Radial transport calculations for tandem mirrors

Abstract

The existence of a non-axisymmetric magnetic field in the transition regions between the central cell and end-plugs of a tandem mirror device can lead to significant radial transport of central-cell ions. Self-consistent calculation of the consequences of this non-ambipolar process requires the solution of a highly non-linear charge balance equation for the ambipolar potential. In this paper, radial transport in tandem mirrors is studied, with particular emphasis on the charge balance equation and its consequences. A timedependent radial transport code is presented. Simulations of the Tandem Mirror Experiment (TMX) are performed. Generally, good agreement between code and experiment is obtained. The phenomenon of quenching of radial transport is analysed and demonstrated numerically.

Neoclassical transport in stellarators

“…Figure 6 shows that the ambipolar condition T e = r i is satisfied at C « 0.7 for a peak density n Q = 2 X10 14 cm -3 . As n Q decreases to 10 14 cm" 3 , the ambipolar condition is satisfied at three different values of C. This behavior of multiple roots for the ambipolar field has been discussed for stellarators by Hynick and Hitchon, 26 for tandem mirrors by Mirin et al,, 27 and for Elmo Bumpy Torus by Jaeger et al…”

Thermal-Barrier Production and Identification in a Tandem Mirror

“…7,8 Measurements show radial as well as axial ion losses in the tandem mirror experiment upgrade device (TMX-U). The radial lifetime is in the range of 2 to 100 ms, depending on operating conditions, and appears to be independent of thermalbarrier formation.…”

SYMTRAN - A Time-dependent Symmetric Tandem Mirror Transport Code

“…∂(n p /∂t) + (n p /t p ) = S p = n p N b sv (4) n p t p = (n C t ie )[1 -(f i + f e )/ E B ] (5) f i = T e ln(n P /n C ) (6) (f e /T e ) exp (f e /T e ) = t | | /t ee {(2L p /R M L C )(n p 2 /n C ) + n C }{(2L p /R M L C )n p (t | | /t p ) + n C } -1 ª (m i /m e ) 1/2 (T i /T e ) 3/2 (f i /T i ) exp (f i /T i )…”

“…The SYMTRAN code differs from the earlier tandem mirror radial transport code TMT [5] in that our code is focused on axisymmetric tandem mirrors and classical diffusion, whereas TMT emphasized non-ambipolar transport in TMX and MFTF-B due to yin-yang plugs and non-symmetric transitions between the plugs and axisymmetric center cell. Both codes exhibit interesting but different non-linear behavior.…”