RESULTS OF BACKGROUND SUBTRACTION TECHNIQUES ON THE SPALLATION NEUTRON SOURCE BEAM LOSS MONITORS

Recent improvements to the Spallation Neutron Source (SNS) beam loss monitor (BLM) designs have been made with the goal of significantly reducing background noise. This paper outlines this effort and analyzes the results. The significance of this noise reduction is the ability to use the BLM sensors (1), (2) distributed throughout the SNS accelerator as a method to monitor activation of components as well as monitor beam losses. OVERVIEW Any study of the effects and causes of system noise must contain some identification of the nature of the system noise and its sources. We will identify the sources of noise in the BLM circuits and show the results of reduction techniques used to mitigate these noise sources. Identifying Noise Sources The SNS BLM sensors are primarily high -gain transimpedence amplifiers that collect the change in charge when particles or energy are incident on the sensor. The effects of noise associated directly with components used in high-gain transimpedence amplifiers are actually surprisingly low. The largest source of noise is induced currents and Electro Motive Interference (EMI) (3) on the long cables from the sensors located in the LINAC tunnel and the data acquisition system located in the instrument galleries. The distance between the sensors and the front end amplifier is large typically on the order of 100 meters. External influences such as electrical and electromagnetic sources make up the majority of the background noise seen at the front end amplifier (Fig. 1).