Codes for Mirror and Open Systems
Open-field-line configurations like magnetic mirrors need codes that model end losses, ambipolar potentials, and direct energy conversion rather than closed flux surfaces.
A different geometry
Closed configurations like tokamaks confine plasma on nested flux surfaces. Open systems, such as magnetic mirrors and tandem mirrors, confine along field lines that terminate outside the plasma, relying on magnetic mirroring and electrostatic potentials to reduce end losses. Modeling them requires codes for open systems built around end confinement, ambipolar potential profiles, and loss-cone physics rather than flux-surface transport.
The physics questions shift: instead of a safety-factor profile and pedestal, the central quantities are the mirror ratio, the confining potential, and the loss rate through the ends.
Loss-cone kinetics
In a mirror, particles whose velocity vector lies within the loss cone escape through the ends. This makes the distribution inherently non-Maxwellian and anisotropic, so kinetic Fokker-Planck modeling is essential to compute the confinement time and the potential that plugs the ends.
Direct energy conversion
Open systems can convert the kinetic energy of escaping charged particles into electricity directly by decelerating them against an electric field, rather than through a thermal cycle. Modeling this direct-energy-conversion stage couples the end-loss distribution to an electrostatic collector model.
Design relevance
The Aegis and MetroVolt burner is a deuterium-helium-3 tandem-mirror generator with a 26.49 T plug, a 17 T throat, and a direct-energy-conversion stage. Open-system codes model its end confinement, plug potential, and conversion efficiency in simulation. The low neutron fraction of 5.44% for this fuel is a distinctive feature these codes quantify, all at design stage.
- Model open field lines, not closed surfaces
- Center on mirror ratio and confining potential
- Loss-cone kinetics need Fokker-Planck modeling
- Include direct energy conversion of end losses