Ion-source and low-energy beam-transport issues with the front-end systems for the spallation neutron source

Abstract

H -ions are being used in high-energy accelerators and spallation neutron-sources because of the efficiency with which they can be converted into protons at high energy, a mechanism utilized in schemes that provide injection into a ring by means of charge. This paper discusses new trends and recent developments in the field of H -plasma generators, extraction systems, and Low-Energy BeamTransport (LEBT) systems, with emphasis on low-emittance systems delivering beams in the 50-mA range.

Negative hydrogen ion sources for accelerators

“…During ion extraction, the plasma of the SNS multicusp source is excited using 20-50 kW of 2 MHz RF. To speed the high powered ignition, the plasma is sustained continually with 200 W of 13.56 MHz RF [67]. The RF power is coupled into the plasma using an internal water-cooled copper-antenna that is coated with porcelain.…”

“…Drawing of the SNS cesiated multicusp H source and low-energy beam transport system[67]. (Reused with permission from R. Keller, Rev.…”

Sputtering and nitridation of transition metal surfaces under low energy, steady state nitrogen ion bombardment

“…The interaction of a plasma with a metal surface is a common phenomenon in a multitude of scenarios: solar winds interact with satellite shielding [1]; particles in accelerators collide with electrostatic optics [2]; divertors in fusion reactors face high ion fluxes [3]; diffuse plasmas in extreme ultraviolet (XUV) lithography may interact with reflective optics [4][5][6]; magnetically confined plasmas in sputter deposition systems bombard metallic targets [7]. In nearly all cases, with the exception of sputter deposition, the interaction is unwanted and possibly damaging to the metal surface.…”

Beam Extraction and Transport

“…There are three locations, which are generally used for dumping the electron beam in negative ion sources: 1. Puller electrode with low voltage with respect to the ion source can be used as an electron dump [18,17], 2. a separate intermediate electrode before the puller electrode can be used if a higher voltage is needed on the puller electrode [19] or 3. the electrons are dumped on an electrode after the puller electrode, as shown in Fig. 19.…”