Efficient kinetic simulations in the Z inner MITL

The Z inner magnetically insulated transmission line (MITL)

is subjected to extreme fields, of the order of 100s of Tesla

and 100s of MV/m. Kinetic simulations, preferred in MITL numerical design,

can be very computationally expensive. The challenge comes from

two main constraints on the time step, the small Larmor period of electrons

and the Courant condition. To lift these restrictions, we utilize the

operational parameters on Z, namely, the time scale of the current pulse

on Z (~100ns) and the dimensions of the inner MITL (~10cm).

For such parameters, one could use an electrostatic and magnetostatic

fields model to remove the Courant limit. In the strong magnetic fields, we show

that a drift kinetic guiding center model for electrons can be used

as an approximation, removing the need to resolve the Larmor period.

As a test problem we model space charge limited emission (SCL) from the

cathode due to field stress. We show that typically observed vortex

formation and evolution can be well reproduced by using only drift kinetic

particles. We also discuss the possibility of a hybrid full kinetic and

drift kinetic approach.