Collisionless m=1 tearing mode

The instability of a magnetically confined plasma against macroscopic modes is analyzed in collisionless regimes where magnetic reconnection occurs because of finite electron inertia and the ion gyroradius ${\mathrm{\rho }}_{\mathit{i}}$ replaces the skin depth d as the width of the mode boundary layer. Growth rates γ/${\mathrm{\omega }}_{\mathit{A}}$∼(d/${\mathit{r}}_{\mathit{s}}$)(${\mathrm{\rho }}_{\mathit{i}}$/d${)}^{2/3}$ are found, with ${\mathrm{\omega }}_{\mathit{A}}$ the Alfvén frequency and ${\mathit{r}}_{\mathit{s}}$ the radius of the reconnecting surface. For typical JET parameters, ${\gamma }^{\mathrm{-}1}$∼50–100 μs, which compares favorably with the observed instability growth time of internal plasma relaxations.