High performance experiments in JT-60U reversed shear discharges

Fujita, T.; Kamada, Y.; Ishida, S.; Neyatani, Y.; Oikawa, T.; Ide, S.; Takeji, S.; Koide, Y.; Isayama, A.; Fukuda, T.; Hatae, T.; Ishii, Yasutomo; Ozeki, T.; Shirai, Hiroshi; Team, Jt

doi:10.1088/0029-5515/39/11y/302

Cited by 115 publications

(115 citation statements)

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“…A similar regime was also discovered in the DIII-D tokamak 3 at about the same time and has since been studied in several tokamaks, including JT-60U 4 and the Joint European Torus ͑JET͒. 5 Although it is produced by a different heating method, namely neutral beam injection, the ERS regime has strong similarities to two other regimes of improved confinement involving modification of the q profile, namely the pellet enhanced performance mode in JET 6 and that occurring in Tore-Supra with lower-hybrid current drive.…”

Section: Introductionsupporting

confidence: 63%

“…Similar difficulty in achieving q min Ͻ2 has also been experienced by the JT-60U team developing reversed-shear plasmas in that device. 4 Once a reliable startup had been developed, it was found that ERS transitions resulting in an improvement in global confinement, such as those observed at 1.6 MA, did not occur spontaneously under similar conditions at high current, possibly because the threshold power for the transition had increased beyond the available NBI power. ͑The peak deuterium NBI power available for ERS studies has been limited to about 29 MW because a longer total NBI heating duration is required in this mode of operation to span the prelude and postlude phases.͒ However, the transient formation of regions of increased gradient in the temperature profiles, particularly of the electron temperature, as opposed to the density profile, was observed in some 2.2 MA reversed-shear plasmas.…”

mentioning

confidence: 99%

“…Comparing the 1.6 and 2.2 MA data in this figure, it can be seen that the location of the transport barrier has indeed expanded with the increase in min , as observed in similar regimes in other devices. 4,12 Analysis of the transport in the high-current ERS plasmas shows that, as at lower current, the ion thermal and the particle diffusivities are reduced but that the electron thermal diffusivity is only slightly affected. The suppression of the transport in the ERS regime is correlated with a reduction inside the transport barrier in the level of turbulent density fluctuations measured by a multi-channel microwave reflectometer.…”

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confidence: 99%

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Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor

et al. 1997

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Experiments in the Tokamak Fusion Test Reactor ͑TFTR͒ ͓Phys. Plasmas 2, 2176 ͑1995͔͒ have explored several novel regimes of improved tokamak confinement in deuterium-tritium ͑D-T͒ plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region ͑high l i ͒. New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (q a Ϸ4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-l i plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D-T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D-T plasmas with q 0 Ͼ1 and weak magnetic shear in the central region, a toroidal Alfvén eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions.

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Section: Introductionsupporting

confidence: 63%

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confidence: 99%

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confidence: 99%

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Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor

et al. 1997

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“…minor radius > local minimum at ρ ~ 0.6. ITBs which only exist at minor radius < local (or absolute) minimum, generate a peak in the bootstrap current profile at a smaller radius than is required for alignment with the peak in the total current density profile, resulting in a progressive shrinking of the ITB radius {see, for example, [14,15]}. The observation of ITBs extending into the positive magnetic shear region has been made on several tokamaks, with monotonic q-profiles such as in [16,17]; and in q-profiles with strong shear reversal in the core, such as in [2].…”

Section: Fully Noninductive Operationmentioning

confidence: 99%

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Garofalo¹,

Gong²,

Grierson³

et al. 2015

Nucl. Fusion

117

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Recent EAST/DIII-D joint experiments on the high poloidal beta tokamak regime in DIII-D have demonstrated fully noninductive operation with an internal transport barrier (ITB) at large minor radius, at normalized fusion performance increased by ⩾30% relative to earlier work (Politzer et al 2005 Nucl. Fusion 45 417). The advancement was enabled by improved understanding of the 'relaxation oscillations', previously attributed to repetitive ITB collapses, and of the fast ion behavior in this regime. It was found that the 'relaxation oscillations' are coupled core-edge modes amenable to wall-stabilization, and that fast ion losses which previously dictated a large plasma-wall separation to avoid wall over-heating, can be reduced to classical levels with sufficient plasma density. By using optimized waveforms of the plasma-wall separation and plasma density, fully noninductive plasmas have been sustained for long durations with excellent energy confinement quality, bootstrap fraction ⩾80%, β ⩽ 4 N , β ⩾ 3 P , and β ⩾ % 2 T . These results bolster the applicability of the high poloidal beta tokamak regime toward the realization of a steady-state fusion reactor.

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“…If the same conditions had been realised in deuterium-tritium plasmas, it would, have resulted in a Q value of about 1.25, i.e. conditions better than breakeven [12].…”

Section: -Progress In Recent Yearsmentioning

confidence: 98%

Fusion: A true challenge for an enormous reward

Ongena

2015

EPJ Web of Conferences

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Summary. -From nuclear physics we know that energy can be released not only from the fission of heavy nuclei but also from the fusion of light nuclei. Steady progress shows that fusion-one of the few possible options for the future-can be a clean and safe solution for mankind's long-term energy needs, with minimal environmental impact. A source of energy which would be inexhaustible, inherently safe and environmentally friendly, is this not a marvellous prospect? Nuclear fusion has been the energy source of our Sun and the stars in the universe for billions of years. This process requires temperatures of tens of millions of degrees, so extremely high and foreign to our daily experience as to seem out of reach. Nevertheless, these extremely high temperatures are routinely realised in several laboratories all over the world, and since the early 1990s, large amounts of energy have been released in a controlled way from fusion reactions. We are witnessing the birth of a new technology destined to meet the gigantic future energy needs of mankind with minimal impact on the environment. -Fusion reactions in our Sun and on EarthThe dominant fusion reaction in our Sun converting hydrogen into helium is the p-p fusion chain, the other being the carbon-nitrogen-oxygen or CNO cycle. The CNO cycle is dominant in stars that are about 1.3 times heavier than our Sun, and only about 1.7% of the 4 He nuclei in the Sun are estimated to originate from the CNO cycle.

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High performance experiments in JT-60U reversed shear discharges

Cited by 115 publications

References 15 publications

Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor

Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor

Compatibility of internal transport barrier with steady-state operation in the high bootstrap fraction regime on DIII-D

Fusion: A true challenge for an enormous reward

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