A Hybrid Ion Source Concept for a Proton Driver Front End

Abstract

Abstract.A novel concept for creating intense beams of negative hydrogen ion beams has been devised, and first steps towards its realization have been taken. In this approach, an ECR plasma generator operating at 2.45 GHz frequency is utilized as a plasma cathode, and electrons are extracted instead of ions and injected at moderate energy into an SNStype multi-cusp H -ion source. This secondary source is then driven by chopped d. c. power, rather than rf power, but does not need filaments which are the cause for the rather short lifetime of conventional H -sources. The development of this ion source is primarily aimed at the future beam-power goal of 3 MW for the Spallation Neutron Source (SNS) [1] that will be pursued after the start of SNS operations. The first two phases of this development effort have been successfully passed: assembly of a test stand and verification of the performance of an rf-driven SNS ion-source prototype and extraction of electrons with more than 200 mA current from a 2.45-GHz ECR ion source obtained on loan from Argonne National Laboratory. An electron-extraction chamber that joins these ECR and H -sources has been fabricated, and the next goal is the demonstration of actual H -ion production by this novel, hybrid ion source. This paper describes the source principle and design in detail, reports on the current status of the development work, and gives an outlook on future lines of development.

Gasdynamic ECR ion source for negative ion production

“…These molecules then propagated into the second trap and produced H − ions there as the result of dissociative electron attachment (DEA) with "cold" electrons. Such approach is similar to the one suggested in [4] where 2.45 GHz ECR discharge was used as a plasma cathode producing "hot" electrons. The scheme of the experimental facility is presented in figure 1.…”

First experiments on applying the gasdynamic ECR ion source for negative hydrogen ion production

“…Thus, the plasma confined in the second trap presumably consists of two electron populations enabling the volume production of H -ions. Such approach is similar to the one suggested in [5] where heating 2.45 GHz ECR discharge was used as a plasma cathode producing "hot" electrons. A simple two-electrode extraction system was used for the ion beam extraction.…”

First Results on the Path Towards a Microwave-Assisted H>sup<->/sup<Ion Source

“…Lastly, with the original HYBRIS configuration [17] the electrons were extracted from the ECR plasma, accelerated to 5 keV energy, and then decelerated to 50 -250 eV upon injection into the H-discharge chamber. The attempt to start a discharge in the H-chamber using this approach failed, however, because at pressures where a dc discharge could have been ignited, a plasma formed in the electron extraction gap, shortening out the accelerating Cathode Filter Magnets Outlet Figure 1: Schematic diagram of HYBRIS.…”