Proposed Experiment to Study Relaxation Formation of a Spherical Tokamak with a Plasma Center Column

Hsu, S. C.; Tang, Xian-Zhu

doi:10.1007/s10894-006-9032-7

Cited by 5 publications

(6 citation statements)

References 24 publications

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“…In this case, however, the stability thresholds are higher due to the field line-tying at the electrodes, which is not considered by the theoretical criterion. This effect, not considered in previous works, 4,6 produces a significant stability enhancement for configurations with e ¼ 2 and f in the range 0.7-0.9 but becomes less important for higher elongations and smaller values of f.…”

Section: Introductionmentioning

confidence: 71%

“…While the helicity injection from a single CHI has proven to be a robust method not only for the formation but also for the sustainment of related configurations, [7][8][9] the requirement of auxiliary current drive and heating schemes, such as rf and neutral beam injection, is foreseen in order to achieve high temperatures and good particle confinement. 4,6 This is because the current drive by helicity injection relies on the tendency of the plasma to relax, and this necessarily involves MHD fluctuations that could degrade the confinement. However, we note that this is a highly non-linear process, and the dynamics of the fluctuations is very sensitive to the operation regime; 17 thus, it is not clear what steady or quasi-steady conditions could achieve in ST-PCC configurations sustained by helicity injection.…”

Section: A Description Of the Configurationmentioning

confidence: 99%

“…Another configuration of this type is the spherical tokamak with plasma center column (ST-PCC). 4,6 This configuration can be naturally formed by driven relaxation inside a cylindrical flux conserver. The required injection of magnetic helicity is provided by the PCC along with a coaxial helicity injector (CHI).…”

Section: Introductionmentioning

confidence: 99%

“…Since these scenarios necessarily involve deviations from the relaxed state, the requirement of auxiliary current drive and heating such as rf and neutral beam injection is foreseen. 4,6 The operating conditions must be carefully selected in order to avoid deleterious modes (in particular, due to the absence of a material center column). In order to study the stability as well as the dynamics of magnetohydrodynamic (MHD) modes in these scenarios, the development of a reliable non-linear MHD code is required.…”

Section: Introductionmentioning

confidence: 99%

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Relevant parameter space and stability of spherical tokamaks with a plasma center column

2017

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A spherical tokamak (ST) with a plasma center column (PCC) can be formed inside a simply connected chamber via driven magnetic relaxation. From a practical perspective, the ST-PCC could overcome many difficulties associated with the material center column of the standard ST reactor design. Besides, the ST-PCC concept can be regarded as an advanced helicity injected device that would enable novel experiments on the key physics of magnetic relaxation and reconnection. This is because the concept includes not only a PCC but also a coaxial helicity injector (CHI). This combination implies an improved level of flexibility in the helicity injection scheme required for the formation and sustainment phases. In this work, the parameter space determining the magnetic structure of the ST-PCC equilibria is studied under the assumption of fully relaxed plasmas. In particular, it is shown that the effect of the external bias field of the PCC and the CHI essentially depends on a single parameter that measures the relative amount of flux of these two entities. The effect of plasma elongation on the safety factor profile and the stability to the tilt mode are also analyzed. In the first part of this work, the stability of the system is explained in terms of the minimum energy principle, and relevant stability maps are constructed. While this picture provides an adequate insight into the underlying physics of the instability, it does not include the stabilizing effect of line-tying at the electrodes. In the second part, a dynamical stability analysis of the ST-PCC configurations, including the effect of line-tying, is performed by numerically solving the magnetohydrodynamic equations. A significant stability enhancement is observed when the PCC contains more than the 70% of the total external bias flux, and the elongation is not higher than two.

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Section: Introductionmentioning

confidence: 71%

Section: A Description Of the Configurationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Relevant parameter space and stability of spherical tokamaks with a plasma center column

2017

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“…All the spherical/compact tokamak configurations can reach large toroidal plasma current I p with a low value of the applied magnetic field [34,35]. The magnetic field needed to keep the plasma stable can be a factor of up to ten times less than in a conventional tokamak.…”

Section: Advantages and Potential Developments Of The Proto-sphera Apmentioning

confidence: 99%

Progress of the Plasma Centerpost for the PROTO-SPHERA Spherical Tokamak

et al. 2016

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Plasma properties can be useful in a wide spectrum of applications. Experimental projects on controlled nuclear fusion are the most challenging of these applications and, at the same time, the best way to approach plasma science. Since nuclear fusion reactors can ensure a large-scale, safe, environmentally-friendly and virtually inexhaustible source of energy, several fusion-oriented megaprojects and innovative companies are appearing all over the world. PROTO-SPHERA (Spherical Plasma for HElicity Relaxation Assessment) is the first plasma project with a simply connected configuration, namely not requiring additional objects inside the plasma volume. This is obtained by a plasma arc, shaped as a screw pinch, acting as the centerpost of a spherical torus with minimal aspect ratio. Due to its intrinsic physical, engineering and economic advantages, this new approach is attractive also on an industrial scale and with several developments that still needs to be explored. This paper presents the PROTO-SPHERA basic principles, its first encouraging results and its expected and potential evolutions.

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Reactor prospect of spheromak concept by electrostatic helicity injection

Tang

Boozer

2008

Physics of Plasmas

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The highest performing spheromaks in the laboratory are formed by electrostatic helicity injection. Discharges with up to 1MA plasma current and core electron temperature as high as 500eV have been recently obtained. For such a scheme to scale-up to a reactor, however, a much higher current multiplication factor (plasma current over injector current) must be achieved. It is shown here that spheromak current multiplication is linearly proportional to flux amplification (ratio of poloidal fluxes inside and outside the separatrix of the mean field). Hence, spheromak optimization is centered around achieving high flux amplification, which is provided by linear or nonlinear resonant coupling between helicity injector and the spheromak force-free eigenmode. The nonlinear resonant field amplification is the most promising route to high flux amplification in a realistic plasma that often significantly deviates from the Taylor state. Accessing such nonlinear resonant field amplification can be facilitated by auxiliary current drive around the magnetic axis and auxiliary heating to break the electron temperature constraint on flux amplification.

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Proposed Experiment to Study Relaxation Formation of a Spherical Tokamak with a Plasma Center Column

Cited by 5 publications

References 24 publications

Relevant parameter space and stability of spherical tokamaks with a plasma center column

Relevant parameter space and stability of spherical tokamaks with a plasma center column

Progress of the Plasma Centerpost for the PROTO-SPHERA Spherical Tokamak

Reactor prospect of spheromak concept by electrostatic helicity injection

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