3.5 HTSC-driving body

The driving body is a component of the HTSC-sabot (Figure 7). In our study, we consider a superconductor on the basis of MgB2-cables because of its potential for applications at high magnetic field [28, 29]. However, under using MgB2-driving

#### Figure 14.

HTSC-sabots with several detached wings. In (a) and (b): overview of model #4 and model #5; in (c) and (d): acceleration (T = 80 K) of the different components of model #4 (1—hollow parallelepiped, 2—wing) along the magnetic track 3 by the field coil 4.

#### Figure 15.

Levitation of the model #4 and model #5 at T = 80 K. In (a): lack of levitation for the model #4 (its motion is caused by a magnetic track inclination, that is, by gravity under the inclination angle less than 10°); in (b): the same HTSC-sabot (model #4) levitates just on a Gd123 tape (i.e., model #5 levitates stably).

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

body, the acceleration parameters which are of interest for IFE (injection velocity Vinj = 200 m/s) become unsuitable for the laboratory-scale tests. Therefore, the POP experiments (Figure 8) have been carried out with HTSC-sabots (Gd123) without any MgB2-coils in their design. The HTSC-sabot (Model #2) is accelerated using the magnetic field B1 generated by the field coil (ARP). The acceleration process maintenance is caused by the surface currents induced in the bulk Gd123 itself due to ARP, which results in arising the driving force along the acceleration length. The HTSC-sabot obtains a velocity of 1 m/s and keeps it over the whole magnetic track (22.5 cm). This is a demonstration of the one-stage accelerator.

Below, we discuss the issue related to a multiple-stage accelerator. The first problem is as follows: what characteristics of MgB2-cables are required to reach the required lower limit on the injection velocity Vinj = 200 m/s. We list below some distinguish features of MgB2, which are important for our study [28, 29]:


For estimations of the acceleration length, La, for a multiple-stage accelerator with a superconducting driving body (in our case MgB2-cables), we use the following ration [8]:

$$L\_{\rm at} = \frac{\pi}{2} \cdot V\_{\rm inj}^2 \cdot \frac{R\_{\rm FC}}{R\_{\rm SC}} \cdot \frac{M\_{\rm sab}}{F\_{\rm pin} V\_{\rm S}}, \\ F\_{\rm pin} = J\_C(B\_0, T\_{\rm S}) \cdot B\_0,\tag{4}$$

where Msab is the mass of the "HTSC-sabot + target" assembly, RFC is the field coil radius, RSC is the radius of the superconducting coils (RFC/RSC = 5), Fpin is the pinning force density, JC is the critical current density, which depends on the magnetic induction in the coil center B0 and superconductor temperature TS. The value of JC (defined as the current density where the pinning force and the Lorentz force become equal) determines the onset of resistivity [28–30]. In (4), a difficulty arises in calculation of La because only knowing the relationship between JC and B0,

• Model #5, "hollow parallelepiped + 5 wings" on a Gd123 tape

superconducting material becomes less and less diamagnetic.

): total mass is 1.97 g.

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Nevertheless, Figure 15a shows that the Model #4 (the Model #2 in assembly with five wings) as an independent target carrier is inefficient. The wings keep the Model #4 "nonlevitated" so that it comes into contact with the magnetic track. However, if using the same Model #5 (the Model #4 placed on a superconducting Gd123 tape), the levitation effect occurs again (Figure 15b), because the Model #5 is a combination of the levitating Gd123 tape and the Model #4 as a

These results can be explained by a special mapping of the magnetic lines which are bending around the Model #4 creating the magnetic field close to the second critical value, BC2, or even more this value (T = 80 K is close to TC = 92 K). At a step-like surface relief (critical bending of the magnetic lines), the magnetic field is able to considerably slip through the HTSC material of the Model #4, and the normal cores of vortexes begin to adjoin and then the volume superconductivity disappears. In other words, under roughening of a surface, the number of vortices becomes so numerous that there is no space left for superconductivity, and the

The driving body is a component of the HTSC-sabot (Figure 7). In our study, we consider a superconductor on the basis of MgB2-cables because of its potential for applications at high magnetic field [28, 29]. However, under using MgB2-driving

HTSC-sabots with several detached wings. In (a) and (b): overview of model #4 and model #5; in (c) and (d): acceleration (T = 80 K) of the different components of model #4 (1—hollow parallelepiped, 2—wing) along

Levitation of the model #4 and model #5 at T = 80 K. In (a): lack of levitation for the model #4 (its motion is caused by a magnetic track inclination, that is, by gravity under the inclination angle less than 10°); in (b): the

same HTSC-sabot (model #4) levitates just on a Gd123 tape (i.e., model #5 levitates stably).

(35 <sup>12</sup> 0.3 mm<sup>3</sup>

load capacity.

3.5 HTSC-driving body

Figure 14.

Figure 15.

70

the magnetic track 3 by the field coil 4.
