The effective secondary electron yield in the space-charge limited ...

I.V. Tsvetkov, T. Tanabe / Journal of Nuclear Materials 258±263 (1998) 927±933 931Fig. 4. E€ective electron yield d e for W, Mo, C and Be against E p . T e ˆ 30 eV, n 0 ˆ 10 18 m 3 .of plasma density (Figs. 4 and 6). That is because thegyro-radius of high-energy electrons is close to thesheath thickness and electrons easily escape from anoblique magnetic ®eld. Even if the magnetic ®eld wasparallel to the surface, d e would not be zero owing tohigher re¯ection.Below a primary electron energy E p ˆ 4 keV thesecondary electron yield is nearly the same for a sheaththickness d ˆ 10k D as for d ˆ 5k D , as shown in Fig. 7.Above 4 keV, d e is smaller for d ˆ 10k D . For d ˆ 5k Dthe secondary electron yield increases above 4 keV andfor d ˆ 10k D above 16 keV, because the energy has to beFig. 5. Contribution of the re¯ected electrons on the e€ective electron yield as a function of E p . T e ˆ 30 eV, n 0 ˆ 10 18 m 3 .