Transient Vacuum study of Electric Arc in Radio Frequency Quadrupole of the Linear Particle Accelerator IFMIF

A transient vacuum study of an electrical discharge at the Radio Frequency Quadrupole (RFQ) of the Linear IFMIF prototype accelerator (LIPAc) was performed using Mo1flow+, a test-particle Monte-Carlo (TPMC) software for ultra-high vacuum systems. In the RFQ there are eight couplers that make possible Radio Frequency (RF) power to be injected. The couplers are known to produce electric arcs in the interior during the RF conditioning. But the relationship between the electric arcs and the pressure readings of the gauges is unclear. The electrical discharge has been simulated as an injection of particles in the surface where it is likely to happen. A 3D model of the vacuum chamber of the RFQ was made and boundary conditions were set. Results have been retrieved for one coupler and they have been contrasted with experimental data in which the presence of this electric arc was known.

I. Introduction

LIPAc is the prototype accelerator for the IFMIF project (International Fusion Materials Irradiation Facility). The accelerator consists of six different sections, and the main focus of this paper is the second section, the RFQ (Radio Frequency Quadrupole). The RFQ section is a four-vane cavity arranged over 9.8 m long structure divided into 18 modules. Each module has two sets of four openings in the lateral sides, used to pump down the cavity, to attach the couplers for RF injection or to tune the cavity [1]. The vacuum requirement of the RFQ is to be lower than 5e-7 hPa along the cavity, it is equipped with ten cryopumps and four ion sputter pumps to make it possible.