Studies of a magnetically compressed electron beam

An experimental investigation of the problem of magnetically compressing a perveance 0.54 \times 10^{-6} A/V 3/2 beam is reported. The feasibility of magnetic compression is demonstrated by passing this beam, compressed in area by a factor of 1000, through a drift tube 0.014 inch in diameter and 1 inch long with 95 percent transmission. The success of the magnetic-compression technique rests on the hitherto unsuspected ability of the beam to damp out undulations and to lose its thermal structure within a relatively short distance. A semiempirical theory from which the field required to maintain the compressed beam can be calculated is also presented.