Low betta superconducting cavity for the new injector linac for nuclotron-nica*

The results of the RF, mechanical and multipactor discharge simulations of the 162 MHz quarter wave resonator (QWR) for New Superconducting Injector Linac for Nuclotron-NICA are presented. Cavity design in conjunction with manufacturing features is discussed. INTRODUCTION The New Injector Linac for Nuclotron-Nica is the proposed replacement for LU-20 accelerator. This linac SC part general layout is showed on Fig. 1 [1-2]. Figure 1: Proposed NICA injector layout of normal and superconducting structures. The accelerating structures development for first SC group of linac cavities are under development by collaboration of Russian and Belorussian institutions since 2016. Cavity is planned to be produced by Physical-TechnicalInstitute of the National Academy of Sciences of Belarus (PTI NASB). It has a successful experience in manufacturing of single cell elliptical superconducting test resonators. SC quarter-wave resonators (QWR) are proposed for the first group of cavities of accelerator cold part. Initial accelerating gradient requirement for this group of cavities is 7.5 MV/m [2]. Different types of cavities were considered for acceleration beamline development. Cavities should provide high gradient operation to minimize sections length. However QWRs are more difficult to fabricate comparing to single cell elliptical test cavities because they have more elements and welded assemblies. Production facilities at PTI NASB allow to manufacture these types of structures, but every additional design complication increases the production time, cost and brings new challenges for fabrication process. Estimation of possibilities and manufacturing experience together with an expert opinion show that optimal solution for successful superconducting QWR manufacturing is the choice of a cavity design as simple as possible. This is necessary for example for material behaviour estimation under forming and welding along with cavity treatment development. In this article the optimization results of simple 162 MHz 0.12c beta QWR are presented. ELECTROMAGNETIC DESIGN The QWR design for the first section of SC Linac Nuclotron-NICA is presented in Fig. 2. Figure 2: QWR for β=0.12. Cavity RF simulations and optimization for peak magnetic and electric fields at the cavity surface were carried out. The results are summarized in Table 1. The cavity operation frequency is 162 MHz. The ratio of the maximum electric field Ep and the maximum magnetic field Bp at the cavity surface to the accelerating field Eacc are determined. The values of the shunt impedance Rsh, the geometric factor G and the transit time factor T are calculated. Practical experience from several projects for similar cavities show that this QWR design could operate at 6 MV/m accelerating gradient [3]. Therefore we had to reduce our initial design requirement for Eacc from 7.5 to 6 MV/m [4]. It provides expectations to reduce a production presetting time, to obtain the first prototypes and gain experience in fabrication for QWR. ___________________________________________ * This project is supported in part by the MEPhI 5/100 Program of the Russian Academic Excellence Project MOPVA087 Proceedings of IPAC2017, Copenhagen, Denmark ISBN 978-3-95450-182-3 1058 Co py rig ht © 20 17 CC -B Y3. 0 an d by th er es pe ct iv ea ut ho rs 07 Accelerator Technology T07 Superconducting RF Table 1: RF Parameters of QWR