Capsule performance optimization in the National Ignition Campaign

Abstract

A capsule performance optimization campaign will be conducted at the National Ignition Facility [G. H. Miller et al., Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition by laser-driven hohlraums [J. D. Lindl et al., Phys. Plasmas 11, 339 (2004)]. The campaign will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models before proceeding to cryogenic-layered implosions and ignition attempts. The required tuning techniques using a variety of ignition capsule surrogates have been demonstrated at the OMEGA facility under scaled hohlraum and capsule conditions relevant to the ignition design and shown to meet the required sensitivity and accuracy. In addition, a roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget.

Observation of strong electromagnetic fields around laser-entrance holes of ignition-scale hohlraums in inertial-confinement fusion experiments at the National Ignition Facility

“…The capsule inside a hohlraum was a warm plastic (CH) one with ∼2 mm diameter and filled with D 3 He gas. Each hohlraum was driven by 192 laser beams forming four single irradiation rings, with total laser energy of ∼1-1.5 MJ in a typical [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] four-shock pulse (lasting ∼14.9-19.9 ns). The individual laser beams had full spatial and temporal smoothing [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…Such an exciting scientific breakthrough is being vigorously pursued at the National Ignition Facility (NIF) [5] through the indirect-drive approach, in which the capsule implosion occurs in response to tremendous radiation pressure generated by the thermal x-rays in a high-Z enclosure, i.e. hohlraum, when the enclosure's inner wall is irradiated by high-power lasers [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. The lasers would have a temporal pulse shape designed to launch four radially convergent shock waves which would coalesce at the capsule center, creating a self-igniting 'hot spot' which would generate a self-sustaining burn wave that propagates into the main fuel region.…”

“…The National Ignition Campaign (NIC) aims to eventually realize this important goal at the NIF, which has unique capabilities including 192 laser beams and 1.8 MJ of 3ω (0.35 µm) laser energy, enhanced pulse-shaping capabilities and pulse durations and greatly improved irradiation symmetry, etc [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Several ongoing experimental campaigns have been conducted to tune implosion conditions and to address a wide range of critical physics issues relevant to ignition sciences, including laser coupling, implosion dynamics and symmetry, hot spot formation and burn physics, etc.…”

Charged-particle spectroscopy for diagnosing shock ρR and strength in NIF implosions

“…2,3 In particular, the cold DT (deuterium and tritium) fuel must reach a high enough areal density (ρR), which is primarily measured by the magnetic recoil spectrometer [4][5][6][7] and neutron time of flight (nTOF) spectrometers. 8 Non-cryogenic experiments are conducted as part of the NIF tuning campaign, 9,10 such as implosions to correct asymmetries in the radiation drive by measuring the compressed shape 11,12 with x-ray self-emission imaging, and similar experiments 13 to measure the implosion velocity and remaining mass, and thus the implosion kinetic energy, with x-ray radiography. In these capsules, the cryogenic fuel layer is replaced with a surrogate mass of plastic (CH) and the capsules are filled with a D 2 + 3 He gas fuel mixture, which produces the fusion reaction D + 3 He → 4 He(3.6 MeV) + p(14.7 MeV) among others.…”

Shock timing on the National Ignition Facility: First experiments

“…This situation of near simultaneous mergers is achieved by making adjustments to the power history of the drive pulse, which in turn adjusts the strength and timing of the shocks. Over the previous decade we have developed an experimental plan to diagnose the shock sequence in order to set the pulse shape [1][2][3]. This plan has now been realized with the first experiments performed in late 2010.…”