https://doi.org/10.1140/epjd/e2014-50695-y
Regular Article
Overlapping laser profiles used to mitigate the negative effects of beam uncertainties in direct-drive LMJ configurations
1 Centre de Mathématiques et de Leurs
Applications, ENS Cachan and CNRS, 61 Av. du President Wilson, 94235
Cachan Cedex,
France
2 CEA, DIF, 91297
Arpajon Cedex,
France
3 AWE plc, Aldermaston, Reading,
Berkshire,
RG7 4PR,
UK
4 ETSI Aeronáuticos, Universidad
Politécnica de Madrid, 28040
Madrid,
Spain
a
e-mail: mauro.temporal@hotmail.com
Received:
22
September
2014
Received in final form:
31
October
2014
Published online:
13
January
2015
A direct-drive shock ignition scheme in the context of the Laser MegaJoule facility has been considered. The irradiation uniformity provided by two laser beam configurations using a total of 10 or 20 quads to drive the first compression phase has been analyzed. Firstly, a numerical method is used to optimize the laser intensity profiles in the context of the illumination approximation model; then these profiles are used to calculate the irradiation non-uniformity of a spherical target of radius r0 = 1000 μm assuming the beam uncertainties: power imbalance 5%, pointing error 50 μm and target positioning 20 μm. These uncertainties deteriorate the quality of the irradiation increasing considerably the irradiation non-uniformity; moreover, it is found that the pointing error provides the major contribution to the degradation of the irradiation. A strategy to mitigate the negative effect induced by the beam uncertainties is proposed. It consists in using a composite profile in each beam: a first large and flat intensity profile provides a background that reduces pointing error and target positioning effects, whilst a second overlapping profile optimizes the illumination irradiation. It is found that the introduction of the flat background with an intensity of 55% with respect to the maximum intensity reduces by about 40% the non-uniformity of the irradiation due to beam uncertainties.
Key words: Plasma Physics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2015