Numerical study of tilt stability of prolate field-reversed configurations Page: 4 of 34
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
I. INTRODUCTION
The Field-Reversed Configuration (FRC) is a compact toroid with negligible toroidal
field, in which plasma is confined by a poloidal magnetic field associated with toroidal dia-
magnetic current carried by the plasma. The FRC offers a unique fusion reactor potential
because of its compact and simple geometry, translation properties, and high plasma beta.
Although many MHD modes are predicted to be unstable, prolate FRCs have been produced
successfully by several formation techniques and show surprising macroscopic resilience.
A substantial literature exists of FRC stability studies in both the MHD (ie, fluid) and
kinetic (ie, particle ion) descriptions. The n = 1 tilt instability is thought to be the
most dangerous MHD instability because it is both strongly growing and a global mode
that is not readily stabilized when kinetic effects are included. This mode is internal to
the magnetic separatrix in the prolate FRC and thus cannot be effectively stabilized by
external means. MHD simulations show that the tilt mode growth rate is on the order of
the inverse Alfven transit time and depends only weakly on the equilibrium profiles (within
a factor of two). Plasma rotation and the inclusion of the Hall term have been considered as
stabilizing mechanisms for this mode and were found to reduce the growth rate2. However a
change in the linear mode structure prevented the complete stabilization that was predicted
earlier based on a trial function dispersion analysis. In MHD calculations including the
effect of gyro-viscosity5, up to a factor of 3 reduction in growth rate has been found, but not
complete stability. It has also been found that there is no nonlinear saturation of the n = 1
tilt instability in the MHD description2 7.
The key parameters related to the finite Larmor radius (FLR) stability of the FRC are
s, which measures the number of thermal ion gyro-radii in the configuration and E, the
separatrix elongation. These are defined by
Rs rdr
no Rapi'
and E = ZS/Rs. Here Ro and Rs are the magnetic null and the separatrix radius at the
midplane, p2 is the local ion Larmor radius, and Z is the separatrix half-length at r = 0.
The kinetic parameter s indicates the importance of finite Larmor radius (FLR) effects,
which are strong for s - 1, while the s 1 (small Larmor radius) limit corresponds to the2
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Belova, E. V.; Jardin, S. C.; H. Ji, M. Yamada & Kulsrud, R. Numerical study of tilt stability of prolate field-reversed configurations, report, June 21, 2000; Princeton, New Jersey. (https://digital.library.unt.edu/ark:/67531/metadc712508/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.