Observations of high-current electron beam transport in a curved system with periodic solenoid lenses

Abstract

Experiments were performed on high-vacuum transport of a relativistic electron beam (130 A, 300 keV) through a 180° section of a curved transport system. The system was constructed for high-current betatron experiments. The electron beam was directed by a sector-type bending field and focused by an array of 18 solenoidal lenses. The lenses could be operated with the same field polarity (modulated toroidal field) or with alternating polarity (cusp array). The reversing field of the cusp array canceled beam drift motions. Consequently, the beam was quite stable and could tolerate vertical field errors of ±100%. In contrast, beam motion in the toroidal field was dominated by drifts. After propagation through the 3.2-m-long transport tube, significant beam loss was observed with only an 8% vertical field error. Measured displacements of the beam centroid at the end of the transport system were well described by theory in both field geometries.