Local transport in Joint European Tokamak edge-localized, high-confinement mode plasmas with H, D, DT, and T isotopes

Abstract

The edge-localized, high-confinement mode regime is of interest for future Tokamak reactors since high performance has been sustained for long durations. Experiments in the Joint European Tokamak [M. Keilhacker et al., Nuclear Fusion 39, 209 (1999)] have studied this regime using scans with the toroidal field and plasma current varied together in H, D, DT, and T isotopes. The local energy transport in more than fifty of these plasmas is analyzed, and empirical scaling relations are derived for energy transport coefficients during quasi-steady state conditions using dimensionless parameters. Neither the Bohm nor gyro-Bohm expressions give the shapes of the profiles. The scalings with β and ν* are in qualitative agreement with Ion Temperature Gradient theory.

Size Scaling of Turbulent Transport in Magnetically Confined Plasmas

“…As we increase the device size further (up to a = 1000ρ i ), there is a gradual transition from Bohm-like scaling to gyro-Bohm scaling. Interestingly, recent transport studies of the JET tokamak [8] and a scan of power thresholds for the formation of internal transport barriers [20] show a similar trend. These findings show that extrapolations from present-day experiments to larger devices based on empirical scalings or mixing length rules can be unreliable.…”

“…In particular, dimensionless scaling studies on the DIII-D tokamak found that ion transport and energy confinement time exhibit Bohm-like behavior, while fluctuation characteristics suggest a gyro-Bohm scaling [7] for transport. In the high confinement regime (H-mode), transport scalings have been reported to be either Bohm [8] or gyro-Bohm in limited operational parameter space [6]. The uncertainty here may, in part, reflect the difficulty in varying ρ * while keeping all other dimensionless parameters fixed (e.g., Mach number of toroidal rotation in H-mode).…”

Validation metrics for turbulent plasma transport

“…Verification and validation of the various codes and models used in these power balance calculations are challenging exercises in their own right, and it is essential to always bear in mind that the lack of direct measurements of local fluxes is a significant constraint on the validation of these tools. However, through combinations of extensive verification exercises, 95 global cross-checks (e.g., comparisons of predicted and measured neutron production rates to constrain fast ion densities injected by neutral beams [96][97][98] or hard X-ray emissions associated with interactions between fast electrons and lower hybrid, electron cyclotron, and ion cyclotron waves [99][100][101] ) and comparisons with both measured changes in equilibrium profiles [102][103][104][105][106] and core fluctuations, 107,108 quantitative confidence in these models to a fairly high level has been established for many operating conditions of interest. Nonetheless, power balance analyses are still subject to significant aleatory (i.e., statistical) and systematic uncertainties.…”

The 2008 Public Release of the International Multi-tokamak Confinement Profile Database

“…mass on confinement to be studied (#42794, #42997, #43002, #43134 and #43452) [52,53]. The scaling of confinement with ρ * was studied in dedicated experiments on JET.…”

“…Forty JET discharges are included in PR08, covering a wide range of confinement regimes: ELMy H-mode plasmas with broad ranges of parameters [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]; hybrid scenarios [56,58,59]; and plasmas with ITBs [60][61][62][63][64][65][66][67][68][69][70][71]. The PR08 JET discharges include examples of high performance ITER-relevant operation: H-mode scenarios at high magnetic fields and high plasma currents close to the Greenwald density limit n G ; DT plasmas with high fusion performance; and ITB discharges with high fractions of non-inductively driven plasma current and quasi-stationary operation.…”