Test Results of the LEDA Beam-Position/Intensity Measurement Module*

This paper describes progress in the design and testing of the log-ratio-based beamposition/intensity measurement module being built for the Low Energy Demonstration Accelerator (LEDA) and Accelerator Production of Tritium (APT) projects at Los Alamos National Laboratory. The VU-based module uses four, 2 MHz if inputs to perform two-axis position measurements and one intensity measurement. To compensate for systematic errors, real-time error-correction is performed on the four input signals after they are digitized and before calculating beam position and intensity. Beam intensity is computed by using the average of the four log-amplifier outputs. This method provides a better off-axis intensity response than the traditional method of summing the rf power from the four lobes. Several types of test data are presented including results of the real-time error correction technique, a working dynamic range of over 80 dB, and achievable resolution and accuracy information. INTRODUCTION This paper reports progress on the design and testing of the LEDA beamposition/intensity module reported earlier (1). Key areas are the real-time errorcorrection technique, showing results with more complete data than was presented earlier, and an improved method of performing the intensity measurement. A block diagram of the module is shown in Figure 1. The position-measurement technique is based on the log-ratio transfer function which has been described by several authors (2,3,4). The log-ratio technique is defined in Equation 1: Vlog ratio = l”dT) l”dB) (1) * Work supported by the US Department of Energy. where T and B represent the power in the intermediate-frequency (if! signals for opposite top and bottom lobes of a beamline probe. Subtraction is easier to perform than division and can be done either by digital or analog techniques.