Plasma expansion from a dielectric electron cyclotron resonance source

The boundary conditions in an electron cyclotron resonance (ECR) source have been modified to mimic the operating conditions where current-free double-layers (DLs) have been recently measured in rf helicon plasmas. The plasma is heated or generated by the ECR at 875 G inside a dielectric source tube, and expands into a grounded diffusion chamber (terminated by a glass plate) by a rapidly decreasing magnetic field. Preliminary studies of the plasma expansion have been performed. For the present conditions (1 mTorr, 500 G and 500 W), no DL is observed near the source exit and the plasma diffusion is well described by a Bolzmann expansion.