Emittance growth due to space charge compensation and beam intensity instabilities in negative ion beams

Abstract

The need to extract the maximum beam intensity with low transversal emittance often comes with the drawback of operating the ion source to limits where beam current instabilities arise, such fluctuations can change the beam properties producing a mismatch in the following sections of the machine. The space charge compensation (SCC) generated by the beam particles colliding with the residual gas reaches a steady state after a build-up time. This paper shows how once in the steady state, the beam ends with a transversal emittance value bigger than the case without compensation. In addition, we study how the beam intensity variation can disturb the SCC dynamics and its impact on the beam properties. The results presented in this work come from 3-D simulations using tracking codes taking into account the secondary ions to estimate the degree of the emittance growth due to space charge and SCC.

Compact −300 kV dc inverted insulator photogun with biased anode and alkali-antimonide photocathode

“…To better understand the remarkable lifetime improvement observed using the biased anode, the anode-cathode gap and a portion of the adjacent beam line were modeled using the ion beam simulator code, IBSIMU [38], which is a powerful suite of libraries based on C++ programming language for low-energy particle tracking in electric and magnetic fields. The open source distribution code has been utilized in the design of ion sources [39,40]. IBSIMU is designed for unbunched (dc) beams only.…”