  During the initial phase of microwave (MW) power launch inside a MW discharge
ion source (MDIS), plasma and the electric fields are evolved with time
together in the plasma volume. The spatio-temporal evolution pattern in the
cavity of a MDIS is reported here, highlighting the role of these electric
fields on power coupling processes. Evolution of electric field and so power
coupling processes are calculated using Finite Element Method (FEM). Unlike
PIC/MCC or hybrid fluid, here FEM model uses time dependent Poisson solver
through drift-diffusion approach. In presence of plasma gradient in the volume
ambipolar electric field is generated which interacts with the MW electric
field to form resultant total electric field which continuously vary during
this evolution period. It is observed that 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, electro-static (ES)
ion acoustic wave heating method are important heating mechanisms during the
over-dense plasma condition, when density is above critical density for
launched MW frequency, 2.45 GHz. An indirect verification of simulated temporal
evolution of hot electron temperature and plasma density with the experiment,
is done under similar configuration and operating environment. The experimental
results are found to be agreed reasonably well with the simulation in the low
power range.
