Multiple source 2.45 to 28 GHz electron cyclotron heating on the levitated dipole experiment

The levitated dipole experiment (LDX) is investigating a magnetic dipole field configuration similar to planetary magnetospheres as an alterative confinement concept for fusion plasmas. Recent experiments have confirmed that stationary, highly peaked plasma density profiles (> 50 core to edge) are formed by the conservation of the product of plasma density and differential flux tube volume (V = ∮dl/B). These natural peaked profiles are maintained by ambient plasma turbulence, contrary to experience with plasmas inside a set of coils where turbulence acts to flatten profiles. LDX uses a 1.1 MA, 34 cm mean radius, 560 kg superconducting coil (F-coil) that is freely floated by a 280 kA levitating coil for over 2 hours between cryogenic recoolings. Plasmas are started and sustained by electron cyclotron heating (ECH) on closed flux surfaces encircling the F-coil that cross the outer midplane radius between 67 and 177 cm. The magnetic field strength varies from 0.007 to 3.2 Tesla around the F-coil on these flux surfaces corresponding to EC resonance between 0.2 to 90 GHz. Consequently, ECH in a magnetic dipole is possible with a multiplicity of sources at many frequencies.