4. (a) A one-dimensional plasma chamber has a thickness of a = 8cm. Initially the plasma chamber is empty (it is a vacuum). An 8 cm wavelength TEM wave is propagated through the chamber and the phase shift A of the wave between x = 0 and x = a is recorded. The experiment is repeated, this time with a plasma of density n is filling the chamber. The resulting (6) phase shift is A 42. The difference in phase shifts between the two measurements is found to be A-A = n/5. Calculate the plasma density? (6) (b) For a plasma consisting of electrons and ions, the diamagnetic drift results in a current flow. Explain how this current, which is not due to a guiding centre drift, can arise.