n=2 Rotational Mode (Suppressed by Octopole Fields)
Mitigating this instability is essential for extending FRC plasma duration and confinement.
01 Definition
A destructive rotational plasma instability in FRCs caused by ion spin-up, mitigated by applying external multipole magnetic fields.
02 Detailed_Analysis
The n=2 rotational mode is a macroscopic magnetohydrodynamic (MHD) instability commonly observed in Field-Reversed Configurations. As the plasma torus spontaneously accelerates its rotation due to end-shorting or particle loss, it deforms into an elliptical cross-section, leading to plasma-wall contact and rapid loss of confinement. The standard mitigation is the application of external barrier octopole (or quadrupole) magnetic fields.
03 Key_Facts
- ▸ Driven by spontaneous azimuthal plasma rotation and particle transport.
- ▸ Causes the plasma cross-section to become elliptical and strike vessel walls.
- ▸ Suppressed effectively by applying external octopole or quadrupole magnetic fields.
- ▸ Historically the primary lifetime-limiting instability in theta-pinch FRCs.
04 Deep_Dive_Intelligence
Overview
Intelligence asset in the Stability Solutions.
Entity Type: Concept — n=2 Rotational Mode (Suppressed by Octopole Fields) is a technical concept or theoretical framework.
06 Related_Terms (3)
08 Timeline_Mentions (3)
LANL Field-Reversed Experiment (FRX) Series
Foundational research at Los Alamos National Laboratory (FRX-A, B, C) masters the control of the n=2 rotational instability in FRCs using quadrupole magnetic fields.
fusion-physicsFRX-B Operations and Anomalous Stability Discovery
Upgraded experiment FRX-B identifies the n=2 rotational instability and discovers that FRCs are 100x more stable than MHD theory predicts.
fusion-physicsFRX-C Quadrupole Stabilization Breakthrough
The FRX-C experiment at LANL demonstrates that weak quadrupole magnetic fields can suppress the n=2 rotational instability, extending FRC lifetimes to 300 microseconds.
fusion-physics09 FAQ
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Quick_Facts
- Category
- Plasma Physics
- Aliases
- n=2 Rotational Mode (Suppressed by Octopole Fields), n2-rotational-mode-suppressed-by-octopole-fields, n=2 Rotational Instability, FRC Rotational Mode, Octopole-Suppressed Rotational Mode
- Sources
- 0
- Related Terms
- 3
- Timeline Events
- 3