Microwave Plasma Interactions

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*Selected Topics in Plasma Physics*

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**Chapter 3**

**Abstract**

**1. Introduction**

**33**

Evolution of Microwave Electric

during Ignition Phase

Field on Power Coupling to Plasma

*Chinmoy Mallick, Mainak Bandyopadhyay and Rajesh Kumar*

During the gas ignition process, the plasma and the microwave electric fields are evolved with time together in the plasma volume. The spatio-temporal evolution pattern of microwave-radiated plasma parameters is reported here, highlighting the role of these electric fields on power coupling processes. Evolutions of electric field and so power coupling processes are calculated using the finite element method (FEM). It is observed that the main power coupling mechanism is electron cyclotron resonance (ECR) method; however, with the evolution of plasma, the mode shifts from ECR to off-ECR-type heating with time. Off-ECR heating in the form of upper hybrid resonance (UHR) method, electrostatic (ES) ion acoustic wave heating method is important heating mechanisms during highly dense plasma condition, when density is above critical density for launched frequency, 2.45 GHz. The conclusions on the shifting of heating mechanisms are also drawn based on the 3D maps of spatio-temporal plasma density and hot electron temperature evolution.

**Keywords:** microwave plasma simulation, COMSOL multi-physics,

electric field evolution, hot electron temperature, experimental validation

magnetized plasma evolution, ECR, off-resonance, ion source, electrostatic heating,

Gaseous particles are ionized to bring them in the form of plasma through the various heating techniques. One of the popular heating techniques is the injection of high frequency microwaves (MW) to a cylindrical cavity that has comparable dimension to the injected MW wavelength. The MW plasma generated by the continuous or pulse feeding of the MW is used in the applications of industrial and accelerator fields for the material science and nuclear applications, respectively. In both of the feeding cases, the plasma is basically produced due to the power

absorption by the electrons from the space-time dependent electric field of the MW. The spatio-temporal dynamics and also the steady-state behaviors of the plasma are governed by the ways the MW are coupled to the plasma sustained inside a cavity. The behavioral pattern of the electric field during the plasma evolution can help us to comment on the different MW coupling ways/mechanisms that are involved in the formation of plasma particles and their confinement scenarios. By mastering the basic concepts on those different coupling mechanisms, the coupling efficiency and so the performance of that particular plasma source can be optimized. Performance
