Measurement and Reconstruction of a Beam Profile Using a Gas Sheet Monitor by Beam-Induced Fluorescence Detection in J-PARC
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I. Yamada, M. Wada
Doshisha University, Graduate School of Engineering, Kyoto, Japan
J. Kamiya, M. Kinsho, K. Moriya
JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken, Japan
A high-intensity beam accelerator requires a non-destructive beam profile monitor since a destructive monitor, such as a wire-scanning-type profile monitor, may be broken by deposited energy. We have been developing a non-destructive transverse beam profile monitor using a gas sheet. The sheet-shaped gas flow is formed by a technique of rarefied gas dynamics and enables two-dimensional profile measurement. One of the issues on development of the profile monitor based on beam-gas interaction is reconstruction of the beam profile from the obtained signal by the monitor. Our gas sheet monitor captures the beam-induced fluorescence using an image intensifier and a CCD camera. Photons produced by beam-gas interaction are integrated along the normal direction of the detector; the luminous intensity distribution of the obtained image can be written as an integral of the product of the sheet-gas density distribution and the beam profile. To solve the equation and reconstruct the profile, the sheet-gas density distribution needs to be measured. The gas density distribution was quantified using an electron beam narrow enough as compared with the beam whose profile needs to be measured. The narrow electron beam induces local photon emission from the gas sheet, and the gas density distribution can be measured by scanning the electron beam position on the gas sheet while monitoring the photon signal intensities. An advantage of this measurement method of the gas density distribution is the obtained distribution includes the sensitivity distribution of the detector, such as a CCD camera and an image intensifier. The measured gas density distribution including the sensitivity distribution was applied to the profile reconstruction of 3 MeV, 60 mA negative hydrogen ion beam in J-PARC Linac, and the beam profile was successfully obtained.
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