Lithium in inertial fusion targets

May 18, 2008 by daumic

Has lithium been already tested with D-T fuel in target fusion?

A small addition of lithium in target could perhaps boost the beginning of inertial fusion.

Inertial fusion tries to make the fusion of deuterium and tritium by implosion of a target irradiated with lasers. This implosion is obtained in an indirect way by the expansion under the impact of lasers of an ablative material that surrounds the mixture D-T.

Molten lithium in blanket around the reactor is envisaged to receive the energetic neutrons emitted by fusion. Tritium is regenerated by the reactions:

Li6 + n => He4 + T + 4.8 MeV
or
Li7 + n => He4 + T + n – 2.5 MeV

The heat recovered in molten lithium will be used in electric generator to produce electricity. The generated tritium will permit to make new targets.

The last experiments of this sort of fusion have demonstrated the beginning of reaction between deuterium and tritium but with an insufficient level.

In the case of a target made of tritium and deuterium, the neutron generated by the reaction (T + D => He4 + n + 17 MeV) has a great energy (14 MeV). The cross section of reaction of this fast neutron with deuterium or tritium is very small. The neutron can quit the imploded target without loosing energy.

The cross section of this neutron with Li6 or Li7 isn't so small:
- cross section for neutron-Li6 with 14 MeV neutron is in order of 0.01 barn,
- cross section for neutron-Li7 with 14 MeV neutron is in order of 0.1 barn,
- comparison: cross section for D-T fusion with 10keV ionic energy is in order of 0.002 barn.

If lithium is present in the very dense plasma during the implosion, it could capture the great energy of neutrons emitted by the first fusions and contribute to the heating of plasma. More, one of the nukes produced by the reaction between neutron and lithium is a fast tritium that can participate in fusion reactions. The relatively high cross sections of n-Li reactions in regard of cross section of fusion could limit the addition of lithium in a small part of D-T fuel.