Diamagnetic Loop Diagnostics in CMFX

Abstract

The Centrifugal Mirror Fusion Experiment (CMFX) harnesses azimuthal rotation of plasma through an ExB drift caused by an imposed radial electric field to enhance plasma confinement within a magnetic mirror. The centrifugal forces caused by the rotation of the plasma, also change the total magnetic flux of the mirror. Four Diamagnetic Loops (DML) are wound around the outer wall of the vacuum vessel to measure these flux changes caused by the changing magnetic field. The voltage induced in the DMLs from the changing flux is then numerically integrated to obtain the magnetic flux. The magnetic field derived from the measured flux changes is used to estimate plasma density and assess plasma stability. Integration, filtering, and detrending of this data is necessary to obtain useful signals when high amplitude noise is present. Because of this noise, new DMLs were constructed with an increased number of turns. Each DML contains 4 turns and is constructed from 18 AWG copper wire. Cables are then attached to measure the induced voltage in the loops which is then sent to a digitizer for analysis. RF-shielding foil covers the DML windings to reduce the pick-up of electromagnetic noise. Details of the DMLs, processing algorithms, and sample data are presented.