Plasma chamber style fusion reactors, by me :] want input.

[Aquariumnerd]

Ok i love Google sketchup. Now i have finished A levels and I’m hopelessly trying to get a summer job, i have spare time. So aside form my fusion project I have drawn what i think a small fusion power station internals should look like. Correction ‘drawing’. But i cant wait to post it and get peoples input. In my idea two large fusion chambers are used in series. Maybe one larger one would be better. A high vacum is present in the fusion chambers and the conventional high voltage DC is applied between the electrodes. The idea i have is to use the vacuum needed for fusion in the chambers, but circulate the primary coolant ‘the deuterium and helium itself’ through a closed loop. In a section of this loop a turbo molecular pump and another direct drive pump is used to compress the gas to atmospheric pressure. This increase in pressure increases the temperature proportionally creating a larger temperature gradient for heat exchange to secondary coolant and the heat engine. The idea of circulating gas in a high vacuum through a heat exchange seemed insane and wouldn’t work very well. Although the heat pump requires an energy input i believe this is the only sensible way of harvesting the energy form this kind of fusion. Also less or no insulation is now required on the fusion side of the loop.The gas which is now near atmospheric pressure is circulated through the heat exchanges, then a reducer. I like to think of it as being the turbo-molecular and direct drive pump creating the vacuum. As you can see i have just about started drawing the turbo-molecular pump. Based on what we where taught in physics this term, im aware that the energy gain by the deuterium nuclei is not effected by the radius. Other than the fact more collisions with other gas molecules are likely at a larger radius, and so less individual gain in kinetic energy of many nuclei. However it seems logical since area is proportional to radius squared, more gas molecules from the radius that gives them the correct gain in kinetic energy will be accelerated:/ So the reaction chambers need to be large. I was messing with a flyback transformer, and it made me think maybe something similar but larger would be good as a power supply.. Just on a larger scale and driven by igbt’s.. Originally i was thinking crockford walton voltage multiplier :/
Here is the link http://sketchup.google.com/3dwarehouse/details?mid=bf2294b28f9ca58847c4b29672dcdc93&prevstart=0
To see details download it. Normal sketchup is free.

I decided to use two IR cameras mounted on the sides of the chambers. I’m not sure what u guys think about this method of viewing the inside of the chambers running :/. There is a power bus to run the cameras shown in the drawing and the cameras will be shown wired up by serial fiber optic data bus soon along with all other sensory devices i will include 🙂 Any thoughts on the drawing and the ideas I’m incorporating into it :/? I’m aware there are a few problems with the support for the power bus in the drawing 😉 The cables supplying the large magnitude negative voltage to the inner grid are thick. They need not have a large conductor cross sectional area, but the extra insulation does not hurt. I have some slices of grid power cables and I’m aware that most are very over-insulated like this. Disk insulators are used at the connection to prevent flash over to the outer grid if connection is dodgy. These could be made of pvc or anything. Very thick concrete walls will be used to absorb radiation form fusion reactors. I would have thought when the chambers minus dc power supply is cut, technician could straight away service the reactors. Am i right in thinking the only source of radiation, ‘gamma, beta etc’ is from radioisotopes made by neutron bombardment decaying :/ and there should be no neutron flux.

[Aquariumnerd]

uploading pictures failed because of file size :/

[jamesr]

The bulk of the radiation would, I think, be bremsstahlung x-rays. So if you’re running at say +/-20kV on the power supply, then electrons accelerated upto 40keV can emmit a photon of upto that energy when they scatter off an ion. Of course this is a lot softer than the other sources if you actually get any nuclear reactions, and so mostly won’t penetrate the chamber walls. But they shouldn’t be ignored as they could give you a serious dose if you were standing in front of the camera windows.

You should build in interlocks – so you can only turn it on from outside the room/behind concrete wall.

[Aquariumnerd]

sorry keeps posting everything twice.

[Aquariumnerd]

thanks man. Could the xrays them self possibly used for imaging :/ With a number of sensors containing a photo phosphore and photo-diodes and collimator in-between etc or something :/ physics is all coming back to me :] Would the absorption by the walls be too much to produce a good image like this. Wouldn’t IR be cheaper anyway and better quality. Could someone explain to me, is the emittion of xrays anything like pair production, so i know its caused by the photoelectric effect but is there any way of pinpointing the virtual point at which the xray came from without a sensor all around the device :/ :/ Seems mad but just asking because it sounds possible. I just like to ask these things if u get me.

[Aquariumnerd]

One more thing. I know this isn’t that relevant, but this is the lounge. If you don’t mind could everyone who is good at electronics post as many abbreviations like rss used on data sheets. and the meaning Its taking me ages to get good at reading them. If it where not for these abbreviations, i would probably be pro by now lolol.

[jamesr]

Aquariumnerd wrote: thanks man. Could the xrays them self possibly used for imaging :/ With a number of sensors containing a photo phosphore and photo-diodes and collimator in-between etc or something :/ physics is all coming back to me :] Would the absorption by the walls be too much to produce a good image like this. Wouldn’t IR be cheaper anyway and better quality. Could someone explain to me, is the emittion of xrays anything like pair production, so i know its caused by the photoelectric effect but is there any way of pinpointing the virtual point at which the xray came from without a sensor all around the device :/ :/ Seems mad but just asking because it sounds possible. I just like to ask these things if u get me.

From http://en.wikipedia.org/wiki/Bremsstrahlung:

Bremsstrahlung (German pronunciation: [ˈbʁɛmsˌʃtʁaːlʊŋ], from bremsen “to brake” and Strahlung “radiation”, i.e. “braking radiation” or “deceleration radiation”) is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typically an electron by an atomic nucleus. The moving particle loses kinetic energy, which is converted into a photon because energy is conserved. The term is also used to refer to the process of producing the radiation. Bremsstrahlung has a continuous spectrum, which becomes more intense and shifts toward higher frequencies when the energy of the accelerated particles is increased.

In a plasma the electrons are constantly scattering through small angles, emitting relatively low energy 10-100eV photons, as the angle of scatter increases more of the energy is transferred, and the photon is in the 10’s keV range.

There is very little radiation in the IR->visible region, since this corresponds to the kind of energies of bond vibrations (IR) and electrons dropping down from excited states in bound atoms (visible). In a fully ionized plasma there is simply no mechanism for emission in this range. The plasma only glows with the characteristic redish purple at the coolest places, where some recombination to neutral hydrogen is taking place (ie. where the temperature is less than a ~10eV).

The X-rays can be used for imaging directly. Since they cannot be focus easily, the best way is with a simple pin-hole camera. That is a metal plate with a small hole in and a piece of photographic film a short distance behind. You can use B/W photographic paper directly leaving it in a sealed envelope so as to not expose it to light, then develop as per normal.

However, only the highest energy x-rays will have a chance of getting through the window, due to photoelectic absorbtion. Unless the window is made from something like Beryillium (not possible in an amateur setup). So, with the window acting as a high pass filter the image formed will only be of the hottest parts of the plasma. The combination of Xray and visible image therefore gives you lots of information about the temperature distribution.

Other X-ray interaction mechanisms only become important at even high energies. 100keV->2MeV for Compton scattering, and >1.02MeV for Pair production can (ie the rest mass of an electron and position)

[Aquariumnerd]

thanks. I i find that very interesting :], what is it about the arrangement of electrons in the beryllium that means there is no or less photoelectric absorption, physics teacher never liked to talk about that. :/ and does the photoelectric absorption always result in the release of electromagnetic waves of a different wavelength :/ How broad would the range of wavelengths be released and what wavelength :/ For the home project i was thinking of something simple lol just to prove i am getting fusion. im getting closer, just ordered the microwave caps 😀

[jamesr]

Aquariumnerd wrote: does the photoelectric absorption always result in the release of electromagnetic waves of a different wavelength

You have it backwards. The photoelectric effect is the absorption of a photon by an atom, kicking out an electron, not the release of a photon. As such the absorption cross section rises with the number of electrons in the material the x-ray photons are passing through, ie the atomic number of the element. (The electron will just bounce around depositing its energy as heat (lattice vibrations) until it recombines with another atom).

The absorption cross-section is roughly proportional to atomic_number^4/(photon_energy^3). Since Beryillium is only Z=4, it is the lowest atomic number material that is strong enough to make vacuum chamber windows from.
This datasheet shows even Beryllium absorbs most photons below around 1.5keV
http://www.profluxpolarizer.com/PDF/Windows/Duraberyllium.pdf

If the window was normal glass (silicon dioxide) then the aborption would be much higher, and lead glass would absorb almost all x-rays. Just to be complete, the absorption curves of materials also have spikes where if the energy of the photon is just over the threshold to kick out one of the inner electons from an atom the probability of absorption goes up, these are known as the K,L & M edges corressponding to the energy of the first three atomic shells of an atom.

[Aquariumnerd]

thanks 🙂 yeh i kind of remember the photoelectric effect and work fucntion stuff now from college i just forgot it quickly haha. 🙂

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