Modeling of the multiple-toroidicity stellarator/heliotron magnetic fields

2001

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Specific features of charged particle confinement and ripple transport in the low-collision frequency ͑1/͒ regime have been investigated in stellarator-type devices with discrete toroidal or modular field coils. For such stellarator configurations, a multiple-helicity and a multiple-toroidicity character of the magnetic field is typical, manifested itself in the presence of the distant harmonics j,N with high-order Nу2 toroidal mode numbers in a Fourier-decomposition of the magnetic field. The main purpose of the paper was an analysis of the role of these distant harmonics in controlling both direct and indirect losses of charged particles in stellarators. It has been discovered that in configurations, as considered, the level of the neoclassical transport in the 1/ regime can be one order reduced by properly chosen coil currents generated in Fourier decomposition, the distant N ϭ2 satellite harmonics with strong amplitudes and suitable ripple phases.

“…The investigation, carried out in the paper on the basis of specific magnetic-field models developed in Ref. 44, suggests the following conclusions:…”

Section: Discussionmentioning

confidence: 75%

“…͑35͒ of Ref. 44, using the full range of the magnetic-field harmonics of decomposition ͑1͒. Usually, the results of these calculations do not coincide with those of Eq.…”

Section: ͑6͒mentioning

confidence: 96%

Section: ͑6͒mentioning

confidence: 99%

Section: Changes In T Under the High-order Nð2 Harmonics Effectmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Transport and confinement properties of stellarators/heliotrons with the multiple-toroidicity magnetic fields

2001

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A theory of the helical ripple-induced stochastic behavior of fast toroidal bananas in torsatrons and heliotrons

2001

A theory of the helical ripple-induced stochastic behavior of fast toroidal bananas in torsatrons and heliotrons [K. Uo, J. Phys. Soc. Jpn. 16, 1380 (1961)] is developed. It is supplemented by an analysis of the structure of the secondary magnetic wells along field lines. Conditions, under which these wells are suppressed in torsatrons–heliotrons by poloidally modulated helical field ripple, are found. It is shown that inside the secondary magnetic well-free region, favorable conditions exist for a transition of fast toroidal bananas to stochastic trajectories. The analytical estimation for the value of an additional radial jump of a banana particle near its turning point, induced by the helical field ripple effect, is derived. It is found to be similar to the corresponding banana radial jump in a tokamak with the toroidal field ripple. Critical values of the helical field ripple dangerous from the viewpoint of a banana transition to stochastic behavior are estimated.

Direct losses of fast particles in multiple-toroidicity stellarators

2001

Direct losses of fast ions are investigated numerically in current multiple-toroidicity stellarator configurations, in which magnetic field harmonic spectra can be described adequately by a sum of hundreds harmonics with different toroidal and poloidal mode numbers. For these configurations it is typical that amplitudes of distant harmonics with high-order N⩾2 toroidal mode numbers can exceed, near the plasma boundary, one-half of the amplitude of the main magnetic-field harmonic. This leads to the appearance of additional ripple wells along field lines which can trap charged particles (toroidally field ripple-trapped particles). An investigation of the role of these particles in plasma confinement in stellarators is the main goal of the paper. It is shown that a complication of the magnetic-field harmonic spectrum of a stellarator causes direct losses of transition and toroidally field ripple-trapped particles several times higher than losses of corresponding particles in rippled tokamaks.