The performance of a fusion generator depends, in part,on accurate measurements of the number of neutrons being producedfor a given operating condition and the ratio of neutrons fromdeuterium-deuterium (D-D) and deuterium-tritium (D-T) reactions. Direct and rapid measurements of this ratio at several locationsabout the plasma can provide information on the uniformity ofneutron production and on the radial position of the fusing portionof the plasma. In this Phase I project, superheated drop detector(SDD) compositions, recently introduced for health physicsapplications, will be adapted for this challenging fusionmeasurement task. These SDD compositions, containing tens ofthousands of superheated drops in a host gel, respond to neutronsthrough the initiation of drop vaporization, as in the bubblechamber. The resulting vapor bubbles occupy 250 @ the volume ofthe drops that created them, thereby leading to a macroscopicnonelectronic measure of the total number of neutrons to which thecomposition was exposed. Moreover, superheated drop compositionsemploying different sensitive materials have different energythresholds. A count of both D-D and D-T neutrons can be obtainedby using one material with a 2 MeV threshold. By using anothercomposition with a 6 MeV threshold, counts of just 14 MeV neutronsfrom the D-T reaction will be obtained. Thus the D-D/D-T ratio canbe computed. The planned project will explore the range ofconditions under which the SDD system will operate in the plasmafusion environment, introduce modifications in the SDD compositionsto operating conditions, and decide among a number of options forreading out the changes @fested in the composition after they havebeen exposed at several positions about the fusing portion of theplasma.Anticipated Results/Potential Commercial Applications as described by the awardee:The results of this research may lead to a newdiagnostic tool for plasma-co nuclear fusion. The samehigh neutron flux considerations in this project may obtain inother applications. For example, in applications of high energyaccelerators for cancer therapy, a fraction of the dose is fromneutrons. Other applications of high energy accelerators (when theincident energy exceeds 10 MeV) may also produce significantnumbers of neutrons. The new SDD compositions designed for fusionwork will have applications in these high dose environments. Accurate measurements of these neutrons not only have researchvalue, but can be used to better inform health physics personnel ofsituations dangerous to workers and others.
