Characterization of energy confinement in net-current free plasmas using the extended International Stellarator Database

Abstract

International collaboration on development of a stellarator confinement database has progressed. More than 3000 data points from nine major stellarator experiments have been compiled. Robust dependences of the energy confinement time on the density and the heating power have been confirmed. Dependences on other operational parameters, i.e. the major and minor radii, magnetic field and the rotational transform , have been evaluated using inter-machine analyses. In order to express the energy confinement in a unified scaling law, systematic differences in each subgroup are quantified. An a posteriori approach using a confinement enhancement factor on ISS95 as a renormalizing configuration-dependent parameter yields a new scaling expression ISS04; . Gyro–Bohm characteristic similar to ISS95 has been confirmed for the extended database with a wider range of plasma parameters and magnetic configurations than in the study of ISS95. It has also been discovered that there is a systematic offset of energy confinement between magnetic configurations, and its measure correlates with the effective helical ripple of the external stellarator field. Full documentation of the International Stellarator Confinement Database is available at http://iscdb.nifs.ac.jp/ and http://www.ipp.mpg.de/ISS.

Effect of Neoclassical Transport Optimization on Electron Heat Transport in Low-Collisionality LHD Plasmas

“…The enhancement factor shows an inverse dependence on the effective helical ripple. This tendency is consistent with the recent global confinement study in stellarators [13], where the effective helical ripple dependency of the global confinement time has been shown including the experimental results by several helical devices.…”

Extended estimations of neoclassical transport for the TJ-II stellarator: The bootstrap current

“…They are also in agreement with a predictive transport code [39] using the plasma profiles, absolutely calibrated H α signals and EIRENE code simulations to estimate flux surface averaged particle sources [40]. The fair agreement found between the neoclassical energy confinement time and the International Stellarator Scaling ISS04 [41] points to the importance of the neoclassical channel for the TJ-II. The procedure implemented in this work to correct the bootstrap estimation given by Eq.…”

Effect of pressure-driven MHD instabilities on confinement in reactor-relevant high-beta helical plasmas

“…Figure 1 shows the normalized global energy confinement time by the ISS04 empirical scaling 19 as the function of hbi. Here, the normalized one is defined as an improvement factor, H ISS04 , and hbi is a volume averaged beta value based on the diamagnetic measurements.…”

“…Here, the normalized one is defined as an improvement factor, H ISS04 , and hbi is a volume averaged beta value based on the diamagnetic measurements. 18 According to our previous research, 20 it looks that the degradation of the global energy confinement time scaling can be explained by taking the renormalization factor induced in the newer empirical global energy confinement scaling (ISS04), 19 which is reflected to the difference of geometrical effects like magnetic configurations except for an averaged rotational transform value (especially difference of magnetic axis positions in LHD), into account. However, according to local thermal transport analysis taking the geometrical effects into account, 20 the degradation of the thermal transport property is observed in the peripheral region as the beta increases in LHD.…”