Residual gas fluorescence monitor for relativistic heavy ions at RHIC

Abstract

A residual gas fluorescence beam profile monitor at the Relativistic Heavy Ion Collider (RHIC) has successfully recorded beam images of various species of relativistic heavy ions during FY2012 operations. These fully striped ions include gold, copper, and uranium at 100, 99.9, and 96:4 GeV=n, respectively. Their beam profiles give an independent measurement of the RHIC beam size and emittance. We estimated their corresponding fluorescence cross sections to be 2:1 Â 10 À16 , 1:8 Â 10 À17 , and 2:6 Â 10 À16 cm 2 , and obtained their rms transverse beam sizes of 0.36, 0.37, 0.24 mm for gold, copper, and uranium ions, respectively. They are the smallest ion beam width, thus lowest beam emittance, ever produced at RHIC or any other high-energy heavy ion colliders. These extremely small beam sizes may have reached a fundamental limit to residual gas fluorescence based beam profile monitor. Nevertheless, this beam diagnostic technique, utilizing the beam-induced fluorescence from residual gas where hydrogen is still the dominant constituent in nearly all vacuum systems, represents a passive, robust, truly noninvasive, monitor for high-energy ion beams.

Noninvasive LHC transverse beam size measurement using inelastic beam-gas interactions

“…Therefore, by using Eqs. (6) and 7, the transverse beam size can be directly measured, without having to correct it for the IP (i.e., tracking) resolution. This is valid only for tracks originating from the primary vertex.…”

“…Based on Eqs. (6) and 7, the line slope in Fig. 10(a) is an estimator of 1 2 ðσ 2 x þ σ 2 y Þ and that of Fig.…”

“…On the other hand, beam-induced fluorescence (BIF) monitors detect the image from the fluorescence light emitted after the excitation of the gas by the passing particle beam (see, for example, Ref. [6]). Fluorescence cross sections are relatively small, and, in addition, fluorescence photons are emitted in all directions; the solid angle coverage of a fluorescence detector is of the order of 10 −4 .…”

Characterization of a supersonic gas jet for charged particle beam profile monitor

“…Ionization profile monitors (IPMs) [1][2][3] and beam induced fluorescent monitors (BIFs) [4][5][6][7][8] are widely used as non-invasive beam profile monitors in many accelerators. In such monitors, the particle beams interact with the residual gas, causing the gas molecule to either ionise or emit fluorescent light.…”

Design and first operation of a supersonic gas jet based beam profile monitor

“…Previously, noninvasive gas-based beam profile monitors have been considered, including residual gas ionization profile monitors (IPM) [4][5][6][7][8] and beam induced fluorescence monitors (BIF) [6,[9][10][11]. IPMs operate by using an external electric field to collect the ions or electrons produced by the interaction of the projectile beam with the residual gas in the vacuum chamber, while BIFs observe the images from the fluorescence light emitted after the excitation of the residual gas by the projectile beam.…”