Liquid Metal Bremsstrahlung Converters for High Power Electron Beams

There are numerous important applications for high power electron beams. In addition to use for fundamental nuclear physics, possible applications of this type of beam include x-ray sterilization, active interrogation, radiography, and isotope production. Most of these uses rely on a target acting as a bremsstrahlung converter to produce a high energy, high flux x-ray beam. By incorporating an additional conversion process, such a target can also be optimized for positron production. Conventional converters are made of solid, high Z metals with a high melting point, such as tungsten or tantalum. These solid converters cannot absorb more than a few kilowatts of beam power without complicated cooling methods which limit photon or positron flux density. A continuous-wave (CW) superconducting linac creates a potential for machines with very high density photon or positron fluxes, but these require converters which can withstand the higher power of the CW electron beam (~ 100 kW). A liquid metal target removes the concerns of thermal damage to the converter. We propose to produce a liquid metal target capable of converting high electron beam power (e.g. 10 MeV at 10 mA) into a high flux x-ray and positron source. This design will be collaboratively developed with material science experts from Los Alamos National Laboratory (LANL). Phase I results have led us to choose lead bismuth eutectic (LBE) to serve as a converter and coolant medium which is impervious to radiation and thermal damage. This converter can be optimized for two modalities: creation of a very high density x-ray flux, and maximization of positron production. Testing for both systems will take place at Niowave or the Idaho Accelerator Center (IAC). Most of the technologies the proposed design will draw on are a direct continuation of Niowaves Phase I developments. This includes a natural circulation driven liquid metal converter. A proprietary converter based on an electromagnetic (EM) liquid metal pump has also been developed and successfully tested. Finally, a mechanically pumped molten metal converter is on the drawing board. The natural circulation driven liquid LBE converters has already undergone preliminary beam conversion and thermomechanical testing with a kilowatt of electron beam power. Once prototype EM and mechanically pumped systems have also been constructed, these loops will be subjected to a similar battery of testing. In addition to beam conversion and thermo-mechanical testing, photon and positron production as well as corrosion tests will be devised and performed at IAC and LANL respectively.