| 摘要 |
A scanner (12, 13) deflects the electron beam (17) transversely back and forth over a set angle, with respect to the strands (19a-e). Separate deflection magnets (16, 16') further control the beam, altering the directions (R1, R2) at which it encounters the strands. An Independent claim is included for the corresponding equipment. Preferred features: Deflection magnets (16, 16') are controlled. They produce a varying magnetic field of instantaneous uniform strength and direction, in the fanned-out region of the beam. Field strength is controlled synchronously with the primary beam deflection, to redirect (R1, R1) the beam. The scanning frequency is fs. The steering magnet (16, 16') field frequency is fB, which is greater than, equal to or less than fs. The frequencies are equal. Directions (R1, R2) of encounter change at each reversal of beam scanning direction. fs and fB are in a set harmonic relationship, hence altering the scanning pattern (illustrated by graphs in the disclosure). The strands run at speed v beneath the scanner. The scanning beam width measured along the strands (i.e. transversely to the scanning deflection) is W. The minimum magnetic field frequency is then v/W. Salient features of the equipment claimed, include the oscillator (22) determining scanning frequency and the control gear (23, 24, 25) relating magnetic field and beam redirection frequency, to that of the oscillator. This equipment includes a frequency divider (23) and function generator (24). The parallel arrangement of magnetic coils, yoke structure and air gap redirecting the beam, is described. Primary scanner (12) with deflector (13) may be followed by the redirection magnets (16') and an electron beam window (15).
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