arXiv subjects

R. Perillo

Publications and source records attributed to R. Perillo.

2 recordsLinked to original sources

arXiv2026

Overview of Enhanced D-alpha and Quasi Continuous Exhaust H-modes at DIII-D

We review the Enhanced D-alpha (EDA) and Quasi-continuous Exhaust (QCE) H-modes that have recently been achieved in the DIII-D tokamak. These scenarios are free of large type-I edge-localized modes (ELMs) and achieved at high fueling compatible with divertor detachment. This makes them promising operational regimes as ELMs are a major risk for fusion pilot plants (FPPs). Access to EDA H-mode and the associated quasi-coherent mode (QCM) was observed at low heating power barely above the L-H power threshold, and increased density enabled access to EDA H-mode even at higher heating powers. The QCE H-mode was achieved at simultaneously high density and heating power, characterized also by a QCM and small ELMs with transient peaks of the total power into the divertor below about 3MW, in line with observations at ASDEX Upgrade. During the QCE H-mode, the turbulence parameter alpha_t at the separatrix is about 1 and does not separate ELMy or EDA from QCE H-modes well. Peeling ballooning stability calculations suggest that the EDA H-mode pedestal is limited by transport far away from ideal magnetohydrodynamic instability, and the QCE H-mode pedestal operates close to the ballooning branch of the stability boundary. BOUT++ simulations qualitatively reproduce the pressure collapse characteristics of the different regimes and suggest an important role of n ~ 50 resistive ballooning modes localized near the separatrix at the X-point during EDA and QCE H-modes. This work provides a foundation and guidance for further research on the access conditions and physics mechanisms of EDA and QCE H-modes necessary for the extrapolation of these regimes towards an FPP.

physics.plasm-ph↗

arXiv2026

First step toward multi machine ELM energy scalings and extrapolations to SPARC and ITER

It is shown that the ELM energy loss normalized by the plasma stored energy (ΔEELM/Wplasma) for high-density small/QCE ELM regimes scales inversely with the separatrix turbulence parameter a_t. In contrast, the neoclassical electron collisionality at the pedestal top, nu*e,neo, expected to regulate ΔEELM/Wplasma according to the Loarte scaling (Plasma Phys. Control. Fusion 2003 45 1549), does not adequately capture ΔEELM/Wplasma data for peeling-ballooning-limited type-I ELMs and ballooning-limited small/QCE ELMs, limiting its applicability for extrapolation to one scenario window. A multi-machine database including seven tokamaks and with ΔEELM/Wplasma ranging from 0.5% to 14%, has been analyzed. A regression analysis on only type-I ELMs yields ((ΔE_ELM)/W_plasma )_(Type-I ) [%]=6.8*T_(e,ped)^0.03 n_(e,ped)^(-0.4) \k{appa}^(-0.4) R_major^0.4, corresponding to ΔEELM/Wplasma =4.5% for nominal SPARC pedestal parameters and 12% for the ITER D-T Q=10 scenario. For the small/QCE ELM class, however, as a_t increases, the pedestal moves toward a ballooning-limited boundary, the toroidal mode number increases, the ELM frequency rises following the scaling f_ELM=46e^((2.25*a_t)), and ΔEELM/Wplasma decreases via the relation (ΔE_ELM)/W_plasma [%]=1.6e^(-(α_t/2)). For SPARC QCE-relevant a_t=0.86 and ITER high-fueling scenario a_t = 0.64, the scaling favorably predicts ΔEELM/Wplasma of 1.0% and 1.2%, respectively, with values below 1% if the small/QCE ELM regime is pushed beyond a_t >1. The small/QCE ELM-fitted results represent an initial step toward future analysis on broader datasets, which will be necessary to improve the accuracy of projections for future reactor-relevant scenarios.

physics.plasm-ph↗