THE INFLUENCE OF A HELICAL COIL SPLITTING ON MAGNETIC CONFIGURATION OF THE l = 2 TORSATRON WITH AN ADDITIONAL TOROIDAL MAGNETIC FIELD

Abstract

Проведено изучение свойств магнитных поверхностей в модели двухзаходного (l = 2) торсатрона с катушками дополнительного тороидального магнитного поля (торсатрон типа У-2М) в зависимости от величины тороидального угла полного и частичного расщепления его винтовых обмоток на две равные части. Показано, что в рассматриваемой модели l = 2 винтовой магнитной системы так же, как и в модели l = 2 винтовой магнитной системы без катушек дополнительного тороидального магнитного поля (гелиотрон типа LHD), частичное расщепление винтовых обмоток является эффективным методом управления положением конфигурации магнитных поверхностей относительно поверхности опорного тора. Применение метода может способствовать созданию увеличенного зазора между плазмой и 1-й стенкой в термоядерном реакторе на основе магнитной системы стеллараторного типа. Расчёты также показали, что при углах расщепления больше некоторой предельной величины появляются признаки деградации магнитных поверхностей, свойственные торсатронам/гелиотронам с повышенной заходностью винтовых обмоток (l > 2). Ключевые слова: l = 2 торсатрон, гелиотрон, винтовые обмотки, расщепление, магнитные поверхности, численный расчёт. THE INFLUENCE OF A HELICAL COIL SPLITTING ON MAGNETIC CONFIGURATION OF THE l = 2 TORSATRON WITH AN ADDITIONAL TOROIDAL MAGNETIC FIELD. V.G. KOTENKO, D.V. KURILO, Ju.F. SERGEJEV, E.L. SOROKOVOJ, Ye.D. VOLKOV. Numerical studies were undertaken to elucidate the magnetic surface behavior in the model of the l = 2 U-2M torsatron type with additional toroidal magnetic field coils as a function of the toroidal angle of the total and partial helical coil splitting into two equal parts. It is shown that in the l = 2 torsatron helical magnetic system considered similar to the l = 2 helical magnetic system without additional toroidal magnetic field coils (the LHD heliotron type), a partial splitting of the helical coil is an effective method to control the magnetic surface configuration position relative to the surface of the supporting torus. The application of the method can facilitate creation of the enlarged plasma-1st wall clearance in a fusion reactor based on stellarator-type magnetic systems. Also, the calculations show the signs of the magnetic surface degradation inherent in the torsatrons/heliotrons with polarity l > 2, if the toroidal angle of the helical coil splitting becomes larger than some boundary value.

Magnetic field of a combined plasma trap

“…As one can gather from Figure 3 a, the configuration in the regime with the planar magnetic axis and last closed magnetic surface, which exceeded the limits of the torus surface, was chosen as the initial magnetic surface configuration. The possibility of the existence of a regime like that in l=2 torsatron with the additional magnetic field coils was demonstrated analytically [6,7] which confirmed well by the numeric calculations [8,9]. The regime was brought into existence by selecting the value of the transverse compensating magnetic field B z and that of the additional toroidal magnetic field B о .…”

“…The dashed line indicates that part of the boundary where the disruption of the bifurcation point line of the inner separatrix was observable. The emergence of the inner separatrix in the form of figure 8 in the calculated model of l=2 torsatron can be attributed to the splitting of its helical coils [5]. In the classic stellarators (b o =0) during the superposition of the ripple turn the region of existence of closed magnetic surfaces is found on the straight line K ϕ =0, while in the torsatrons/heliotrons without the additional toroidal magnetic field coils (p>1, B o =0), on the straight line K ϕ =1.…”

A special correcting winding for the l=2 torsatron with split-type helical coils

“…Numerical simulations [7][8][9] confirm the possibility of the existence of a mode with plane magnetic axis (minor radius of magnetic axis r ax → 0) in the l = 2 torsatron comprising the coils of additional toroidal magnetic field with standard and split-type helical windings. The mode is realized at a certain compensating magnetic field value B z = B zm which weakly depends on the splitting angle value ϕ, if ϕ < /2ml.…”

The basic regime characteristics of thel= 2 torsatron with additional longitudinal magnetic field coils

“…One method implies a change in the basic helical line law [4]; the other involves a change in the conductor turn packing in the poles of the helical windings [8]. The B zm value is also Characteristics of the l = 2 torsatron 257 independent of the parameter K φ and can be considered as a fundamental definition of the basic regime.…”

“…The calculation model of the l = 2 torsatron magnetic system with ACs was based on the design characteristics of the URAGAN-2M torsatron with ACs [7,8]. The parameters of the calculation model were as follows.…”