Flute instability and the associated radial transport in the tandem mirror with a divertor mirror cell

Abstract

The flute instability and the associated radial transport are investigated in the tandem mirror with a divertor mirror cell ͑the GAMMA10 A-divertor͒ with help of computer simulation, where GAMMA10 is introduced ͓Inutake et al., Phys. Rev. Lett. 55, 939 ͑1985͔͒. The basic equations used in the simulation were derived on the assumption of an axisymmetric magnetic field. So the high plasma pressure in a nonaxisymmetric minimum-B anchor mirror cell, which is important for the flute mode stability, is taken into account by redefining the specific volume of a magnetic field line. It is found that the flute modes are stabilized by the minimum-B magnetic field even with a divertor mirror although its stabilizing effects are weaker than that without the divertor mirror. The flute instability enhances the radial transport by intermittently repeating the growing up and down of the Fourier amplitude of the flute instability in time.

The Stability of Flute Modes in the GAMMA10 A-divertor

“…(1) exactly in the non-paraxial divertor mirror. The results in the present paper revealed that the linear phase of the flute instability was almost the same as those in the previous works [4,7].…”

“…9 in the GAMMA10 A-divertor magnetic geometry, where the computer simulation was performed by solving Eqs. (5)- (8) with the initial conditions of D E (x) = 1, T E (x) = 1 [7]. Figure 9 is the radial profiles of D E and T E in the quasi-steady state, where plasma continues to be lost radially by the classical transport.…”

“…8 is that the gradient Fig. 9 Radial profiles of D E (x) and T E (x) observed in the simulation [7].…”

An interchange instability in an open system and the line-tying effect on it

“…Here p is the plasma pressure, γ is the specific heat index, U ≡ dχ/B 2 is the magnetic specific volume, where B is the magnetic field, the coordinate χ is defined as B = ∇χ, and the integration is carried out along a magnetic field line. Noting that ∇(pU γ ) • ∇U = U γ (∇p • ∇U + γp|∇U | 2 /U ), the interchange mode is stabilized by the good magnetic field line curvature in the case of ∇p •∇U 0, while the interchange mode is stabilized by the plasma compression in the case of ∇p • ∇U < 0 but ∇p • ∇U + γp|∇U | 2 /U 0 [5][6][7][8]. Here ∇U = −2 κ dχ/B 2 in the vacuum magnetic field, where κ is the magnetic field line curvature vector with the relation ∇B = Bκ [9].…”

Calculation of Ion Orbits in the Divertor/Dipole Regions of the GAMMA10 A-Divertor

“…However, recently the original purpose of installing a magnetic divertor has been changed to be one of performing the simulation experiments of the divertor in the closed system. Thus the investigation of transport on the GAMMA10 A-divertor is in progress [3][4][5]. The study of ion orbits in the divertor and dipole regions is a part of the investigation of the GAMMA10 A-divertor with the aim of plasma wall interaction.…”