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More Current Make Toks Work Better
More Current Make Toks Work Better
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millions of amps in various plasmas
Hello, this is my first post on this board which I often read.
I second hanelyp's question. Sandia's Z machine injected 18 million amps in its wire-array Z pinch, imploded into an ultra dense, ultra hot plasma on axis (about one-millimeter diameter). It successor ZR triggers 26 million amps, and still the plasma does NOT organizes itself in a helical way. Could someone explain such a difference?
Same thing with the JET tokamac which went up to 4.5 million amp.
I second hanelyp's question. Sandia's Z machine injected 18 million amps in its wire-array Z pinch, imploded into an ultra dense, ultra hot plasma on axis (about one-millimeter diameter). It successor ZR triggers 26 million amps, and still the plasma does NOT organizes itself in a helical way. Could someone explain such a difference?
Same thing with the JET tokamac which went up to 4.5 million amp.
Re: millions of amps in various plasmas
It may be a matter of time. Microseconds vs milliseconds.tokamac wrote:Hello, this is my first post on this board which I often read.
I second hanelyp's question. Sandia's Z machine injected 18 million amps in its wire-array Z pinch, imploded into an ultra dense, ultra hot plasma on axis (about one-millimeter diameter). It successor ZR triggers 26 million amps, and still the plasma does NOT organizes itself in a helical way. Could someone explain such a difference?
Same thing with the JET tokamac which went up to 4.5 million amp.
Engineering is the art of making what you want from what you can get at a profit.
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Re: millions of amps in various plasmas
The Z-pinch is a vertical cylinder, not a torus. Gyromagnetic ratio is the magnetic field (B) over angular precession frequency, and you only get angular precession in a helix inside a torus, because you have to move in two curves to have precession. Therefore you can't get this in a Z-pinch, which is by definition linear.tokamac wrote:Hello, this is my first post on this board which I often read.
I second hanelyp's question. Sandia's Z machine injected 18 million amps in its wire-array Z pinch, imploded into an ultra dense, ultra hot plasma on axis (about one-millimeter diameter). It successor ZR triggers 26 million amps, and still the plasma does NOT organizes itself in a helical way. Could someone explain such a difference?
Same thing with the JET tokamac which went up to 4.5 million amp.
If the JET Tokamak wasn't designed with this effect in mind, then the helical phase change (that's just a guess but I bet it pans out) would be disastrous, and it wouldn't matter if it got smooth above 1.5 MA because the JET can't tolerate the helix at all.
Bussard refers to this helical behavior in the torus when he talks about the size of a Tokamak being dictated by the gyromagnetic ratio, and about what that does to the size and cost of the power plant, in the Google video.
The question posed is [appears to be] "if the Z-pinch machine is unstable, why is a tokamak any better?"
The answer is, essentially, it isn't. What a tokamak has, though, is a thing called a divertor. The notion bandied around that it is a 'magnetic bottle' is quite false because the best that magnets can do is generate an inverted bottle without a stopper. The divertor is the stopper, without which all the plasma would simply escape in an instant. There is a lot of physics that go on at this divertor, which is the [hopefully only] point at which the plasma comes into contact with anything physical.
A Z-pinch machine has no such confining element as a divertor, so all its plasma escapes [over a very short timescale]. A tokamak's divertor slows that process down.
The discussion on helicity is relevant, but a red-herring on this question. Tokamaks are a toroidal z-pinch. But if it were just so, then the plasma would shoot outwards because of the radial asymmetry. By adding a poloidal field, the plasma is caused to rotate as well, such that the inner plasma rotates out to become the outer plasma during its motion around the toroid. This 'evens things out' a little and makes the whole somewhat quasi-uniform. Of course, there is plasma on the outside doing different stuff to that on the inside so it is not uniform at any given moment. The number of times the plasma rotates poloidally to its toroidal rotations is called the 'safety factor' and it is somewhat intutively obvious that the more poloidal rotations can be induced into the plasma for each toroidal rotation then the more stable this setup is.
The answer is, essentially, it isn't. What a tokamak has, though, is a thing called a divertor. The notion bandied around that it is a 'magnetic bottle' is quite false because the best that magnets can do is generate an inverted bottle without a stopper. The divertor is the stopper, without which all the plasma would simply escape in an instant. There is a lot of physics that go on at this divertor, which is the [hopefully only] point at which the plasma comes into contact with anything physical.
A Z-pinch machine has no such confining element as a divertor, so all its plasma escapes [over a very short timescale]. A tokamak's divertor slows that process down.
The discussion on helicity is relevant, but a red-herring on this question. Tokamaks are a toroidal z-pinch. But if it were just so, then the plasma would shoot outwards because of the radial asymmetry. By adding a poloidal field, the plasma is caused to rotate as well, such that the inner plasma rotates out to become the outer plasma during its motion around the toroid. This 'evens things out' a little and makes the whole somewhat quasi-uniform. Of course, there is plasma on the outside doing different stuff to that on the inside so it is not uniform at any given moment. The number of times the plasma rotates poloidally to its toroidal rotations is called the 'safety factor' and it is somewhat intutively obvious that the more poloidal rotations can be induced into the plasma for each toroidal rotation then the more stable this setup is.