Volume production negative hydrogen ion sources

Abstract

We review the evolution of volume production negative hydrogen ion sources since the discovery in 1977 of the new phenomenon, designated as volume production and attributed to dissociative electron attachment of low energy electrons to rovibrationally excited molecules. The experimental verification in 2005 of the reality of this mechanism is reported. The magnetically filtered tandem sources, using hot filaments or inductively coupled radio frequency discharges, proposed in order to make use of the volume production mechanism, are used as continuous wave sources for cyclotrons and short pulse sources for synchrotrons. The extraction physics, required to correlate the negative ion and electron densities near the extraction opening with the extracted currents, is discussed taking into account the recently measured H/sup -//D/sup -/ ion temperatures. It is also shown that the extracted negative ion current can be predicted from the directed flow velocity (measured by two laser photodetachment) and the negative ion density measured in the extraction region plasma. Progress in modeling the volume production negative hydrogen ion sources is briefly summarized. Main attention has been paid to some recent topics, such as negative ion temperature and specific for two negative species plasmas transport in a weak transverse magnetic field. A new view on the potential of volume production making use of the vibrationally excited molecules produced on surfaces (plasma electrode, walls) by recombinative desorption is presented.