1. J. Kelly, Adv. Electron. Electron Phys. 43, 116 (1977).
2. L. P. Ovsyannikova and T. Ya. Fishkova, Zh. Tekh. Fiz. 70(8), 104 (2000) [Tech. Phys. 45, 1058 (2000)].
3. L. P. Ovsyannikova and T. Ya. Fishkova, Zh. Tekh. Fiz. 56, 1348 (1986) [Sov. Phys. Tech. Phys. 31, 791 (1986)].
4. L. P. Ovsyannikova and T. Ya. Fishkova, Zh. Tekh. Fiz. 58, 1176 (1988) [Sov. Phys. Tech. Phys. 33, 692 (1988)].
5. A. M. Strashkevich, in Electron Optics of Electrostatic Systems (Énergiya, Moscow, 1966), p. 141.