**Author details**

**6. Conclusion**

*Selected Topics in Plasma Physics*

**64**

The evolution of the spatial and temporal plasma parameters are presented in the current chapter during the gas ignition process made by injecting the 2.45 GHz microwave to an ion source cavity. The simulated results supported by the experiment confirm that the plasma parameters are influenced significantly by the electric fields during the plasma ignition period. Due to the shifting of the microwave coupling mechanisms to the plasma, the plasma density and the hot fraction of the electron temperature are also getting affected during the plasma generation period. The initial rise of the hot fraction of the plasma electron temperature from the start of microwave interaction into the plasma is argued to be caused by the electron cyclotron resonance heating phenomenon. After certain instant of microwave launch, the slight increase in the plasma density and the decrease in the plasma electron temperature are proved to be happening from the electrostatic heating mechanism. The electrostatic heating near the upper hybrid resonance region causes to shift the inhomogeneous part of the electric field at the velocity of the ion

acoustic speed when the plasma density reaches above the critical density

generated electrostatic waves in the present experimental device.

has similar system configuration and the operating environment as that of the simulation. The comparison shows a reasonable agreement with the simulated results. The plasma density especially in the overdense plasma condition is found to be agreeing more in the overdense plasma than in the underdense plasma condition. During plasma evolution after the microwave launch, the microwave coupling mechanisms are modified following the corresponding electric field (electrostatic and electromagnetic) distribution pattern throughout the ion source cavity. Initially, the electron cyclotron resonance heating comes into play to ionize the gaseous particle and generate plasma that contains the maximum fraction of the highenergy electrons in the ion source plasma. Then, as the density reaches in the overdense condition, the coupling mechanisms are the electrostatic wave heating in the ion acoustic frequency range. As the electrostatic wave does not suffer any density cut-off, the density is increased further above the critical density. Simultaneously, the polarity of the axial electric field is reversed near the electron cyclotron resonance region signifying the creation of the plasma density gradient due to the generation of strong ambipolar electric field near the resonance region. In future, it is intended to study the different power coupling mechanisms in the overdense plasma state that are caused due to the heating at the cyclotron harmonics by the

The experimental plasma parameters are obtained in an experimental set-up that

corresponding to the launch microwave, 2.45 GHz.

Chinmoy Mallick1,2\*, Mainak Bandyopadhyay1,2 and Rajesh Kumar1,2

1 Institute for Plasma Research (IPR), Gandhinagar, Gujarat, India

2 Homi Bhabha National Institute (HBNI), Mumbai, Maharashtra, India

\*Address all correspondence to: chinmoyju1990@gmail.com

<sup>© 2020</sup> The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
