Implosion dynamics in direct-drive experiments

Increasing the ablation pressure is a path to achieving cryogenic implosion performance on the OMEGA laser that will hydrodynamically scale to ignition on the National Ignition Facility. An increased ablation pressure will allow a more-massive shell (i.e. thicker and more hydrodynamically stable) and a higher adiabat to achieve ignition-relevant velocities (>3.5 × 107 cm s−1), areal densities (>300 mg cm−2) and hot-spot pressures (>100 Gbar). Two approaches have demonstrated increased ablation pressure: (1) a target design is shown that uses a Be ablator to increase the hydrodynamic efficiency, resulting in a ~10% increase in the ablation pressure, in comparison to a CH ablator; (2) reducing the beam size is shown to recover all of the ablation pressure lost to cross-beam energy transfer (CBET), i.e. the ablation pressure calculated without CBET, but the degraded illumination uniformity reduces the integrated target performance. The hydrodynamic efficiency is measured for the current cryogenic design, multiple ablator material design and CH capsule designs with various beam focal-spot sizes. In each case, an excellent agreement is observed with 1D hydrodynamic simulations that include CBET and nonlocal heat-transport models.

[1]  V. Goncharov,et al.  Performance of Direct-Drive Cryogenic Targets on OMEGA , 2007 .

[2]  John Kelly,et al.  Crossed-beam energy transfer in direct-drive implosions , 2011 .

[3]  S. Skupsky,et al.  Reduction of laser imprinting using polarization smoothing on a solid-state fusion laser , 1999 .

[4]  T. C. Sangster,et al.  Laser-beam zooming to mitigate crossed-beam energy losses in direct-drive implosions. , 2013, Physical review letters.

[5]  I. E. Golovkin,et al.  SPECT3D - A Multi-Dimensional Collisional-Radiative Code for Generating Diagnostic Signatures Based on Hydrodynamics and PIC Simulation Output , 2007 .

[6]  Samuel A. Letzring,et al.  Improved laser‐beam uniformity using the angular dispersion of frequency‐modulated light , 1989 .

[7]  P. B. Radha,et al.  Increasing hydrodynamic efficiency by reducing cross-beam energy transfer in direct-drive-implosion experiments. , 2012, Physical review letters.

[8]  S. Starikovskaia.  Plasma-assisted ignition and combustion: nanosecond discharges and development of kinetic mechanisms , 2014 .

[9]  P. B. Radha,et al.  Triple-picket warm plastic-shell implosions on OMEGA , 2011 .

[10]  P. Lovoi,et al.  Laser paint stripping offers control and flexibility , 1994 .

[11]  P. B. Radha,et al.  Improving cryogenic deuterium–tritium implosion performance on OMEGAa) , 2013 .

[12]  V N Goncharov,et al.  Demonstration of the improved rocket efficiency in direct-drive implosions using different ablator materials. , 2013, Physical review letters.

[13]  W. Manheimer,et al.  Steady‐state planar ablative flow , 1981 .

[14]  J. Nuckolls,et al.  Laser Compression of Matter to Super-High Densities: Thermonuclear (CTR) Applications , 1972, Nature.

[15]  J D Lindl,et al.  Tuning the implosion symmetry of ICF targets via controlled crossed-beam energy transfer. , 2009, Physical review letters.

[16]  Samuel A. Letzring,et al.  Initial performance results of the OMEGA laser system , 1997 .

[17]  J. Delettrez.  Thermal electron transport in direct-drive laser fusion , 1986 .

[18]  C Sorce,et al.  Shell trajectory measurements from direct-drive implosion experiments. , 2012, The Review of scientific instruments.

[19]  P. B. Radha,et al.  Demonstration of the highest deuterium-tritium areal density using multiple-picket cryogenic designs on OMEGA. , 2010, Physical review letters.

[20]  Jonathan D. Zuegel,et al.  Mitigation of cross-beam energy transfer: Implication of two-state focal zooming on OMEGA , 2013 .

[21]  J. A. Marozas,et al.  Theory of hydro-equivalent ignition for inertial fusion and its applications to OMEGA and the National Ignition Facilitya) , 2014 .

[22]  J. D. Kilkenny,et al.  Development and characterization of a pair of 30–40 ps x‐ray framing cameras , 1995 .

[23]  J. A. Marozas,et al.  Improving the hot-spot pressure and demonstrating ignition hydrodynamic equivalence in cryogenic deuterium–tritium implosions on OMEGAa) , 2014 .