Advances in target design for heavy ion fusion

Abstract

Over the past few years, the emphasis in heavy ion target design has moved from the distributed radiator target to the "hybrid" target because the hybrid target allows a larger beam focal spot than the distributed radiator (~ 5 mm radius rather than ~ 2 mm radius). The larger spot relaxes some of the requirements on the driver, but introduces some new target physics issues. Most notable is the use of shine shields and shims in the hohlraum to achieve symmetry rather than achieving symmetry by beam placement.The shim is a thin layer of material placed on or near the capsule surface to block a small amount of excess radiation. While we have been developing this technique for the heavy ion hybrid target, the technique can be used in any indirect drive target. We have begun testing the concept of a shim to improve symmetry using a double-ended zpinch hohlraum on the Sandia Z-machine. Experiments using shimmed thin wall capsules have shown that we can reverse the sign of a P 2 asymmetry and significantly reduce the size of a P 4 asymmetry. These initial experiments demonstrate the concept of a shim as another method for controlling early time asymmetries in ICF capsules.

Progress in symmetric ICF capsule implosions and wire-arrayz-pinch source physics for double-pinch-driven hohlraums

“…Capsules imploded at time-integrated asymmetries of <2% to convergence ratios of 20 would be comparable to the present best laser-indirect-drive implosions [139] and would scale to conditions required for high yield ICF at 220 eV hohlraum temperatures. The double z-pinch source is also being used as a test bed for P 4 control techniques compatible with all indirect drive concepts including laser-driven ignition on the NIF [20,46,47].…”

“…This technique may allow per centlevel early-time asymmetries to be nullified with the least overall penalty on secondary drive temperature. Experiments are currently validating this concept [46,47] in the double z-pinch at drive temperatures similar to the foot-pulse required for ignition capsules [20].…”

“…Other P 4 control techniques have been explored with the double z-pinch that are applicable to heavy-ion beam fusion and also possibly to ignition in laser-driven hohlraums. In these experiments, performed in collaboration with Lawrence Livermore National Laboratory [46,47], a thin (sub-µm) layer of high-Z material with angularly dependent thickness is directly deposited on the ablator surface [83]. This technique may allow per centlevel early-time asymmetries to be nullified with the least overall penalty on secondary drive temperature.…”

Target design for high fusion yield with the double Z-pinch-driven hohlraum

“…38 The on-axis shine shield already present in the double Z-pinch hohlraum eliminates a gross pole-hot flux that would be seen by the capsule due to Z-pinch stagnation radiation. The symmetry shield design strategy described below is akin to the capsule shimming approach, 39 but offsets the symmetry control structures from the capsule surface to avoid potential hydrodynamic coupling of the shield to the capsule. Consider a set of purely absorbing, non-expanding shields, each defined as a section of a sphere with material occupying a specific polar angle range.…”

Study on Magnetic Polymer ICF Target Prepared by the Electroless Plating

“…The inertial confinement fusion is one of the most important method producing the controlled thermonuclear fusion energy, which may be one of the main energy sources, and has received considerable attention by many countries in the world [1][2][3]. In the ICF reaserches, the preparation of high quality target is one of the important foundation.…”