2.3 FST layering time for direct-drive high-gain targets

In [15], we proposed a model for rapid fuel layering inside moving, freestanding targets. It is based on solving the Stephen's problem for moving boundaries between the fuel phases (gas, liquid, and solid) and for nonlinear boundary condition onto the outer shell surface. The heat transport through the target is conduction through a small contact area. The computational tools allow one to model the layering time as a function of the target and LC parameters and other experimental

• LC is a special insert into the layering module cryostat; it is manufactured as a

The FST-LM operation with a rate of 0.1 Hz at T = 5.0 K. In (a) FST-layering results: 1—40-μm-thick layer (D2 + 20% Ne) in the CH shell of 1.23-mm diameter (20% Ne-additives are used for modeling T2 in the D-Т fuel), 2—44-μm-thick H2 layer with (H2 + 5% HD) in the CH shell of 1.2-mm diameter; in (b) horizontal

Nuclear Fusion - One Noble Goal and a Variety of Scientific and Technological Challenges

• combined LC (CLC) is one of the most interesting cases, which consists of two

• targets move top-down in the LC in a rapid succession of one after another that allows to realize a high injection rate during finished target delivery to the TC

• TC is a prototypical interface unit between the layering module and target

The goal of the target characterization program is to provide reliable data in an available time. In this respect, two technologies are important: (1) fuel layering technique development (detailed information about the spatial modes, which break the target symmetry) and (2) reaction chamber fueling of a commercial power plant (targets must be injected at significant rates (10 Hz) which indicates evi-

The first technology requires enhancing the obtained data, and the second needs shortening the characterization time. This indicates that the process details for the characterization technology dealing with the operational times and information

A hard development work is needed to take into account the specifics of both technologies for developing a reliable characterization system to control the IFE target parameters. In the FST-LM, the reconstruction algorithms for tomographic data processing of the target layering stage are used in a hundred-projection microtomograph with a spatial resolution of 1 μm [9, 10]. Moving target tracking is a challenge task and it is becoming increasingly important for IFE applications.

• TC is currently used for finished target quality control using precise

tomographic and threshold characterization.

dence of a threshold behavior of the characterization process).

spirals (acceleration spiral and deceleration spiral) in order to reduce

practically to zero the target speed at the CLC output;

TC: 1—1 target (0 s), 2—10 targets (100 s); in (c) vertical TC: 12 targets in 100 s.

• TC has two types of target collectors: vertical and horizontal;

spiral (cylindrical or conical);

(Figure 3);

Figure 4.

injector;

58

content are of critical importance.

conditions. The total layering time is typically less than 15 s (for targets less than 2 mm in size).

At the current stage of research, the FST model was adaptable and scalable for IFE targets (4 mm). For comparison, in our analysis, we consider several directdrive target designs for different laser energies EL:


Figure 5 scales the FST layering time for cryogenic targets of a few millimeters long.

of the theoretical efforts have focused on the development of computational models of the IFE target response during FST-formation cycle [1]: fuel filling–fuel layering– target injection. Using the codes allows planning experiments and studying the

The FST layering time for several direct-drive target designs was calculated using the computational codes

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

D2 fuel D-T fuel Tin (K) τliquid (s) τform (s) Tin(K) τliquid (s) τform (s) 35.0 17.48 22.45 37.5 22.14 28.52 27.5 7.08 12.05 28.0 7.87 14.25

Current status of the FST technologies underlies the future research that focuses

on the FST-LM prototype development, challenges and advances in IFE target fabrication. We use the CHGT to design a high rep-rate FST-LM and analyze recent experiments with different LCs. Our experiments were made with the mockups of different designs, and the required LC geometry was found. The time-integral performance criterion is that the target residence time tres in the LC must be more than the fuel layering time τform. Figure 6 shows three mockups: mockup 1 M-1 (one-fold spiral), tres = 9.8 0.5 s; mockup 2 M-1 (two-fold spiral), tres = 23.5 1.7 s;

Different LC mockups which are planned to be used in the FST-LM to promote development of effective

behavior of these targets in the FST-LM.

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

Figure 5.

Table 1.

Figure 6.

61

affordable technology alternatives.

developed at LPI [15].

FST layering time for CHGT.

mockup 3 M-2 (three-fold spiral), tres = 35.0 2.0 s.

Table 1 presents our new modeling results obtained for CHGT, which is of special interest. The FST layering time (τform) does not exceed 23 s for D2 fuel and 30 s for D-T fuel. In order to overcome the gravitational fuel sag to the shell bottom, the FST layering uses a moving target that allows avoiding the difficulties inherent in the cryogenic layer formation in the fixed targets. The shell rotation causes a spread of liquid fuel over the inner shell surface, and under certain conditions (sufficient value of τliquid), it results in a uniform layer formation. This important effect makes topical to study a dynamical spread of the liquid fuel inside the moving target and to develop numerical models of the process. The obtained results (theoretical and experimental) can be found in [10, 15].

Thus, for dynamical fuel symmetrization in a batch of rolling targets (Figure 3), the time of liquid phase existence, τliquid, is a key parameter and must be sufficient for a cryogenic layer symmetrization. This depends on a temperature Tin of the target entry in the LC (initial target temperature before FST layering). Decrease in temperature Tin will lead to decrease in the total layering time at the expense of τliquid (Table 1). Therefore, when designing the FST-LM for CHGT, it is essential to manage the value of Tin in a way that limits the risks and achieves maximum possible growth of τliquid.

In near-term plans, we consider the approach based on the FST layering method as a credible path for creating a repeatable operating FST supply system (FST-SS). The first step in this direction is the development of the next-generation FST-LM for high-gain direct-drive targets, which are the shells of 4 mm in diameter with the shell wall of different designs from compact and porous polymers. The layer thickness is 200 μm for pure solid fuel and 300 μm for in-porous solid fuel. Most Mechanical Mockup of IFE Reactor Intended for the Development of Cryogenic Target Mass… DOI: http://dx.doi.org/10.5772/intechopen.81518

#### Figure 5.

conditions. The total layering time is typically less than 15 s (for targets less

Nuclear Fusion - One Noble Goal and a Variety of Scientific and Technological Challenges

drive target designs for different laser energies EL:

foam, there is a 120-μm-thick pure solid fuel;

consists of a CH foam (10 mg/cm<sup>3</sup>

environment.

possible growth of τliquid.

long.

60

shell with a 3-μm wall and a fuel layer of 100-μm thick;

At the current stage of research, the FST model was adaptable and scalable for IFE targets (4 mm). For comparison, in our analysis, we consider several direct-

• OMEGA (EL = 30 kJ) baseline target [23]: a 0.46-mm-diameter polymer (CH)

• High-power laser energy research (HiPER, EL = 200 kJ) baseline target (BT): the HiPER-scale targets are of two types [18]. The first one (BT-2) is a 2.094-mm-diameter CH shell with a 3-μm wall. The solid layer thickness is 211 μm. The second (BT-2a) consists of a 2.046-mm-diameter CH shell with a 3-μm wall having fuel-filled CH foam (70 μm) on its inner surface. Onto the

• Classical high-gain target (CHGT, EL = 1.3 MJ KrF laser) developed by Bodner and coauthors [24]: "…a new direct-drive target design that has a predicted energy gain of 127 using a 1.3 MJ KrF laser, and a gain of 155 using 3.1 MJ." For 1.3 MJ KrF laser, the target specifications are as follows: the vapor cavity has a 1500-μm radius. The pure D-T (190 μm) fuel is surrounded by an ablator that

ablator is surrounded by a 1-μ plastic coating (polystyrene, polyimide, etc.) to contain the D-T fuel. The plastic coating is then surrounded by an overcoat of a

Figure 5 scales the FST layering time for cryogenic targets of a few millimeters

Thus, for dynamical fuel symmetrization in a batch of rolling targets (Figure 3), the time of liquid phase existence, τliquid, is a key parameter and must be sufficient for a cryogenic layer symmetrization. This depends on a temperature Tin of the target entry in the LC (initial target temperature before FST layering). Decrease in temperature Tin will lead to decrease in the total layering time at the expense of τliquid (Table 1). Therefore, when designing the FST-LM for CHGT, it is essential to manage the value of Tin in a way that limits the risks and achieves maximum

In near-term plans, we consider the approach based on the FST layering method as a credible path for creating a repeatable operating FST supply system (FST-SS). The first step in this direction is the development of the next-generation FST-LM for high-gain direct-drive targets, which are the shells of 4 mm in diameter with the shell wall of different designs from compact and porous polymers. The layer thickness is 200 μm for pure solid fuel and 300 μm for in-porous solid fuel. Most

Table 1 presents our new modeling results obtained for CHGT, which is of special interest. The FST layering time (τform) does not exceed 23 s for D2 fuel and 30 s for D-T fuel. In order to overcome the gravitational fuel sag to the shell bottom, the FST layering uses a moving target that allows avoiding the difficulties inherent in the cryogenic layer formation in the fixed targets. The shell rotation causes a spread of liquid fuel over the inner shell surface, and under certain conditions (sufficient value of τliquid), it results in a uniform layer formation. This important effect makes topical to study a dynamical spread of the liquid fuel inside the moving target and to develop numerical models of the process. The obtained results (theoretical and experimental) can be found in [10, 15].

thin high-Z material such as gold to withstand the thermal chamber

) filled with frozen D-T (261 μm). The

than 2 mm in size).

The FST layering time for several direct-drive target designs was calculated using the computational codes developed at LPI [15].

