While shielding in collisional, strongly magnetized (one-dimensional) plasmas obeys the standard Debye result, shielding in collisionless, immobile ion plasmas is far more complex than commonly believed. In some circumstances, the plasma will antishield a positive test charge; i.e., the plasma becomes more positive in the neighborhood of a positive test charge. When shielding does occur, it results solely from electrons dynamically trapped in the neighborhood of the test charge. The new theory of dynamic shielding, developed herein, is in good agreement with experiments in pure electron plasmas.

• Received 23 November 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.4209