Adapting Direct-Current Current Transformers for contactless ion beam measurements of electric propulsion systems

Abstract For electric propulsion (EP) systems, measurement of plume ion currents and densities is a core diagnostic tool. The state of the art, Faraday-Cups (FCs), terminate the beam, since the ions must impinge on a collector plate. Chief among the issues associated with this approach are the emission of secondary electrons, the unknown transmission function of the screening grid used, and backscattering, thus requiring calibration. Direct-Current Current Transformers (DCCT) provide, in principle, an absolute and contactless option for inductively measuring any direct current. For application in typical EP systems, the concept needs to be adapted for small currents $$&lt;{1}\ {\upmu }\text{A}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>&lt;</mml:mo> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mi>μ</mml:mi> <mml:mtext>A</mml:mtext> </mml:mrow> </mml:math> compared to the established use case in particle accelerators ( $$\gg {1}\ {\upmu }\text{A}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>≫</mml:mo> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mi>μ</mml:mi> <mml:mtext>A</mml:mtext> </mml:mrow> </mml:math> ). A modular prototype was developed and investigated for possible optimizations as well as error sources. The system was tested in the far field of the ion beam of a gridded ion source. However, the measurement does not align with the theoretically expected value. Susceptibility to electromagnetic interference (EMI) and non-periodic drifts in the measurement signal across various timescales were found to introduce noise. Wire-bound test currents down to $$&lt;{10}\ {\upmu }\text{A}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mo>&lt;</mml:mo> <mml:mn>10</mml:mn> <mml:mspace/> <mml:mi>μ</mml:mi> <mml:mtext>A</mml:mtext> </mml:mrow> </mml:math> could be reliably measured. The wire-bound tests show promise for DCCTs to complement FCs as a calibration device and alternative for use cases in which FCs show limitations, i.e. for extended, integral, near field, or combined diagnostics.