1. D. Boussard, CERN LABII/RF/INT/75-2(1975).
2. V.K. Neil and A.M. Sessler, Rev. Sci. Instr., 36, 429 (1965).
3. A.M. Sessler and V.G. Vaccaro CERN 67-2 (1967).
4. A.G. Ruggiero and V.G. Vaccaro, ISR-TH/68-33 (1968).
5. E. Keil and W. Schnell, CERN-TH-RF/69-48 (1969).