Progress in field ionization source development for compact neutron generators

Summary form only given. Low power, compact neutron sources have applications in areas such as oil-well logging and homeland security. In oil-well logging they have the potential to replace the radioactive sources that are widely used today. Critical parameters of these generators are size and energy consumption as well as neutron yield and source lifetime. The neutrons are normally generated in deuterium-deuterium (or deuterium-tritium) reactions at acceleration voltages of about 100kV. A common method to generate the deuterium ions required is to use a Penning-type source or an rf-plasma source. In our experiments we use field ionization at sharp emitter tips, such as carbon nanofibers, to create deuterium ions. The use of a plasma-free environment could lead to lower power consumption and a longer lifetime of the source. In this presentation we give an overview of our experimental work and discuss challenges and possible solutions. The main focus will be on uniformity issues in large carbon nanofiber arrays (le6 tips/cm2). Variations in the length and diameter of the fibers leads to different field-enhancement factors, which result in different ion currents at each tip. Single tips can produce around 100pA in well-optimized conditions. In order to scale from one tip to a large array of tips, uniformity across the entire sample needs to be well-controlled. We utilize field-ionization experiments as well as electron emission experiments to characterize a variety of sample geometries and report on our findings.