Magnetic diagnostics of plasma - Surface interactions

The secondary electron emission (SEE) from solids plays an important role in plasma, accelerator and high power microwave applications. A recent study proposed that the SEE yield, which is ratio of secondary to primary electron fluxes, approaches unity in the limit of zero energy of incident electron. If this were indeed the case, this effect would have profound implications especially for plasma applications, including, for example, plasma thrusters for spacecraft propulsion and electric probes. It appears that, the proposed high SEE at low electron energies contradicts to numerous previous experimental studies of the secondary electron emission. This talk presents a technique for measurements of SEE yield in a low-pressure plasmas in the presence of transverse magnetic field. It is shown that for poly-crystal surfaces, the SEE yield can be indeed very high (~ 0.8) but still not approaching unity. This result is explained by additional reflection of primary electrons from a potential barrier near the poly-crystal surface. The contribution of electron reflection from the barrier and the surface has been identified and studied.