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Progress was made during the past decade towards a better understanding of halo formation caused by beam mismatch in high-intensity beams. To test these ideas an experiment was carried out at Los Alamos with proton beams in a 52-quadrupole focusing channel. Rms emittances and beam widths were obtained from measured beam profiles for comparison with the maximum emittance growth predictions of a free-energy model and the maximum haloamplitude predictions of a particle-core model. The experimental results are also compared with multiparticle simulations. In this paper we will present the experimental results and discuss the implications with respect to the validity of both the models and the simulations.

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 radio frequency 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 approximately 10 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.

Within the halo experiment presently being conducted at the Low Energy Demonstration Accelerator (LEDA) at Los Alamos National Laboratory, specific beam instruments that acquire horizontally and vertically projected particle-density distributions out to approximately 10 5 :1 dynamic range are located throughout the 52-magnet halo lattice. We 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 Instruments LabVIEW virtual instrument to control the motion and location of the scanner/scraper assembly. Secondary electrons from the wire scanner 0.033-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 System's Interactive Data Language subroutines analyze and plot the acquired distributions. This paper describes this beam profile instrument, describes our experience with its operation, compares acquired profile data with simulation, and refers to other detailed papers. HALO INSTRUMENTATIONAt LEDA a 100-mA, 6.7-MeV beam is injected into a 52-quadrupole magnet lattice (see Fig. 1). Within this 11-m FODO lattice, there are nine wire scanner/halo scraper (WS/HS) stations, five pairs of steering magnets and beam position monitors, five loss monitors, three pulsedbeam current monitors, and two image-current monitors for monitoring beam energy [1].The WS/HS instrument's purpose is to measure the beam's transverse projected distribution. These measured distributions must have sufficient detail to understand beam halo resulting from upstream lattice mismatches [2,3]. The first WS/HS station, located after the fourth quadrupole magnet, verifies the beam's transverse characteristics after the RFQ exit. A cluster of four WS/HS located after magnets #20, #22, #24, and #26 provides phase space information after the beam has debunched. After magnets #45, #47, #49, and #51 reside the final four WS/HS stations. These four WS/HS acquire projected beam distributions under both matched and mismatched conditions. These conditions are generated by adjusting the first four quadrupole magnetic fields so that the RFQ output beam is matched or mismatched in a known fashion to the rest of the lattice. Because the halo takes many lattice periods to fully develop, this final cluster of WS/HS are positioned to be most sensitive to halo generation. As the RFQ output beam is mismatched to the lattice, the WS/HS actually observe a variety of distortions to a properly matched Gaussian-like distribution [2,3]. These distortions appear as distribution tails or backgrounds. It is the size, shape, and extent of these tails that predict specific types of halo. However, not every lattice WS/HS observes t...

Beam diagnostics systems being designed for the Low Energy Demonstrator Accelerator (LEDA) at Los Alamos include beam synchronous-phase and beam energy measurements [1]. The LEDA machine will utilize an RFQ front end operating at 350 MHz, followed by several 700-MHz DTL accelerating structures. Signals from cavity-field probes and beam image-current probes will be down-converted to 2 MHz for phase measurement in VXI modules. Each 2-MHz signal is sampled at 8 MHz with a 12-bit ADC and the resultant data stream is converted into I and Q components which update at a 2-MHz rate. The I and Q signals are then converted to a relative phase measurement. Each VXI module will contain four channels of phase measurement hardware which allow for two channels of differential-phase measurement. Lownoise AGC circuits will accommodate signal variations over a 64 dB dynamic range. An on-board calibration system provides a system absolute accuracy of ±1 degree. DSP filtering allows 200-kHz bandwidth measurements to be made with a resolution of <0.1 degrees over a dynamic range of 46 dB.