Transport Barriers and Self-Organization of Plasmas

Abstract

На основе представлений о самоорганизации плазмы в токамаке предлагается метод анализа характеристик турбулентного механизма, ответственного за перенос тепла по радиусу. Показано, что тепловой поток переносится преимущественно низкими модами МГД-неустойчивости. Чем больше поток, создаваемый в результате искажений профиля давления внешними факторами, тем шире спектр мод и тем меньше номер моды нижней границы спектра. Обсуждается роль мод с низкими полоидальными номерами в процессе формирования транспортных барьеров. Предлагается нетрадиционное объяснение формирования режимов с улучшенным удержанием.

Features of self-organized plasma physics in tokamaks

“…Transport and turbulence in TB regions is reduced (however, the physical mechanism of the turbulence is the same as outside the TB region; thus to conserve the flux along the radius in these zones a higher value for ∇p is required. This is confirmed experimentally [17]. If many TBs are present in the plasma such that they start to overlap, p N (r) remains the same, figure 6.…”

“…Absence of low-m rational surfaces in the TB zone complicates transport for low-number turbulent modes and reduces the thermal conductivity in this region. Because of the large radial heat flux, the lower the turbulent mode m 1 involved in the process [17], the number of gaps, reducing the heat transport, increases. For a sufficiently large zone of low magnetic shear (dq/dr) and in presence of high-power heating, gaps, complicating the heat transport, may interlock, and the so-called 'advanced tokamak regime' is established with enhanced confinement over a wide region.…”

“…DIII-D 'advanced tokamak' regime (a) pressure profile; stars correspond to an approximating formula for normalized self-organized pressure profile. (b) Calculated density of rational magnetic surfaces (RMS) for the experimental q(r) profile; m 1 is the poloidal number of lowest mode, which takes part in energy transport [17]. Reproduced with permission from [17].…”

“…(b) Calculated density of rational magnetic surfaces (RMS) for the experimental q(r) profile; m 1 is the poloidal number of lowest mode, which takes part in energy transport [17]. Reproduced with permission from [17].…”

Physical Processes That Occur in Self-Organized Tokamak Plasma

“…Some authors call them "advanced tokamak" or "hybrid" regimes [23][24][25][26][27][28], but we believe that the method of programming the q(r) profile is not essential, and they are the same regimes. Figure 10 shows the pressure profile for such a high-confinement regime [29]. We see that the profile coincides with the self-consistent profile, and since the flow Γ1 is blocked, the plasma at the edge has an unperturbed coefficient χ0.…”