In certain applications, the surface wave driven plasma column can replace metal as the guiding medium in radio frequency antennas. Such plasma antennas offer the possibility of low radar detectability and negligible mutual coupling when de-energized. Experimental results are presented confirming that the two most important physical issues, namely antenna efficiency and noise, are not compromised by the use of a plasma. It is also shown that the relatively high efficiency of the surface wave driven plasma column can be predicted by a simple calculation.

Low and improved confinement modes in the H-1 heliac ͓M. G. Shats et al., Phys. Rev. Lett. 77, 4190 ͑1996͔͒ are studied experimentally in rf-sustained ͑Ͻ100 kW, 7 MHz͒ argon discharges at low magnetic fields ͑Ͻ0.15 T͒. Surprisingly high ion temperature, measured using a retarding field energy analyzer, is found which increases across the transition to improved confinement mode from 40 to 80 eV, while the electron density increases by about 50%. Both toroidal and poloidal plasma flow velocities do not change across the transition. The increase in a radial electric field in high mode is balanced on average by a corresponding increase in the ion pressure gradient.

The first experimental observation of the sudden transition to the improved particle confinement mode in the H-1 heliac is reported and shows a clear dependence on magnetic configuration. In a lowtemperature plasma a transition to improved confinement followed by a twofold increase in the electron density is observed when the magnetic field exceeds a critical value B cr. At B ഠ B cr the transition occurs spontaneously (within 1 ms). This B cr strongly decreases with increasing rotational transform. The improvement in confinement correlates with the suppression of the fluctuations and fluctuationinduced particle flux and with the increase in the radial electric field. [S0031-9007(96)01636-5]

Excitation of terahertz radiation by an electron beam in a dielectric lined waveguide with rippled dielectric surface Phys. Plasmas 19, 093105 (2012) Inductance and near fields of a loop antenna in a cold magnetoplasma in the whistler frequency band Phys. Plasmas 19, 093301 (2012) Radiofrequency antenna for suppression of parasitic discharges in a helicon plasma thruster experiment Rev. Sci. Instrum. 83, 083508 (2012) First results from EBW emission diagnostics on COMPASS Rev. Sci. Instrum. 83, 10E327 (2012) Additional information on Appl. Phys. Lett.

Articles you may be interested inA segmented multi-loop antenna for selective excitation of azimuthal mode number in a helicon plasma source Rev. Sci. Instrum. 85, 093509 (2014); 10.1063/1.4896041 Towards an optimal antenna for helicon waves excitation J. Appl. Phys. 98, 083304 (2005); 10.1063/1.2081107Measurements and code comparison of wave dispersion and antenna radiation resistance for helicon waves in a high density cylindrical plasma source A magnetohydrodynamic numerical model, based on the finite element method, is employed to analyze the antenna radiation resistance in a cylindrical helicon wave driven plasma source. The antenna radiation resistances of four commonly used antennas are compared. The effects on antenna radiation resistance of frequency, plasma density, density profile and the system dimensions are investigated. It is confirmed that mϭϩ1 is the most strongly excited mode. It is shown that the plasma density gradient tends to suppress the excitation of negative m-modes. Some wave field patterns are also presented which demonstrate commonly observed features in the experiments such as the beat patterns of copropagating radial modes. The findings highlight the importance of antenna radiation resistance modelling as a first step to a self consistent model of the discharge physics of cool dense helicon wave driven sources.