Corr, C. S.Boswell, R. W.2015-12-022015-12-021070-664Xhttp://hdl.handle.net/1885/16969In this work, high-beta plasma effects are investigated in a low-pressure helicon plasma source attached to a large volume diffusion chamber. When operating above an input power of 900 W and a magnetic field of 30 G a narrow column of bright blue light due to Ar II radiation is observed along the axis of the diffusion chamber. With this blue mode, the plasma density is axially very uniform in the diffusion chamber; however, the radial profiles are not, suggesting that a large diamagnetic current might be induced. The diamagnetic behavior of the plasma has been investigated by measuring the temporal evolution of the magnetic field Bz and the plasma kinetic pressure when operating in a pulsed discharge mode. It is found that although the electron pressure can exceed the magnetic field pressure by a factor of 2, a complete expulsion of the magnetic field from the plasma interior is not observed. In fact, under our operating conditions with magnetized ions, the maximum diamagnetism observed is 2%. It is observed that the magnetic field displays the strongest change at the plasma centre, which corresponds to the maximum in the plasma kinetic pressure. These results suggest that the magnetic field diffuses into the plasma sufficiently quickly that on a long time scale only a slight perturbation of the magnetic field is ever observed.7 pages© 2007 American Institute of Physics. AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. The following article appeared in Physics of Plasmas and may be found at http://doi.org/10.1063/1.2802080 http://publishing.aip.org/authors/copyright-reuse http://www.sherpa.ac.uk/romeo/issn/1070-664X Author can archive publisher's version/PDF (Sherpa/Romeo as of 2/12/2015).high-beta plasmalow-pressure helicon plasma sourcelarge volume diffusion chamberinput power of 900 Wmagnetic field of 30 GAr II radiationblue light200710.1063/1.28020802015-12-08