Abstract

Experiments are carried out in CIMPLE-PSI, to understand the recrystallization behavior of tungsten (W) exposed under very-high target temperature and ITER relevant long He⁺-fluence. The effect of helium bubbles on possible retardation of the recrystallization process is also studied. W samples were simultaneously exposed under He plasma and annealed by the plasma heat-load, in contrast to previously reported experiments in literature, which were carried out sequentially. Exposed samples are characterized by field emission scanning electron microscopy (FESEM), Vickers surface micro-hardness, nano-hardness and electron backscattered diffraction (EBSD). It is observed that the sample exposed to plasma under the highest temperature (1866 K) suffered acute retarded grain growth. This also contained small, unrecovered grains on the exposed surface. FESEM imaging of the cross-sections confirms that relatively smaller helium bubbles still form even at very high temperature conditions, which can impede the grain growth locally, whenever they are forming right on the grain boundaries. This results in an inhomogeneous mixture of surface grains with sizes ranging from a few micrometers to a few tens of micrometers. EBSD estimates that the plasma exposed surface was only 34% recrystallized. The second sample exposed at a lower temperature (1699 K) but for three times higher fluence (ion fluence: 1.19 × 10²⁷ m⁻²) was almost fully recrystallized, which shows retardation diminishes very fast with the duration of the exposure. Hardness measurements were undertaken to understand the variation with plasma exposure/annealing temperature and the extent of recrystallization, with three different probing length scales, spanning from a few hundred nanometers to several micrometers. Both helium plasma exposed W samples are observed to undergo retarded softening up to a depth of a few hundred nanometers from the surface, compared to when the metal may be recrystallized by simple heating, without any plasma exposure.

• Book : 65(1)
• Pub. Date : 2025
• Page : pp.016017
• Keyword :

• Book : 1010()
• Pub. Date : 2025
• Page : pp.116753
• Keyword :

• Book : 1010()
• Pub. Date : 2025
• Page : pp.116751
• Keyword :

• Book : 217()
• Pub. Date : 2025
• Page : pp.111604
• Keyword :

• Book : 18(1)
• Pub. Date : 2025
• Page : pp.101218
• Keyword :

Abstract

In indirect-drive inertial confinement fusion (ICF) research, the meticulous design and optimization of laser parameters are crucial for achieving high-gain ignition. The intensity of the toe laser, used for ablating the hohlraum sealing membrane, is a subtle but equally critical parameter. This study introduces a novel experimental approach using the Velocity Interferometer System for Any Reflector (VISAR) to assess the impact of toe laser intensity on the compression of fusion capsules. By tracking the reflectivity of tracer layers and shock velocities in liquid deuterium, the adverse effects of insufficient toe laser intensity on capsule compression have been unveiled for the first time. From a comparison with hydrodynamic simulations, we show that below a critical threshold of 0.23 × 10¹⁴ W cm⁻², the adiabat, a measure of the fuel’s compression efficiency, increases markedly with the toe laser intensity decreases, whereas it remains stable within the range of (0.23 ∼ 7) × 10¹⁴ W cm⁻². Our findings provide critical insights on toe laser parameter design, enhancing our understanding of the role of toe laser intensity in ICF experiments. This research not only refines the parameters for laser operation but also underscores the importance of precision in achieving the desired implosion efficiency, contributing to the development of nuclear fusion as a clean energy source.

• Book : 65(1)
• Pub. Date : 2025
• Page : pp.016032
• Keyword :

• Book : 1070(p2)
• Pub. Date : 2025
• Page : pp.170020
• Keyword :

• Book : 1070(p1)
• Pub. Date : 2025
• Page : pp.170042
• Keyword :

• Book : 1070(p1)
• Pub. Date : 2025
• Page : pp.170031
• Keyword :

• Book : 1070(p1)
• Pub. Date : 2025
• Page : pp.170038
• Keyword :