mattman wrote:Hello,
1. If the gas is puffed in, then the ions are formed in the center, through collision with electrons at ~12,500 eV, then the ions are already in the center. How do ions then "fly in" at 10,000 eV to hit and fuse?
this is a blessing and a curse of gas puff injection - theoretically the protons will never leave a closed boundary - the maximum puff size, so to speak. this is a blessing because hey, that's called confinement. it's a curse, because a lot of those protons are going to find their zero-inertia point at a fairly low potential energy, so yeah, they're not going to have high KE in the center. on the flip side, they will contribute to the density more.
gas puff injection though is a bit of a god-send, as it completely bypasses any electromagnetic issues with injecting charged particles in from the outside. it's largely thought of as the ideal injection method for larger machines, which don't require as much timing precision.
2. If the ions are formed outside the center, at the gun, how are they injected? There is a 12,500 voltage drop to attract the electrons towards the rings. This is an uphill battle for any ion. There is a 10,000 volt negative cloud attracting the ion, but that still leaves a 2,500 hill the ion needs to overcome. You can inject at over 2,500 eV - there is probably some tuning here - but doing that means you will need to make a gap in the 12,500 volt downhill for the electrons.
???
the fusion takes place in the center, not on the rings.
it's a two-step process:
1) the electrons are held in the center by the magnetic fields.
2) the ions are attracted to the center by the electrons.
it's done this way because ions are on the order of 1,000 times as heavy as electrons, so they take on the order of 1,000 times as much force to accelerate, and since magnetic field strength (the lorentz force) is a function of _velocity_ rather than inertia, and at the same inertia the electrons are going 1,000 times faster than the ions, so that's 1,000 times the lorentz force, and f=ma, so a unit of force accelerates an electron 1,000 times more than a proton, multiply the two together and you see that a magnetic field effects an electron 1,000,000 times as much as a proton!
so the magnetic fields confine the electrons a million times better than they do protons. so the whole machine is designed to confine ELECTRONS rather of protons.
but you say, "well that's quite pointless, electrons don't create fusion at all". no they don't but they, attract protons better than anything else in the universe!
so the coils confine the electrons electro-magnetically, which in turn confine the protons electro-staticly. a rather elegant solution, me thinks.
EDIT:
--oh the electrons actually travel uphill. they're pushed that way by the magnetic field which twists and turns them back around. once inside the magrid the protons have a downhill path. outside the magrid, not so much. i presume ion injectors are theoretically on cusps at an electrostatic inflection point, or a little outside and shot w/KE at least high enough to reach the inflection point.