K.F. Johnson

A transverse phase-space measurement technique for high-brightness, H− beams

Abstract A common method of measuring transverse phase-space distributions in charged-particle beams is to intercept the beam with slits, pinhole plates, or wire grids, and to measure the beam distribution after a drift with a parallel-channel collector or a fluorescent screen. Many of the next generation of accelerator applications (e.g., in heavy-ion fusion and transmutation of nuclear waste) will utilize high-beam currents with small phase-space distributions. The power densities of beams will be too large to permit the interception of entire beams. This paper describes a measurement technique that is applicable to H − beams: a small portion of the beam is separated from the full beam by means of photoneutralization with a laser that is upstream from a sweep magnet. Phase-space measurements are made on only the neutralized beam.

LEDA and APT beam diagnostics instrumentation

A 20-MeV 100-mA-CW proton-accelerator, Low Energy Demonstration Accelerator (LEDA), is presently being developed, fabricated, and tested at Los Alamos National Laboratory (LANL). The beam diagnostic instrumentation for LEDA and the final 1700-GeV Accelerator Production of Tritium (APT) are classified into two categories: operation and characterization instrumentation. The operational instrumentation does not intercept or minimally-intercepts the beam and are sufficiently prompt and robust to provide accurate information to the operators and commissioners during full-current CW beam operation. The characterization instrumentation, primarily utilized during commissioning project-phases, operates under more traditional 100-mA-peak and approximately 0.1-mA-average beam-current conditions. This paper will review some of the LEDA and APT operational beam diagnostic instrumentation.

Experience with the ground test accelerator beam‐measurement instrumentation

During the past two years, the Ground Test Accelerator (GTA) has used a variety of off‐ and on‐line beam diagnostic measurements to understand and verify the transverse and longitudinal phase space characteristics of a 35‐mA, low‐energy (2.5‐ to 3.2‐MeV) H−‐beam. For the transverse phase‐space characterization measurements, a slit and collector device samples of the x−x’ and y−y’ phase space, to determine the transverse emittance and Courant–Snyder parameters. The longitudinal phase‐space data are acquired by a laser neutralization technique developed at Los Alamos know as the laser induced neutralization diagnostics approach (LINDA). The transverse and longitudinal phase‐space centroids of the low‐energy, 425‐MHz‐bunched beam are directly measured using the microstrip probe systems. Beam current and transmission are measured by various toroid systems. Beam‐loss‐detection techniques have just been installed and a non‐interceptive beam‐profile measurement has been commissioned. All of these measurement sys...

Measurement of longitudinal phase space in an accelerated H− beam using a laser-induced neutralization method

Abstract Laser-induced neutralization of H − ions is a process that can be used to measure the longitudinal phase space of accelerated H − beams. The laser-induced neutralization diagnostic approach (LINDA) measures the longitudinal emittance of an H − beam by photoneutralizing different phase slices of beam microbunches and analyzing the energy distribution of the neutral slices. A LINDA system utilizing a pulsed laser and time-of-flight analysis has successfully measured longitudinal emittance of the 5 MeV H − beam exiting the drift-tube linac of the Los Alamos Accelerator Test Stand. Design considerations associated with the LINDA laser-based emittance measuring system are given. The present LINDA system is described and its limitations are discussed. Experimental results are given from an application of the LINDA system to the measurement of longitudinal emittance growth in a drift space and following insertion into the beamline of beam transport elements comprising a single-arm funnel. A new system is proposed which uses a mode-locked laser and spectrometer to improve resolution and shorten measurement time.

Commissioning of the Low Energy Demonstration Accelerator (LEDA) radiofrequency quadrupole (RFQ)

Initial commissioning of a 6.7-MeV 100-mA RFQ is underway. The RFQ is part of LEDA, the He injector for the Accelerator Production of Tritium (APT) project. To benchmark the RFQ performance, beam physics experiments will be done with low and high current beams for both pulsed and cw beam operation. Commissioning efforts thus far have been limited to low-current pulsed beam LEDA operation. Measurements to fully characterize the RFQ will ultimately include the dependence of RFQ beam transmission on RFQ vane voltage, input beam energy, input match, and input transverse centroids. Other commissioning measurements for the RFQ will include output beam energy, phase, noise, transverse profiles, and transverse RMS emittances. This paper contains initial LEDA RFQ commissioning results, including RFQ pulsed output beam currents up to 40 mA.

Measurements and performance of a microstrip beam probe system

Microstrip probes and associated processing electronics have been designed and used to measure charged-beam position, angle, intensity, output phase, and energy. The authors describe the system that uses the probes and discuss typical beam-cavity interaction data, measurement errors, and system performance. As a bunched, charged beam periodically passes through a microstrip probe, a bipolar signal proportional to the beams current and position is induced into each of the probes four axial symmetric lobes. Processing electronics and computer algorithms transform two probe signals into beam intensity and into centroids of the six-dimensional, phase-space beam distributions. These beam centroids can then be plotted with cavity data so that output beam characteristics can be expressed as a function of cavity power and phase.<<ETX>>

Commissioning plan for a high-current proton linac

High-power proton linacs (E>500 MeV) are potentially useful for transmutation applications, such as the production of tritium, In production applications, high availability is essential. Achieving high availability requires an accelerator design that simplifies maintenance and accommodates commissioning procedures designed to minimize tune-up time. These are worthwhile goals for any accelerator, but the high beam powers (170 MW) and heavy beam loading of the Accelerator Production of Tritium (APT) linac introduce significant new challenges. This paper describes the commissioning plan, as developed to date.

Beam-dynamics design and performance of the RF deflector in the Los Alamos single-beam funnel experiment

A single-beam funnel experiment exploring the beam dynamics and physics issues of a discrete-element funnel has been completed at Los Alamos National Laboratory (LANL). The only known beam dynamics issue of concern in a two-beam funnel not addressed was the beam-beam interaction, which is negligible. The RF deflector, in which beam merging occurs, is a key component of a discrete-element funnel. The beam dynamics design procedure and experimental results for the RF deflector are reported.<<ETX>>

Unexpected matching insensitivity in DTL of GTA accelerator

The intertank matching section (IMS) of the Ground Test Accelerator (GTA) contains four variable-field quadrupoles (VFQs) and is designed to match beam exiting the radio-frequency quadrupole to the first tank of the Drift-Tube Linac (DTL-1). By varying the VFQ field strengths to create a range of beam mismatches at the entrance to DTL-1, one can test the sensitivity of the DTL-1 output beam to variations in the DTL-1 input beam. Experimental studies made during commissioning of the GTA indicate an unexpected result: the beam exiting DTL-1 shows little variation for a range of mismatches produced at the entrance. Results of the experiment and simulation studies are presented.

Phase-scan analysis results for the first drift tube linac module in the Ground Test Accelerator: data reproducibility and comparison to simulations

The Ground Test Accelerator (GTA) had the objective of producing a high-brightness, high-current H/sup -/ beam. The major accelerator components were a 35 keV injector, a Radio Frequency Quadrupole, an intertank matching section, and a drift tube linac (DTL), consisting of 10 modules. This paper discusses the phase-scan technique which was used to experimentally determine the rf operating parameters for the commissioning and routine operation of the first DTL module.