Loss-Cone Microinstabilities

The mirror's hole in velocity space drives kinetic instabilities — DCLC and Alfvén ion-cyclotron modes — that sloshing ions and warm plasma must suppress.

Instabilities from a gap in velocity space

A mirror plasma has an empty loss cone in velocity space, and that non-thermal distribution carries free energy. It can drive microinstabilities — short-wavelength kinetic modes that scatter ions into the loss cone faster than collisions alone. The two most important are the drift-cyclotron loss-cone (DCLC) mode and the Alfvén ion-cyclotron (AIC) mode.

The proven remedy is to fill in the velocity-space gap: a warm plasma stream and sloshing-ion distributions reduce the sharp loss-cone feature that drives DCLC, while AIC is controlled by limiting the anisotropy of the fast ions. Historic mirror experiments demonstrated these stabilisation techniques at their parameters.

At burner parameters

Whether the same control holds at the burner's density, field, and fast-ion energy is unverified. Microstability is intimately tied to the plug distribution that also builds the confining potential, so it is inseparable from the plug-regime gate.

These modes are subtle because they can be benign at low fast-ion energy and virulent at high energy, so a machine can appear stable in a small experiment and not in a reactor-scale plug. That scale dependence is exactly why microstability cannot be signed off from historic data alone and must be probed at higher parameters by the test burner.

• Loss-cone gap carries free energy
• Drives DCLC and Alfvén ion-cyclotron modes
• Warm plasma + sloshing ions damp them
• Unverified at burner-scale plug parameters