Beam Loss Detection Research Articles

Beam loss detection based on generation of Cherenkov light in optical fibers in the CERN Linear Electron Accelerator for Research

Cherenkov optical beam loss monitors (oBLMs) based on optical fibers are a revolutionary achievement among the monitoring systems in particle accelerators. Due to the nature of the Cherenkov phenomenon and the intrinsic characteristics of optical fibers, the photon production and fiber light transmission need to be studied to deduce the total amount of Cherenkov photons detected by the photosensors attached at the end of the system. Simulations of the Cherenkov oBLM detector system have been implemented using the software with postprocessing considering the light attenuation and capture factors in the optical fiber. In addition, the study includes the longitudinal beam loss localization of the controlled beam losses produced along the CERN Linear Electron Accelerator for Research (CLEAR) test facility line. In this paper, the Cherenkov photon detection by an oBLM installed in the CLEAR facility is simulated, analyzed, and compared with experimental data. Published by the American Physical Society 2024

Experimental studies and Monte Carlo simulations for beam loss monitors

Beam loss detection is essential for the machine protection and the fine-tuning of the accelerator to reduce the induced radioactivity. Monte Carlo simulations are also vital for the choice of beam loss monitor (BLM) type, for predicting and understanding the BLM response to beam losses. At the China Spallation Neutron Source (CSNS), the cylindrical ionization chamber (IC) filled with $\mathrm{Ar}/{\mathrm{N}}_{2}$ gas mixture is the main type of the BLM to detect the beam losses. This paper presents the detailed beam loss experiments and fluka simulations for the CSNS BLM system. It includes the response functions of the BLM detectors by taking into account the contributions of different secondary particles to the energy deposition in the sensitive volume of the BLM. Dedicated experiments were compared with fluka simulations. It was found that in the low energy section of the linac the usual ion chamber based BLMs are not sensitive enough. A BLM based on ${\mathrm{BF}}_{3}$ enclosed by a high-density polyethylene (PE) moderator is effective to detect the beam losses through detecting thermal neutrons. Its signal is about 3 orders of magnitude higher than that of $\mathrm{Ar}/{\mathrm{N}}_{2}$ BLM for a beam energy of 15 MeV. The simulations provide the results of the intrinsic delay time for the ${\mathrm{BF}}_{3}$ monitor and the thickness optimization for PE to reduce the delay. Finally, the simulated spatial resolution of loss location by detection of neutrons is also evaluated for a beam energy of 15 MeV, which presents a resolution of $\ensuremath{\sim}2\text{ }\text{ }\mathrm{m}$ in our experimental configuration.

Beam-loss detection for the high-rate superconducting upgrade to the SLAC Linac Coherent Light Source

The Linac Coherent Light Source (LCLS) x-ray free-electron laser is driven by the third kilometer of the 3-km SLAC linac, which accelerates electrons in normal-conducting copper cavities pulsed at 120 Hz. The first kilometer is being replaced by LCLS-II, a superconducting (SC) electron linac driven by continuous rf at 1.3 GHz and with a normal-conducting photocathode gun using continuous rf at a subharmonic, 186 MHz. Its 4-GeV, 120-kW beam has a 1-MHz maximum rate, with an upgrade to 8 GeV in planning. The beam from either linac can be switched pulse by pulse to either of two new undulators, to generate hard and soft x rays. Control of beam loss is critical for machine and personnel safety. Previous SLAC protection systems have depended on ionization chambers, including both local devices at expected loss sites and long gas-dielectric coaxial cables providing distributed coverage. These devices are unsuited to the SC-linac beam, because their ion collection time, over 1 ms, may allow the space charge of accumulated ions to null the electric field inside the detector, blinding it to an increase in loss. Instead, both the local and the distributed detectors have been replaced with faster devices. The full 4 km will be spanned by multiple radiation-hard optical fibers in lengths of up to 200 m, each coupled to a photomultiplier tube, to capture Cherenkov light from loss showers. These are supplemented by single-crystal diamond detectors at expected loss sites. Signals are integrated with a 500-ms time constant; the beam is stopped within $\mathrm{200}\mathrm{\text{ }}\mathrm{\text{ }}\ensuremath{\mu}\mathrm{s}$ if a threshold is exceeded. We report on our extensive tests of the detectors and the new signal processing.

Fast PIN-diode beam loss monitors at Tevatron

The article is devoted to results of fine temporal structure of particle losses in the Tevatron ring obtained with use of fast beam loss monitors (BLM) based on PIN-diodes. In the Tevatron fixed target operation regime, these monitors were able to distinguish proton losses from bunches spaced by only 19 ns. Besides measurements of main characteristics of the BLMs, we studied the proton losses over 10 decades of time intervals – from a dozen of minutes to a dozen of nanoseconds. Due to huge dynamical range and fast response the PIN-BLMs perfectly fit the task of the beam loss detection at the Tevatron collider upgrade with as small as 132 ns bunch spacing.

Beam-loss monitoring system with free-air ionization chambers

A monitoring system for proton beam losses was installed in the proton synchrotron at the National Laboratory for High Energy Physics in Japan (KEK). The system consists of 56 air ionization chambers (AIC) for radiation detectors, 56 integrators, 56 variable gain amplifiers, two multiplexers, a computer interface circuit, a manual controller and a high tension power supply. The characteristics of the AIC, time resolution, radiation measurement upper limit saturation, kinetic energy dependence of the sensitivity, chamber activation effect, the beam loss detection system and the results of observations with the monitoring system are described.

Linac Beam Loss Detection System Using Self-Powered Detectors

A beam loss detection system employing self-powered gamma detectors to monitor the radiation produced by stray beam has been installed on the 35 MeV linac. The system enables the operator to optimize machine and beam transport parameters to a precision not possible using conventional monitors alone.