A step toward fusion power: MIT advance helps remove contaminants that slow fusion reactions

Dec 02, 2010 by David L. Chandler, MIT News
Photo of the interior of Alcator C-Mod during a test run shows the glowing hot plasma, which can reach more than 55 million degrees Celsius. Image: Plasma Science and Fusion Center

The long-sought goal of a practical fusion-power reactor has inched closer to reality with new experiments from MIT’s experimental Alcator C-Mod reactor, the highest-performance university-based fusion device in the world.

The new experiments have revealed a set of operating parameters for the reactor — a so-called “mode” of operation — that may provide a solution to a longstanding operational problem: How to keep heat tightly confined within the hot charged gas (called plasma) inside the reactor, while allowing contaminating particles, which can interfere with the fusion reaction, to escape and be removed from the chamber.

Most of the world’s experimental fusion reactors, like the one at MIT’s Plasma Science and Fusion Center, are of a type called tokamaks, in which powerful magnetic fields are used to trap the hot plasma inside a doughnut-shaped (or toroidal) chamber. Typically, depending on how the strength and shape of the magnetic field are set, both heat and particles can constantly leak out of the plasma (in a setup called L-mode, for low-confinement) or can be held more tightly in place (called H-mode, for high-confinement).

Now, after some 30 years of tests using the Alcator series of reactors (which have evolved over the years), the MIT researchers have found another mode of operation, which they call I-mode (for improved), in which the heat stays tightly confined, but the particles, including contaminants, can leak away. This should prevent these contaminants from “poisoning” the fusion reaction. “This is very exciting,” says Dennis Whyte, professor in the MIT Department of Nuclear Science and Engineering and coauthor of some recent papers that describe more than 100 experiments testing the new mode. Whyte presented the results in October at the International Atomic Energy Agency International Fusion Conference in South Korea. “It really looks distinct” from the previously known modes, he says.

While in previous experiments in tokamaks the degree of confinement of heat and particles always changed in unison, “we’ve at last proved that they don’t have to go together,” says Amanda Hubbard, a principal research scientist at MIT’s Plasma Science and Fusion Center and coauthor of the reports. Hubbard presented the latest results in an invited talk at the November meeting of the American Physical Society’s Division of Plasma Physics, and says the findings “attracted a lot of attention.” But, she added, “we’re still trying to figure out why” the new mode works as it does. The work is funded by the U.S. Department of Energy.

Alcator C-Mod, shown here, is the most powerful university-based fusion device in the world. Recent findings there could help point the way to power-producing fusion reactors. Image: Plasma Science and Fusion Center

The fuel in planned tokamaks, which comprises the hydrogen isotopes deuterium and tritium, is heated to up to more than 100 million degrees Celsius (although in present reactors like Alcator C-Mod, tritium is not used, and the temperatures are usually somewhat lower). This hot plasma is confined inside a doughnut-shaped magnetic “bottle” that keeps it from touching — and melting — the chamber’s walls. Nevertheless, its proximity to those walls and the occasional leakage of some hot plasma causes a small number of particles from the walls to mix with the plasma, producing one kind of contaminant. The other kind of expected contaminant is a product of the fusion reactions themselves: helium atoms, created by the fusing of hydrogen atoms, but which are not capable of further fusion under the same conditions.

When a fusion reactor operates, the impurities accumulate. Whyte says there have been various experimental observations and theoretical proposals for removing them at intervals after they accumulate. Now, he says, “We seem to have discovered a completely different flushing mechanism … so they don’t build up in the first place.”

One of the keys to triggering the new mode was to configure the magnetic fields inside the tokamak in a way that is essentially upside-down from the usual H-mode setup, Hubbard says.

The findings could be significant in enabling the next step forward in fusion energy, where fusion reactions and power are sustained mostly by “self-heating” without requiring a larger constant addition of outside power. Researchers expect to achieve this milestone, referred to as “fusion burn,” in a new international collaboration on a reactor called ITER, currently being built in France. The findings from MIT “almost certainly could be applied” to the very similar design of the ITER reactor, Whyte says.

Patrick Diamond PhD ’79, professor of plasma physics at the University of California at San Diego, says, “The findings are potentially of great importance,” because they could solve a key problem facing the design of next-generation reactors: the occurrence of unpredictable bursts of heat from the edge of the confined plasma, which can “fry” some of the tokamak’s internal parts. “The I-mode eliminates or greatly reduces” these bursts of heat, “because it allows a steep temperature gradient — which is what you want — but does not allow a steep density gradient, which we don’t really need,” he says.

Diamond adds that theorists will have their work cut out to explain this mode. “Why do heat and particle transport behave differently? This is a really fundamental question, since most theories would predict a strong coupling between the two,” he says. “It’s a real challenge to us theorists — and important conceptually as well as practically.”

Rich Hawryluk, a researcher at the Princeton Plasma Physics Laboratory, says this is a "significant advance" which has generated considerable international interest and that other groups are now planning to follow up on these results. One area of research will be whether it is possible to "reliably operate in the I-mode and not go into the H-mode, which might have these violent edge instabilities. The operating conditions and the control requirements to stay in I-mode need to be better understood."

Hubbard explained that one of the key differences that made it possible to discover this phenomenon in MIT’s Alcator C-Mod was that this relatively small reactor, though large enough to produce results relevant to future reactors such as ITER, has great operational flexibility and can easily follow up on new findings. While larger reactors typically plan all their tests up to two years in advance, she says, “with this smaller machine, we have the ability to try new things when they appear. This ability to explore has been a key.”


This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

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User comments : 34

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gopher65
4.6 / 5 (9) Dec 02, 2010
Wow, this is a really big deal. I'm not sure that anyone predicted that this was even possible a few years ago. I wonder if these results will be integrated into ITER?
Bob_Kob
3.4 / 5 (7) Dec 02, 2010
Fusion is going to be the greatest device ever created by man.
Mr_Man
2.3 / 5 (3) Dec 02, 2010
I'm sure it wouldn't be possible to post a thorough answer to my question here, but I'm interested to know how a magnetic field can control/contain plasma at 55 million degrees - or how a magnetic field can contain matter like plasma at all. Can anyone provide some insight?
SincerelyTwo
5 / 5 (2) Dec 02, 2010
Mr Man,

http://en.wikiped...physics)

There's a heading titled 'Magnetization' which might be more to the point;

http://en.wikiped...physics)#Magnetization
rgwalther
5 / 5 (4) Dec 02, 2010
It is something of an understatement to use the term 'melting' to describe what happens when a 100 million C temperature interacts with an unprotected, man-made surface.
Sonhouse
5 / 5 (4) Dec 02, 2010
Wow, this is a really big deal. I'm not sure that anyone predicted that this was even possible a few years ago. I wonder if these results will be integrated into ITER?


The good news is ITER has not even been fully designed much less built so if this development turns out to be really significant with no gotcha's, it for sure can be incorporated into the design.
Mr_Man
5 / 5 (2) Dec 02, 2010
Mr Man,

http://en.wikiped...tization


yeah that is perfect, I found what I was looking for there. Thanks!!
that_guy
1 / 5 (5) Dec 02, 2010
I'm sure it wouldn't be possible to post a thorough answer to my question here, but I'm interested to know how a magnetic field can control/contain plasma at 55 million degrees - or how a magnetic field can contain matter like plasma at all. Can anyone provide some insight?


Did you think to google? The definition of plasma is ionized gas (Stripped of electrons), therefore a plasma is inherently magnetic.
Skepticus
2.3 / 5 (3) Dec 02, 2010
Somehow I got the feeling that the current approach to fusion is like trying to make a needle from rubbing down a crowbar...theoretically and practically it will get there, but very, very slowly. What we need is a major techonological break through. I hope some bright minds will hit on the better way to control the fusion plasma soon.
that_guy
2.8 / 5 (4) Dec 02, 2010
Somehow I got the feeling that the current approach to fusion is like trying to make a needle from rubbing down a crowbar...theoretically and practically it will get there, but very, very slowly. What we need is a major techonological break through. I hope some bright minds will hit on the better way to control the fusion plasma soon.


I hear your sentiment skepticus. In the world of fusion though, this counts as the biggest breakthrough in the decade. With this insight It'll be 50 years until the first commercial reactor instead of 60.
Modernmystic
1 / 5 (1) Dec 02, 2010
Fusion is going to be the greatest device ever created by man.


Actually that's going to be an nano-assembler...but it's hard to thing of a better second place than a working fusion reactor...
Skepticus
3 / 5 (2) Dec 02, 2010
Somehow I got the feeling that the current approach to fusion is like trying to make a needle from rubbing down a crowbar...theoretically and practically it will get there, but very, very slowly. What we need is a major techonological break through. I hope some bright minds will hit on the better way to control the fusion plasma soon.


I hear your sentiment skepticus. In the world of fusion though, this counts as the biggest breakthrough in the decade. With this insight It'll be 50 years until the first commercial reactor instead of 60.


Damn... I'd been looking towards my first fusion-powered flying jet for the celebration of my 100th birthday...!
holoman
3.5 / 5 (2) Dec 02, 2010
1. Too many assumed assumptions will kill Torroid
fusion designs.

2. BeO panels are not homogenous monolithic parts.

3. Coconut husks used to clean debris in core.

4. Boraxo used to capture some atomic species.

5. Magnetic dissconnects will always permeate the
designs because of inherent flaws.

These any many other problems that will keep this fascination energy technology in the realm of give
me more research money and SOMEDAY a solution may be found. Universities not really interested in
producing a product just conducting more research.

I say scrap the torroid concept and start over.

StandingBear
1 / 5 (7) Dec 02, 2010
Someone has not been paying attention to how magnetism can at sufficient intensities levitate seemingly non magnetic matter. Who knows, form follows function, UFO's all over assume circle shapes. Possibly the early ones those people developed contained working tokomak type fusion reactors, used magnetoelectrohydrodynamic forces to a central plasma thruster similar to Deep Space 1 but wayyys stronger, and later moved to using magnetic forces to levitate the craft in gravity wells whilst the thruster for space propulsion. This could be made photonic with the Shawson principle, Hi Q propellantless at the axis of the Tokomak. Keep the saucer shape to minimize mass for gravity well travel. Later when the gravity equals vector cross product of dark energy and magnetic force tech is discovered as a corollary of the discovery of how to generate dark energy, then this can also become part of the design of interstellar drives that bend space
eachus
not rated yet Dec 02, 2010
I say scrap the torroid concept and start over.


Most people working in the field were not born when the decision (by the US Government) to focus on tokamak reactors for research was originally made. Every so often a group of scientists will try, not so much to get the decision changed, but to get funding for the research applicable to real fusion power plants.

Toakamks require a magnetic field which changes, in fact it has to continue to grow stronger during operation. So at best with a tokamak you are looking at confinement times on the order of one second. With a magnetic mirror configuration, some plasma will always leak out the ends. One early solution was to glue the ends together, but this lead to problems caused by particles constantly circling around. Tokamaks were a way of making this an advantage.

If you are designing a power plant, just make it big enough. Now the reaction keeps the plasma hot enough and the leaking plasma can be used for power generation.
nevermark
3.7 / 5 (3) Dec 03, 2010
Fusion is going to be the greatest device ever created by man.


Actually that's going to be an nano-assembler...but it's hard to thing of a better second place than a working fusion reactor...


I vote for artificial intelligence, once it is marginally smarter than us, as being the greatest device ever created by man, especially since that will signal the end of humankind's need to make its own devices.

But nano-assemblers and fusion reactors will be nice to have around!
Bob_Kob
not rated yet Dec 03, 2010
However I think that fusion power will be the catalyst to lead to those technologies. Nano assemblers and AI will need a lot of juice!
_ilbud
1 / 5 (1) Dec 03, 2010
Busard solved all the problems before he died.
gopher65
5 / 5 (2) Dec 03, 2010
_ilbud: Actually, the currently polywell design has been found to be highly flawed. Recent simulations suggest that in order to make a small, "mobile" polywell reactor hit Q=1, the reactor core would have to be a minimum of 150 metres in diameter... and that's in a perfect, simplified simulated world. In reality the core would have to be much larger. Since a spherical core 150 metres in diameter is already unwieldy, the currently polywell design won't work.

Fortunately it may be possible to reduce the current design issues to manageable levels with only a modest redesign:). So there's still hope for polywell to work.

But to claim that Bussard solved all the problems with Fusion? That's just incorrect. We don't even know yet if he was on (one of) the right path(s) to fusion power.
ekim
1 / 5 (2) Dec 03, 2010
http://www.genera...ign.html
A working fusion reactor in four years.
PPihkala
1 / 5 (1) Dec 03, 2010
I wish they would throw same amount of money that is today used to research hot fusion to research cold fusion or what ever name one wants to use for it. It's much more manageable because one does not need these huge power plants that tokamaks will give us, if they ever reach the point of surplus energy, which is needed for them to produce net energy. Cold fusion devices are much smaller and therefore are more suitable for decentralized power generation. The biggest problem might be that solid state physics is not that advanced yet, which has given problems because there are no generally accepted theories what is happening at those cold fusion reactions. They are real, that is certain, but lack of accepted theory has kept main stream researchers away from it. Another factor is hot fusion competing for research money. For anybody that don't think so, just look at www.lenr-canr.org and there should be enough to educate to think otherwise.
PPihkala
1 / 5 (1) Dec 03, 2010
I think this is a good explanation why there has been slow progress with cold fusion:
http://www.lenr-c...rtra.pdf
robbor
not rated yet Dec 05, 2010
1 problem solved...10,000 more to conquer?
TAz00
5 / 5 (1) Dec 05, 2010
I'm sure it wouldn't be possible to post a thorough answer to my question here, but I'm interested to know how a magnetic field can control/contain plasma at 55 million degrees - or how a magnetic field can contain matter like plasma at all. Can anyone provide some insight?


Plasma has a charge, and thats why we can manipulate it with magnetic fields. Take a look at the vasimr engine.
MorituriMax
2.3 / 5 (3) Dec 05, 2010
I'm sure it wouldn't be possible to post a thorough answer to my question here, but I'm interested to know how a magnetic field can control/contain plasma at 55 million degrees - or how a magnetic field can contain matter like plasma at all. Can anyone provide some insight?


that_guy excreted,
Did you think to google? The definition of plasma is ionized gas (Stripped of electrons), therefore a plasma is inherently magnetic.


I'm sure he thought to google, but it's always easier when someone can point you to a specific link among the thousands or hundreds of thousands of hits google can return. Sort of like what you could have done yourself, and then post the best link you found. Instead of just shitting on him to make yourself feel good. Payback is better if you actually help people.
rbrtwjohnson
not rated yet Dec 05, 2010
I believe a steadier step toward fusion power is by using electrostatic fusion methods.
http://www.crossf...iew.html
sender
5 / 5 (1) Dec 05, 2010
Seems like quantum thermometric field effects are eluding standard fluid theory from what the article reads?
stefunsea
not rated yet Dec 05, 2010
Mode I actually seems more interesting than another mode of operation of tokamak, it has the advantage of not having instabilities called "ELM'S" created by the H mode, but this mode of operation is now very difficult to get .. the road to fusion energy is still a long hard ... ITER will show us the way!
this remains the best solutions for providing energy for future generation ...

Ratfish
not rated yet Dec 06, 2010
Fusion is really interesting and I'm sure we are gaining knowledge that can be used elsewhere, but realistically speaking, the best reactors for the near-term are going to be something like LFTRs, right?
Dummy
1 / 5 (1) Dec 06, 2010
C'mon strap some boilers on that thing and lets generate some steam!
ekim
5 / 5 (1) Dec 08, 2010
I believe a steadier step toward fusion power is by using electrostatic fusion methods.
http://www.crossf...iew.html

Nice reactor design. Innovative in generating electricity and doesn't suffer from neutron degradation of the reactor walls. However the technology seems advanced and it would take time to sort out the bugs. I still favor General Fusion's reactor being the first to produce energy commercially. Of course Crossfire would be more portable and beneficial in the long run.
that_guy
1 / 5 (2) Dec 08, 2010
that_guy,
Did you think to google? The definition of plasma is ionized gas (Stripped of electrons), therefore a plasma is inherently magnetic.


I'm sure he thought to google, but it's always easier when someone can point you to a specific link among the thousands or hundreds of thousands of hits google can return. Sort of like what you could have done yourself, and then post the best link you found. Instead of just shitting on him to make yourself feel good. Payback is better if you actually help people.

If it was for something involved and not easily searchable, I would agree with you, but if it shows that you know absolutely nothing about the article you're reading, then google it, especially this, which will get you a relevant result in the first or second option. I would only ask, if the information I'm looking for is not easily available. If I don't even know all the basics to an article, I'll wikipedia or google info on the subject firt.
Olivia
not rated yet Dec 14, 2010
It is something of an understatement to use the term 'melting' to describe what happens when a 100 million C temperature interacts with an unprotected, man-made surface.


Yeah, it is an understatement of the century. Well but, there shouldn't be any word that can describe change from solid to plasma phase in ONE word.
Kny
not rated yet Jan 25, 2011
It is something of an understatement to use the term 'melting' to describe what happens when a 100 million C temperature interacts with an unprotected, man-made surface.


Actually 'melting' is a huge exageration. The plasma might be 100 million degrees hot, but its mass is so low, that the only measurable outcome of a plasma containment failure is that it cools and shuts down. It's all down to heat capacity...

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