CERNBox User Forum

The TE-VSC section leases two Windows Terminal servers that users can offload long simulation tasks to. This short talk would show how we delegate computation tasks and synchronize results back to our local PCs, among the issues we encountered

Recent developments of Monte-Carlo codes Molflow+ and Synrad+

Molflow+ and Synrad+ are Monte Carlo simulation tools for ultra-high vacuum and synchrotron radiation, respectively. Over the years they have become a common tool for designing and analysing the vacuum system of particle accelerators. This contribution gives a short summary about new features added since the last IPAC contribution [1]. Synrad+ now supports low flux mode, a weighted Monte Carlo technique where the represented number of photons is reduced at every reflection, providing significantly better statistics at low flux regions. As for Molflow+, angle maps allow recording the molecules’ directional distribution at any point, and then desorb a reduced gas quantity according to the recording. In linear systems, this allows iterative simulations that have been proven to treat systems up to 7 orders of magnitude of pressure difference. Without the new technique the computing time would be prohibitively slow on desktop computers, which is what most users of the two codes use. Both codes now have a built-in geometry builder that allows creating simple models through a set of 3D operations and modifying those imported from CAD tools. Molflow+ has been extended with additional diagnostic tools, such as a logger that records properties of all hits on a scoring surface, and histogram plotters that visualize the distribution of the number of bounces, the distance to absorption and the time of flight of the gas molecules. The codes have recently become open source, and it has been made compatible with, and tested on different versions of Linux and macOS

Monte-Carlo simulation of Synchrotron Radiation power for the LHeC interaction region quadrupoles using SynRad+

The LHeC is in the design stage and various interaction region optics have been considered. The power emitted by the synchrotron radiation in the quadrupoles have been previously calculated by analytic and numerical methods. This note shows that SynRad+, a Monte-Carlo tool developed at CERN is a viable alternative for such calculations, and the initial learning curve might be shorter for users who are new to SR simulations. Moreover, results that are in good agreement with previous simulations are obtained on a desktop computer within seconds. This note presents an approximate calculation for comparison with previous results, and then a more complex and more accurate one

Photodesorption and Electron Yield Measurements of Thin Film Coatings for Future Accelerators

The performance of future accelerators could be limited by electron cloud phenomena and high photodesorption yields. For such a reason, the study of secondary electron and photodesorption yields of vacuum materials is essential. The eradication or mitigation of both secondary electron and molecule desorption could strongly reduce the beam scrubbing time and increase the availability of nominal beams for experiments. Surface modifications with the desired characteristics can be achieved by thin-film coatings, in particular made of amorphous carbon and non-evaporable getters (NEG). In the framework of a new collaboration, several vacuum chambers have been produced, and different coatings on each of them have been applied. The samples were then irradiated at KEK’s Photon Factory with SR light of 4 keV critical energy during several days, allowing the measurement of the photodesorption yield as a function of the photon dose. This paper presents the experiment and briefly summarizes the preliminary photodesorption and photoelectron yield data of different coatings. The results can be used for future machine design with similar conditions, such as the FCC-hh

Development of a hardware-accelerated simulation kernel for ultra-high vacuum with Nvidia RTX GPUs

Molflow+ is a Monte Carlo (MC) simulation software for ultra-high vacuum, mainly used to simulate pressure in particle accelerators. In this article, we present and discuss the design choices arising in a new implementation of its ray-tracing–based simulation unit for Nvidia RTX Graphics Processing Units (GPUs). The GPU simulation kernel was designed with Nvidia’s OptiX 7 API to make use of modern hardware-accelerated ray-tracing units, found in recent RTX series GPUs based on the Turing and Ampere architectures. Even with the challenges posed by switching to 32 bit computations, our kernel runs much faster than on comparable CPUs at the expense of a marginal drop in calculation precision

Propagation of Radioactive Contaminants Along the Isolde Beamline

The vacuum system of RIB facilities is entirely hermetical, with storage of effluents and controlled release to atmosphere after a decay time. In Isolde, distributed primary pumping is sectorized in three parts, but all effluents are conveyed together in a unique tank. Thus, highly contaminated gas from the target and front end may be mixed with less contaminated gas from the beam transfer lines. This study aims at analysing and quantifying the distribution and propagation of neutral rare gas radioactive isotopes along the Isolde beam-line by numerical simulation (steady-state and time resolved Test-Particle Monte-Carlo, Molflow+) and experimental means. The time-resolved Monte-Carlo integrates decay time for the propagating species. To measure the distribution of contaminants, sampling filters are installed at the exhaust of the vacuum turbo-molecular pumps. Comparison between simulation and experiment shows excellent agreement, confirming the pertinence of the Monte-Carlo tool to radioactive species propagation. The filtering effect of magnetic sectors, the RFQ Cooler, and Buncher on the propagating neutral isotopes are quantified

Comparing Behaviour of Simulated Proton Synchrotron Radiation in the Arcs of the LHC with Measurements

In previous work it was shown that at high proton-beam energies, synchrotron radiation is an important source of beam-screen heating, of beam-related vacuum pressure increase, and of primary photoelectrons, which can contribute to electron cloud formation. We have used the Synrad3D code developed at Cornell to simulate the photon distributions in the arcs of the LHC, HL-LHC, and FCC-hh. Specifically, for the LHC we studied the effect of the sawtooth chamber. In this paper specific results of the Synrad3D simulations are compared with simulations in Synrad+, developed at CERN; and later on compared with experimental data for actual LHC vacuum-chamber samples

Development of supersonic gas-sheet-based beam profile monitors

Non-destructive beam profile monitoring is very desirable, essentially for any particle accelerator but particularly for high-energy and high-intensity machines. Supersonic gas jet-based monitors, detecting either the ionization or fluorescence of a gas sheet interacting with the primary beam to be characterized, allow for minimally invasive measurements. They can also be used over a wide energy range, from keV to TeV beams. This contribution gives an overview of the jet-based ionization and fluorescence beam profile monitors which have been developed, built and tested at the Cockcroft Institute. It discusses gas sheet generation, vacuum considerations, choice of gas species and detection methods

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

Recent Progress on the Commissioning of a Gas Curtain Beam Profile Monitor Using Beam Induced Fluorescence for High Luminosity LHC

For the high-luminosity upgrade of the Large Hadron Collider, active control of proton/ion beam halo will be essential for safe and reliable operation. Hollow Electron Lenses can provide such active control by enhancing the depletion of halo particles, and are now an integral part of the high luminosity LHC collimation system. The centring of the proton beam within the hollow electron beam will be monitored through imaging the fluorescence from a curtain of supersonic gas. In this contribution we report on the recent progress with this monitor and its subsystems, including the development of an LHC compatible gas-jet injection system, the fluorescence imaging setup and preliminary test measurement in the LH