The Axisymmetric Experiment (AXE): Desktop Scale RF Heated Magnetic Mirror

The Axisymmetric Experiment (AXE) is a desktop-scale linear magnetic plasma confinement device being constructed for performing experiments with low-temperature plasmas and for pedagogical purposes within the plasma physics laboratory class offered at UW-Madison. The experiment was designed and constructed by students, achieving first plasma within 3 months. The design of AXE involved the use of finite element analysis tools to calculate the background magnetic mirror field and single particle orbits. A set of water-cooled copper coils generates a peak magnetic field of 1.1 kG on-axis with an adjustable mirror ratio between 8 to 20.

In addition, frequency-domain simulations were also carried out to evaluate radio frequency heating scenarios. Up to 3 kW of power at 13.56 MHz is available to feed a water-cooled helicon antenna via a matching network in steady-state, generating a capacitively or inductively coupled plasma which impinges on biased electrodes in the expander, making the experiment useful for plasma-material interaction studies. AXE is also a flexible platform capable of rapidly testing innovative technologies such as an additively manufactured, biased tungsten limiter and a permanent magnet Halbach array for a mid-plane divertor. Diagnostics such as Langmuir probes, B-dot probes and line ratio spectroscopy will be described. Future plans for the experiment include the addition of electron cyclotron resonance heating at 2.45 GHz and an additively manufactured tungsten antenna.