Beam-profile instrumentation for beam-halo measurement: overall description and operation

Abstract

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...

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

“…Throughout the halo lattice there are specific beam instruments that acquire horizontally and vertically projected particle-density distributions out to approximately 10 5 :1 dynamic range [4]. We measure the core of the distributions using traditional wire scanners, and the tails of the distribution using water-cooled graphite scraping devices.…”

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

“…A large compliment of beam diagnostics is provided [6]. The key diagnostic component is a special transverse beam profile scanner [7] consisting of a thin, 33µ diameter, carbon wire for measurement of the dense beam core, and a pair of 1.5-mm thick scraper plates to provide greater sensitivity for measurement of the outer halo regions. Each wire and its associated pair of scraper plates are mounted on a common movable frame.…”

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

“…4) contains 52 singlet quadrupole magnets, ten x-y steering magnet pairs, ten stripline beam position monitors, nine x-y beam profile monitors (each unit contains a wire scanner and two halo scrapers as described in [25]), five PMT-based beam-loss monitors, and three AC current toroids [26]. The HS/WS diagnostic device [25] records the beam profile with~10…”