Improving symmetry tuning with I-raum in indirect-driven implosions br

Indirectly driven inertial confinement fusion implosions using a three-step-shaped pulse are performed at a100 kJ laser facility. At late time of the pulse, deposition of laser energy and distribution of X-ray radiation aresignificantly disturbed by motion of gold plasma in the original gas-filled cylindrical hohlraum with gold wall.As a result, owing to the lack of X-ray drive at the equator of the capsule, an unacceptable oblate implosion isproduced. In the I-raum modified from the above cylindrical hohlraum, the initial positions of outer laser spotsand gold bubbles are appropriately shifted to modify the disturbed radiation distribution due to plasmaevolution, resulting in a spherically symmetric drive on the capsule. In the implosion shots with almost the samedrive pulse, owing to improved symmetry, an spherical hotspot is observed in the new I-raum, and YOS (theratio of measured neutron yield over simulated one) is up to 30%, while an oblate hotspot is observed in thecylinder, and YOS is only 13%. The simulation calculations and experimental measurements show that theI-raum can be used to significantly reduce the impact of gold bubble expansion in the three-step-shaped pulsedriven implosion, which helps to tune the drive and implosion symmetry, and to improve its over-allperformance