# In-Line Target Production for Laser IFE
## 1 Introduction  
In the frame of International Atomic Energy Agency (IAEA) project (IAEA CRP F13016), one of the specific objectives was to define options for fuel target material choice and mass manufacturing methods, requirements, development pathways and potential solutions [1]. In this paper we identify the principle challenges associated with progression from single shot to high repetition rate operation with regard to manufacturing methods of a cryogenic fuel target (everywhere further--target) for laser IFE. A fusion power plant will consume as many as one million targets per day. Therefore, the free-standing target transmission line (FST-TL) is an integral part of any IFE reactor. Hereupon, methodologies of the fabrication and injection processes must be applicable to mass-production layering at low cost. To meet the above requirements, the LPI has proposed to use line-moving and free-standing targets to develop a scientific and technological base for repeatable target supply at the laser focus [2; 3; 4; 5]. Precisely moving targets co-operate all production steps in the FST-TL that is considered as a potential solution of mass-production layering and noncontact target delivery in pulsed, repetitively cycled IFE systems. This approach includes also the development of nano-layering technologies, which supports the fuel layer survivability under target injection and transport through the reactor chamber (everywhere further--FST layering method) [6; 7; 8]. The target production area includes high-precision technologies for target fabrication, injection and tracking. These technologies are currently an important research stage in the leading laboratories of the world [9; 10; 11; 12; 13; 14; 15; 16; 17; 18]. Target compression and ignition is regarded as a major challenge to the IFE community. In addition, to maintain an acceptable tritium inventory, it is needed the development of reasonably fast layering techniques. An overview of various fuel layering methods is given in Reference [2; 19]. A traditional approach is based on the following concept: targets for laser experiments are filled by permeation, and a uniform D\(-\)T ice layer (molecular composition: 25% of D\({}_{2}\), 50% of DT molecules,and 25% of T\({}_{2}\)) is formed by \"beta layering\" method [19; 20; 21]. This method involves crystallization from a single seed crystal in the fixed target. The process takes place in the anisotropic hydrogen isotopes with extremely slow cooling (q \(\sim\) 3\(\cdot\)10\({}^{-5}\) K/s) and precise temperature control (\(<\)100 uK) for obtaining cryogenic layers like a single crystal. Long-run beta-layering process at very strict isothermal conditions requires \(\sim\)24 h for one attempt. But routine practice is between 1 and 4 attempts, or even 6 attempts [20; 21] which generally require several days or a week. The beta-layering method can form a spherical fuel layer in the uniform thermal environment, but the ability of the D\(-\)T targets to withstand acceleration during injection is a key issue in terms of surface perturbation growth in the anisotropic layers under thermal and mechanical loads. Such layers also do not contribute to avoiding the Rayleigh-Taylor instabilities during implosion that decreases the odds for achieving ignition [22]. Moreover, this method is not efficient for repetitively cycled schedule of the target fabrication and injection because the target must be precisely located in the reaction chamber under precise temperature control. We emphasize that even in the single-shot laser experiments an important role for achieving ignition (apart from anisotropic layers) can play some other factors, such as effect of the target support on ice-layer quality, cryogenic shroud retraction, vibration control, target alignment, etc.