The Beam Loss Detection Research On High Current Proton Linear Accelerator In Low Energy Region

Superconducting linear accelerator is used as injector for the ADS(Accelerator Driven Subcritical System). With the increasing of beam energy and intensity, beam loss due to different reasons are also increased, which will produce strong secondary radiation field and will influence the environment and staff, high power beam loss may also damage the accelerator components. Therefore, the beam loss monitoring system is essential in the construction of high intensity accelerator. At present, the beam loss detection is mainly concentrated on the intermediate and high energy region, but for low-energy region, there is no feasible solution, which is one of the key issues that restrict the development of high intensity linear accelerators.In this paper, some problems about beam loss monitoring system for the injector Ⅱ of CI-ADS are studied. First, secondary radiation field caused by beam loss in superconducting cavity was calculated with Monte-Carlo methods, secondary particle species, energy spectra and angular distribution are obtained. And the variation of secondary radiation field caused by beam loss on different points is also studied, which may indicated the suitable place to set the beam loss detectors. Second, characteristic of different types of detectors are studied to select the suitable detector. Third, the factors affecting the beam loss detection are analyzed, the field emission radiation is measured which is the most important disturbance.The research shows that charged particles, such as protons and electrons, are unable to penetrate the vacuum pipeline due to the energy of proton beam in the injector Ⅱ of CI-ADS is low, which cause some problems to detect the beam loss in the low-energy region. The main particles of the secondary radiation are neutron and γ-rays. However, because of field emission, the strongly γ-rays background makes it difficult to distinguish the photons caused by beam loss. At the same time, the beam loss on different locations will generate different secondary radiation field, thus an appropriate location for detector makes it possible to obtain the information about beam loss position.The characteristic of EJ-420 plastic scintillator detector and CVD diamond detector are studied. The result shows that the EJ-420 plastic scintillator can discriminate the γ-rays by setting a proper threshold, because the energy deposition of the neutron and gamma in the detector is different. The CVD diamond detector is more suitable due to its fast-responding time and high radiation resistance.