1. Introduction

The goal of IFE research is development of high-precision and mass production technologies for fueling a commercial power plant at the rate of 10 Hz [1]. The conventional approach to solid layering based on the beta-layering method [2] is unable to ensure the IFE requirements, as it (a) works with targets fixed on a suspension (no repetition rate operation), (b) has a long layering time (more than 24 h that leads to a large tritium inventory), (c) shows the grain boundaries dynamic under thermal and mechanical loads in time between the moment just after target preparation and the laser shot, which results in roughening of the layer surface and may lead to implosion instabilities, and (d) has a high production cost (more than \$1000/target).

The beta-layering method can form a spherical fuel layer in a uniform thermal environment; however, it is inefficient in preventing local defects. Therefore, the

modern requirements are asking for development of structure-sensitive methods aimed at new layering techniques meeting the IFE needs. This is due to the fact that the progress in plasma implosion up to intensive fusion reactions lies in formation of a given fuel structure that must be isotropic for reaching fusion conditions.

2. Target mass production

depend on the layer structure as well.

DOI: http://dx.doi.org/10.5772/intechopen.81518

(clay) that can be written as definition (1):

MATERIAL ¼

55

(1) can be transformed in (2):

account the properties of the hydrogen isotopes.

2.1 Structure-sensitive methods

The fuel structure is very important for the progress toward ignition. Considering the issue of high-quality cryogenic layer fabrication, we have to rely, first of all, on structural properties of hydrogen isotopes and their mixtures. Survivability of the fuel layers subjected to the environmental effects during target delivery may

Mechanical Mockup of IFE Reactor Intended for the Development of Cryogenic Target Mass…

Many important properties of materials are structure-sensitive, and often a relatively small number of defects have a disproportionately large effect on the material properties. Material structuring is very promising for creation of fusion materials with required properties. The role of structure-sensitive methods when developing new functional materials is especially underlined in [13]: "All materials have different chemical composition, aggregate states (solid body, liquid, and gas), allotropic modifications (graphite-diamond), or can be a mix of several substances

½Chemical composition Að Þþ Aggregate state Að Þþ Allotropic modification Að Þ�þ <sup>½</sup>Chemical composition Bð Þþ Aggregate state Bð Þþ Allotropic modification Bð Þ� þ …"

However, this is obviously an inexact characteristic. The natural or introduced imperfection in the material is more important. Defects or, more generally, microstructure, define many major structure-sensitive properties of the materials. Critical for material property parameters are the type of available defects, their spatially organized packing, and interaction at multiple hierarchy levels. Chemical composition, aggregate state, and allotropic modification as a cooperative characteristic can be replaced with a more common concept "Phase." Then, the previous definition

The defect structure plays an important role in determining many material properties. From technological applications, a particular interest is the mechanical and thermal characteristics. In the IFE, a practical tool for correlating the structure and properties of the hydrogen fuel is the thermal target environment; cooling rates, fuel doping, periodic mechanical influence on the target under the cryogenic layer freezing, etc. [1]. For example, depending on the cooling rates, the solid fuel layer can be in the state with a different microstructural length or grain size: isotropic ultrafine layers and anisotropic molecular crystals (real single crystals, coarse-grained crystalline). This becomes particularly important if one takes into

In the equilibrium state, the solid hydrogen isotopes consist of anisotropic molecular crystals. In our analysis, we are guided by the fact that the angular dependence of the sound velocity, V, is known for a number of substances crystallizing in the hexagonal close-packed (hcp) phase. As found in [14], the sound velocity anisotropy is inherent to hcp-H2 and hcp-D2 as well, and makes nearly 20% (longitudinal sound) and 33% (transverse sound). In accordance with the Debye theory, the lattice thermal conductivity is directly proportional to the value of V.

Material ¼ Phase sð Þþ Microstructure (2)

(1)

At the LPI, the concept of a mechanical mockup of IFE reactor has been proposed [3] to develop reactor-scale technologies applicable to mass production of IFE targets at significant rates (Figure 1). The LPI program also includes extensive development work on creation of different designs of the hybrid accelerators for IFE target transport with levitation (noncontact acceleration systems).

The MM-IFE is a modular facility representing in essence a free-standing target (FST) transmission line (integral part of any fusion reactor) designed to produce IFE targets and to provide their noncontact delivery at the laser focus and synchronous irradiation by a laser (1–10 Hz). It consists of 3 main blocks: (1) cryogenic target factory (CTF) operating with isotropic fuel layers of 200–300 μm thick (Figure 1a) [1]; (2) cryogenic IFE-target injector operating at accelerations <500 g and injection velocities Vinj ≥ 200 m/s [4–8]; and (3) tracking systems for online characterization and control of the injected targets [9–12]. Replacement of the FSTlayering module, being the main part of CTF, on the extruder of the solid fuel pellets allows developing the technologies for continuous fuel supply into magnetic fusion energy (MFE) facilities (Figure 1b).

Basic elements of the MM-IFE have been tested at LPI as prototypes for risk minimization at the stages of MM-IFE construction and startup. We especially highlight that moving targets are the necessary condition for realizing the repeatable target production at required rates, their mass manufacturing and noncontact delivery.

In this chapter, we discuss some challenging scientific and technological issues associated with IFE targets, the current status of the R&D program on MM-IFE, and further trends in developing the advanced IFE technologies for high-repetition rate laser facilities.

#### Figure 1.

Repeatable and mass production of the fuel targets/pellets for IFE (a) and for MFE (b) reactors. In (a): 1—fuel-filled polymer shell, 2—FST-layering module, 3—cryogenic targets batch, 4—shuttle, 5—pusher, 6—target carrier (sabot), 7—drum of a revolver type, 8—extruder for protective cover production, 9—coin for the protective cover formation and delivery, 10—field coil for "sabot + target + protective cover" pull out and delivery to the start point of injector. In (b): 1—extruder of solid fuel pellets, 2—pellet carrier (sabot), made from superconductor or ferromagnetic, 3—module for sabot-repeatable delivery to the rotating drum, 4—rotating drum for rep-rate assembly of the units "sabot + pellet," 5—heater for pellets production, 6—pusher, 7—linear electromagnetic accelerator (injector), 8—sabot brake.

Mechanical Mockup of IFE Reactor Intended for the Development of Cryogenic Target Mass… DOI: http://dx.doi.org/10.5772/intechopen.81518
