Progress on the Beam Energy Monitor for the SPIRAL2 Accelerator.
The first part of the SPIRAL2 project entered last year in the end of the construction phase at GANIL in France. The facility will be composed by an ion source, a deuteron/proton source, a RFQ and a superconducting linear accelerator. The driver is planned to accelerate high intensities, up to 5 mA and 40 MeV for the deuteron beams. A monitoring system was built to measure the beam energy on the BTI line (Bench of Intermediate Test) at the exit of the RFQ. As part of theMEBT commissioning, the beamenergy will be measured on the BTI with an Epics monitoring application. At the exit of the LINAC, another system will have to measure and control the beam energy. The control consists in ensuring that the beam energy stays under a limit by taking account of the measurement uncertainty. The energy is measured by a method of time of flight; the signal is captured by non-intercepting capacitive pick-ups. This paper describes the BTI monitor interface and presents the system evolution following the design review.
MEASUREMENT AND CONTROL OF THE BEAM ENERGY FOR THE SPIRAL 2 ACCELERATOR
The first part of the SPIRAL2 facility, which entered in the construction phase at GANIL in France, will be composed of an ion source, a deuteron/proton source, an RFQ and a superconducting linear accelerator delivering high intensities, up to 5mA and 40MeV for the deuteron beams. As part of the MEBT commissioning, the beam energy will be measured on the BTI (Bench of Intermediate Test) at the exit of the RFQ. At the exit of the LINAC, the system has to measure but also to control the beam energy. The control consists in ensuring that the beam energy is under a limit by taking account of the measurement uncertainty. The energy is measured by a method of time of flight; the signal is captured by nonintercepting capacitive pick-ups. This paper presents also the results obtained in terms of uncertainties and dynamics of measures. INTRODUCTION The beam energy at the exit of the LINAC will be measured for the beam tuning but also for the energy control. The energy is monitored in order to ensure the respect of the accelerator operating range and the protection of the machine (MPS). The energy is measured by a method of time of flight (TOF) [1]. As the energy control is part of the safety functions, Failure Modes and Effects Analysis (FMEA) and the measurement uncertainty are required on this control device. ELECTRONIC DESCRIPTION The phase measurement of the TOF is based on an electronic system which realizes the lock-in amplifier function [2]. The pulse signals come from 3 pick-up electrodes. The phase of first harmonic is measured by the TOF device. The TOF electronic system is composed by:  ADCs card with a clock part  FPGA card  Microcontroller card  High Frequency Amplifier  Alarm card Figure 1: Electronic synoptic. TEST BENCH IN LABORATORY Phase coherence, which is a stable phase relationship between signals, is essential when measurements require more than one RF output. The inherent phase instability among multiple signal generators is mostly overcome by using a common signal/LO source for each generator [4]. The function generator Tektronix offers two tightly synchronized outputs. The phases of each channel can be independently adjusted. The first output is used as the reference signal of the TOF system. The reference frequency is 88MHz at a fixed level. The second signal is used to simulate the first harmonic from a diagnostic and is connected to the inputs of the TOF system, via a splitter. To adjust levels in a large dynamic, various attenuators are located before the splitter. Figure 2: Measurement chain. VELOCITY AND ENERGY UNCERTAINTY Velocity Calculation The level of the energy threshold has to take into account the measurement uncertainty. Threshold level = Required threshold-uncertainty _________________________________________ lecoz@ganil.fr Proceedings of IBIC2013, Oxford, UK WEPF32 Beam Charge Monitors and General Diagnostics ISBN 978-3-95450-127-4 897 C op yr ig ht c ○ 20 13 by JA C oW — cc C re at iv e C om m on sA tt ri bu tio n 3. 0 (C C -B Y3. 0) The Time of Flight Method consists in measuring the time difference between signals produced by bunches on two pick-ups. The time can be calculated from the pick-up phase. As the length between pick-ups is known, the velocity is obtained (see Eq. 1) [3]. However the number of bunches included between the first two pick-ups has to be taken into account. The third pick-up is thus used to determine this number N of bunches.
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