Compact ion beam source for feedback control of plasma instabilities

A compact ion beam source has been constructed for use in the Columbia Linear Machine for feedback control of plasma instabilities. This source has been used in a feedback configuration to stabilize the collisionless trapped particle instability [Phys. Rev. Lett. 67, 204 (1991)]. The source was based on an E×B hot cathode, magnetron‐type design. It utilized the background magnetic field and a radial discharge voltage to obtain the azimuthal E×B drifts. The pressure inside the discharge chamber was maintained in the mTorr range via differential pumping. The source had a stable operating window in gas pressure of over 50% about the chosen operating parameters. Typical source plasma parameters were a plasma potential of 100 V, an electron temperature of 10 eV, and a plasma density of 109–1010 cm−3. The power dissipated was around 30 W. The ion beam energy was typically 100 eV with an energy spread of 20 eV and it could be modulated 100%. In addition, external control of the ion beam energy was provided via t...