LAMPF Accelerator Research Articles

LAMPF beam-line polarimeters

The beam-line polarimeters at the LAMPF accelerator are routinely used to measure all three components of the proton-beam polarization with an absolute accuracy of 1%. They have been cross-calibrated with a variety of polarimeters and polarized targets at the TRIUMF, PSI, and SATURNE accelerators. The design, performance, and calibrations are discussed.

Muon-neutrino carbon charged-current interaction near the muon threshold.

A measurement of the muon-neutrino carbon charged-current cross section, {sup 12}C({nu}{sub {mu}},{mu}{sup {minus}}){ital X}, was performed using the in-flight pion-decay neutrino source at the LAMPF accelerator. At an average interacting neutrino energy of 202 MeV an inclusive cross section of (15.9{plus minus}2.6{plus minus}3.7){times}10{sup {minus}39} cm{sup 2} was measured. This value is in best agreement with the Fermi-gas model and is in disagreement with a previous experiment and subsequent calculations that yielded substantially lower cross sections. However, the muon energy spectrum shows a marked depletion of events at high energies compared to the Fermi-gas model. From a small sample of events in which the final-state nucleus was in the ground state of {sup 12}N, a cross section for the reaction {sup 12}C({nu}{sub {mu}},{mu}{sup {minus}}){sup 12}N(g.s.) of (1.7{plus minus}0.8{plus minus}0.3){times}10{sup {minus}39} cm{sup 2} or about 11{plus minus}5 % of the total event rate was obtained.

Medium-energy neutron physics

Facilities for detecting neutrons from nuclear reactions and for producing secondary neutron beams with good resolution (< 1 MeV) at medium energies (100 MeV < T n < 1000 MeV) exist or are under development at the IUCF, TRIUMF and LAMPF accelerator laboratories. These facilities are being used principally for the study of (p, n) and (n, p) reactions. At medium energies these reactions proceed primarily by impulsive one-step processes, which are described well by the distorted-wave impulse approximation (DWIA) with a free nucleon-nucleon (N-N) t-matrix as an effective interaction. The (p, n) and (n, p) reactions are thus excellent tools for studying one-particle one-hole excitations in nuclei. Additionally, the quantum numbers of nuclear states act as a “filter” and permit examination of selected terms of the N-N interaction.

Utilization of an intense beam of 800 MeV protons to prepare radionuclides

Since the early 1970s, a program has been under way at this institution to employ the excess proton beam emerging from the major experimental areas of the LAMPF accelerator to make a wide variety of radioactive nuclides. This article presents a review of the targets irradiated, cross section data and nuclide yield measurements.

The search for neutrino oscillations in the appearance mode νν→ νe for neutrino energies near the muon threshold

A search for neutrino oscillations in the appearance mode ν ν → ν e was performed using the in-flight pion-decay neutrino source at the LAMPF accelerator. An all-active scintillator detector was exposed to a muon-neutrino beam produced by five Coulombs of 800 MeV protons on target. Oscillations events would have appeared as high-energy electrons from the reaction ν e+C→e −+X. We also measured charged-current muons events in the detector to normalize our results. Our data show no evidence for neutrino oscillations and we place 90% CL upper limits on sin 2(2 φ) < 0.008 at Δm 2 = 11 eV 2, and Δm 2 < 0.67 eV 2 for complete mixing.

The status of the LAMPF control system upgrade

This paper discusses the present state of the LAMPF accelerator control computer upgrade. This includes a summary of our recent operational experience and the status of the application programs in the new system. In addition, we describe several optimization techniques which have been used to improve system-wide performance, and a limited VAX/VMS operating system environment which has been made available to the accelerator operators. We also describe our plans for upgrading the LAMPF control system computer network.

The Development of a Current Monitor System for Measuring Pulsed-Beam Current over a Wide Dynamic Range

This report documents the development of a current transformer system to measure pulsed ion beam currents at the LAMPF accelerator. Measured peak currents typically range from 100 nA to 30 mA with pulse widths varying from 30 ?s to 1 ms. Signal conditioning of the peak current output provides an average current readout with a range of 1 nA to 2 mA, noise of approximately ±0.5 nA, and accuracy of ±0.1%. The system requires no operating adjustments and has proved stable and reliable during a year of operation.

MAGNETS FOR THE PROTON STORAGE RING AT LOS ALAMOS

The Proton Storage Ring at Los Alamos will store 800-MeV protons from the LAMPF accelerator. The magnets are mostly dc excited, of high quality. Special features include construction of a curved 36/sup 0/ laminated dipole core on a straight reference bar, septum magnets with sol-gel glassy insulation, and a high-gradient dipole to strip H/sup -/ to H/sup 0/ for injection.

Four-Dimensional Beam Tomography

A computer code has been developed to reconstruct the 4-D transverse phase-space distribution of an accelerator beam from a set of linear profiles measured at different angles at three or more stations along the beam line. The code was applied to wirescan data obtained on the low-intensity H- beam of the LAMPF accelerator. A 4-D reconstruction was obtained from 10 wire-scan profiles; 2-D projections of the reconstruction agree fairly well with slit-and-collector measurements of the horizontal and vertical emittance distributions.

Beam Analysis Tomography

Projections of charged particle beam current density have been used for many years as a measure of beam position and size. The conventional practice of obtaining only two projections, usually in the horizontal and vertical planes, puts a severe limit on the detail that can be recovered from the projections. A third projection provides sufficient improvement to justify the addition of a wire to the conventional wire scanner in certain cases. A group of programs using algebraic reconstruction techniques was written to reconstruct beam current density from beam projections obtained at 3 or more specific or arbitrary angles around the beam. A generalized program, which makes use of arbitrary 2 x 2 transfer matrices between projections, can be used to reconstruct transverse or longitudinal emittance from appropriate projections. Reconstruction examples of beam current density and transverse and longitudinal emittance using experimental data from the LAMPF accelerator beam are given. The method may be applied to extract emittance and beam current density information using non-intercepting profile measuring devices in high-current accelerators.

Low-Frequency Klystron for Accelerator Applications

Recent advances in computer simulation of the electron-field interaction in the high-power klystron have resulted in major improvements in klystron performance and a better agreement of calculated and measured characteristics. Designs for two klystrons to drive the four Alvarez sections of the LAMPF accelerator are presented in this paper. The output powers for the two klystrons are 0.5 and 3.0 MW at 201 MHz. The length required for the ?-MW klystron is only 3.25 m, and the 3-MW klystron requires 3.75 m due to the higher power collector. A brief description of the computer codes and logic used to achieve these designs is presented. Full-scale test cavities for the ?-MW klystron have been built, and the input cavity is being built to validate the fabrication procedures. The low-frequency, high-power problems in klystron technology are discussed. General scaling laws are derived to produce efficient, compact, narrow-band klystrons with peak output power in the megawatt range. As an example, the salient design features of a 3-MW, 100-MHz klystron are presented. A novel feature of this design is a cavity which is simultaneously excited at two frequencies. Use of such cavities could reduce construction costs and significantly improve the performance of low-frequency klystrons, which should make them more attractive as components in future heavy ion accelerators.

The use of minicomputers in particle accelerators

A substantial number of the world's research laborstories in low-, medium-, and high-energy physics have been among the earliest users of minicomputer data acquisition and control systems. A decade ago, the commercially available minicomputers were put to use gathering data from physics experiments using particle beams from accelerators. As early as 1965, engineers and physicists at several North American accelerator laboratories were installing minicomputer-based control systems for the purpose of automating particle-beam transport lines. Since that time, the use of minicomputers for special instrumentation, data acquisition, and supervisory control has mushroomed throughout the accelerator world. The application of minicomputers to the accelerator beam diagnostics, experimental interface development, accelerator structure tuning, magnet field mapping, ion source operation, nuclear instrumentation, and data handling as practiced at LAMPF and other accelerator laboratories throughout the world will be related in this paper.

The Injector Complex for the LAMPF Accelerator

The present planning and design goals for the LAMPF injector complex include a high-intensity H+ beam, an H- beam, and polarized H+ and H- beams. Since simultaneous acceleration of H+ and H- beams will be attempted by the LAMPF accelerator, a dual beam-transport system for blending these beams into a common channel will be necessary in the injector area. Provision also is made for injecting either H+ or H- polarized beams into the system. A high-quality beam of protons (? cm-mrad emittance and 26 mA) has been produced by a von Ardenne duoplasmatron and a Pierce extraction accelerating column. Problems of simultaneous bunching and matching of H+ and H- beams of different intensities have been studied. The entire injector complex is under computer control and should provide reasonably sophisticated pulse programming flexibility.