Study of the low aspect ratio limit tokamak in the Heidelberg spheromak experiment

Bruhns, H.; Brendel, Ronny; Raupp, G.; Steiger, J.

doi:10.1088/0029-5515/27/12/017

Cited by 22 publications

(12 citation statements)

References 8 publications

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“…The first STs were obtained by inserting a central rod into an existing fusion experiment, as in the Lucas Heights Rotamak [4], the Heidelberg Spheromak [5], and in the SPHEX 'rodamak' [6]. Each of these small experiments yielded interesting and promising equilibrium and stability results -for example, it was found in the Heidelberg device that a small rod current stabilised the tilt instability of the spheromak, and use of a pre-existing toroidal field in SPHEX improved energy coupling from gun to plasma -but all had cold plasmas.…”

Section: Experimental Results From Stsmentioning

confidence: 99%

The spherical tokamak programme at Culham

Sykes

1999

Nucl. Fusion

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The Spherical Tokamak (ST) is the low aspect ratio limit of the conventional tokamak, and appears to offer attractive physics properties in a simpler device. The START (Small Tight Aspect Ratio Tokamak) experiment provided the world's first demonstration of the properties of hot plasmas in an ST configuration, and was operational at Culham from January 1991 to March 1998, obtaining plasma current of up to 300kA and pulse durations of ~ 50ms. Its successor, MAST is scheduled to obtain first plasma in Autumn 1998 and is a purpose built, high vacuum machine designed to have a tenfold increase in plasma volume with plasma currents up to 2MA. Current drive and heating will be by a combination of induction-compression as on START, a high-performance central solenoid, 1.5MW ECRH and 5MW of Neutral Beam Injection. The promising results from START are reviewed, and the many challenges posed for the next generation of purpose-built STs (such as MAST) are described.

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Section: Experimental Results From Stsmentioning

confidence: 99%

The spherical tokamak programme at Culham

Sykes

1999

Nucl. Fusion

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“…[10][11][12][13] It has been found that the global MHD activity of those plasmas such as the n ϭ 1 tilt mode is not effected by these insulators, though the plasma decay time becomes shorter by 5%-30%. A two-dimensional ͑2-D͒ magnetic probe array on the r-z ͑radial-axial͒ plane is used as shown in Fig.…”

Section: Methodsmentioning

confidence: 99%

“…Particularly, the installation of a center conductor in spheromaks permits the application of an external toroidal field to the plasma, that has brought about the tilt stabilization. 11 This configuration is considered to be that of ULART as the edge q(q a ) exceeds 1. The important question is how large an external toroidal field is required to suppress the n ϭ 1 mode, and whether the tilt stabilized configuration is considered to be that of tokamaks with q a Ͼ 1.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation on tilt stabilizing effect of external toroidal field in low aspect ratio tokamak

et al. 1997

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This paper describes experimental investigations on the equilibrium and global stability of low aspect ratio tokamaks with different aspect ratios ranging from 1.1 to 1.9. The Z-θ pinch spheromak formation technique is used to produce low aspect ratio tokamaks in an external toroidal field generated by the center conductor. Using this operation, the plasma stability has been investigated in the transition regime from tokamaks to spheromaks. It has been found that there exists a lower critical value of the center conductor current to surpress the global plasma instability of the n=1 tilt and/or shift modes. The ratio of this critical current to plasma current is experimentally measured for the first time as a function of the aspect ratio. Glass-tube cylindrical limiters with different radii are installed along the symmetric center axis of the Spherical Torus-3 device [Y. Ono et al., Phys. Fluids B 5, 3691 (1993)]. As the aspect ratio is decreased from 1.9 to 1.1, it is observed that the critical ratio of the center conductor current to plasma current decreases from 1.2 to 0.2. The safety factor q at the plasma edge corresponding to this critical current is roughly 1.5 to 3.0. Similar experiments are also carried out with a thin metal cover surrounding the surface of the glass tube limiter. The thin metal cover permits the decrease in the critical current and the corresponding edge q value of q∼1. These experimental results of the critical current ratio are found to be comparable to that predicted from theoretical models where the restoring force against the tilt motion is considered to be generated by the interaction of the external toroidal field with the n=1 induced surface currents in the tilt motion.

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“…The spherical tokamak concept was tested in the late eighties by the insertion of current-carrying central rods into small existing devices [2][3] [4]. These experiments were limited to cold plasmas (electron temperatures of a few tenths of eV) but gave evidence to the advantage of combining the favorable characteristics of both the compact torus and the conventional tokamak.…”

Section: Spherical Tokamak Experiments Worldwidementioning

confidence: 99%