I saw this 3D printing technology and think it is the best one out there:
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(some cool videos)
It can print metal (ie titanium, stainless steel) 3D objects from melting metal powder one thin layer at a time in a vacuum using an electron beam.
How hard is it to make an electron beam like this? :) I guess it is very similar to a CRT electron beam except for the power levels and/or focus diameter of the beam? Also an electron beam lithography system has some similarities:
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For hobbyist applications this is a good 3D printer for plastics:
I built a 3-axis positioner with a dremel mounted on it. Did some drilling and routing... I too was fascinated by the makerbot and considered building the extruder head and bolting it to my machine. But I was put off by the $50/spool cost of the plastic filament.
There are guys doing this with computer projectors and a vat of photo-initiated polymer. See :
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You will have to join to see the pix, but they are awesome. These guys are doing it with used DLP projectors and home-made vats with leadscrew elevators.
As in an elephant being very similar to a mouse except for the weight difference.
phy
The electron beam microfabricator that I worked on at Cambridge Instruments had a 20uA primary beam, and could be focussed down to a
10nm diameter spot (though you couldn't get anything like 20uA into a spot that small - the current density at the imaged spot can't be any higher than it was a source).
The machines Jamie is talking about use milliamps of beam current, and look a lot more like an electron beam welder.
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They talk about splitting the beam into multiple spots, which gets around the problem of not being able to get a lot of current (and power) into a small spot.
Not the beam width, but the diameter of the focussed spot. I've no real idea of the depth of focus, but it wasn't large - some microns.
The magnetic lenses were easy enough to focus and if you'd mapped the surface you wanted to write you could vary the focus across the written field.
The deflection from ambient magnetic fields depended on the field. One of my bosses had a great diagnostic moment when riding a lift up to an up-stairs electron beam microfabricator installation that had been giving problems - patterns would spontaneously move by a few hundred microns while being written.
He was an engineering history buff, and recognised the lift as an old hydraulic lift, which consisted big lump of - magnetic - iron pushed up and down in a shaft by water pressure. When the lift was up, and the block of iron was close to the electron-beam microfabricator, the magnetic field at the electron-beam microfabricator was different from when the lift was on the ground floor.
Problem recognised was problem solved - the guys using the machine got to keep the lift out of service when they were writing a pattern.
I was at the Photonics West show. Lumera Laser makes picosecond-pulse lasers that ablate most anything. They had some superb machined/sculpted samples, super resolution, that were made by laser ablation, one from tungsten carbide and one from mastodon ivory (which is legal, whereas elephant ivory isn't.)
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Precision electronic instrumentation
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Do electron beams diverge as they travel due to the electron charge? I guess if they do it also depends on the density of electrons in the beam? And also the divergence angle would depend on the beam velocity.
Incidentally, as you might notice from varying the intensity on a scope, the spot size generally varies with intensity, because the grid cuts off all but a spot of the cathode's surface. Larger spot = larger spot. Although a larger spot delivers more total brightness (same voltage, higher beam current), the intensity is about the same, because the current density of the beam is about the same.
Exceptions include very nicely made tubes, where spot size is dominated by other features, and intensity is particularly high thanks to the accelerator voltage. Some Tek tubes used a mesh grid at the end of the electrode structure to enhance deflection sensitivity, while allowing much higher acceleration voltages; the grid causes some dispersion I think, sinking beam current and causing the beam to be somewhat thicker, more or less independent of intensity setting.
At very high current densities and velocities (relativistic I think), the magnetic field generated by the beam current itself focuses it tighter, much like a high intensity laser beam heats the air, making a light pipe that keeps it from dispersing as quickly.
Tim
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So for an EBM application, would this be a good type of setup for the electron gun?
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Also when searching for "electron gun" on ebay, mostly these come up: ebay search: "Airco Temescal Supersource Electron Beam Gun"
What exactly are they? They look like they are meant for metal sputtering I think.
Also for focusing the beam and deflecting for EBM applications would modules like these work (of the appropriate sizes), also would more than one focusing solenoid be required?
deflection coil: ebay: "Deflection Yoke Coil for Monochrome CRT"
In our case, these would be the scan coils, they diverge the beam on the 1 mil titanium sheet window that keeps the vacuum in check but is thin enough for the electrons to pass/displace.
The focus coils sit above the scan horn and scan coil section. They are responsible for confining the beam to a focal point on the target, the titanium window in this case. THe focus is calibrated to not produce the smallest point, otherwise, we'd be creating holes and enjoy nice implosions from the near perfect vacuum.
Our system uses 100-200 hz of electron beam scanning. Steering coils are in place on some of them to avoid structures that tend to miss align the beam that is not part of the scanning. Also, These are employed with what is called wobble coils to oscillate the beam using 60 hz. This prevents burning of the window material.
At the tips of each scan, on the outer edges of the window (horn), Trapezoid peeks are added in the scan signal to help start the beam back on its return path sooner. The theory here is, the beam spends more time on the edges as it gets ready to scan on the return and thus may heat that section of the window more. So, this wave form was added to help this out however, from what I've seen over all, it does not seem to do much for it. The signal at the peeks are getting lost in the induction of the scan coils.
If you need more specifics, I can supply more but this was just a general break down. As for cooling, we use chilled water that needs to be circulated around the drift tube, aperture and scan horn sections. With out this, thermo distortion in the structure would cause steering problems and heat would cause vacuum leaks.
I guess it is necessary to have the focus and deflection coils aligned very accurately coaxially to the electron beam to allow for a fine focus and proper XY sweeps. For an application with extreme accuracy like an electron microscope, what is the method for aligning the electron beam to these coils? I think for CRT's they can use permanent magnets to move the beam to the center of the coils.
The electron-beam microfabricator used double deflection in two successive sets of X and Y saddle coils to route the beam through the same point at different angles - first you diverted the beam away from the column axis through the deflection angle you wanted, then you bent the beam back through twice the angle to get it going through the column axis at the angle you wanted.
The Cambridge Instruments EBMF 10.5 which I worked on was a bit of a dinosaur in covering a large - 4mm by 4mm - field (which is how we got the job of making the holograms for Australia's plastic bank notes). The beam steering electronics worked to 18-bits - writing 10-bit sub- fields at the rate of one pixel per 100nsec but using a wider, slower DAC to step between sub-fields, where we had to wait a millisecond or two for everything to settle down. There were all kinds of high order corrections for the (small) non-linearity of the deflection system - it was a delightful example of fast precision analog electronics, though it was a bit obvious that it had evolved rather than having been created with the capability of doing everything that it could do in the 10.5.
In particular, the corrections were applied serially, rather than in parallel - there was a problem with the delay through the op amps and DACs creating the correction terms. The system - never built - for which I was in charge of the hardware development, was going to do that in parallel and our best analog engineer designed a phase-linear low-pass filter to delay the main signal enough to allow us to sum in corrections terms generated in parallel.
Thanks, that sounds pretty interesting! :) I was wondering about correcting non-linearities of the deflection and focus coils. I guess there are several important variables including XY desired position of the beam, focus diameter and beam intensity. If beam intensity and focus diamter are constants that makes it a lot easier to calibrate the XY positions probably.
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