Negative Energy Wave Destabilized by a Resistor in Electron Plasmas

Diocotron waves are 2-dimensional ExB drift waves in an unneutralized plasma surrounded by a cylindrical conducting boundary. The m_θ=1 wave is a displacement d of the plasma from the trap axis that rotates about this axis.

This wave is negative energy; that is, the electrostatic energy of the off-axis plasma is less than the on-axis plasma, because the unneutralized plasma column is attracted to its image charge in the wall. Therefore dissipation can destabilize this wave [1]. In particular, energy loss due to wall resistance can cause d to grow exponentially.

Experiments measuring this instability are conducted with pure electron plasmas confined in a Penning-Malmberg trap. Three sectors of an azimuthaly sectored electrode are used to excite and detect the wave. A fourth sector is used to destabilize the wave with a resistor. The measured growth rate following the destabilization is exponential and is dependent upon the resistance and capacitance attached to the sector.

[1] W.D. White, J.D. Malmberg and C.F. Driscoll, Phys. Rev. Lett. 49, 1822 (1982).