A Fluxgate-Based Approach for Ion Beam Current Measurement in ECRIS Beamline: Design and Preliminary Investigations

Abstract

Beam diagnostic and especially beam current measurements represent a key aspect in the production of a high-quality beam. Due to the known interplay between beam current and beam and plasma properties, many solutions have been addressed to solve this need. Although precise beam current measuring systems exist, they cannot provide noninvasive solutions for the measurement of very low-frequency currents in electron cyclotron resonance ion source (ECRIS) beamline, with a range from tens to hundreds of microamperes. To address the above-mentioned needs, this paper proposes an indirect measurement methodology based on the estimation of the magnetic field produced by target current exploiting a residence time difference fluxgate and a flux concentrator (a mechanical structure able to constrain produced magnetic field in a given area). The main advantage of this approach is related to the possibility to perform a noninvasive current measurement. An optimal geometry for the flux concentrator has been investigated by using a finite-element method analysis that has led to the definition of a minimum value of the magnetic field generated by the minimum value of the target current, around $5.0~\mu \text{A}$ , equal to 3.07 nT. To assess the solution, an experimental setup, miming real magnetic flux intensity inside ECRIS beamlines, has been realized. The measuring strategy has a magnetic resolution of 1 nT and a current resolution of $1.6~\mu \text{A}$ , that is, in line with requirements. Results obtained demonstrate the suitability of the measurement system for the specific application addressed in this paper, both in terms of operating range and resolution.