1. J. Marshall, inPlasma Acceleration, edited by S. W. Kash (Stanford University Press, Stanford, California, 1960), p. 60;
2. P. Gloersen, General Electric R60SD454 (1960);
3. I. Granet, W. J. Guman, Republic Aviation Corporation, PPL-120 (1959);
4. W. L. Starr, J. T. Naff, inPlasma Acceleration, edited by S. W. Kash (Stanford University Press, Stanford, California, 1960), p. 47.