scholarly journals Demonstration of reduced neoclassical energy transport in Wendelstein 7-X

Nature ◽  
2021 ◽  
Vol 596 (7871) ◽  
pp. 221-226
Author(s):  
C. D. Beidler ◽  
H. M. Smith ◽  
A. Alonso ◽  
T. Andreeva ◽  
J. Baldzuhn ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Energy Transport ◽  
Magnetic Confinement ◽  
Record Values ◽  
Triple Product ◽  
Geometrical Factor ◽  
Helical Axis ◽  
Strong Temperature Dependence ◽  
Field Geometry

AbstractResearch on magnetic confinement of high-temperature plasmas has the ultimate goal of harnessing nuclear fusion for the production of electricity. Although the tokamak1 is the leading toroidal magnetic-confinement concept, it is not without shortcomings and the fusion community has therefore also pursued alternative concepts such as the stellarator. Unlike axisymmetric tokamaks, stellarators possess a three-dimensional (3D) magnetic field geometry. The availability of this additional dimension opens up an extensive configuration space for computational optimization of both the field geometry itself and the current-carrying coils that produce it. Such an optimization was undertaken in designing Wendelstein 7-X (W7-X)2, a large helical-axis advanced stellarator (HELIAS), which began operation in 2015 at Greifswald, Germany. A major drawback of 3D magnetic field geometry, however, is that it introduces a strong temperature dependence into the stellarator’s non-turbulent ‘neoclassical’ energy transport. Indeed, such energy losses will become prohibitive in high-temperature reactor plasmas unless a strong reduction of the geometrical factor associated with this transport can be achieved; such a reduction was therefore a principal goal of the design of W7-X. In spite of the modest heating power currently available, W7-X has already been able to achieve high-temperature plasma conditions during its 2017 and 2018 experimental campaigns, producing record values of the fusion triple product for such stellarator plasmas3,4. The triple product of plasma density, ion temperature and energy confinement time is used in fusion research as a figure of merit, as it must attain a certain threshold value before net-energy-producing operation of a reactor becomes possible1,5. Here we demonstrate that such record values provide evidence for reduced neoclassical energy transport in W7-X, as the plasma profiles that produced these results could not have been obtained in stellarators lacking a comparably high level of neoclassical optimization.

The JET project: introduction and background

1987 ◽  
Vol 322 (1563) ◽  
pp. 3-15 ◽  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Electric Discharge ◽  
Western Europe ◽  
Magnetic Confinement ◽  
Thermonuclear Fusion ◽  
Fusion Reactors ◽  
Temperature Plasma ◽  
High Temperature Plasma ◽  
Controlled Thermonuclear Fusion

The Joint European Torus, JET, is an experiment, undertaken by 15 partners from 12 nations of Western Europe, to get information on the magnetic confinement of high-temperature plasma in conditions close to those needed for energy-producing controlled thermonuclear fusion reactors. Physically, JET is a very powerful toroidal-pinch electric discharge in a strong stabilizing magnetic field, a system known as a tokamak. The paper summarizes the main features of a tokamak and relates them to the papers in this symposium.

scholarly journals Experimental signatures of nodeless multiband superconductivity in a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ single crystal

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Chanhee Kim ◽  
Dilip Bhoi ◽  
Yeahan Sur ◽  
Byung-Gu Jeon ◽  
Dirk Wulferding ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Crystal ◽  
Zero Magnetic Field ◽  
Anisotropy Ratio ◽  
Strong Temperature Dependence ◽  
Critical Fields ◽  
Band Theory ◽  
Plane Field ◽  
Low Field ◽  
Out Of Plane

AbstractIn order to understand the superconducting gap nature of a $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 single crystal with $$T_{c} = 3.13 \text { K}$$ T c = 3.13 K , in-plane thermal conductivity $$\kappa $$ κ , in-plane London penetration depth $$\lambda _{\text {L}}$$ λ L , and the upper critical fields $$H_{c2}$$ H c 2 have been investigated. At zero magnetic field, it is found that no residual linear term $$\kappa _{0}/T$$ κ 0 / T exists and $$\lambda _{\text {L}}$$ λ L follows a power-law $$T^n$$ T n (T: temperature) with n = 2.66 at $$T \le \frac{1}{3}T_c$$ T ≤ 1 3 T c , supporting nodeless superconductivity. Moreover, the magnetic-field dependence of $$\kappa _{0}$$ κ 0 /T clearly shows a shoulder-like feature at a low field region. The temperature dependent $$H_{c2}$$ H c 2 curves for both in-plane and out-of-plane field directions exhibit clear upward curvatures near $$T_c$$ T c , consistent with the shape predicted by the two-band theory and the anisotropy ratio between the $$H_{c2}$$ H c 2 (T) curves exhibits strong temperature-dependence. All these results coherently suggest that $$\hbox {2H-Pd}_{0.08} \hbox {TaSe}_2$$ 2H-Pd 0.08 TaSe 2 is a nodeless, multiband superconductor.

The activation energy U(T,B) in high temperature superconductor

2020 ◽  
Vol 92 (2) ◽  
pp. 20601
Author(s):  
Abdelaziz Labrag ◽  
Mustapha Bghour ◽  
Ahmed Abou El Hassan ◽  
Habiba El Hamidi ◽  
Ahmed Taoufik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Activation Energy ◽  
Phase Diagram ◽  
High Temperature ◽  
Apparent Activation Energy ◽  
High Temperature Superconductor ◽  
Flux Flow ◽  
Resistivity Measurements ◽  
Vortex Phase ◽  
The Magnetic Field

It is reported in this paper on the thermally assisted flux flow in epitaxial YBa2Cu3O7-δ deposited by Laser ablation method on the SrTiO3 substrate. The resistivity measurements ρ (T, B) of the sample under various values of the magnetic field up to 14T in directions B∥ab-plane and B∥c-axis with a dc weak transport current density were investigated in order to determine the activation energy and then understand the vortex dynamic phenomena and therefore deduce the vortex phase diagram of this material. The apparent activation energy U0 (B) calculated using an Arrhenius relation. The measured results of the resistivity were then adjusted to the modified thermally assisted flux flow model in order to account for the temperature-field dependence of the activation energy U (T, B). The obtained values from the thermally assisted activation energy, exhibit a behavior similar to the one showed with the Arrhenius model, albeit larger than the apparent activation energy with ∼1.5 order on magnitude for both cases of the magnetic field directions. The vortex glass model was also used to obtain the vortex-glass transition temperature from the linear fitting of [d ln ρ/dT ] −1 plots. In the course of this work thanks to the resistivity measurements the upper critical magnetic field Hc2 (T), the irreversibility line Hirr (T) and the crossover field HCrossOver (T) were located. These three parameters allowed us to establish a phase diagram of the studied material where limits of each vortex phase are sketched in order to optimize its applicability as a practical high temperature superconductor used for diverse purposes.

Jupiter's internal magnetic field geometry relevant to particle trapping

1977 ◽  
Vol 82 (32) ◽  
pp. 5187-5194 ◽  
Author(s):  
Juan G. Roederer ◽  
Mario H. Acuña ◽  
Norman F. Ness
Keyword(s):  
Magnetic Field ◽  
Internal Magnetic Field ◽  
Particle Trapping ◽  
Field Geometry

scholarly journals Could a change in magnetic field geometry cause the break in the wind-activity relation?

2015 ◽  
Vol 455 (1) ◽  
pp. L52-L56 ◽  
Author(s):  
A. A. Vidotto ◽  
J.-F. Donati ◽  
M. Jardine ◽  
V. See ◽  
P. Petit ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Geometry ◽  
Wind Activity

Magnetic Confinement and Control of Trajectories of Discharge Species in Atmospheric-Pressure Analytical Spark Discharges

1987 ◽  
Vol 41 (2) ◽  
pp. 200-207 ◽  
Author(s):  
Vahid Majidi ◽  
David M. Coleman
Keyword(s):  
Magnetic Field ◽  
Atmospheric Pressure ◽  
Magnetic Confinement ◽  
Post Discharge ◽  
Conducting Channel ◽  
Filamentary Structure ◽  
Spark Discharges ◽  
Time Space ◽  
Series Of Experiments ◽  
And Control

A series of experiments, designed to help characterize the behavior of an analytical spark discharge in an external pulsed magnetic field, is described. Results include controlled formation and deformation of a spark's post-discharge torus utilizing different magnetic field configurations. One manifestation of this research was discovery of a new filamentary structure which extends from the spark conducting channel to the magnet pole face(s). These features were investigated via their refracted light (Schlieren) and spectroscopic (time/space/wavelength-resolved) properties. Practical ramifications of this control are discussed.

scholarly journals Measurements and Analysis of AC Losses in HTS Windings of Electrical Machine for Different Operation Modes

2021 ◽  
Vol 11 (6) ◽  
pp. 2741
Author(s):  
Sergey Zanegin ◽  
Nikolay Ivanov ◽  
Vasily Zubko ◽  
Konstantin Kovalev ◽  
Ivan Shishov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
High Temperature Superconductor ◽  
High Temperature Superconductors ◽  
Transport Current ◽  
Operating Conditions ◽  
Ac Losses ◽  
Electrical Machine ◽  
2Nd Generation ◽  
Motor Mode

The article is devoted to the study of losses in devices based on high-temperature superconductors of the 2nd generation. The complexity of the devices under study increases from a single rack coil to a winding assembled from several coils, and finally to an electric machine operating in generator mode. This is the way to experimentally study the behavior of 2nd generation high temperature superconductor (2G HTS) carrying a transport current in various conditions: self-field, external DC, and AC magnetic field. Attention is also paid to the losses in the winding during its operation from the inverter, which simulates the operating conditions in the motor mode of a propulsion system.

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