http://www.technologyreview.com/energy/21790/page1/
Quote from the article...
"We never know for sure what our budget will be," says Marmar. "ITER is our best hope, but funding is caught in limbo."
Hmmm
BS
MIT Fusion
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Art Carlson
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I don't understand this. I thought there was no way to push a reactor-grade plasma into significant rotation with neutral beams or anything else. The ratio of momentum to energy of a particle beam is (mv)/(0.5mv^2)=2/v. For electromagnetic waves (in vacuum - and ICRH waves do start out in the vaccum), it is 1/c, much smaller.
I thought radio/microwave heating of the plasma has been a major part of the energy input into Tokamaks for years.
http://en.wikipedia.org/wiki/Joint_European_Torus
Perhaps, the use of helium radioheating is new? Or, the evolution of monitering and intervention methods hinted at in the thead below.
viewtopic.php?t=930
Or, old news restated as new...
Dan Tibbets
http://en.wikipedia.org/wiki/Joint_European_Torus
Perhaps, the use of helium radioheating is new? Or, the evolution of monitering and intervention methods hinted at in the thead below.
viewtopic.php?t=930
Or, old news restated as new...
Dan Tibbets
To error is human... and I'm very human.
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Mike Holmes
- Posts: 308
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They sure talk like it's something new and revolutionary.
I think that one of you physics brainiacs is going to have to read the paper in question. Sans that, all we have is a mainstream accounting that can't answer questions like this.
This is, in fact, the third thread discussing this news. It is a testament to my ignorance about the process of information dissemination in the physics community that I was momentarily astonished that Art Carlson (as an example of an intelligent, well-informed physicist) wasn't instantly aware of this development. I'm sure that I have an overblown expectation of the human capacity to absorb all of the new developments that come out.
This makes me somewhat optimistic, as it happens. It means that even Art's skepticism may be based on not knowing something important! Polywell still has a chance!
And, heck, maybe even ITER, too?
Mike
I think that one of you physics brainiacs is going to have to read the paper in question. Sans that, all we have is a mainstream accounting that can't answer questions like this.
This is, in fact, the third thread discussing this news. It is a testament to my ignorance about the process of information dissemination in the physics community that I was momentarily astonished that Art Carlson (as an example of an intelligent, well-informed physicist) wasn't instantly aware of this development. I'm sure that I have an overblown expectation of the human capacity to absorb all of the new developments that come out.
This makes me somewhat optimistic, as it happens. It means that even Art's skepticism may be based on not knowing something important! Polywell still has a chance!
And, heck, maybe even ITER, too?
Mike
News is they have induced a "controlled" rotation in the plasma, thus demonstrating the possibility of stabilising a plasma via a momentum mechanism rather than magnetic.
Fluid dynamic turbulence is THE big problem in plasmas, only secondarily complicated by EM effects. The EM plasma types don't do fluids but do primarily do EM. Most fluid guys do a little turbulence but most avoid it like the pox, none do plasmas.
Rotational flows are a mechanism for stabilising turbulence.
How to sense-calculate-actuate (i.e. control) a rotation in a plasma is a big technical challenge. Sounds like MIT work has made some big steps, particularly novel way of sensing rotation (via a seeded tracer technique common in most fluid experiments) and novel way of actuation of rotation with the large antennae.
snipped (rotation actuation demonstrated):
MIT researchers led by John Rice and Yijun Lin have experimentally demonstrated that radio waves--which will be able to penetrate large plasmas like ITER's--can give plasma both energy and momentum. The MIT group placed powerful antennas at the edge of the reactor to launch two frequencies of radio waves into the plasma. One group of waves is attuned to protons. When these waves collide with protons, they heat up; the protons, in turn, collide with the hydrogen isotope fuel. The second group of waves is attuned to lightweight helium isotopes that the MIT group adds to the mix. These waves collide with the helium, imparting their momentum to the isotopes, which push the rest of the plasma.
snipped (rotation sensing demonstrated):
"People have been thinking about doing this for a long time, but the results were always inconclusive," says Marmar. He says that the key to the MIT group's success with radio waves was its development of more-effective methods for monitoring the plasma. "Most of the time, [physicists] do the measurements using the same neutral beams used to drive flow," says Marmar. The MIT group tracks the flow of its plasma by introducing impurities that it can monitor using x-ray spectroscopy."
Without sensing or actuation you can have no control, it's basics of control engineering theory. With both sensors and actuators you can stabilise an inherently unstable system, like the flight dynamics of a stealth for example, caveat being that you do the math right and wrap the right controller into the loop.
Fluid dynamic turbulence is THE big problem in plasmas, only secondarily complicated by EM effects. The EM plasma types don't do fluids but do primarily do EM. Most fluid guys do a little turbulence but most avoid it like the pox, none do plasmas.
Rotational flows are a mechanism for stabilising turbulence.
How to sense-calculate-actuate (i.e. control) a rotation in a plasma is a big technical challenge. Sounds like MIT work has made some big steps, particularly novel way of sensing rotation (via a seeded tracer technique common in most fluid experiments) and novel way of actuation of rotation with the large antennae.
snipped (rotation actuation demonstrated):
MIT researchers led by John Rice and Yijun Lin have experimentally demonstrated that radio waves--which will be able to penetrate large plasmas like ITER's--can give plasma both energy and momentum. The MIT group placed powerful antennas at the edge of the reactor to launch two frequencies of radio waves into the plasma. One group of waves is attuned to protons. When these waves collide with protons, they heat up; the protons, in turn, collide with the hydrogen isotope fuel. The second group of waves is attuned to lightweight helium isotopes that the MIT group adds to the mix. These waves collide with the helium, imparting their momentum to the isotopes, which push the rest of the plasma.
snipped (rotation sensing demonstrated):
"People have been thinking about doing this for a long time, but the results were always inconclusive," says Marmar. He says that the key to the MIT group's success with radio waves was its development of more-effective methods for monitoring the plasma. "Most of the time, [physicists] do the measurements using the same neutral beams used to drive flow," says Marmar. The MIT group tracks the flow of its plasma by introducing impurities that it can monitor using x-ray spectroscopy."
Without sensing or actuation you can have no control, it's basics of control engineering theory. With both sensors and actuators you can stabilise an inherently unstable system, like the flight dynamics of a stealth for example, caveat being that you do the math right and wrap the right controller into the loop.
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Art Carlson
- Posts: 794
- Joined: Tue Jun 24, 2008 7:56 am
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They talk like they're looking for funding. Americans in particular (at least in the fusion business) have a reputation for hype. Sorry. Make that "effective marketing".Mike Holmes wrote:They sure talk like it's something new and revolutionary.
You're right about that. I'll see what I can do.Mike Holmes wrote:I think that one of you physics brainiacs is going to have to read the paper in question.
Remember that I am no longer actively involved in fusion research. Fortunately the sum of the rate at which progress is made and the rate at which I forget things is small enough that I can still pass as being "well-informed" on a good day.Mike Holmes wrote:... I was momentarily astonished that Art Carlson (as an example of an intelligent, well-informed physicist) wasn't instantly aware of this development.
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Art Carlson
- Posts: 794
- Joined: Tue Jun 24, 2008 7:56 am
- Location: Munich, Germany
Sorry. My local Max-Planck library seems to be a month behind in their subscription to PRL. If somebdy can dig up a copy and mail it to me, I'd be happy to do a book report.Art Carlson wrote:You're right about that. I'll see what I can do.Mike Holmes wrote:I think that one of you physics brainiacs is going to have to read the paper in question.
reply on that page:
The only thing I can think of is the term "over-unity" which I tend to associate with bullshit.
I never heard the term "unity" being used in context of efficiency.
What is unity?ddanimal on 12/10/2008 at 8:35 PM
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3
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Fusion is the energy source of the future, and always will be!
Do they even have a plan for turning this heat energy from fusion into electricity? Steam? Wonder how long it will take to get above unity once steam turbine losses are factored on. Another 50 years?
Rate this comment: 12345
(Reply)
The only thing I can think of is the term "over-unity" which I tend to associate with bullshit.
I never heard the term "unity" being used in context of efficiency.
It seems like everyone missed icarus's summary.
Here's my attempt at a summary:
Turbulent plasma flow reduces fusion. Spinning the plasma like a rifle bullet stabilizes the plasma.
The MIT team is injecting the plasma with impurities (not stated what's used) and using x-ray spectroscopy to measure plasma flow.
They then inject lightweight helium into the plasma. They fire RF energy at the helium to push it. This pushes the plasma as a whole.
They've done basic proof of concept experiments, but because the reactor only works 3 to 4 months out of the year, they need more time to refine the technique.
The technique may be applicable to ITER, but more research is required. That research may not happen because US funding of ITER has stagnated.
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Hope that sums it up fairly well. To me, it sounds like just a really big, complex microwave oven.
Here's my attempt at a summary:
Turbulent plasma flow reduces fusion. Spinning the plasma like a rifle bullet stabilizes the plasma.
The MIT team is injecting the plasma with impurities (not stated what's used) and using x-ray spectroscopy to measure plasma flow.
They then inject lightweight helium into the plasma. They fire RF energy at the helium to push it. This pushes the plasma as a whole.
They've done basic proof of concept experiments, but because the reactor only works 3 to 4 months out of the year, they need more time to refine the technique.
The technique may be applicable to ITER, but more research is required. That research may not happen because US funding of ITER has stagnated.
-----------------
Hope that sums it up fairly well. To me, it sounds like just a really big, complex microwave oven.
What the poster means is "net energy". Energy is required to sustain the fusion reactions. If there's not enough fusion reactions taking place, you have a net loss of energy. At some point, the reaction becomes self sustaing. Energy in equals energy out. Above that point, you're generating excess energy that you can then use for other things.vernes wrote:reply on that page:What is unity?ddanimal on 12/10/2008 at 8:35 PM
Posts:
3
Avg Rating:
2/5
Fusion is the energy source of the future, and always will be!
Do they even have a plan for turning this heat energy from fusion into electricity? Steam? Wonder how long it will take to get above unity once steam turbine losses are factored on. Another 50 years?
Rate this comment: 12345
(Reply)
The only thing I can think of is the term "over-unity" which I tend to associate with bullshit.
I never heard the term "unity" being used in context of efficiency.
You're right, though. Usually when someone talks about "unity", they mean getting energy for free. Here, the cost of the fuel is cheap, but it's not "free".
I've heard of radio waves being used to drive plasma rotation, before this but I haven't gone into any of the theory and I haven't thought that much about the issue of momentum injected over energy injected.Art Carlson wrote:I don't understand this. I thought there was no way to push a reactor-grade plasma into significant rotation with neutral beams or anything else. The ratio of momentum to energy of a particle beam is (mv)/(0.5mv^2)=2/v. For electromagnetic waves (in vacuum - and ICRH waves do start out in the vaccum), it is 1/c, much smaller.
So don't take what I'm about to say at face value as these are just wild guesses but here may be a few ways of inducing rtation without applying net torque to the plasma.
1) Maybe they are talking about inducing a rotation with radio wave in one direction in the centre and the opposite direction at the edge making the net applied torque close to zero.
2) Maybe they are causing fast (He?) particles with low collisionality to rotate in one direction and the main plasma body to rotate in the other.
3) I've also calculated on the back of the envelope that any inducement of net radial current will both set up a radial electric field and set up a plasma rotation and the poynting vector/c (i.e. the electro magnetic momentum associated with the cross product of the radial electric and poloidal magnetic field) is always equal and opposite to the kinetic momentum induced by the radial v cross b current.