Gas dynamic trap as high power 14 MeV neutron source

Abstract

It is now widely recognized that further progress toward a commercial fusion reactor critically depends on the availability of low activated materials to be operated for many years in the fusion neutron environment without degradation of their properties. Therefore, high power neutron source (NS) for extensive material tests is in great demand. The realistic NS can be built on the basis of the gas dynamic trap (GDT) which is one of the simplest system for magnetic plasma confinement. GDT is an axisymmetric mirror machine of the Budker–Post type, but with a high mirror ratio ( R>10), and operated with warm and relatively dense plasma. Thus, due to frequent collisions, the plasma confined in a trap is very close to isotropic Maxwellian, and hence many instabilities are not excited and plasma behavior is similar to a classical one. It is proposed to use the oblique injection of neutral tritium and deuterium beams with an energy of the order of 100 keV into the GDT “warm” target plasma (electron temperature T e≥750 eV) to produce high intensity neutron flux. In this case, due to the ionization and charge-exchange collisions with plasma particles the energetic atoms will turn into ions confined in the trap. The axial density profile of these anisotropic energetic ions will be strongly inhomogeneous. Namely, the maximum of the fast ion density will be located in the vicinities of mirrors and the minimum—at the middle plane of the device. Thus, a strongly inhomogeneous fusion neutron flux, mostly generated in the fast deuterium–tritium (D–T) ion collisions will appear. GDT NS looks to be rather flexible system. It enables to construct the source stepwise, starting from rather moderate parameters. Increasing the testing zone length and neutral beam power one can increase both neutron flux and the flux density. Calculations show that even in the modest version of the NS with T e∼250 eV quite appreciable neutron flux density in the range of 0.2–0.3 MW/m 2 can be produced. At present, the maximum temperature about 130 eV is obtained in the experiments at the model GDT device at Budker INP. Further increase of the electron temperature in the device requires higher neutral beam power and now is considered to be straightforward.