Improvements Make More Radiation

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Jason C Wells
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Improvements Make More Radiation

Post by Jason C Wells »

I changed out my planar target for a spherical target. I also added a +400V target bias to attract ejected electrons. My previous target bias was overly complicated and in my estimation, ineffective. My beam current indication is down from 10 μA to 1.0-1.5 μA. (My VDG does 10 μA through a dead short.) The various undesired phenomena like glowing and sparking have been significantly reduced.

Most interestingly, I had to kick my low range geiger counter up to x100 and observed 15 mr/hr at about 4 inches from the target. Last time I mentioned radiation I was excited to report .3mr/hr. I now report a factor of 50 improvement. I'm slowly zeroing in on an effective apparatus!

I don't run my VDG for long periods of time.

The performance dies off over time if I run the VDG continuously. I assume that my glass glass accelerator column is building up charge and killing my beam. I can actually pull tiny sparks off the outside of my column with my finger. Those charges are presumably electrons pulled from the air. My garage does start to smell like ozone. I'm going to have to read up on ozone safety.

Tonight's festivities were not fueled with boron.

Regards,
Jason C. Wells
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Richard Hull
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Re: Improvements Make More Radiation

Post by Richard Hull »

Sounds like you are improving the machine and the 15mr x-rays you are probably looking at at least 40-50kv on the target, but this is just a guess. Even with a few microamps, 100kv would produce a very dangerous blast of x-rays.

Long run times can build up charges on all insulators but far worse is the electrostatic accumulation of dust particles on things that bleed off voltage and, effectively, reduce the efficiency of the insulators involved. Keeping dust off the column and sphere electrode is a major effort. All these should be wiped down prior to every run with a dry cloth.

One of the latest things in model railroading is "static grass". On old layouts, you just put a thin layer of glue on the table and sprinkled this terrible amorphous green grain on the table to represent grass. Now, as model railroading gets more realistic, the green grass is in the form of micro needles. You put dilute water based glue on the table, jab a pin into the wet surface that has a wire going to a hand held wand with a battery powered 20,000 volt DC supply in it, (ultra low current). There is a screened metal cup of the opposite polarity on the other end of the wand filled with needle grass. As the wand is shaken, the oppositely charged needle grass is attracted to the wet table surface where the pin supplies the opposite charge. The grass falls, hits the table, gets stuck in the glue which holds it and with the cup still charged, the needle grass stands straight up stuck on its tail to the table. The result is real indivdual blades of micro grass pointing upward stuck that way forever in the hardening glue.

This same effect, (negative effect), plagues the VDG with dust particles attaching themselves to high tension surfaces, bleeding off the charge. It is to be remembered that the energy from a VDG is merely stored charge due to the terminal's isotropic capacitance only!!!! There is no low impedance power source connection via copper wires in the device to its storage unit, (the large sperical terminal). A larger terminal capacitance means more stored energy and more beam current provided you control bleed points.

Yes, if you choose a VDG for your HV source in an accelerator, you need to have an intimate knowledge of static electricity, isotropic capacitance, and all the ways in which nature hates excess energy at one point and seeks to always leven it out away from its source. With a formal electronic HV power supply nature always loses the battle as a continuous, overpowering source of copper delivered energy is present. The best nature can hope for here is for a horrid arc to kill the supply. Dust and bleed points are here too, but they do not matter unless their accumulation and build up leads to a destructive arc.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jason C Wells
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Re: Improvements Make More Radiation

Post by Jason C Wells »

Did I ever mention that I tried to build a low dollar pelletron? I managed to pull a 1/16 inch spark from it. :) Then I gave up.

Later,
Jason C. Wells
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Dennis P Brown
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Re: Improvements Make More Radiation

Post by Dennis P Brown »

Yes, an electro-static power supply for an accelerator is a difficult approach; Richard hit the nail on the head when he said belt widths of at least six inches are what is needed rather than these tiny belt commercial units that all talk about voltage (often they increase belt length for higher voltage but this provides little help with current and, as I'll address shortly, hinders current) - the issue for any electro-static linear accelerator (ESLA) is manly generating the required current by the VdG; an overlooked issue that may occur is that higher voltage actually works against this goal. A 200 kV unit is superior, in many ways to a 600 kV unit considering dust, humidity and problems installing the accelerator tube become more serious at these higher voltages. In fact, humidity problems, and accelerator tube design to suppress shorting of the VdG will cause headaches for any home made unit; these are issues that laboratories can easily deal with/solve. Belt width (read as current), and providing a a dry environment are the two main issues that no commercial unit will address. I'd guess besides these first two, dust and accelerator current draw/loss from the unit are the others.

Another issue is the VdG itself. Most commercial units are terrible at suppressing voltage leakage; the base of the sphere has the belt tube enter into the sphere in a manner that leaves the entry hole with abrupt edges. A large diameter copper tube should surround this entry point to suppress electric corona discharge at this critical point. Also, copper corona rings should be spaced along the axial length of the belt tube. This also should be done for the accelerator tube. These steps (I took with my system) increase current by reducing loss. Making a larger belt and "sphere" are my next objectives for my unit. Obviously, these later changes aren't modifying an existing commercial unit but rather, a manufacture of an entirely new VdG unit itself.

I did not see you address the manner of how you control polarity of your VdG sphere? This is critical. If it isn't positive than your unit will not accelerate deuterium ions at all. So, I assume you are "spraying" the base of your VdG belt with positive ions (i.e. a corona system charged by a 25 kV positive power supply.) If not, your unit may or may not be positive! Using a spray PS will also increase the VdG's current capability a good bit - or at least in theory (lol.)

Besides the losses along the accelerator tube, deuterium gas entry into the end of the accelerator tube via any type of low pressure line can be a serious current loss - that is, the tube needs to be at atmosphere entering into the sphere (and even then, issues of current loss will still occur but at a significantly reduced rate.) If this line is at vacuum, the gas will light up when the VdG is running and short the sphere (after someone pointed this out to me I saw the effect and it was serious.) I "solved" this problem by installing a small deuterium tank (that I fill to atm pressure with deuterium gas after I pull a high vac on the small bottle) inside my VdG sphere (doing this was far easier than I thought - you can see photo's of my sphere with all its hardware installed; search the "Ion Gun" topic area with my name and view the latest posts or use this link: viewtopic.php?f=12&t=10161.) Of course this means that gas flow into the accelerator tube has to be adjusted with the sphere open but this isn't difficult. Once my accelerator tube is at high vac, I use a fine leak valve to adjust the deuterium flow (i.e the vacuum in the accelerator tube is allowed to go from low 10^-6 torr to mid 10^-6 torr) the sphere can then be closed and the VdG started. The gas supply would last for days.

Building a real dry box that does not create more problems than it solves is a major task that should be considered; your use of wood is self defeating - besides the issue that wood is an excellent conductor at these very high voltages (above 75 kV), it is also extremely dirty (i.e. creates large amounts of conducting dust via wood fibers and particles.)

A strange point that Richard also pointed out (and this anyone building a working ESLA had better take extremely careful note) is that a properly functioning ESLA can be a ferociously powerful x-ray machine. For this reason, I designed a dirt cheap, non-conducting radiation shield wall for my entire system (see my posts on this topic.) I would strongly suggest that you provide your system with shielding if you are serious about getting it to work. ESLA units that produce 10 micro-amps or more at 200 kV will cause your target to "glow" if it isn't properly cooled and if electrons are around (say your suppressor isn't as effective as you think), then the issues of x-rays can be very serious. Obviously, the proton beam itself isn't a radiation hazard.

To see a non-VdG ESLA that is simply beautiful and really professional, see this link:

viewtopic.php?f=12&t=9922

(Aside: this whole thread really should be under the "Ion Gun" topic area, I would think. Maybe post there rather than in the fusor topic area because until you make a proven system, you really aren't making a fusor but rather a "Ion Gun". Just saying.)
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Jason C Wells
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Re: Improvements Make More Radiation

Post by Jason C Wells »

I had considered where I should post. I figured if I was actually trying to do fusion it should go here. Feel free to move the thread.

Regards,
Jason
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Richard Hull
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Re: Improvements Make More Radiation

Post by Richard Hull »

Jason's post here is correct. He is not making an ion gun, but an accelerator that might use one as one of its components. The goal is beam on target fusion. Overall construction is being discussed.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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