Hi! I have a question about Home Assignment 5, problem #4.

First of all, it says that the given approximate formula is for the beam-plasma collision frequency. But since it is denoted by tau, I was assuming that it was supposed to be the collision time. To check this, I did an analysis of the dimension - which made me even more confused, because I can't get it to either seconds or 1/s.... (I get kg*m3*s-3*A-2)

What should tau be? Time or frequency? Or something else? :P

Thanks!