Superconducting ECR ion source: From 24-28 GHz SECRAL to 45 GHz fourth generation ECR

The development of superconducting ECR source with higher magnetic fields and higher microwave frequency is the most straight forward path to achieve higher beam intensity and higher charge state performance. SECRAL, a superconducting third generation ECR ion source, is designed for 24-28 GHz microwave frequency operation with an innovative magnet configuration of sextupole coils located outside the three solenoids. SECRAL at 24 GHz has already produced a number of record beam intensities, such as ⁴⁰Ar¹²⁺ 1.4 emA, ¹²⁹Xe²⁶⁺ 1.1 emA, ¹²⁹Xe³⁰⁺ 0.36 emA, and ²⁰⁹Bi³¹⁺ 0.68 emA. SECRAL-II, an upgraded version of SECRAL, was built successfully in less than 3 years and has recently been commissioned at full power of a 28 GHz gyrotron and three-frequency heating (28 + 45 + 18 GHz). New record beam intensities for highly charged ion production have been achieved, such as 620 eμA ⁴⁰Ar¹⁶⁺, 15 eμA ⁴⁰Ar¹⁸⁺, 146 eμA ⁸⁶Kr²⁸⁺, 0.5 eμA ⁸⁶Kr³³⁺, 53 eμA ¹²⁹Xe³⁸⁺, and 17 eμA ¹²⁹Xe⁴²⁺. Recent beam test results at SECRAL and SECRAL II have demonstrated that the production of more intense highly charged heavy ion beams needs higher microwave power and higher frequency, as the scaling law predicted. A 45 GHz superconducting ECR ion source FECR (a first fourth generation ECR ion source) is being built at IMP. FECR will be the world’s first Nb₃Sn superconducting-magnet-based ECR ion source with 6.5 T axial mirror field, 3.5 T sextupole field on the plasma chamber inner wall, and 20 kW at a 45 GHz microwave coupling system. This paper will focus on SECRAL performance studies at 24-28 GHz and technical design of 45 GHz FECR, which demonstrates a technical path for highly charged ion beam production from 24 to 28 GHz SECRAL to 45 GHz FECR.