# Micro-Faraday cup matrix detector for ion beam measurements in fusion plasmas

## TL;DR

This paper introduces a micro-Faraday cup matrix detector designed for precise ion current measurements near plasma edges in fusion devices, utilizing PCB technology and magnetic confinement to improve plasma diagnostics.

## Contribution

The paper presents a novel micro-Faraday cup matrix detector with secondary electron suppression, suitable for plasma edge ion current measurements in fusion experiments.

## Key findings

- Effective secondary electron confinement demonstrated
- Low cross talk achieved in laboratory tests
- Detector successfully integrated into COMPASS tokamak setup

## Abstract

Atomic Beam Probe (ABP) is an extension of the routinely used Beam Emission Spectroscopy (BES) diagnostic for plasma edge current fluctuation measurement at magnetically confined plasmas. Beam atoms ionized by the plasma are directed to a curved trajectory by the magnetic field and may be detected close to the wall of the device. The arrival location and current distribution of the ions carry information about the plasma current distribution, the density profile and the electric potential in the plasma edge. This paper describes a micro-Faraday cup matrix detector for the measurement of the few microampere ion current distribution close to the plasma edge. The device implements a shallow Faraday cup matrix, produced by printed-circuit board technology. Secondary electrons induced by the plasma radiation and the ion bombardment are basically confined into the cups by the tokamak magnetic field. Additionally, a double mask is installed in the front face to limit ion influx into the cups and supplement secondary electron suppression. The setup was tested in detail using a Lithium ion beam in the laboratory. Switching time, cross talk and fluctuation sensitivity test results in the lab setup are presented, along with the detector setup to be installed at the COMPASS tokamak.