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Increasing hydrodynamic efficiency by reducing cross-beam energy transfer in direct-drive-implosion experiments.
D H Froula1, I V Igumenshchev, D T Michel
1Laboratory for Laser Energetics, University of Rochester, Rochester, New York 14636, USA. dfroula@lle.rochester.edu
Physical Review Letters
|May 1, 2012
Summary
Optimizing laser-beam radius in inertial confinement fusion experiments significantly boosts neutron yield by reducing cross-beam energy transfer (CBET). However, excessively small spots increase nonuniformities, causing neutron yield to saturate.
Area of Science:
- Physics
- Plasma Physics
- Nuclear Fusion
Background:
- Cross-beam energy transfer (CBET) is a key process affecting energy deposition in inertial confinement fusion (ICF).
- Illumination nonuniformities can degrade ICF target performance.
Purpose of the Study:
- To determine the optimal laser-beam radius for ICF by balancing CBET reduction and illumination nonuniformities.
- To investigate the impact of laser spot size on hydrodynamic efficiency and neutron yield.
Main Methods:
- Experimental investigation of laser-beam radius effects on ICF parameters.
- Hydrodynamic simulations incorporating nonlocal and CBET models.
Main Results:
- Reducing laser-spot size by 20% increased hydrodynamic efficiency by ~35% and neutron yield by a factor of 2.6.
- Absorption increased by 15%, leading to a 17% rise in implosion velocity and 10% earlier bang time.
- Reducing the laser-spot size to target radius ratio below 0.8 led to saturated neutron yield due to increased nonuniformities.
Conclusions:
- There exists an optimal laser-spot size that maximizes neutron yield in ICF.
- Exceeding this optimum by reducing spot size leads to performance degradation due to increased nonuniformities.
