Experimental Dependence of the Neutron Yield on the Discharge Current for Plasma Focus Chambers Filled with Deuterium and Deuterium–Tritium

Resumo

Results of measurement of the mean neutron yield from plasma focus (PF) chambers filled with deuterium and deuterium–tritium are compared for various Mather-type and spherical PF devices at discharge currents in the range of 200−1000 kA. On the basis of the experimental results, an expression for the ratio of the neutron yields \({{\xi }_{{{\text{exp}}}}} = \left\langle {{{Y}_{{{\text{DT}}}}}} \right\rangle {\text{/}}\left\langle {{{Y}_{{\text{D}}}}} \right\rangle \) in the D + T and D + D reactions as a function of the discharge current is derived, according to which ξ_exp decreases from 150 to 110 (by ≈1.4 times) as the PF discharge current increases from 200 to 1000 kA. Assuming the beam–target mechanism of neutron generation in the PF, the ratio ξ_exp for D + T and D + D reactions is compared with the ratio σ_DT/σ_DD of the cross sections for the corresponding nuclear reactions at different mean energies of accelerated ions. Taking into account the mean energies of accelerated ions (~50–70 keV) determined from the measured space–energy anisotropy of neutron emission, it is suggested that the mean effective energy of accelerated D⁺ and T⁺ ions in the plasma beam formed in the pinch decay stage increases with increasing PF discharge current, which leads to a decrease in the ratio \({{\xi }_{{{\text{exp}}}}} = \left\langle {{{Y}_{{{\text{DT}}}}}} \right\rangle {\text{/}}\left\langle {{{Y}_{{\text{D}}}}} \right\rangle \) with increasing current.