We report preliminary test results for a 6.7-MeV, 100-mA cw radio-frequency quadrupole. During the time this structure was in design, fabrication, assembly, tuning, and installation, we tested a 75-keV proton injector, 350-MHz high-power RF systems, EPICS controls, diagnostics, beam stop, and other hardware in preparation for the 670 kW beam test. Initial LEDA RFQ beam operation has commenced. This paper summarizes work in the past year, concentrating on RFQ assembly, tuning, installation, high-power conditioning and initial beam operation. We include summaries of injector tests, 1.25-MeV RFQ-beam tests, beam-transport and beam-stop performance, and cavity resonance control. The technology being developed in this first section of the APT (accelerator production of tritium) linac is also appropriate for several other applications, including the transmutation of waste and medical isotope production.

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Operation of the Low-Energy Demonstration Accelerator: the proton injector for APT

We report measurements of transverse beam halo in mismatched proton beams in a 52-quadrupole FODO transport channel following the 6.7-MeV LEDA RFQ. Beam profiles in both transverse planes are measured using beam-profile diagnostic devices that consist of a movable carbon filament for measurement of the dense beam core, and scraper plates for the halo measurement. The gradients of the first four quadrupoles can be independently adjusted to mismatch the RFQ output beam into the beam-transport channel.

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Experimental study of proton-beam halo induced by beam mismatch in LEDA

A 52 quadrupole-magnet FODO lattice has been assembled and operated at the Los Alamos National Laboratory. The purpose of this lattice is to provide a platform to measure the resulting beam halo as the first four magnets of the lattice produce various mismatch conditions. These data are then compared with particle simulations so that halo formation mechanisms may be better understood. The lattice is appended to the LEDA 6.7-MeV radiofrequency quadrupole (RFQ) and is followed by a short high-energy beam transport (HEBT) that safely dumps the beam into a 670-kW beam stop. Beam diagnostic instruments are interspersed within the lattice and HEBT. The primary instruments for measuring the beam halo are nine interceptive devices that acquire the beam's horizontal and vertical projected particle density distributions out to an approximate 10/sup 5/:1 dynamic range. These distributions are acquired using both traditional wire scanners and water-cooled graphite scraping devices. The lattice and HEBT instrumentation set also includes position, bunched-beam current, pulsed current, and beam loss measurements. This paper briefly describes and details the operation of each instrument compares measured data from the different types of instruments, and refers to other detailed papers.

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Experience with the low energy demonstration accelerator (LEDA) halo experiment beam instrumentation

The LEDA 75 keV injector and 6.7 MeV RFQ have been tested with pulsed and cw proton beam currents up to 100 mA. Several LINAC2000 papers give the results of those measurements. A follow-on experiment, to intentionally introduce and measure beam halo on the RFQ output beam, is reported in several papers at this conference (PAC2001). In this paper we summarize the LEDA RFQ commissioning results and the beam-halo measurements and we discuss future test plans for this high-current, high-average-power RF structures test bed.

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Low-Energy Demonstration Accelerator (LEDA) test results and plans

The Low Energy Demonstration Accelerator (LEDA) facility has been used to characterize the pulsed- and cw-beam performance of a 6.7 MeV, 100 mA radio frequency quadrupole (RFQ). Diagnostic instrumentation, primarily located in a short beam transport downstream of the RFQ, allow facility commissioners and operators to measure and monitor the RFQ’s accelerated and total beam transmission, beam loss, bunched beam current, beam energy and output phase, and beam position. Transverse beam profile measurements are acquired under both low and high duty-factor pulsed beam conditions using a slow wire scanner and a camera that images beam-induced fluorescence. The wire scanner is also used to acquire transverse beam emittance information using a technique known as a “quad scan”. This paper reviews the measurement performance and discusses the resulting data.

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LEDA beam diagnostics instrumentation: Measurement comparisons and operational experience

The halo experiment presently being conducted at the Low Energy Demonstration Accelerator (LEDA) at Los Alamos National Laboratory (LANL) has specific instruments that acquire horizontally and vertically projected particle-density beam distributions out to greater than 10{sup 5}:1 dynamic range. They measure the core of the distributions using traditional wire scanners, and the tails of the distribution using water-cooled graphite scraping devices. The wire scanner and halo scrapers are mounted on the same moving frame whose location is controlled with stepper motors. A sequence within the Experimental Physics and Industrial Control System (EPICS) software communicates with a National Instrument LabVIEW virtual instrument to control the motion and location of the scanner/scraper assembly. Secondary electrons from the wire scanner 0.03-mm carbon wire and protons impinging on the scraper are both detected with a lossy-integrator electronic circuit. Algorithms implemented within EPICS and in Research Systems Interactive Data Langugage (IDL) subroutines analyse and plot the acquired distributions. This paper describes this beam profile instrument, describes their experience with its operation, compares acquired profile data with simulations, and discusses various beam profile phenomena specific to the halo experiment.

https://cern.ch/AccelConf/d01/papers/CT05.pdf

Beam-Profile Instrumentation For Beam-Halo Measurement: Overall Description, Operation, And Beam Data

Beam diagnostic instrumentation is being developed for the LEDA, a 6.7-MeV, 100-mA-cw proton accelerator, presently being commissioned at the Los Alamos National Laboratory (LANL). This instrumentation will be the basis for much of the Accelerator Production of Tritium and the Spallation Neutron Source linac. Located in the LEDA injector and the high energy beam transport (HEBT) this initial instrumentation suite's purpose is to verify the RFQ pulsed and cw operation. The instrumentation include a series of DC, pulsed- and bunched-beam current measurements from which RFQ beam-transmission efficiency will be determined. Ionization-chamber beam loss measurements are mounted above the HEBT and provide input signals to a fast equipment protection system. Central beam phase and energy measurements provide RFQ longitudinal performance information. Beam position measurements provide information to properly center the beam within the HEBT beam pipe. Finally, two types of transverse profile measurements including a slow wire scanner and a video fluorescence monitor provide beam width and projection information in the LEDA HEBT. This paper will discuss these measurements developed for LEDA and summarize how they performed during RFQ verification experiments.

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J. Kamperschroer

Papers

Experience with the low energy demonstration accelerator (LEDA) halo experiment beam instrumentation

Beam-Profile Instrumentation For Beam-Halo Measurement: Overall Description, Operation, And Beam Data

Low Energy Demonstration Accelerator (LEDA) beam instrumentation: RFQ-accelerated beam results