A fast transverse instability has been observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam intensity reaches more than 2/spl times/10/sup 13/ protons per pulse. Understanding the cause and control of this instability has taken on new importance as the neutron-scattering community considers the next generation of accelerator-driven spallation-neutron sources, which call for peak proton intensities of 10/sup 14/ per pulse or higher. Previous observations and theoretical studies indicate that the instability in the PSR is most likely driven by electrons trapped within the proton beam. Recent studies using an experimental electron-clearing system and voltage-biased pinger-electrodes for electron clearing and collection support this hypothesis. Experiments have also been performed to study the instability threshold when varying the electron production rate. Theoretical studies include a computer simulation of a simplified model for the e-p instability and the investigation of possible electron confinement in the ring-element magnetic fields. This paper reports some recent results from these studies.

Foil stripping of H- directly to H+ is being considered for proton injection in the next generation of high-current proton storage rings. This technique can result in significant losses because excited states of H0, which are also produced in the foil, are field stripped in the downstream bending magnets. Without due care in the injection system design, many of the resulting protons will be outside the acceptance of the storage ring and will be quickly lost. We measured the production of such H0 excited states at the LAMPF High Resolution Atomic Beam Facility. An 800-MeV H- beam was passed through carbon foils of thicknesses 70, 100, 200, and 300 μg/cm2 and the excited states were analyzed by a special magnet downstream of the foil. The magnet had a linear field gradient so that the trajectories of the outgoing protons could be used to reconstruct the field values at which the various H0 stripped. We found that about 1% of the H0 emerge in excited states which can be stripped to protons by ring-bending magnets

A fast transverse instability with beam loss has been observed in the 800-MeV Los Alamos Proton Storage Ring (PSR) when the injected beam intensity reaches 2 to 4×1013 protons per pulse. Previous observations indicate that the instability is most likely driven by electrons trapped within the proton beam. Theoretical study has shown that beam leakage into the inter-bunch gap leads to electron trapping. Recent experiments were carried out by using the newly installed “pinger” and by varying the machine transition gamma to explore further the “e-p” instability and the nature of the instability. This paper summarizes some of these recent experimental results and theoretical studies

g/cc). For production angles of 30"<%60", DER estimates Neutron dose equivalent rates have been measured for are made with both sets of parameters defining a range of 800-MeV proton beam spills at the Los Alamos Meson possible values. Physics Facility. Neutron detectors were used to measure the neutron dose levels at a number of locations for each beam- spill test, and neutron energy spectra were measured for several beam-spill tests. Estimates of expected levels for various detector locations were made using a simple analytical model developed for 800-MeV proton beam spills, A comparison of measurements and model estimates indicates that the model is reasonably accurate in estimating the neutron dose equivalent rate for simple shielding geometries. The model fails for more complicated shielding geometries, where indirect contributions to the dose equivalent rate can dominate. Table 1. Analytical Model Parameters for Estimating Neutron Dose 800-MeV Proton Beam Spills. I

Monte Carlo simulations of 800-MeV proton beam spills in common shielding materials show that neutron dose equivalent rates in the forward direction can be characterized by a Moyer Model-like formula. Particle transport codes were used to determine the neutron flux at depths up to 6 meters and for production angles from 0° to 30° for primary proton-beam spills on cylindrical beam stops. The flux was then converted to dose equivalent rate as a function of depth and angle. The results for three common shielding materials were combined and the resulting fitted formula provides a quick method for estimating the dose equivalent rates and shielding effectiveness outside thick shielding at forward angles