Recent Publications

Nonlinear polarization effects on plasma screening for thermonuclear reactions

Hanxiang Huang, Binbing Wu, Zhengfeng Fan, Congzhang Gao, Jie Liu, Baisong Xie

We investigate two-center plasma screening effects on thermonuclear reactions of D-T, p-$^{11}$B, and $^{12}$C-$^{12}$C, spanning from classical to degenerate regimes. The two-center screening potential is obtained within a finite-temperature Thomas-Fermi-Dirac framework, capturing two-ion correlations as the leading-order many-body effect. Combining the resulting screened Coulomb potential with a complex Woods-Saxon nuclear potential, we solve the stationary Schrödinger equation to obtain the fusion tunneling probabilities and the corresponding reaction rates. Compared to Debye-Hückel results, the present screening potential is stronger in weakly coupled and weakly degenerate regimes but weaker in strongly coupled and strongly degenerate regimes. Consequently, the fusion enhancement factors are amplified in the former but suppressed in the latter. An underlying interplay between two mechanisms is identified: the nonlinear polarization of ions tends to reduce the screening effect, whereas the nonlinear polarization of electrons tends to enhance it. This subtle competition is governed by the plasma coupling strength and degeneracy. These findings highlight that a two-center treatment is important for predicting fusion rates in dense plasmas.

Parameter Scan of Multi-Fluid Equilibria in Rotating p-11B Plasmas: Effects on Fusion Power and Bremsstrahlung Losses

Xingyu Li, Huasheng Xie, Lai Wei, Zhengxiong Wang

We present VEQ-MF, a fast spectral parameter-scan framework for two-dimensional axisymmetric multi-fluid equilibria with prescribed species-dependent toroidal rotation. The solver couples generalized Boltzmann density responses, quasineutral electrostatic polarization, and a generalized Grad--Shafranov equation, extending reduced-parameter Grad-Shafranov and VEQ formulations to multi-species rotating equilibria. Rotating $p\text{-}^{11}\text{B}$ spherical-tokamak configurations are used as a demanding test case. Independent scans of the proton and boron rotation frequencies are performed in EHL-2 and EHL-3B geometries. The computed fields are then post-processed to obtain fusion power from a drift-Maxwellian reaction-rate coefficient and bremsstrahlung power from an analytical radiation model. Three in-range EHL-3B finite-difference benchmarks give global stored-energy, bremsstrahlung-power, and fusion-power differences of $1.7$--$3.4\%$, while a representative convergence check shows sub-percent sensitivity to increasing the spectral-parameter number and negligible sensitivity to Gaussian-grid refinement. The core equilibrium solve remains fast for repeated scans, with representative nonzero EHL-3B cases requiring $0.032$--$0.050$~s per point in MATLAB, excluding post-processing, interpolation, plotting, and file export. The scans identify two competing multi-fluid effects. Under iso-rotation, outward boron accumulation increases the volume-integrated $n_e^2$, so the fusion-to-bremsstrahlung power ratio $\mathcal{R}_{\mathrm{fb}}$ decreases with increasing rotation. Species-dependent toroidal rotation weakens centrifugal polarization and lowers bremsstrahlung power, while the relative toroidal flow in the larger EHL-3B geometry raises the drift-Maxwellian reaction-rate coefficient and thereby modifies fusion power.

Alpha particle generation and confinement in D-3He scenarios in JT-60SA

R. Coelho, Ye.O. Kazakov, R. Novara, M. Nocente, K. Särkimäki, A. Snicker, S. Sipilä, J. Garcia

Università di Milano-Bicocca, VTT Technical Research Centre of Finland, Instituto Superior Técnico, Universidade de Lisboa, LPP-ERM/KMS, Aalto University

Future fusion reactors will rely on a significant fraction of self-heating by fusion born alpha particles coming from the DT plasma fuel mix. Understanding alpha particle generation and confinement is therefore critical and, in anticipation of ITER, should be subject to thorough research. Experimentally, however, no current large device can operate with DT fuel and therefore alternative schemes for alpha particle generation come into play. Since DT operation is not foreseen in the scientific exploitation of JT-60SA, a fusion scheme relying on 3 He seeding and highly energetic 500 keV neutral beam is proposed similarly to what has been used in other devices such as JET although in there the original ∼100 keV scale beam ions were further accelerated using RF waves. In this work we investigate the generation and confinement of alpha particles stemming from this 3 He + NBI scheme, taking the forthcoming OP2 and future hybrid scenarios as reference plasmas. We will show that owing to the high-energy N-NBI system on JT-60SA, significantly higher values of alpha/neutron production rates can be achieved when considering similarly scoped experiments on JET while using significantly lower 3 He concentrations. Loss power and particle rates will also be discussed and optimised alpha birth rates shown for specific variants performed on the hybrid scenario where plasma density, position and temperature were varied at constant plasma current and magnetic field.

Development of a Reduced Multi-Fluid Equilibrium Model and Its Application to Proton-Boron Spherical Tokamaks

Hua-Sheng Xie, XingYu Li, Jiaqi Dong, Zhiwei Ma, Yunfeng Liang, Yuejiang Shi, Wenjun Liu, Yueng-Kay Martin Peng, Lai WEI, Zheng-Xiong Wang, et al.

ENN Science and Technology Development Co., Ltd, Dalian University of Technology, Beijing VeloAlpha Technology Co., Ltd, Southwestern Institute of Physics, Zhejiang University

Proton-Boron (p-$^{11}$B) fusion represents a promising pathway toward aneutronic clean energy but requires extremely high ion temperatures and robust magnetic confinement. Spherical Tokamaks/Torus (ST) driven by high-power neutral beam injection are a primary candidate for this regime. In such devices, the combination of strong toroidal rotation and the significant mass disparity between protons and boron ions leads to complex multi-fluid effects---specifically centrifugal species separation and electrostatic polarization---which standard single-fluid magnetohydrodynamic (MHD) models fail to capture. Conversely, comprehensive multi-fluid models that include poloidal flows often suffer from numerical stiffness and excessive complexity, hindering their use in routine engineering analysis. To address these challenges, we have developed a \textit{reduced multi-fluid equilibrium model} designed to balance physical fidelity with computational robustness. By retaining the dominant toroidal rotation and self-consistent electrostatic potential while neglecting secondary effects such as poloidal flow inertia and pressure anisotropy, the model is formulated as a generalized Grad-Shafranov equation coupled with species-specific Bernoulli relations and a quasi-neutrality constraint. The model is applied to analyze the equilibrium configurations of two representative p-$^{11}$B ST devices designed by the ENN Group: the experimental EHL-2 and the reactor-scale EHL-3B. Simulation results demonstrate that the equilibrium modification is governed by the ion Mach number ($M$). In the low-rotation regime ($M < 0.5$), multi-fluid effects are weak, and the solution converges toward the single-fluid limit. However, in the high-rotation regime ($M > 2$), strong centrifugal forces drive significant boron accumulation at the low-field side (LFS) and generate an internal electrostatic potential on the order of 10 kV. These results confirm the necessity of multi-fluid modeling for accurate p-$^{11}$B reactor design within the assumptions quantified in this work.

Experimental observation and integrated modelling of proton-beryllium fusion in He and D plasmas at JET

Žiga Štancar, Jacob Eriksson, James Oliver, Vasily Kiptily, Sean Conroy, Aljaz Cufar, Anders Hjalmarsson, Yevgen Kazakov, Zamir Ghani, Marina Gorelenkova, et al.

United Kingdom Atomic Energy Authority, Uppsala University, Jožef Stefan Institute, Ecole Royale Militaire, Princeton Plasma Physics Laboratory

Validated integrated modelling of JET ITER-like wall experiments in which fusion performance is driven by reactions between fast ions and intrinsically present metal wall impurities is presented. A steady-state L-mode plasma with dominant proton-beryllium fusion and neutron yields of up to ≈ 6·10 13 s -1 is developed in He and D, via radiofrequency heating of a H minority. The fusion drive is unambiguously confirmed by the neutral particle analyser, fast ion loss detector, and γ-ray diagnostics. Experiments are analysed via an integrated modelling framework, developed to model the two-stage proton beryllium-fusion chain and produce high-fidelity fusion product source terms. The modelling chain comprises TRANSP and JETTO for plasma core modelling, LOCUST for full orbit product tracking and collisional slowing-down, DRESS to resolve two- and three-body fusion kinematics, and MCNP for neutron transport calculations. Modelling shows that the primary 9 Be(p,n) 9 B reaction is the dominant neutron emitter at naturally present concentrations of beryllium in these experiments. The yield contribution of secondary reactions between fusion products and beryllium, 9 Be(d,n) 10 B and 9 Be(α,n) 12 C, is found to be negligible. The proton-deuteron knock-on effect in D plasmas is modelled, which is calculated to contribute ≈ 25 % to the total neutron yield. For both He and D discharges the total computed neutron rates match fission chamber measurements within the combined experimental and computational uncertainty, with an average discrepancy of ≈ ± 20 %. Realistic proton-beryllium neutron sources are propagated through JET's MCNP neutron transport model which shows that 235 U fission chambers' response is sensitive to p-Be source changes, with up to ≈ 10 % variation compared to a D-D neutron source. We show that the high-energy tail of the fast proton minority can be studied with multi-foil neutron activation. The framework is also applied to the study of interactions between fast protons and boron impurities, of relevance to ITER. We calculate that in JET conditions a significant alpha source with DT-like energies could be generated through 11 B(p,α)2α, and detected via γ-emission in secondary interactions between fast alphas and boron. The work represents an important step towards validating predictive integrated modelling capabilities for non-standard fusion reactions.