COMSOL 6.4 - Pulsed Discharges

Particular care must be taken when using the option in the feature. The interface defines the characteristic period using an additional independent variable, which must be discretized in space using a mesh. To resolve the RF modulation within the on period, at least 30 mesh elements are required per RF period. Consider the case where the discharge is on for 10 cycles at 13.56 MHz (780 ns), then off for another 100 cycles (7.8 μs). During the on-cycle, you need to use 30 mesh elements for each RF period (78 ns). During the off-cycle, there is no RF modulation, so we can use around 100 mesh elements for the entire 7.8 μs. So, we need a total of 400 mesh elements to discretize the extra coordinate representing the characteristic period. This represents a 10-fold increase in computation demand compared to a continuous mode discharge, which would only require 30 mesh elements in the extra coordinate. Therefore, the pulsed option is very computationally expensive, and even 1D models are expected to take a significant amount of time to solve.

The Dual pulse option, where the off-period is replaced by a low power period is even more computationally expensive, since the low power period also needs 30 mesh elements per RF period. So, for the above example, where the 100 cycle off period is replaced by low power operation, we would need 3000 mesh elements to resolve this part. This would make such a model 100 x more expensive than the same continuous mode discharge.

When considering using the pulsed discharge option, use the following to estimate the computation demand: