Patent GB-1318374-A (GB)
Title: Electron beam heating apparatus
IPC: H05B7/00
Filed: 1970-08-27
Abstract: 1318374 Programme control of electron beam heating apparatus AIRCO Inc 27 Aug 1970 [ 24 Sept 1969] 41345/70 Heading G3N [ Also in Division H3] Molten material 16 in a crucible 18 having fluid coolant passages 19 is heated by an electron beam 17 which is deflected in a discrete pre-set pattern (a-j) Fig. 2, (not shown) over the material surface. The dwell time of the beam at each position is set by adjusting the pusle widths of the respective pulse circuits 29, see Fig 5 (not shown), connected in a ring, there being as many pulse circuits as beam positions, and the positions themselves are determined by the setting of the  emitter resistor taps (69) Fig 6 (not shown), in the deflection signal generators 26,27, each containing as many transistors (66), Fig 6 (not shown), as there are beam positions. Transverse and longitudinal deflection of the beam is performed by magnetic deflection systems 23, 24 respectively, the driving current waveforms being displayed in Figs. 3,4 (not shown). The driving amplifier 28, see Fig 7 (not shown) includes, for each deflection channel, a tap (101) which enables an adjustable D.C. component to be inserted into the driving current waveforms derived from the generators 26, 27. Electrons  emanate from an elongated filament in gun 22. A skull 21 of solidified material acts as a barrier to inter-action between the crucible 18 and the material. The material may be evaporated on to a substrate. Adjustable pulse circuit Fig 5 (not shown). Each circuit comprises a monostable multivibrator, triggered by a positive going pulse on input (52), causing a square pulse, which is fed to both the signal generators 26, 27 via gate circuits (not shown) and whose duration is set by variable resistor (39), to appear at the collector of transistor (34). A trigger circuit including transistor (56) receives the differentiated (network 57, 58,) pulse, and because of blocking diode (59) is sensitive only to the negative going spike of the differentiated waveform, causing triggering of the next pulse circuit in the ring. Operation commences with a start pulse on terminal 31. Deflection signal generators Fig 6 (not shown). Each generator receives signals from all pulse circuits 29, causing one of the transistors (66) corresponding to one of the points a-j to be conducting at any time, and feeding via diodes (71) an output, each portion of which is determined by the setting of one of the taps (69) to correspond to the respective waveforms Figs. 3, 4 ( not shown) to the emitter follower stage (74). The tap (79) determines the overall amplitudes of the waveforms, network (73, 76) protecting subsequent stages against the transmission of spikes. Driving amplifier Fig 7 (not shown). Each channel includes an isolating stage (81) whose emitter follower output is connected between a pair of zener diodes (88, 87) shunted by capacitors (96, 94) in a D. C. carrying chain between voltages +V 2 , -V z , and the respective waveforms from the ends of the zener diodes remote from the emitter follower output are mixed to give controlled D. C. insertion at tap (101). The deflection coils may be driven directly by the ring connter.