R. Macek

Computed tomography using proton energy loss

An experiment has been performed to demonstrate the feasibility of proton computed tomography. The proton energy loss was used to measure the projections of the relative stopping power of the phantom. High quality reconstructions were obtained from scans of 19 cm and 30 cm diameter performance phantoms. Comparison with reconstructions from an EMI CT-5005 X-ray scanner showed the proton technique is more dose efficient by a large factor.

Observations of a fast transverse instability in the PSR

Abstract A fast instability with beam loss is observed in the Los Alamos Proton Storage Ring (PSR) when the injected beam current exceeds a threshold value, with both bunched and unbunched beams. Large coherent transverse oscillations occur prior to and during beam loss. The threshold depends strongly on rf voltage, beam-pulse shape, beam size, nonlinear fields, and beam environmental. Results of recent observations of the instability are reported; possible causes of the instability are discussed. Recent measurements and calculations indicate that the instability is an “e-p”-type instability, driven by coupled oscillations with electrons trapped within the proton beam. Future experiments toward further understanding of the instability are discussed, and methods of increasing PSR beam storage are suggested.

Proton computed tomography of human specimens

The experimental procedure and results of a comparative study of the imaging characteristics of proton and X-ray CT scans are presented. Scans of a human brain and heart are discussed. The proton produced images are found to be similar in information content while providing a decided dose advantage.

Development of thick, long-lived carbon stripper foils for PSR of LANL

Abstract Thick carbon stripper foils (multi-layer thickness ≈ 200 μg/cm 2 ) have been developed for use with 800 MeV, H + ion beam in the Proton Storage Ring (PSR) at Los Alamos National Laboratory. Foils were prepared by means of the modified controlled ACDC arc discharge method (mCADAD). The lifetime measurements of the foils made by different methods were performed using an 800 MeV proton beam of up to 85 μA in the PSR, and a 3.2 MeV Ne + ion beam of 3 μA at Tokyo Institute of Technology. The foils made by the mCADAD method showed very long lifetimes, as compared to other foils tested, for both 800 MeV p and 3.2 MeV Ne + beam bombardments.

Status of the experimental studies of the electron cloud at the Los Alamos proton storage ring

The electron cloud (EC) at the Los Alamos Proton Storage Ring (PSR) has been studied extensively for the past several years with an overall aim to identify and measure its important characteristics, the factors that influence these characteristics, and to relate these to the two-stream (e-p) transverse instability long observed at PSR. Some new results since PAC2001 are presented

First-turn losses in the LAMPF proton storage ring (PSR)

Beam-loss measurements indicate that 0.2-0.3% of the protons injected into the PSR are lost during the first turn. We describe a plausible mechanism, involving field stripping of excited hydrogen atoms, for these losses. Protons are injected into the PSR by transporting a neutral hydrogen beam through a hole in the yoke of one ring bender and then through a carbon foil on the ring axis. The foil strips roughly 93% of the beam atoms to protons. Although the original PSR design assumed that all unstripped atoms would pass through a hole in the yoke of the next downstream bender and on to a beam stop, recent calculations indicate that about 6% of these unstripped atoms will emerge from the foil in an excited state with principle quantum number n/spl ges/3. These calculations also indicate that atoms in excited states with n/spl ges/3 will be stripped quickly to protons in the 1.2-Tesla field of the downstream bender. The trajectories of these protons will be outside the phase-space acceptance of the ring and will be quickly lost by collision with the beam pipe, thereby giving rise to first-turn losses. The estimated numbers of protons that would be lost by this mechanism are consistent with the observed first-turn loss rates. This mechanism has important consequences for the design of future storage rings that use neutral atom or negative ion stripping for injection.<<ETX>>

Electron cloud diagnostics in use at the Los Alamos PSR

A variety of electron cloud diagnostics have been deployed at the Los Alamos Proton Storage Ring (PSR) to detect, measure, and characterize the electron cloud generated in this high intensity, long bunch accumulator ring. These include a version of the ANL-developed retarding field analyzers (RFA) augmented with LANL-developed electronics, a variant of the RFA denoted as the electron sweeping diagnostic (ESD), biased collection plates, and gas pulse measuring devices. The designs and experience with the performance and applicability to PSR are discussed.

Performance of the High-Energy Pion Beam at LAMPF

The Los Alamos Clinton P. Anderson Meson Physics Facility (LAMPF) high-energy pion beam (P3) is a three-bend channel with two achromatic output legs designed for high-intensity and moderate resolution. The best resolution was measured to be 0.2% in ¿p/ p. A phase space of about 25 ¿ mr-cm is transmitted by the channel. A ¿+ flux of 2 × 107 pions/s was measured for 300 MeV/c momentum when a 7 ¿A proton beam struck a 6 cm graphite target. Proton contamination for good quality ¿+ beams up to 450 MeV is negligible when an energy degrader (graphite) is used to separate protons from pions. In actual operation, very little beam tuning is required. Focusing elements are set according to the TRANSPORT computer code. Additional rate and contamination data will be presented, as well as additional information gained from operating experience.

Overview of progress on the improvement projects for the LANSCE accelerator and target facilities

Three projects have been initiated since 1994 to improve the performance of the accelerator and target facilities for the Los Alamos Neutron Science Center (LANSCE). The LANSCE Reliability Improvement Project (LRIP) was separated into two phases. Phase I, completed in 1995, targeted near-term improvements to beam reliability and availability that could be completed in one-years time. Phase II, now underway and scheduled for completion in May 1998, consists of two projects: (a) implementation of direct H injection for the Proton Storage Ring (PSR) and (b) an upgrade of the target/moderator system for the short pulse spallation neutron (SPSS) source. The latter will reduce the target change-out time from about 10 months to about three weeks. The third project, the SPSS Enhancement Project, is aimed at increasing the PSR output beam current to 200 /spl mu/A at 30 Hz and providing up to seven new neutron scattering instruments.

LANSCE short-pulse spallation source target upgrade

A project to upgrade the short-pulse spallation source target at the Los Alamos Neutron Scattering Center (LANSCE) is in progress. This upgrade will reduce the target change out time from about a year to about three weeks and permit the proton beam current to be raised to 200 /spl mu/A. The project includes a new target-moderator-reflector system, a new suite of moderators for four new flight paths, improved auxiliary systems, remote handling capability, and a new crane and service building. The project has also supported calculations and experiments for target neutronics, rod-target thermo-hydraulics, and corrosion-related measurements in a proton beam. The final engineering design is now complete and the project has begun fabrication and procurement. Installation will begin in the fall of this year.