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 875G 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 (1mTorr, 500G and 500 W), no DL is observed near the source exit and the plasma diffusion is well described by a Bolzmann expansion.