First observation of micro-bunch structure of the 100 MHz HIMAC-injector linac beam by a thin SEEM

The characteristics of a thin secondary-electronemission type of beam monitor (SEEM) with three sheets of 1 μm-thick Al foils, an effective area of 40 x 40 mm and gap distances of 2 mm are described. Our SEEM has been routinely used as a dose monitor with an accuracy of 1 % level. The total, forward and backward secondary electron emission yields, γ t, γ f and γ b , from the Al foil were measured under bombardment with He , C , Si ions at an energy of 6 MeV/amu, and their Zdependence was studied. Experimental data showed that the Z dependence is almost valid for the above bare projectiles, i.e., the emission yields are rather well proportional to the electronic energy loss. In addition we report on the first observation of a micro-bunch structure of 1 ns rise-time and 100 MHz repetition-frequency of linac beams with the SEEM. While we can utilize these fast-timing signals of SEEM only for the heavy-ion beam inducing a very high emission yield, it may be noted that a typical traveling time of the emitted electrons is of the order of 100 ps which is comparable with that of the Pestov chamber.