On the cover of HPL: ‘Review on high repetition rate and mass-production of the cryogenic targets for laser IFE’, by I.V. Aleksandrova and E.R. Koresheva.

Controlled inertial fusion energy (IFE) research is aimed at developing a new powerful energy source which is safe, environmentally friendly and cost-effective. The main element of IFE power plant is a target with cryogenic hydrogen fuel (solid hydrogen isotopes or their mixtures) that must be delivered to the reaction chamber center at significant rates of 5−10 Hz. It leads to the amount of targets (5×105 −1×106) each day, and methodologies that are applicable to mass manufacturing of IFE targets are required for fueling a future reactor. Therefore, the research fields related to the elaboration of the efficient fuel layering methods for IFE applications are rapidly expanding. These methods must be integrated in a free-standing target (FST) transmission line which becomes an integral part of any IFE power plant.

A key aspect of the FST transmission line is the development of scientific and technological base for high repetition rate target supply at the laser focus. All target designs contain a fuel core, which is smoothly layered on the inside of a spherical low-Z ablator (plastic shell). The targets must be free-standing (or unmounted), and the fusion fuel inside the targets must have an ultra-fine structure (near-nano or nano-crystalline), which supports the fuel layer survivability under target injection and transport through the reaction chamber.

The isotropic ultra-fine fuel produced upon extremely high cooling (q >1 K/s) refers to as advanced materials for application to fusion targets fabrication in the form that meets the requirements of implosion physics. Therefore, creation of stable ultimate-disordered structures with a high defect density or isotropic medium is of critical importance for solid hydrogen isotopes or their mixtures.

To fulfill the above requirements, at the Lebedev Physical Institute, Russian Academy of Sciences (LPI/RAS) significant progress has been made in the technology development based on high cooling fuel layering inside moving free-standing targets, which refers to as FST layering method. The aim of these targets is to demonstrate large benefits of a “layering + delivery” scheme for a repetition rate target fabrication and delivery. Thus, a fundamental difference of the FST layering method from generally accepted approaches (characteristic of using a mounted target and extremely slow cooling q of about 3×10−5 K/s resulting in a long layering time of about 24 h) is that it works with the free-standing and line-moving targets, which allows one to economically fabricate large target quantities and to continuously (or at a required rate) inject them at the laser focus.

A thorough analysis of the current state of the art in IFE target research and description of the underlying physical principles in the development of target fabrication and delivery technologies were published in High Power Laser Science and Engineering, Vol. 5, No. 2, e11, 2017 (I.V. Aleksandrova and  E.R. Koresheva, Review on high repetition rate and mass-production of the cryogenic targets for laser IFE).

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