Abstract
Large volume helicon plasma sources are of particular interest for large scale semiconductor processing, high power plasma propulsion and recently plasma-material interaction under fusion conditions. This work is devoted to studying the coupling of four typical RF antennas to helicon plasma with infinite length and diameter of 0.5 m, and exploring its frequency dependence in the range of 13.56-70 MHz for coupling optimization. It is found that loop antenna is more efficient than half helix, Boswell and Nagoya III antennas for power absorption; radially parabolic density profile overwhelms Gaussian density profile in terms of antenna coupling for low-density plasma, but the superiority reverses for high-density plasma. Increasing the driving frequency results in power absorption more near plasma edge, but the overall power absorption increases with frequency. Perpendicular stream plots of wave magnetic field, wave electric field and perturbed current are also presented. This work can serve as an important reference for the experimental design of large volume helicon plasma source with high RF power.
Highlights
Large volume helicon plasma has been attracting growing interest in various fields, including large scale semiconductor processing,[1] electrodeless plasma propulsion with high power input,[2,3,4,5] and emerging plasma-material interaction under fusion conditions recently.[6,7,8,9] Large volume allows high power capacity and big heat flux, besides large cross sectional area
Boswell, Nagoya III and loop antennas are widely used for small helicon sources, it is still not yet clear that which type of RF antenna can best couple helicon plasma of large size
Motivated by enhancing the coupling of RF antennas to large volume helicon plasma for high power applications, we study the dependences of power absorption on antenna geometry and driving frequency for helicon source with infinite length and diameter of 0.5 m
Summary
Large volume helicon plasma has been attracting growing interest in various fields, including large scale semiconductor processing,[1] electrodeless plasma propulsion with high power input,[2,3,4,5] and emerging plasma-material interaction under fusion conditions recently.[6,7,8,9] Large volume allows high power capacity and big heat flux, besides large cross sectional area. Except the novel design of spiral antenna to excite helicon plasma from an axial end and with diameter of 75 cm,[10,11] most helicon sources employ cylindrical RF (Radio Frequency) antennas wrapping plasma with diameter less than 40 cm. The presented work is devoted to comparing these typical helicon antennas in terms of power absorption and wave field structure. The motivation is to assist experimental design of RF antenna for helicon sources with large diameter. Since high power is not the particular focus of this work, quartz tube is still kept to separate plasma and antenna radially. A C++ program based on Maxwell’s equations and cold-plasma dielectric tensor will be employed to compute the spatial power absorption and wave field for different antennas, and their comparisons will be analyzed for experimental reference
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