Abstract
The low beta of proton or ion beams favors an electrostatic pickup to measure the transverse beam centroid position. Often papers on beam position monitors (BPM) are focused on a particular aspect of the problem; however, it is important to consider all various issues of a position measurement system. Based on our experience at the IPHI (high intensity injector proton) facility at CEA-Saclay, this paper will address all aspects to design, test, and calibrate a BPM for proton linear accelerators, while emphasizing the determination of the absolute beam position. We present details of the readout electronics, and describe the calibration of the BPM using a test station. For calculation and simulation of the electrical signals we developed a Mathematica script. The error analysis presented, on the basis of six BPMs installed in the high energy section of IPHI, demonstrates the expected accuracy of the position measurement. These studies also identify the parameters that could improve the performance of the beam position control. The experience from these developments is currently being used for the BPM design and test stand dedicated to the Spiral2 accelerator at Ganil-Caen which will deliver heavy ion beams.
Highlights
For a low beta velocity beam ( < 0:1), the capacitive beam position monitor (BPM) pickup is more efficient in terms of output signal power, than an inductive one of the same physical size [1]
While for storage rings and synchrotron light sources a high resolution and control of the beam orbit is achieved—typically 1 m, or better—a linear accelerator needs a high accuracy of the absolute values reported by the transverse beam position measurement system
The voltage signals from the button electrodes are processed by the commercial Bergoz log-ratio beam position monitor (LR-BPM) electronics module
Summary
For a low beta velocity beam ( < 0:1), the capacitive beam position monitor (BPM) pickup is more efficient in terms of output signal power, than an inductive one of the same physical size [1]. The presented BPM uses four capacitive-coupling electrodes, called ‘‘buttons.’’ The high energy beam line of the high intensity injector (IPHI) [2] is equipped with BPMs of two different sizes: five fit into the vacuum chamber of 33 mm radius, and one is located in the large aperture chamber of 75 mm radius, just in front of the beam stopper. The IPHI aims to produce a continuous wave (CW) high intensity proton beam of 100 mA at 3 MeV, at a bunching frequency of 352.2 MHz. The design and implementation of the BPM diagnostic needs many considerations: signal processing and computation, mechanics, signal transmission and cables, electronics, noise issues, sensitivity, calibration, and numerous tests. While for storage rings and synchrotron light sources a high resolution and control of the beam orbit is achieved—typically 1 m, or better—a linear accelerator needs a high accuracy of the absolute values reported by the transverse beam position measurement system. Based on the recent experience, this paper discusses all the considerations required to deliver accurate results from the beam position measurement of low beta, high intensity beams
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