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If a pulsating electron beam is beamed down the center of a copper pipe, so as to not make any physical contact with the pipe, the beam should create a pulsating magnetic field that will not change in direction yet will change in strength. This pulsating magnetic field should thus create eddy currents in the pipe that are equivalent in terms of eddy currents to a field that changes direction. Therefore, the induced eddy currents in the copper pipe should oppose/resist the flow of the electrons as they travel through the copper pipe and induction heating will occur.

If so, then I believe that a pulsating electron beam can be used to melt and weld two copper pipes together in perhaps a very short time especially if it is a high powered electron beam.

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  • $\begingroup$ In principle, this seems possible, though the eddy currents are likely to cause instabilities in the electron beam. The relevant ratio for the practicality of such a concept is: (power dissipated in eddy currents) / (power required to produce electron beam). I suspect this ratio is very low, i.e. very little power is transferred (and the more power that is transferred, the more unstable your beam becomes). $\endgroup$ – probably_someone Aug 9 '18 at 15:56
  • $\begingroup$ It seems like it would be very difficult to focus the currents/heating onto such a small area to make it even remotely feasible for welding. This would be especially difficult with copper, because it is very conductive to heat; so even if you could localize the currents, you would need to add a lot of extra heat to offset dissipation. I think you'd be better off sticking to more standard welding techniques. $\endgroup$ – JMac Aug 9 '18 at 16:05
  • $\begingroup$ @probably_someone, so even if more power is applied, it will just result in stronger eddy currents produced in the pipe which will cause the electron beam to become unstable due to the increased magnetic resistance/drag it will encounter as it flows down the length of the pipe, is that what you are saying? $\endgroup$ – user202780 Aug 9 '18 at 18:33
  • $\begingroup$ @FanofComets Essentially, yes. $\endgroup$ – probably_someone Aug 9 '18 at 18:47
  • $\begingroup$ I agree that the pulsing electron flow will induce eddy currents in the copper pipe. However, the heating produced by the eddy currents would not compare with the heating produced by the electron beam itself (a guess of 10 times difference would not be out of range). So, it makes no sense to me why you would want eddy currents instead of direct electron beam heating! $\endgroup$ – Guill Aug 15 '18 at 0:10
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The efficiency of the process would be important in any practical application. An induction forge can be used to weld steel bars together, but it uses rapidly changing current in a coil to induce eddy currents in the steel bars. A pulsating electron beam would produce an RF magnetic field, which would not penetrate deeply into, e.g., copper. Much more efficient, I suspect, is direct electron beam welding, in which the electron beam directly impinges on the workpiece, thereby delivering almost all of its energy to a small spot. Note that for any metal like copper that oxidizes easily, it's important to use flux, inert gas, or a vacuum to exclude oxygen from the site of the weld.

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