The MIST-1 and MIST-2 multicusp ion sources for high-current H$_2^+$ beams

TL;DR

This paper introduces the development and testing of the MIST-1 and MIST-2 multicusp ion sources at MIT, designed to produce high-current, high-purity H₂⁺ beams for a novel cyclotron, demonstrating significant current improvements.

Contribution

The paper presents the detailed design, implementation, and initial performance results of the MIST-2 ion source, an advancement over the previous MIST-1, achieving doubled current output.

Findings

MIST-2 achieved 7 mA extracted current, doubling MIST-1's performance.

Experimental results show effective use of different magnet configurations.

First successful operation of MIST-2 in full mode.

Abstract

We present two iterations of the Multicusp Ion Source Technology at MIT (MIST) sources, designed to fulfill the requirements of the HCHC-XX cyclotron design. The HCHC-XX is a novel compact cyclotron accelerating H$_2^+$. Beam is injected through a radio-frequency quadrupole buncher-accelerator (embedded in the cyclotron yoke) and utilizes so-called vortex motion during acceleration. If successful, it will deliver 10 mA of protons at 60 MeV in CW mode. This scheme requires a low-emittance, high-current initial beam with high H$_2^+$ purity. We briefly summarize the design and previous results of the MIST-1 ion source and, for the first time, the detailed design of the new and improved MIST-2, including the mechanical, electrical, and control system design. We further show experimental results of using the MIST-2 backplate on the MIST-1 body, present a study using different types of permanent magnets for confinement (including no magnets), and finally, we present first results of the MIST-2 in full operation. In this first commissioning run, we were able to increase the total extracted current from the MIST-2 to 7 mA - a factor of 2 over the MIST-1.