An energetic electron beam can pass through a titanium foil from a vacuum into air.
“Continue reading” for ideas on how this might happen.
If I can successfully construct a simple x-ray tube then I will proceed on to this more ambitious project. A simple plan of this is shown below.
I have the 0.001 inch thick Titanium foil below. Strong stuff but fortunately can be cut with scissors.
In air an e-beam (=Beta radiation) travels about 1.2 ft in air at 100 KeV. C-14 beta radiation at 150 keV travels about 10 inches mean (mean distribution is around 1/3 of peak for Beta radiation).
Similarly C14 beta will be blocked by .003 inches of lead. I am hopeful that .001 inches of Titanium which has Atomic No 22 (vs Lead of 82) will not be too great a barrier. Even if I lost half the beam I could get perhaps 6 inches of external e-beam along with a fairly small dose of bremsstrahlung x-rays. Not an e-sabre, rather an e-breadknife. Penetration into plastic is about .02 inches.
My basis for hoping that this will work is Bert Hickmans description of the LINAC used to make the spectacular Lichtenberg figures which operates at a huge 5 MeV at 30 mA. He describes a blue glow in operation. The .0023 inch Titanium foil port is 3 x 48 inches ( 144 in2– this sounds huge).
Mine will be using 1/50th the voltage (and hence 1/2500th the power of each electron) and a port of less than 0.25 in2. The foil is only 40% as thick. The current will only be a 100th at less than 1 mA (I haven’t measured my supply performance at 100 kV).
Multiply all these factors and you arrive at one 1/40,000 the power density up to the foil. The foil may improve this ratio a bit but its absorption may still completely overwhelm 100 KeV electrons.
So, beam weapon it aint. Hopefully with a more intense focus in my favour I can get something.
After discussions it seems that the best way to get good bombarding to red heat is to use a separate cold cathode near the Ti foil target, but a bit separated so it takes the full heat rather then the Ti foil.
The top photo is a plan of a possible arrangement for an electron beam in free air with a filament (from an old TV tube) plus the two cold cathodes.
So far so good. A problem now is the glass to metal seal for the Ti foil or the metal block the Ti foil is mounted on. Solvent free epoxy can be used in a hard vacuum. Glass to metal seals use Dumet wire is used for soft glass and tungsten for borosilicate glass.
Another problem may be matching the impedance of tube to supply. If it draws more than 1 mA then the 100 kv will drop unless I pulse it with a triggered spark gap. If I use a Marx generator to boost the input to 200 kV DC then this is not a problem as it is a pulse generator anyway.
Dissipating the power at the Ti foil which will have air convection on one side only and will be fragile. I am surprised that the LINAC manages with this but the beam area is huge. I may need forced air cooling.
I also wonder about uneven charge effects along the length of the tube. At 200 kv these might be significant and might need equalizing rings.
Photo below is a close up of a cold cathode on my argon tube at a low pressure, not a hard vacuum, running on DC perhaps 200 uA, hence the striations. The cold cathode unit is glass joined (the bulge) to the phosphor tube which gives the desired colour – cold colours like blue are argon and warm colours like red are neon. Mercury is added to increase the UV excitation of the phosphor.
A brief mention of Lenard and Coolidges historical electron beams:
For discussion of this topic on the 4HV forum click here.
These guys have a nice beam in a handheld unit.
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Photo Date: 2004