Reply To: minimal size device for focus fusion to work?

[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)