Reference

The plasma effect was originally conceived to explain results obtained with fission fragments, indicating a difference of ~ 10 ns between expected (2 ns) and measured rise times.

Approximate experimental values for the plasma time (e.g. for alpha-particles) have been deduced from measured rise times, by subtracting the calculated contributions of the detector RC-times, the charge collection times, etc.

The 1D and 2D calculation have been done in 1967. The key concept is that the plasma zone behaves like a conductor. Free electrons and holes quickly move to the edge of the plasma forming an internal electric field cancelling out the external field in the plasma zone. The plasma time tp is the time needed to move all charge carriers in the plasma zone out of it.

A detailed calculation assuming thin cylindrical track parallel to the electric field was done by [Seibt in 1973][Seibt73].