Measuring drift velocity and electric field in mirror machine by fast photography

The flute instability in mirror machines is driven by spatial charge accumulation and the resulting E B plasma drift. On the other hand, E B drift due to external electrodes or coils can be used as a stabilizing feedback mechanism. Fast photography is used to visualize Hydrogen plasma in a small mirror machine and infer the plasma drift and the internal electric field distribu- tion. Using incompressible flow and monotonic decay assumptions we obtain components of the velocity field from the temporal evolution of the plasma cross section. The electric field perpen- dicular to the density gradient is then deduced from E=-V B. With this technique we analyzed the electric field of flute perturbations and the field induced by electrodes immersed in the plasma.