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

Abstract

The beam-gas vertex (BGV) detector is an innovative instrument measuring noninvasively the transverse beam size in the Large Hadron Collider (LHC) using reconstructed tracks from beam-gas interactions. The BGV detector was installed in 2016 as part of the R&D for the High-Luminosity LHC project. It allows beam size measurements throughout the LHC acceleration cycle with high-intensity physics beams. A precision better than 2% with an integration time of less than 30 s is obtained on the average beam size measured, while the transverse size of individual proton bunches is measured with a resolution of 5% within 5 min. Particles emerging from beam-gas interactions in a specially developed gas volume along the beam direction are recorded by two tracking stations made of scintillating fibers. A scintillator trigger system selects, on-line, events with tracks originating from the interaction region. All the detector elements are located outside the beam vacuum pipe to simplify the design and minimize interference with the accelerated particle beam. The beam size measurement results presented here are based on the correlation between tracks originating from the same beam-gas interaction vertex.

A gas curtain beam profile monitor using beam induced fluorescence for high intensity charged particle beams

“…Minimally invasive methods based on the interaction between residual gas and particle beams, such as ionization profile monitors (IPM) [7][8][9][10][11] and beam induced fluorescence (BIF) monitors, [12][13][14][15][16] have been used or proposed for various machines. For BIF monitors or the recent beam-gas vertex detector in the LHC, 17 additional residual gas will often be introduced to create a pressure bump, thus increasing the signal to noise (S/N) ratio. As an alternative, a metal vapor jet 18,19 or a gas jet [20][21][22][23][24] can produce a controllable pressure bump more effectively and cause minimal impact on the beam and the surrounding vacuum environment.…”