2.1. Carbon (C5+) - Hydrogen (H) Collision Cross Sections
Most current fusion reactors employ carbon (C) and tungsten (W) as the primary PFCs. C-PFCs are primarily selected for their exceptional ability to withstand thermal shock and endure out-of-the-ordinary events without melting [
1,
2,
21]. C-PFCs, on the contrary, experience significant erosion due to both physical sputtering and chemical erosion, even at low plasma edge temperatures. The presence of a small amount of carbon in the reactor area, such as a limiter and divertor, due to physical sputtering and chemical erosion, may enhance a variety of inelastic interactions with hydrogen atoms and other impurities, which may affect reactor operation efficiency [
5]. In the previous paper [
5], the ionization and the electron capture cross sections of hydrogen target by C
5+ impact have been discussed using both CTMC and QCTMC models. At low energies, the hydrogen target's total ionization cross section by C
5+ impact was observed to be elevated. Which can be attributed to the prevalence of electron-electron interactions in the low energy region. This claim was confirmed by a reduced version of the Monte Carlo code. Alongside, in this section, we present the electron stripping and the system breakdown cross sections in a
collision, see Equations (27) and (28).
At first, let’s start with electron stripping channel when the projectile increased by one and hydrogen atom remains unchanged after collision, see Equation (27):
Figure 2 illustrates the projectile's total electrons stripping cross section as a function of impact energy within the energy range of 10 keV to 160 keV. This data is crucial for fusion research and has been calculated using both the CTMC and QCTMC models. The probability peak at 55 keV is also seen in
Figure 2. The QCTMC findings show a slight elevation compared to the standard CTMC calculations in the low-energy regions below 100 keV, thereby affirming the significance of the Heisenberg correction term. On the other hand, in the high energy range above 100 keV, when the projectile's energy (velocity) is greater than that of an orbital electron (
), the Heisenberg correction component is minimal (see
Figure 2), which means that the CTMC and QCTMC calculations have roughly similar results, and this can be explained by two factors 1) The Heisenberg potential has less influence as projectile momentum increases, and 2) The Heisenberg potential is inversely proportional to the square of the relative distance between colliders
, see Equation (20). As a result, the
potential contributes in the low-to-medium energy region and is negligible in the high-energy region. However, there were no previous theoretical or experimental data to compare.
Simultaneously, the breakdown channel of the
collision system was defined as:
Figure 3 displays the ionization cross sections of both the target and the projectile using the CTMC and the QCTMC methods, yielding the final state of the four free particles as a function of projectile impact. The peak maxima of the cross section is about 30 keV, indicating that the system breakdown cross sections have a high probability at low energy. Furthermore, in comparison to inelastic processes such as electron stripping, excitation, and electron capture, the
collision system has the lowest probability of system breakdown over a wide energy scale. Similarly, as noticed above, CTMC and QCTMC calculations produce the same results in the high energy region above 100 keV, emphasizing the Heisenberg constraints can be negligible at high energy regime.
2.2. Lithium (Li2+) - Hydrogen (H) Collision Cross Sections
The incredible effects of lithium on a fusion reactor's plasma boundary were initially observed in a tokamak operating in limiter mode without a divertor [
22]. It has been found that the energy confinement duration of the discharge in [
22,
23] a keV temperature plasma edge was significantly enhanced by the pulses that were preceded by lithium pellet injections [
22,
24]. In addition, lithium has become increasingly recognized as a potential solution to combating divertor heat flux issues within fusion reactors, as ionized lithium atoms form highly radiative plasma layers which could significantly decrease heat flow into divertors surfaces [
25,
26,
27,
28,
29,
30]. As it happens, evaporated lithium in its ionic form (partially stripped ions) combined with hydrogen, carbon, and oxygen atoms increased the possibility for inelastic collisions between multiply charged ions and neutral atoms - stimulating inelastic collision research not only out of general scientific curiosity but also as essential tools in fusion-related research [
5]. The interaction between ions and H-target, for instance, have a vital role in determining radiation losses, beam penetration efficiency (ionization rate), and reducing the heat flux to the divertor surfaces [
29] in tokamak plasmas. In this section, we present the total cross sections of the electron stripping, the electron captures of the target, the electron captures of the projectile, and the system breakdown in a
collision system, see Equations (29)–(32).
At first, let us commence by discussing the electron stripping channel, wherein the projectile charge is incremented by one while the hydrogen target remains unchanged after the collision, see Equation (29):
Figure 4 illustrates the electron stripping cross section in a
collision as a function of impact energy using CTMC and QCTMC calculation methods. The electron stripping cross sections were fitted by Gaussian curves. The peak maxima appear at 30 keV and this can be explained by using basic kinematic picture. During the collision, at low impact energy, the projectile overlaps with the target atom and remains close to the target for an extended period of time, increasing the possibility of electro stripping process owing to the increased probability of interaction among ionic cores, electrons, and ionic cores-electrons (slow-collision). Furthermore, the QCTMC results, as expected, are greater than the regular CTMC results, this observation clearly illustrates the impact of the quantum correction term in the low energy regime. For high-energy regime, above 100 keV, both the CTMC and QCTMC models provide identical results due to the fact that the Heisenberg correction term influence decrease as the projectile momentum increases. Our model has been validated against both experimental and theoretical calculation approaches [
5,
9,
14,
15], despite the absence of any previous data for comparison with present calculation.
Simultaneously, we considered the electron capture of the target cross section, see Equation (30):
Figure 5 depicts the electron capture cross section of the target in a
collision as a function of impact energy using both CTMC and QCTMC calculation methods. The probability peak at 60 keV is also seen in
Figure 5. However, according to our expectation, the QCTMC results are slightly higher than typical CTMC calculations, emphasizing the role of the Heisenberg correction term at low energy regime. At high energy region, the CTMC and QCTMC results are roughly the same.
Similarly, as in the case of the electron capture of the target, we also calculated the electron capture cross section of the projectile, as described in Equation (31):
Figure 6 depicts the electron capture cross section of the projectile as a function of impact energy between 0.1 keV to 400 keV using CTMC and QCTMC methods. The probability peak appears at 160 keV. At low to intermediate energy regions, the QCTMC results are higher than the CTMC data, indicating the relevance of quantum features in enhancing cross section results, particularly at low energy regime. On the other hand, in the high energy area, both QCTMC and CTMC produce the same results, demonstrating that the Heisenberg correction term can be insignificant in this energy zone as mentioned earlier. Furthermore, as we noticed, the probability of the electron capture process for the projectile in a
collision is dominant and this can be justified by considering the nuclear charge effect, when the nuclear charge increase, the capability to attract high-velocity electrons increases.
Finally, the breakdown channel of the
collision system was defined as:
Figure 7 shows the complete break of the
collision system as a function of impact energy using both QCTMC and CTMC calculation models. The peak maxima of the cross section is about 10 keV. As we expected, QCTMC improves the cross section results at low energy regime.