Quadrupole Stabilization of the Precessional Mode of Relativistic Electron Rings

Experiments show that the precessional instability predicted and observed in weak electron rings trapped in a magnetic mirror field can be suppressed by adding a sufficiently strong magnetic quadrupole Ioffe field to the basic mirror field. In agreement with a theoretical analysis, the instability ceases when the Ioffe field reaches sufficient strength so that the radial gradient ($\frac{d{B}_t}{d\mathcal{r}}$) of the total magnetic field strength becomes positive.