A distributed System for Radiation Monitoring at Linear Accelerators

Abstract

The paper presents a system for an on-line neutron fluence monitoring at a linear accelerator. The system consists of a SRAM-based detector and a radiation-tolerant read-out system. The neutron fluence is measured in several locations of the accelerator. Monitoring of the radiation environment in an accelerator tunnel is necessary to assure a reliable long-term operation of electronic systems placed in the tunnel. The monitoring of the chamber is especially important during the design stage of a linear accelerator. The new design of 20 GeV linear accelerator X-FEL (X-ray Free Electron Laser) is currently approved for construction at DESY Research Centre in Hamburg [1], [2]. The presented paper is based on our research and experimental measurement carried out at 1.2 GeV superconducting electron linac driving the VUV-FEL. The application of a pair of TLD-700 and TLD-500 or superheated emulsion (bubble) dosimeters enables the supervision of neutrons fluence in accelerators [3]. This process requires continuous and arduous calibration of TLD, therefore this method is not convenient. Moreover, it is impossible to monitor the radiation environment in real time. The presented system fill the market nitche of real-time neutron monitoring for high-energy accelerators. Neutron fluence and gamma dose measured in this way can be used for the detailed analysis of the VUV-FEL or X-FEL environments. Monitoring of the radioactive area in a linear accelerator tunnel could be helpful to diagnose and reduce beam losses [4], [5]. We have conducted experiments with the distributed system dedicated to neutron flux measurement at the DESY Research Centre in Hamburg. The devices were exposed to a neutron field from an Americium-Beryllium (n, a) source 241AmBe. The systems were installed in two accelerators: Linac II and VUV-FEL.

The radiation tolerant readout system for srambased neutron detector

“…The device is protected against SEL using a current limited power supply and polymer-based resettable fuses. No SEL was observed in the tested devices in Linac II and TTF2 tunnels [22]. The first version of the RadMon has a serious disadvantage, the maximum operable memory was limited to 128 kB.…”

“…Knowledge of memory temperature is necessary to make an unavoidable temperature correction of the measured SRAM current. The analysis of memory and board supply currents provide information about TID damage effect and dangerous Single Event LatchUps (SELs) [22]. The device is protected against SEL using a current limited power supply and polymer-based resettable fuses.…”

“…*A radiation tolerant readout implemented in FPGA ACTEL APA 600 programmable circuit was chosen to construct the fourth version of the RadMon readout. The device cooperates with a more compact version of four 512 kB stacked memory module [16]. Configuration data are stored in the internal FLASH memory of ACTEL circuit that is much more immune to SEUs comparing to SRAM.…”

“…The device communicates with an external SUN computer using a VME interface. Indeed, processing data are stored in dynamic and static random access memories (DRAMs, SRAMs) that can be also sensible to SEUs [14,14,15,16]. Therefore, a monitoring of both types of radiation may be very useful especially in the initial phase of the FLASH development.…”

Prototype real-time ATCA-based LLRF control system

“…The module equipped with gamma and neutron radiation detectors allows to estimate doses absorbed by the LLRF hardware. A RadFET detector is used for gamma dosimetry, whereas a Static Random Access Memory (SRAM) chip is applied as a reference error counter or neutron fluence detector when it is calibrated [28], [29].…”