HL-LHC Beam Gas Fluorescence Studies for Transverse Profile Measurement

In a gas jet monitor, a supersonic gas curtain is injected into the beam pipe and interacts with the charged particle beam. The monitor exploits fluorescence induced by beam-gas interactions, thus providing a minimally invasive transverse profile measurement. Such a monitor is being developed as part of the High Luminosity LHC upgrade at CERN. As a preliminary study, the fluorescence cross section of relevant gases must be measured for protons at 450 GeV and 6.8 TeV (i.e. the LHC injection and flat top energies). In these measurements, neon, or alternatively nitrogen gas, will be injected into the LHC vacuum pipe by a regulated gas valve to create an extended pressure bump. This work presents the optical detection system that was installed in 2022 in the LHC to measure luminescence cross-section and horizontal beam profile. Preliminary measurements of background light and first signals are presented in this paper

Commissioning of a Gas Jet Beam Profile Monitor for EBTS and LHC

A gas jet beam profile monitor was designed for measuring the electron beam at the electron beam test stand (EBTS) for the Hollow electron lens (HEL) and the proton beam in the large hadron collider (LHC). It is partially installed in the LHC during the second long shutdown. The current monitor is tailored to the accelerator environment including vacuum, geometry, and magnetic field for both the EBTS and the LHC. It features a compact design, a higher gas jet density, and a wider curtain size for a better integration time and a larger detecting range. In this contribution, the commissioning of this monitor at the Cockcroft Institute will be discussed

Gas Jet-Based Fluorescence Profile Monitor for Low Energy Electrons and High Energy Protons at LHC

The ever-developing accelerator capabilities of increasing beam intensity, e.g. for High Luminosity LHC (HL-LHC), demand novel non-invasive beam diagnostics. As a part of the HL-LHC project a Beam Gas Curtain monitor (BGC), a gas jet-based fluorescence transverse profile monitor, is being developed. The BGC uses a supersonic gas jet sheet that traverses the beam at 45° and visualizes a two-dimensional beam-induced fluorescent image. The principle of observing photons created by fluorescence makes the monitor insensitive to present electric or magnetic fields. Therefore, the monitor is well suited for high-intensity beams such as low-energy electron beam of Hollow Electron Lens (HEL), and HL-LHC proton beam, either as a profile or an overlap monitor. This talk will focus on the first gas jet measured transverse profile of the 7keV hollow electron beam. The measurements were carried out at the Electron Beam Test Stand at CERN testing up to 5A beam for HEL. A comparison with Optical Transition Radiation measurements shows consistency with the BGC results. The BGC installation of January 2023 at LHC is shown, including past results from distributed gas fluorescence tests

Optical transition radiation measurements of a high intensity low energy hollow electron beam on electron beam test facility

Optical Transition Radiation (OTR) is commonly used in imaging systems of highly relativistic charged particle beams as the light yield and collection efficiency increase with beam energy. For low beam energies, scintillating screens are typically preferred but they saturate or even get damaged when using a high beam current. For such a beam, OTR screens can, therefore, still be an attractive diagnostic tool when using thermally resistant materials such as Glassy Carbon. This work presents the OTR-based beam imaging measurements of a high-intensity low energy (7~keV) hollow electron beam at the Electron Beam Test Facility (EBTF) at CERN. The mechanical design of the monitor, as well as the expected OTR angular distribution, are presented. Beam images obtained with an aluminium oxide scintillating screen are also shown and compared to the OTR results. This contribution presents the design of the monitor and discusses the initial results obtained with a hollow electron beam at the EBTF

Design of a Prototype Gas Jet Profile Monitor for Installation Into the Large Hadron Collider at CERN

The Beam-Gas Curtain or BGC is the baseline instrument for monitoring the concentricity of the LHC proton beam with a hollow electron beam for the hollow e-lens (HEL) beam halo suppression device which is part of the High-Luminosity LHC upgrade. The proof-of-principles experiments of this gas-jet monitor have now been developed into a prototype instrument which has been built for integration into the LHC ring and is now under phased installation for operation in the upcoming LHC run. This paper describes the challenges overcome to produce a gas-jet fluorescence monitor for the ultra-high vacuum accelerator environment. It also presents preliminary results from the installation of the instrument at CERN

Optimisation of a gas jet-based beam profile monitor for high intensity electron beams

A beam profile monitor using gas jet technology is being designed and manufactured at the Cockcroft Institute for high intensity electron beams. It generates a thin, supersonic gas sheet that traverses the beam at a 45-degree orientation and measures the beam-induced fluorescence interactions to produce a 2D beam profile image. The gas sheet acts similar to a scintillating screen, but remains non-invasive. This contribution summarises the method developed towards optimising the injection of a gas jet monitor for the example use-case of the Hollow Electron Lens. A multi-objective genetic algorithm is used with a Monte-Carlo particle tracking simulation to optimise the geometric features of the jet injection chambers. The algorithm optimises for several key features of the jet that will improve it as a diagnostic tool. Specifically, at the point of interaction, the jet’s density, uniformity and geometric dimensions are considered. The work developed in this contribution is not limited to diagnostics and can be expanded upon in other disciplines such as plasma wakefield gas injections

Imaging a high-power hollow electron beam non-invasively with a gas-jet-based beam profile monitor

The Hollow Electron Lens (HEL) was proposed to actively remove the beam halo of the proton beam for the HL-LHC upgrade. Currently, the concept of generating such an electron beam is being tested in a dedicated Electron Beam Test Stand (EBTS) at CERN. It currently produces a hollow electron beam with 7 keV energy and 0.4 A current 25 us pulsed with 2 Hz which will be confined in a strong solenoid field. A gas curtain-based beam profile monitor was developed to characterize the beam non-invasively during operation. It injects a directional gas sheet at 45 degrees to interact with the electron beam. Gas particles are excited and emit fluorescent photons which are collected by an intensified camera system. This allows the reconstruction of the profile of the hollow electron beam.This contribution presents the design of the monitor and discusses the initial results obtained with a hollow electron beam at the EBTS