Page 1 - Fusion reactivity of the pB11 plasma revisited

International Atomic Energy Agency Nuclear Fusion Nucl. Fusion 59 (2019) 076018 (9pp) https://doi.org/10.1088/1741-4326/ab1a60
Fusion reactivity of the pB11 plasma revisited
S.V. Putvinskia, D.D. Ryutov and P.N. Yushmanov TAE Technologies, Foothill Ranch, CA, United States of America E-mail: putvins@tae.com
Received 18 January 2019, revised 28 March 2019 Accepted for publication 17 April 2019
Published 4 June 2019
Abstract
Fusion reactivity for the pB11 fuel has been reassessed for magnetic confinement devices. This study is based on two factors: new measurements of the fusion reaction cross-sections and an accounting of the kinetic effects that lead to the increase of the number of protons at higher energies (with respect to a pure Maxwellian). The net effect leads to an approximately 30% increase of the fusion yield for the same global plasma parameters compared to the previous assessments.
Keywords: nuclear fusion, pB11, reactivity, kinetic effects (Some figures may appear in colour only in the online journal)
1. Introduction
The fusion systems with pB11 fuel have significant advantages over the systems based on DT or DD fuels in that the neutron production in the former is orders of magnitude lower than in the latter two. In addition, the fuel components, p and B11, are readily available and no breeding of the reaction components is needed. One more fuel with a low neutron flux is DHe3. However, even though the neutron flux is reduced compared to the DT fuel, it remains significant due to DD reactions and secondary DT reactions. Moreover, terrestrial resources of He3 are scarce and it may have to be transported from the Moon, where it is present in the surface layers of regolith [1]. This explains a continuing interest to the magnetic confine- ment schemes based on the pB11 fuel [2, 3], notwithstanding difficulties associated with this approach and briefly men- tioned later in section 2. 11
The main difficulty for the pB11 fuel is actually related to high ion temperatures needed to reach this high reactivity. The electrons then become also quite hot, leading to intense bremsstrahlung radiation. This circumstance has led the authors of earlier analyses (e.g. [4–6]) of the power balance in pB11 plasma to rather pessimistic evaluation of the prospects of this fuel. In particular, it has been concluded in [5] that ‘Bremsstrahlung radiation prevents ignition in p-B11’.
This conclusion has been reached on the basis of the cross- sectional data that were available at the time of publications. Since then, a progress in the instrumentation, together with a correct identification of the orbital momentum of the pri- mary alpha-particle as l = 3 [7–9] have led to a re-evaluation of the cross-sectional data. These new data yielded about 20 percent higher reactivity for Maxwellian plasmas in the rel- evant temperature range, 300–400keV, see figure 5 in [9]. In our paper these improved data will be folded into analysis. In particular, the curve for p11B in figure 1 was obtained based on these new data.
Furthermore, we shall account for the fact that the proton distribution may deviate from the Maxwellian in the energy range that makes the main contribution to reactivity. We shall calculate fusion yield by using a proton distribution found from solution of the kinetic equation. The Boron distribu- tion is considered to be very close to Maxwellian because the cross-section for BB collisions scales as Z4 and is 625 times larger than that of protons.
fuel is not useful because of low reactivity. This is, however, a misconception: reactivity of pB11 fuel, although being by a factor of a few lower than that for DT, is still higher than that for DD and DHe3. If comparing the parameter ⟨σv⟩ Y (with ⟨σv⟩ being a reaction rate averaged over the Maxwellian distribution and Y being a fusion reaction yield), the result becomes even more favorable for pB11. This is illustrated in figure 1 that compares fusion reactivities of Maxwellian plasmas times the energy
yield Y of fusion reactions.
a Author to whom any correspondence should be addressed.
There is a widely shared opinion that pB
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