Daniel A. Burgess

This work presents the compact experimental negative triangularity (NT) reactor (CENTAUR), a low overnight cost, high-field tokamak, breakeven reactor design, achieving a predicted total fusion power of 40 MW and scientific energy gain of 1.3. Ballooning stability calculations confirm that the device’s pedestal is within the first stability regime, which is consistent with the expected ELM-free operation associated with NT plasmas. The geometry of the NT divertor allows for high fraction of radiated power (13.5 % ) between the separatrix and plasma facing components. Heat transport modeling based on simulations of the edge region show heat loads into plasma facing components well below material limits. The magnet system employs rare-earth barium copper oxide high-temperature superconductors in 18 toroidal field coils, an hourglass-shaped central solenoid, and six poloidal field coils to support high-field ( B 0 = 10.9 T) plasma confinement, shaping, and current drive. Neutronics analysis shows that a 12 cm B 4 C shield keeps superconducting magnet heating below the 33 K quench limit during 10 s, 40 MW DT pulses. With this shielding, the modeled fluence indicates HTS components can survive more than ten times the 3000-pulse design lifetime. Iteration of economic analysis in tandem with the technical design process allows CENTAUR to achieve its overnight cost goal of $2 billion US determined using a custom costing model that predicts a total overnight cost of 1.6 B ± 0.2 B US.

This work reports on DIII-D experiments aimed at extending resonant magnetic perturbation (RMP) suppression of edge localized modes (ELMs) to n = 1 fields, where n is the toroidal mode number. Modeling of the 3D ideal MHD plasma response to the RMPs using the GPEC code is used to quantify edge and core resonant fluxes, guiding experimental strategies to increase plasma resilience against core error field penetration, optimize multi-coil phasing, and explore higher q 95 operation. In DIII-D, ELM mitigation is regularly observed across a wide range of n = 1 RMP scenarios. A ∼ 100 ms phase of complete ELM suppression was achieved at q 95 ∼ 3.9 using an odd-parity coil configuration. The suppressed phase exhibited clear signatures of RMP ELM suppression, including the elimination of D α spikes, increased pedestal rotation, enhanced magnetic response, and elevated broadband density turbulence. An optimized coil configuration for edge-to-core resonant flux did show increased edge resonance indicated by increased density pumpout, but did not yield RMP ELM suppression. At q 95 ∼ 5.1 , a bifurcation to a grassy-like ELM regime occurred, while large type-I ELMs persisted. These results demonstrate progress in experimental access to n = 1 RMP ELM suppression in DIII-D, motivating further study for robust access. This work also highlights the potential role of 3D edge stability as well as rational surface alignment in RMP ELM suppression access, which has important implications for the use of low- n RMPs in future reactor-scale devices.

A new classical tearing mode (TM) stability simulation workflow has been developed that solves the resistive inner-layer equations in a plasma slab to yield a linear, quasi-toroidal TM growth rate γ and mode rotation frequency ω . This workflow combines two-fluid and drift MHD effects in a slab approximation of the resistive inner layer (SLAYER) with an effective tearing stability index as Δ ( γ , ω ) = Δ ′ − Δ crit . SLAYER is used to calculate the inner-layer Δ ( γ , ω ) , the STRIDE code is used to calculate a toroidal Δ ′ that includes shaping effects, and the toroidal Δ crit incorporates effects of thermal conduction on Glasser stabilization. This workflow is rapid and numerically robust across reactor-relevant plasma conditions, and yields growth rates that closely align with analytic predictions in well-documented linear growth rate regimes. Using synthetic equilibria, TM stability was calculated across scans of plasma β , inverse aspect-ratio, and toroidal current profile gradient. These scans effectively benchmarked this STRIDE+SLAYER workflow against existing models and showed reliable stability predictions in shaped H-mode-like plasmas. This capability to quickly and robustly predict classical tearing stability in tokamaks will facilitate the mapping of TM stable operational regimes and design of safe discharge trajectories in future devices.

HAWC J1826−128 is one of the brightest Galactic TeV γ-ray sources detected by the High Altitude Water Cherenkov (HAWC) observatory, with photon energies extending up to nearly ∼100 TeV. This HAWC source spatially coincides with the H.E.S.S. TeV source HESS J1826−130 and the “Eel” pulsar wind nebula (PWN), which is associated with the GeV pulsar PSR J1826−1256. In the X-ray band, Chandra and XMM-Newton revealed that the Eel PWN is composed of both a compact nebula (∼15″) and diffuse X-ray emission (∼6′ × 2′) extending away from the pulsar. Our NuSTAR observation detected hard X-ray emission from the compact PWN up to ∼20 keV and evidence of the synchrotron burn-off effect. In addition to the spatial coincidence between HESS J1826−130 and the diffuse X-ray PWN, our multiwavelength spectral energy distribution (SED) analysis using X-ray and γ-ray data establishes a leptonic origin of the TeV emission associated with the Eel PWN. Furthermore, our evolutionary PWN SED model suggests (1) a low PWN B-field of ∼1 μG, (2) a significantly younger pulsar age (t ∼ 5.7 kyr) than the characteristic age (τ = 14.4 kyr), and (3) a maximum electron energy of E max = 2 PeV. The low B-field, as well as the putative supersonic motion of the pulsar, may account for the asymmetric morphology of the diffuse X-ray emission. Our results suggest that the Eel PWN may be a leptonic PeVatron particle accelerator powered by the ∼6 kyr old pulsar PSR J1826−1256 with a spin-down power of 3.6 × 10³⁶ erg s⁻¹.