPP-3 facility. We describe the storage cell technique as applied in this measurement of elastic and inelastic electron scattering from tensor polarized deuterium. An analysis of electron-beam-induced depolarization of the target was performed and experimental tests were carried out which verify the effect. Other effects causing depolarization of the target are discussed as well as the means by which they are overcome. The effective p zz of the target, shown to be stable over 8 months, was 0.57±0.05; the total target thickness was increased over that of a jet target by a factor of fifteen.

Thin film coatings which inhibit spin relaxation of polarized potassium atoms

Abstract A new technique is being developed at Argonne National Laboratory to produce a beam of polarized deuterium atoms. A part of the apparatus consists of a small cell which contains potassium vapor. The potassium atoms are polarized by circularly polarized light from a high-power cw laser. A port feeds deuterium into the cell and the polarization of the potassium is transferred to the deuterium by spin-exchange scattering. It is important that the potassium and deuterium atoms do not lose polarization by scattering from the walls of the exchange cell. We have tried various coatings of the exchange walls in order to inhibit losses from spin relaxation. Methods used to produce these coatings as well as their success will be described.

Laser-driven source of spin-polarized atomic hydrogen and deuterium

Abstract A laser-driven source of spin-polarized hydrogen (H) and deuterium (D) that relies on the technique of optical pumping spin exchange has been constructed. In this source, H or D atoms and potassium atoms flow continuously through a drifilm-coated spin-exchange cell where potassium atoms are optically pumped with circularly-polarized laser light in a high magnetic field. The H or D atoms become polarized through spin-exchange collisions with polarized potassium atoms. High electron polarization ( ≈ 80%) has been measured for H and D atoms at flow rates ≈ 2 × 1017 atoms/s. Lower polarization values are measured for flow rates exceeding 1 × 1018 atoms/s. In this paper, we describe the performance of the laser-driven source as a function of H and D atomic flow rate, magnetic field strength, alkali density and pump-laser power. Polarization measurements as a function of flow rate and magnetic field suggest that, despite a high magnetic field, atoms within the optical-pumping spin-exchange apparatus evolve to spin-temperature equilibrium which results in direct polarization of the H and D nuclei.

An active storage cell for a polarized gas internal target

Abstract The first experiment using an active storage cell for polarized atoms to increase the target thickness in an electron storage ring has been performed at the VEPP-3 facility. A clam-shell storage cell, which is opened while injecting electrons into the storage ring and closed during operation, was used to increase the target thickness viewed by the detector system. The average tensor polarization of the target was found to be p zz = 0.59 ± 0.14 and the figure of merit was increased by more than a factor of thirty in comparison with a direct jet thickness. The measured target thickness and polarization are in a good agreement with the expected values.

Polarized deuteron target in an electron storage ring: Measurements and perspectives

A gas jet of polarized deuterium atoms with a thickness of 2×1011 cm−2 has been used as an internal target in the VEPP‐3 electron storage ring with 2 GeV energy. Source characteristics as well as experimental conditions and results on elastic and inelastic scattering are reviewed.Results of experimental studies and calculations of jet depolarization induced by an electron beam are discussed. For the first time a storage cell for polarized atoms was used in the storage ring in order to increase the target thickness. Depolarization of atoms inside the cell due to wall collisions with a drifilm surace and a magnetic field is proved to be small whereas depolarization due to the transitional magnetic field of the electron beam at 2 GeV energy can be significant.Conditions for small depolarization by the electron beam were found. An effective target polarization in the storage cell was found to be Peffzz=0.8±0.2.

Laser-driven polarized sources of hydrogen and deuterium

Abstract A novel laser-driven polarized source of hydrogen and deuterium which operates on the principle of spin exchange optical pumping is described. The advantages of this method over conventional polarized sources for internal target experiments are presented. Technological difficulties which prevent ideal source operation are outlined along with proposed solutions. At present, the laser-driven polarized hydrogen source delivers 8 × 10 16 atoms/s with a polarization (P z ) of 24%.

A short‐orbit spectrometer for Hall C

A short‐orbit spectrometer capable of detecting particles with momentum <2.0 GeV/c with moderate energy and angular resolution will be available in Hall C for operations in coincidence with the HMS spectrometer or for stand alone operation. The design is based on a QD(‐D) configuration which can meet the needs of a broad spectrum of studies appropriate to Hall C. Measurements will be possible for angles of up to 20 degrees out of plane.

Laser‐driven polarized targets of hydrogen and deuterium

An optical pumping technique used in a laser‐driven source of polarized hydrogen or deuterium is described and measurements of the achievable polarization as a function of flow for both hydrogen and deuterium are presented. Ongoing tests of the feasibility of using a laser‐driven polarized deuterium source coupled to a storage cell as a polarized internal target, including direct measurements of the nuclear polarization, are discussed.