Measured laser fusion gains reproduced by self-similar volume compression and volume ignition for NIF conditions

Abstract

The recent high core gains of 29% in laser fusion experiments at the LLE Rochester are evaluated and compared with related earlier measurements where surprisingly the self-similarity model for volume compression provides a common description. This is a proof that the isentropic conditions of stagnation-free compression were mostly fulfilled at the optimized experimental gains, in contrast to highly entropy-producing shock and central spark conditions. Some projections are given of how these results may be generalized to volume ignition for the parameters of the NIF (National Ignition Facility). The proof of stagnation-free volume compression for the best laser fusion gains indicates the advantages of volume ignition, which not only is ‘robust’ and simply follows the natural adiabatic compression, but also is much less sensitive to instabilities and mixing. However, its essential advantage is that it is free from symmetry problems – in contrast to spark ignition, with its spherical detonation front.

Difference between relativistic petawatt-picosecond laser-plasma interaction and subrelativistic plasma-block generation

“…force~Hora et al, 2002!. It was essential that any prepulse be carefully suppressed since it was discovered from X-ray emission measurements by Zhang et al~1998!, and is a condition to avoid~Hora & Wang, 2001!, relativistic self-focusing~Hora, 1975Jones et al, 1982;Häuser et al, 1992;Esarey et al, 1997;Osman et al, 1999! which is usually occurring Hora, 1991, 2000Haseroth & Hora, 1996!…”

“…mechanism detailed evaluated experimentally from ion emission~Badziak etal., 1999, 2003, 2004a! and recognized as the skin layer process~Hora& Wang, 2001;Hora et al, 2002;Hora, 2003! after the importance of the prepulse was known~Zhang et al, 1998! for avoiding relativistic self focusing and as seen before from the KrF ps-TW interaction with ideal plane geometry nonlinear force acceleration~Sauer-brey, 1996!.…”

Extraordinary strong jump of increasing laser fusion gains experienced at volume ignition for combination with NIF experiments

“…This low gain may not be a surprise because the warning was given by a key expert in a summary at an earlier IAEA-Fusion conference about laser-driven fusion (Meyer-ter-Vehn, 1996), underlining "the most difficult aspects" for spark ignition which is extremely complicate. In contrast to this scheme of ignition, it was known before that the highest gains of neutrons N were 2 × 10 14 with 35 kJ laser pulses (Soures et al, 1996), however, only by using the alternative scheme of direct drive volume ignition (Hora et al, 1998). This kind of ignition uses a much less complicate scheme (Hora et al, 1978;Hora, 1981;1987;1991;Hoffman et al, 2005) as outlined by Lackner et al (1994).…”

“…For volume ignition, such jumps were the result of detailed computations and had led to the discovery of the volume ignition in 1978 (Hora et al, 1978;1987;Lackner et al, 1994;Atzeni, 1995). It was surprising that all experiments with the highest gains by direct drive were achieved with this scheme (Hora et al, 1998). Indeed this was related to the reheat based on Denis Gabors's (1952) collective stopping power used in the computations for volume ignition (Hora, 1991) since 1978.…”

Hohlraum-Driven Ignitionlike Double-Shell Implosions on the Omega Laser Facility

“…A standard metric of implosion performance is the ratio of the measured primary neutron yield [D+D→n(2.45 MeV)+He 3 (0.82 MeV)] to the calculated "clean" yield, i.e., no mix, or "YoC" [9]. All-glass inner-shell double-shell experiments have consistently given YoCs of a few percent at most, thereby challenging our notions of double-shell behavior.…”