# A kinetic study of microwave start-up of tokamak plasmas

## TL;DR

This paper presents a kinetic model for microwave start-up in tokamak plasmas, capturing the evolution of electron distribution functions and predicting plasma current driven by high-energy electrons, aligning with experimental observations.

## Contribution

The paper introduces a simplified two-dimensional kinetic model that predicts plasma current driven by high-energy electrons during microwave start-up, incorporating key experimental effects.

## Key findings

- Model predicts current carried by electrons >70 keV, consistent with experiments.
- Current drive efficiency is smaller than observed, indicating areas for model refinement.
- Includes effects of particle sources, orbital losses, loop voltage, and microwave heating.

## Abstract

A kinetic model for studying the time evolution of the distribution function for microwave start-up is presented. The model for the distribution function is two dimensional in momentum space, but, for simplicity and rapid calculations, has no spatial dependence. Experiments on the Mega Amp Spherical Tokamak have shown that the plasma current is carried mainly by electrons with energies greater than $70$ keV, and effects thought to be important in these experiments are included, i.e. particle sources, orbital losses, the loop voltage and microwave heating, with suitable volume averaging where necessary to give terms independent of spatial dimensions. The model predicts current carried by electrons with the same energies as inferred from the experiments, though the current drive efficiency is smaller.