Dependence Of Energy Confinement Time Research Articles

Experimental energy confinement time scaling with dimensionless parameters in C-Mod I-mode plasmas

The dependence of energy confinement time on gyroradius, , and normalized collisionality in I-mode plasmas is investigated through dedicated C-Mod experiments scanning dimensionless parameters with constant safety factor. The gyroradius scaling is calculated to be , which suggests core transport may scale with gyro–Bohm physics, indicating favorable extrapolation of the I-mode regime to future devices at low . The scaling exponent for is calculated to be small, but positive (), and the exponent for is deemed inconclusive () due to high correlation with the other two dimensionless variables in the dataset, and therefore requires further investigation. The individual dimensionless parameter scaling is compared to calculations from larger C-Mod I-mode datasets as well as multi-machine scaling laws for ELMy H-mode and L-mode plasmas. Multiple regression techniques and principal component analysis are used to clarify the single parameter scalings and analyze parameter significance within the dataset.

Effects of internal inductance on the energy confinement time by using the solution of equilibrium problem

In this work, dependence of energy confinement time on plasma internal inductance has been studied by using the solution of Grad–Shafranov equation (GSE) for circular cross-section HT-7 tokamak. For this, the Shafranov parameter (asymmetry factor) and poloidal beta were obtained from solution of GSE. Then we can find the dependence of energy confinement time, on plasma internal inductance. It is observed that the maximum energy confinement time is related to the low values of internal inductance [Formula: see text].

ELMy H-mode confinement and threshold power by low hybrid wave on the EAST tokamak

Stationary type-III ELMy H-mode plasmas were achieved on Experimental Advanced Superconducting Tokamak (EAST) by low hybrid wave in 2010. The threshold power increases with plasma density, and a significant reduction in the H-mode occurs by decreasing the distance between the X-point and the strike point at the outside lower divertor on EAST. A series of statistics for the H-mode confinement such as the dependence of energy confinement time (τE) on plasma density and loss power is experimentally studied in detail.

Dependence of energy confinement time on toroidal magnetic field in the TUMAN-3M tokamak

The influence of toroidal magnetic field on the energy confinement time τE in the ohmic H-mode has been studied in the TUMAN-3M tokamak with low magnetic field. The experiments were performed at a toroidal magnetic field of BT = 0.68−1.0 T, which is about twice as large as that (0.25–0.5 T) studied in analogous experiments on the NSTX and MAST spherical tokamaks. The results are indicative of a strong dependence of the energy confinement time on toroidal magnetic field: τE ∝ BT0.75–0.8. This scaling is much stronger than that projected for the ITER (τE_IPB98 ∝ BT0.15), while being somewhat weaker than the scalings observed on the NSTX and MAST devices. The stronger (as compared to the ITER scaling) dependence of τE on BT observed in these experiments should be taken into account in designing thermonuclear facilities with small aspect ratios and toroidal magnetic fields—in particular, fusion neutron sources.

Collisionality and safety factor scalings of H-mode energy transport in the MAST spherical tokamak

A factor of 4 dimensionless collisionality scan of H-mode plasmas in MAST shows that the thermal energy confinement time scales as . Local heat transport is dominated by electrons and is consistent with the global scaling. The neutron rate is in good agreement with the ν* dependence of τE,th. The gyrokinetic code GYRO indicates that micro-tearing turbulence might explain such a trend. A factor of 1.4 dimensionless safety factor scan shows that the energy confinement time scales as . These two scalings are consistent with the dependence of energy confinement time on plasma current and magnetic field. Weaker qeng and stronger ν* dependences compared with the IPB98y2 scaling could be favourable for an ST-CTF device, in that it would allow operation at lower plasma current.

Scaling of H-mode energy confinement with Ip and BT in the MAST spherical tokamak

The dependences of energy confinement on plasma current and toroidal magnetic field have been investigated in the MAST spherical tokamak in H-mode plasmas. Multivariate fits show that the dependence of energy confinement time on plasma current Ip is weaker than linear while the dependence on toroidal magnetic field BT is stronger than linear, in contrast to conventional energy confinement scalings. These Ip and BT dependences have also been confirmed by single parameter scans. Transport analysis indicates that the strong BT scaling of energy confinement could possibly be explained by weaker q and stronger ν* dependence of heat diffusivity in comparison with conventional tokamaks.

Study of confinement and LHCD efficiency on the HT-7 tokamak

High power heating of a lower hybrid wave (LHW) was performed (PLHW ∼ 800 kW at 2.45 GHz) recently in the HT-7 tokamak. Lower hybrid current drive (LHCD) efficiency is studied for different injected powers and for different densities. Improved particle confinement is observed by the application of LHCD as characterized by an increase in the central line averaged electron density and the decrease in Dα emission. The particle confinement time (τp) increased by about 1.5 times. The dependence of energy confinement time (τE) on plasma density and LHW power is experimentally studied in detail.

Plasma confinement studies in LHD

The initial experiments on the Large Helical Device (LHD) have extended confinement studies on currentless plasmas to a large scale (R = 3.9 m, a = 0.6 m). Heating by NBI of 3 MW produced plasmas with a fusion triple product of 8 × 1018m-3·keV·s at a magnetic field strength of 1.5 T. An electron temperature of 1.5 keV and an ion temperature of 1.1 keV were achieved simultaneously at a line averaged electron density of 1.5 × 1019 m-3. The maximum stored energy reached 0.22 MJ with neither unexpected confinement deterioration nor visible MHD instabilities, which corresponds to ⟨β⟩ = 0.7%. Energy confinement times reached a maximum of 0.17 s. A favourable dependence of energy confinement time on density remains in the present power density (∼40 kW/m3) and electron density (3 × 1019 m-3) regimes, unlike the L mode in tokamaks. Although power degradation and significant density dependence are similar to the conditions on existing medium sized helical devices, the absolute value is enhanced by up to about 50% from the International Stellarator Scaling 95. Temperatures of both electrons and ions as high as 200 eV were observed at the outermost flux surface, which indicates a qualitative jump in performance compared with that of helical devices to date. Spontaneously generated toroidal currents indicate agreement with the physical picture of neoclassical bootstrap currents. Change of magnetic configuration due to the finite β effect was well described by 3-D MHD equilibrium analysis. A density pump-out phenomenon was observed in hydrogen discharges, which was mitigated in helium discharges with high recycling.