The impact of particle desorption on DARHT-II electron beam dynamics

Summary form only given, as follows. It is well known in the intense beam community that when an intense electron beam raises the surface temperature of a solid target (e.g., electrode or aperture) to 300-400 deg C, that loosely bound adsorbed molecules are rapidly released from the surface often followed by speedy ionization. This can lead to adverse beam or diode behavior. Less well known is that even in the absence of heating, electron induced desorption of neutrals or ions can have deleterious effects on beam dynamics. We discuss computer modeling to assess the importance of desorbed particles on beam dynamics, experimental measurements to determine the level of induced desorption, and cleaning techniques to reduce adsorbed molecules on surfaces for the DARHT-II, 2 kA, 20 MeV, 2 /spl mu/s beam.

It is well known in the intense beam community that when an intense electron beam raises the surface temperature of a solid target (e.g., electrode or aperture) to 300–400 deg C, that loosely bound adsorbed molecules are rapidly released from the surface often followed by speedy ionization. This can lead to adverse beam or diode behavior. Less well known is that even in the absence of heating, electron induced desorption of neutrals or ions can have deleterious effects on beam dynamics. We discuss computer modeling to assess the importance of desorbed particles on beam dynamics, experimental measurements to determine the level of induced desorption, and cleaning techniques to reduce adsorbed molecules on surfaces for the DARHT-II, 2 kA, 20 MeV, beam.