Thermonuclear fusion can be achieved through a controlled reaction between two light variants of hydrogen, called deuterium and tritium - that sounds simple enough but improving the ignition stage of fusion reaction isn't trivial.
Theoretical calculations described in a paper published in EPJ D involve increasing the uniformity of irradiation using high-power laser beams on the external shell of a spherical capsule containing a mix of deuterium and tritium.
Reaching uniformity of irradiation matters. Indeed, if it can be achieved, it rapidly heats up the capsule and makes it implode, compressing the fuel inside to very high density. This, in turn, induces the compression and heating of a small amount of fuel in a hot spot, which is a sine qua non for reaching the ignition conditions of thermonuclear fusion to produce large energy quantities.
The authors analyze the possibility of using the UK-based Orion facility's high-power laser beams to study uniformity. Orion has a few nanosecond-long pulse - 5 kiloJoules in energy - which cannot achieve ignition, but can help to test ways to produce uniform irradiation from non-uniformly distributed beams: a technique called Polar Direct Drive.
Specifically, the authors use numerical simulations to analyze the uniformity of the illumination of a spherical target both in the case of circular or elliptical laser intensity profiles. Their work also takes into account other potentially disruptive factors. These include beam-to-beam power imbalance, laser-beam pointing error and target positioning error.
They demonstrate that this approach could mathematically reduce the non-uniformity of the capsule irradiation considerably — by 50 percent and 35 percent, for elliptical and circular intensity profiles respectively.
Citation: Mauro Temporal, Benoit Canaud, Warren J. Garbett, Franck Philippe, Rafael Ramis, 'Polar direct drive illumination uniformity provided by the Orion facility', The European Physical Journal D
October 2013, 67:205 DOI: 10.1140/epjd/e2013-40362-4