R.E. Pollock

Analyzing powers and spin correlation coefficients for p+d elastic scattering at 135 and 200 MeV

The proton and deuteron analyzing powers and ten of the possible 12 spin correlation coefficients have been measured for p+d elastic scattering at proton bombarding energies of 135 and 200 MeV. The results are compared with Faddeev calculations using two different NN potentials. The qualitative features of the extensive data set on the spin dependence in p+d elastic scattering over a wide range of angles presented here are remarkably well explained by two-nucleon force predictions without inclusion of a three-nucleon force. The remaining discrepancies are, in general, not alleviated when theoretical three-nucleon forces are included in the calculations.

Test of a windowless storage cell target in a proton storage ring

Abstract Stored ion beams offer the possibility to use polarized internal targets that consist of a source of polarized atoms in conjunction with a long, narrow, windowless target cell to enhance the target thickness. In this paper, we discuss the effect of such a cell on the performance of the storage ring, based on measurements carried out with the Indiana Cooler. A prototype target cell was constructed and was operated with a controlled flow of H 2 target gas in a beam of stored protons. Detection of protons scattered at angles from 4° to 15° in coincidence with the associated recoil particles was used to identify elastic scattering. The results show that the presence of a 25 cm long target cell with a rectangular opening of 6.4 mm by 7.9 mm is compatible with operation of the Cooler ring. This demonstrates the feasibility of an important component of experiments with stored, polarized beams and carrier-free polarized, internal targets.

Performance of a polarized-hydrogen storage cell target

Abstract A storage cell has been constructed for use as an internal polarized gas target in the storage ring at the Indiana University Cyclotron Facility. The storage cell has thin teflon walls which allow for detection of low energy recoil particles. We report on nuclear polarization measurements of hydrogen atoms, produced by an atomic beam source, in this storage cell. The results indicate that a target polarization in excess of 0.70 is achieved. We discuss the design and construction details of a storage cell target and the polarization results which are based on low-energy pp spin correlation measurements using the University of Wisconsin tandem accelerator.

Polarized internal gas target for hydrogen and deuterium at the IUCF Cooler Ring

Abstract A polarized internal gas target has been constructed and used at the IUCF Cooler Ring. Polarized hydrogen atoms produced by a high-intensity atomic beam source are injected into a target cell whose Teflon walls are thin enough to allow low-energy recoil particles to be detected in coincidence with forward scattered particles. An average proton target polarization of 0.740±0.013 has been measured.

Interaction of stored, cooled proton beams with fiber targets

Abstract The use of thin fibers as internal targets for nuclear physics experiments in storage rings is discussed. We have measured the lifetime and the energy spread of stored, electron-cooled beams in the presence of an internal carbon fiber target. Measurements have been carried out in the Indiana Cooler with proton beams between 100 MeV and 300 MeV. The effect of the inhomogeneous fiber target on the beam is the same as that of a homogeneous gas target of equivalent thickness within the accuracy of the measurement. The measurements are compared with a Monte Carlo simulation of the stored beam. It is demonstrated that charging of the fiber target can significantly affect the lifetime and energy spread of the stored beam.

Beam loss rates with an internal gas target in an electron-cooled storage ring Implications for luminosity optimization

Measurements have been made in the Cooler ring at the Indiana University Cyclotron Facility (IUCF) of the mean lifetime of stored and electron-cooled proton beams in the presence of various target gas species at two ring locations differing in dispersion. A broad range of beam energy Tb, target atomic number Zt and thickness xt was employed. The loss (removal) cross sectionσL per target atom, extracted from the lifetime measurement, exhibits a minimum for small xt which is found to scale with (ZtTb)2. This behavior is expected because forward Coulomb scattering from target nuclei should be the dominant loss mechanism under the conditions of measurement. A marked increase in σL for larger xt is attributed to emittance growth arising from multiple scattering in competition with the transverse cooling rate. Lattice dispersion at the target increases the contribution to beam heating by electrons in the target atoms and introduces an additional loss mechanism. From the measured σL and beam lifetime, a time cycle may be selected which gives the optimum time-averaged luminosity for a given experiment. Scaling of σL allows prediction of the optimum luminosity over the full operating regime of the cooling ring.

Measurement of high momentum transfer reactions by recoil detection

A method is described for studying reactions at medium energies by measuring the magnetic rigidity, time of flight, and energy loss of the resulting recoil products. The method works best for reactions with two-body final states where one of the outgoing particles is relatively light. A magnetic spectrometer with a special focal plane detector has been used. The detector consists of two position sensitive parallel plate avalanche counters and two proportional counters. Differential cross sections for the 12C(p, π+13C reaction at recoil angles which correspond to the pion being emitted at a backward angle in the center of mass have been measured at bombarding energies of 166 and 186 MeV. Data were also obtained for previously unobserved 12C(p, π0)13N reaction. Several advantages of the method are discussed.

A new generation of small cooling rings

Abstract Over the past few years, a number of laboratories have begun to construct and operate storage rings, of modest dimensions and designed for specialized applications. A subset of this class of projects includes the rings containing cooling devices which can impart properties to the stored beam that make it of particular interest for experimental use. Cooling is only one of a set of operations that may be performed upon a beam once the storage capability exists. This paper summarizes the beam processing options that are possible in a cooling ring in order to show the flexibility of this technology, and then reviews the status and representative application plans for the small cooling rings that make up this new generation.

IUCF Status Report

A report is presented on the status of the Indiana University Cyclotron Facility (IUCF) three years after first operation. The range of accelerator beam characteristics, the beam delivery record for research use and selected observations of unusual features of this facility will be given.

Field Mapping Results of the IUCF 200 MeV Cyclotron

The Indiana University 200 MeV Isochronous Cyclotron is a separated sector (N = 4) machine whose design goals include the acceleration of both protons and heavy ions over a variable energy range up to a maximum energy of approximately 220 Z2/A MeV. The large range in energy and particle mass requires that the radial profile of the magnetic fields be adjustable to match the relativistic mass increase of the accelerated particle. For the acceleration of protons to 200 MeV for example, an increase in the field from injection to extraction radius of about 22% is needed, whereas for heavier ions the field profile must rise approximately 2%.