Andrew J. Jason

Design and operation of a proton microscope for radiography at 800 MeV

A high-magnification high-resolution option is desirable for the study of small-scale dynamic experiments at the LANSCE 800-MeV Proton Radiography Facility. Magnification is achievable by either repowering the existing imaging-lens quadrupoles, using new high-gradient quadrupoles, or some hybrid combination of the two. The large and complex parameter space of magnetic optics solutions was studied extensively with the 3rd order optics code MARYLIE. Some of the hybrid solutions achieve magnifications up to 150, but at the price of high chromatic aberrations. In the end, a design using only new high-gradient permanent-magnet quadrupoles was selected and built at the design parameters that minimized chromatic aberration per unit magnification. The design has a moderate magnification of 7.1 and 15.8 at the two existing image stations. First-beam commissioning results exceeded expectations. Image contrast is produced by multiple Coulomb scattering in the thin objects. Early experimental objectives are to optimize this contrast by collimator design and by adjusting the correlation in the illuminating beam, as well as to characterize the (quite high) resolution limits of the system.

Neutralization of H- Beams by Magnetic Stripping

The stability of H- beams passing through strong magnetic fields has been relevant to accelerator transport problems and, recently, to neutral beam preparation techniques. We have measured the H- electron detachment rate as a function of restframe electric field and provide parameters for a theoretical lifetime expression. We discuss the limitations imposed on H- transport by magnetic stripping, and neutral-beam preparation in emittance growth, magnetic fields, and beam energies. Application techniques are also briefly discussed.

LASL High-Current Proton Storage Ring

The Proton Storage Ring at LAMPF is a high-current accumulator designed to convert long 800-MeV linac pulses into very short high-intensity proton bunches ideally suited to driving a pulsed polyenergetic neutron source. The Ring, authorized for construction at

Cosmic Ray Inspection and Passive Tomography for SNM Detection

19 million, will operate in a short-bunch high-frequency mode for fast neutron physics and a long-bunch low-frequency mode for thermal neutron-scattering programs. Unique features of the project include charge-changing injection with initial conversion from H− to H0, a high repetition rate fast-risetime extraction kicker, and high-frequency and first-harmonic bunching systems.

Los Alamos High-Current Proton Siorage Ring; A Status Report

The Cosmic Ray Inspection and Passive Tomography (CRIPT) project has recently started investigating the detection of illicit Special Nuclear Material in cargo using cosmic ray muon tomography and complementary neutron detectors. We are currently performing simulation studies to help with the design of small scale prototypes. Based on the prototype tests and refined simulations, we will determine whether the muon tracking system for the full scale prototype will be based on drift chambers or extruded scintillator trackers. An analysis of the operations of the Port of Montreal has determined how long muon scan times should take if all or a subset of the cargo is to be screened. As long as the throughput of the muon system(s) is equal to the rate at which containers are unloaded from ships, the impact on port operations would not be great if a muon scanning stage were required for all cargo. We also show preliminary simulation results indicating that excellent separation between Al, Fe and Pb is possible under ideal conditions. The discrimination power is reduced but still significant when realistic momentum resolution measurements are considered.

Injection System for the Proton Storage Ring at LASL

The Proton Storage Ring (PSR),1 whose installation was recently completed at Los Alamos, is a fast-cycling high-current accumulator designed to produce intense 800 MeV proton pulses for driving a spallation neutron source.2 The ring converts long beam pulses from the LAMPF linear accelerator into short bunches well matched to requirements of a high-resolution neutron-scattering materials science program. The initial performance goal for this program is to provide 100-¿A average current at the neutron production target within a 12-Hz pulse rate. Project construction began in May 1982, and was completed in mid-April 1985. First beam was circulated in the ring on April 26. Operation at 20 ¿A is scheduled for September 1985, with full intensity within the next year. The storage ring was originally designed to function in a second mode in which six 1-ns bunches are accumulated and separately extracted every LAMPF macropulse. Implementation of this mode, which would serve a fast-neutron nuclear-physics program, has been deferred in favor of initial concentration on the neutron-scattering program. This paper summarizes the PSR design and status. Unique machine features include high peak current, two-step charge-stripping injection, a low-impedance buncher amplifier to counter beamloading, and a high-repetion-rate strip-line extraction kicker. LINE-A

A Los Alamos design study for a high-power spallation-neutron-source driver

The Proton Storage Ring at LAMPF will accumulate a high current of 800-MeV protons by multiturn charge-changing injection. An 800-MeV neutral hydrogen atomic beam, formed by field ionization of H− ions in a 1.8 T transverse magnetic field, will be stripped to protons by a carbon foil. To minimize peak proton current on the foil, the beam orbit will be deformed so that the edge of the beam grazes the edge of the foil. As the beam diameter grows, the orbit perturbation is decreased, vanishing at the end of the accumulation cycle. The hardware requirements are simple. Single-turn orbit deformation magnets are pulsed to peak field and switched across power dissipation circuits that control the field decay rate.

The los Alamos Proton Storage Ring Fast-Extraction Kicker System

A design study for an accelerator-driven spallation-neutron source is underway at Los Alamos. The driver, based on the LAMPF facility, produces a 1-MW proton beam and is upgradable to 5 MW. After linear acceleration to full energy, an H/sup -/ beam is accumulated for approximately 1.2 ms in an accumulator ring and then extracted to produce an intense proton burst, less than 1 /spl mu/s long, onto a spallation-target system with a 60-Hz pulse rate. The design uses existing infrastructure insofar as possible while maintaining project goals. This paper summarizes the system specifications and design status.<<ETX>>

Beam expansion with specified final distributions

We describe the kicker system used by the Los Alamos Proton Storage Ring1 (PSR) for fast extraction of accumulated 800-MeV proton beam. The system has several severe constraints in terms of rise time, field quality, and magnet dimensions. These are, in turn, defined by characteristics of the stored beam, ring lattice, and the allowable activation of ring components. Design methods to meet the constraints are outlined here and we describe the novel modulators that produce the fast pulses required.

Lattice design of the LANL spallation-source compressor ring

The formation of nearly uniformly distributed beams has been accomplished by the use of multipole magnets. Multipole fields, however, are an inappropriate basis for creating precise distributions, particularly since substantial departures from uniformity are produced with a finite number of multipole elements. A more appropriate formalism that allows precise formation of a desired distribution is presented. Design of nonlinear magnets for uniform-beam production and the optics of an accompanying expansion system are presented.