2D analysis of direct-drive shock-ignited HiPER-like target implosions with the full laser megajoule

Abstract

We present a 2D analysis of direct-drive shock ignition for the laser Megajoule. First, a target design is chosen in the HiPER-like target family generated by scale up and down of the original HiPER target. A first analysis is done considering the 1D fuel assembly and 2D shock ignition by means of the ring at polar angle of 33°2. The intensity profile is top-hat and calculations are done for several different radii. It is shown that larger the radius, lower the minimum spike power is. In addition, the intensity in each quad can stay below 4 × 1014 W/cm2 and is considered non crucial for parametric instabilities such as two plasmons. A 2D analysis of the fuel assembly is done in a second step by considering the two rings located at 49° and 59°5 and their symmetric by the equatorial plane symmetry. It is shown that low mode asymmetries are important at the stagnation and can significantly affect the areal density obtained. Finally, full 2D calculations of shock ignition is done, using all the beams of the LMJ and show that the spike power needed for ignition and gain is increased by a factor greater than 3 regarding the power needed in perfectly isotropic fuel assembly. This increase is mainly due to high level low mode asymmetries generated during fuel assembly.

Direct-drive shock-ignition for the Laser MégaJoule

“…Beams layout is fully described in Ref. [15] and are distributed on rings located at polar angles of 33.2 • , 49 • and 59.5 • . We have showed [4] that DD-fuel assembly is possible with only the rings at 49 • and 59.5 • , and 1 MJ.…”

“…A variation of spike power P spike and pulse timing between driver and spike is performed to find the ignition window and to estimate the thermonuclear gain that is defined fully in Ref. [15]. As it can be seen, the smaller the focal spot, the better the laser-target coupling is, and the lower the ignitor spike power has to be.…”

“…This very promising solution was recently proposed to ignite the Fast Ignition capsule of HiPER [12,13]. We address here the possibility of using this approach for LMJ with HiPER-like targets by a 1D-and 2D-analysis [14,15], considering the LMJ beam layout. Direct-drive shock-ignition of double shell targets [16] is also adressed.…”

Low initial aspect-ratio direct-drive target designs for shock- or self-ignition in the context of the laser Megajoule

“…For NIF- [40] and LMJ-class [38] facilities, high thermonuclear gains are expected in direct drive approach. While NIF could mainly use the PDD [16,17], DD studies, in the context of LMJ, have exhibited the importance of illumination uniformity [48][49][50] to warrant fuel assembly sphericity in order to reduce ignitor spike powers [51]. Indeed strong low mode asymmetries could lead to employ very intense ignitor spike powers.…”

Systematic analysis of direct-drive baseline designs for shock ignition with the Laser MégaJoule

“…For LMJ, directly-driven self-ignition is possible [1] with indirect-drive beam geometry with zooming [5]. Moreover, Shock Ignition (SI) [6] and its application on LMJ [7] bring a new interest for direct-drive approach because it can offer high gain for non selfigniting target and allows to investigate the self-ignition threshold [8]. In this scheme, compression phase and ignition are separated.…”