Low-noise Amplifier for Photomultiplier Tube Detectors for Plasma Diagnostics

Abstract

Photomultiplier Tube (PMT) detectors are commonly used for plasma diagnostics in fusion devices such as tokamaks or stellarators. Thanks to low response time and high sensitivity, this type of sensor is often used in applications that rely on fast digital pulse processing such as a plasma spectroscopy. Large size fusion devices such as ITER tokamak require sensitive electronic devices to be placed far away from the reactor due to high magnetic field, ionizing and non-ionizing radiation. One of the plasma diagnostic system, that use PMT's is ITER Hard X-Ray Monitor (HXRM). In the case of the HXRM system signal to digitizer must be sent over a 100 m long triaxial cable. Electromagnetic interferences can degrade the signal. PMT provides low amplitude signal that requires low-noise amplification before digitalization and transmission. A suitable ultra a low-noise amplifier with at least 100 MHz bandwidth, gain higher than 100x (with possible adjustment) and relatively high voltage output is required.Various available solutions were considered, but none of them fulfill all requirements at once. Finally, a dedicated low-noise amplifier was designed from scratch to meet all specifications required by PMT-involved applications.The paper discusses the design of a low noise amplifier suitable for Photomultiplier Tube applications. Initial measurements and characterization of the developed amplifier are presented in this paper.