EXPERIMENTAL INVESTIGATION OF THE Z2 SCALING LAW OF FAST-ION-PRODUCED SECONDARY-ELECTRON EMISSION

The secondary-electron yields Y are measured for H-1(1+), He-3(2+), He-4(2+), Be-9(4+), B-10(5+), C-12(6+), and O-16(8+) ions with 1.5-11 MeV/amu of kinetic energy hitting gold, aluminum oxide, and tantalum targets. For such fast ions, it is expected that the yield will scale as Y proportional to z2, where z is the charge state of the ion. The yield data are reduced to remove the kinetic-energy dependence and it is found that Y proportional to z1.71 for gold targets, Y proportional to z1.62 for Al2O3 targets, and Y proportional to z1.72 for tantalum targets. Reasons for the deviation of the data from the expected Y proportional to z2 scaling law are explored. The electric fields arising from space-charge separations in the wakes of the fast ions are suspected to be the cause of the lowered scaling law.