Speaker
Description
The Los Alamos Neutron Science (LANSCE) linear accelerator provides an 800 MeV beam of
negative hydrogen ions (H-) to several facilities, e.g., pRad, a proton radiography studies facility
and the PSR, a proton storage ring which accumulates ions to be delivered to a target at the
Lujan Center for the production of neutrons by spallation.
The negative ion branch of LANSCE starts at an ion source which produces H- ions by surface
conversion of hydrogen atoms. This process takes place inside a chamber which contains a
hydrogen plasma created by an arc-discharge of molecular hydrogen gas. Located inside the
chamber there is a negatively biased converter where the actual conversion of hydrogen atoms
into negatively charged ions takes place. The production of H- ions is enhanced by the addition
of Cesium gas into the plasma chamber.
The H- ions produced at the negatively biased converter flow towards the grounded plasma
electrode which provides an aperture for the extraction of the H- beam by a positive potential.
As the H- ions flow through the hydrogen plasma there are several kinetic reactions which may
provide a destruction mechanism. The main reactions are (i) electron detachment, (ii) mutual
neutralization with positively charge plasma components and Cs ions, (iii) associative and nonassociative neutralization by neutral hydrogen gas components.
Since the amount of H- current that can be extracted from this source depends on the amount
of H- ions that survive at the extraction aperture, it is therefore of the utmost importance to
calculate the rate of H- extinction as they move through the plasma environment.
We will present Particle-in-Cell calculations of the H- beam transport through the hydrogen
plasma including charged and neutral components, taking into account the kinetic reactions
mentioned above.
