Dr. Robert F. Bourque
Los Alamos National Laboratory
bourque
lanl.gov
Yes for Ignition - But...
I agree with Dr. Gross that fusion ignition is essential if we are to move forward. But one problem that clouds the decision process, and may well be inherent in all fusion concepts, is that the benefit (y) versus cost (x) curve is very steep, and crosses the x-axis (no benefit) at nonzero cost. A small increase in cost buys a lot of benefit. We have seen this in ITER, where ITER-Lite has much reduced performance - and lower margins - with not that great a decrease in cost.
However, although all fusion concepts are likely to have steep benefit-cost curves, the curve for each concept is likely to be offset from the others. Some may therefore attain comparable benefits at lower cost than tokamaks.
How will we find out if this is the case? By taking some risks. By investing in other concepts, particularly those that do not seem to need massive toroidal fields for containment, do not require particularly high betas for cost effectiveness, and have simpler geometries that should be cheaper to build.
Why do we look for the lost keys only under the streetlight? Because that's the only place we can see. Why do we pursue fusion only with tokamaks? Because that's the only concept we really understand. That still doesn't make it the best one. But we'll never know whether or not it is until we get a flashlight and look beyond the streetlight.
Robert A. Gross
Columbia University, Emeritus
5 May 2002
r_a_grossmindspring.com
Ignition as a Goal for the New Burning Plasma Experiment
I urge that the new burning plasma experiment have ignition as a primary objective. Although this is a more difficult and expensive goal than a "wet wood" burner experiment, it is important for two basic reasons.
1.- Fusion ignition will reveal new physics. For the first time a thermonuclear deflagration wave (fusion flame) will be seen and can be studied.
2.- Ignited plasma offers new ways to obtain a steady state fusion reactor whose economics can be significantly superior to a pulsed device.
An ignited magnetically confined thermonuclear experiment is the fusion equivalent of the famous self-sustained fission pile criticality experiment of Enrico Fermi. We can and we should make fusion ignition a goal for a new burning plasma experiment.
Robert F. Bourque, Ph.D.
tel 505.662.2469
bourquelosalamos.com
WHAT NEW PEOPLE?
In his Comment, Professor Manheimer suggests that we wait for the new people coming along and let them decide on a burning plasma experiment. The sad fact is that they aren't any new people, or very few. And they're won't be unless incentives are created for young people to join the fusion program. Fusion needs to be viewed as an exciting field in which one would want to commit an entire career, not some relic where the only work is rehashing old stuff. Only a much broader program that encourages innovation and risk will accomplish this. If this is not done, I fear the fusion program will become history.
Wallace Manheimer
Senior Scientist for Fundamental Plasma Processes
NRL Code 6707
manheimeccf.nrl.navy.mil
Rick Nebel points out in his comment that we have proposed a burning plasma experiment eight times over the last twenty years, have come up empty, and each time have sacrificed a part of the program for a "paper tokamak". In my opinion, this argues strongly against proposing one a ninth time; but the argument against such a proposal is really much stronger, for two reasons. First, if the community does come together in Snowmass, unites behind another burning plasma proposal, and then fails again to sell it, could the fusion program take this kind of hit and survive? I fear it could not. Second, as several people here have noted in their essays, the fusion program is at the cusp of a demographic time bomb. Many of the lab heads and senior scientists are near or above retirement age. If the fusion program is to have any hope for the future, then in a few years these people will be replaced by a new group of scientists, probably men and women in their forties. Shouldn't these new people propose the big experiments? It is their future after all. I feel it is likely that they would come up with new and different grand strategies. I, myself have proposed one in these comments (Ignition:NO/Hybrid:YES). There are undoubtedly others as well. There is a real argument for the fusion program to propose nothing big for the next few years, but to just coast as best we can until a new generation of leadership takes over.
Robert F. Bourque, Ph.D.
WE NEED TO SPREAD OUR WINGS!
Is the US fusion program
still aimed toward developing the enormous potential of unlimited power
with zero pollution and modest, controllable radioactivity - one of the
most exciting science programs ever? Or have we become rigid with
age and focused on short-term survival.
We need to rethink the long
term. And we desperately need to encourage young people to join our
increasingly geriatric ranks. But they will want to look at new ideas,
not old stuff that seems to be reaching diminishing returns. The
tokamak was the first confinement concept to show reasonable stability
and heating to near fusion temperatures - via the big hammer of massive
toroidal fields. But the end result, as currently envisaged, is not
commercially viable.
I spent five years involved
in the engineering of ITER, and it became clear that extrapolating this
machine to a power plant is fantasy. Some of the individual components,
like central solonoids, weigh over a thousand tons. There are only
a few cranes in the world that can lift that. And if an activated
coil fails (many are very highly stressed), it would be necessary to replace
it, or rewind it, remotely! This could take years. So much
for plant availability. Total reactor weight approaches two battleships
and costs are several times that of a fission core. Surely there
are better ways to do the job than low-beta tokamaks like this. But
we must search for them.
If this is the best we can
do for a power plant, then fusion power will likely remain a fantasy for
the future. The low-beta tokamak is too heavy, costly, and complex.
It's time to get real. If not, those with presumably a better mousetrap,
like wind or photovoltaics, will be lusting after our financial support.
For the tokamak to be at
all viable, higher betas are needed to reduce coil requirements, and it
must be steady state. But the price paid to achieve these must be
considered: High beta requires noncircular plasmas, that tend to
increase aspect ratio in reactors, and close-in, power-hungry shaping coils.
Steady state currently needs complex, inefficient RF drives that require
increasing the total plant output by 10-20% to support them. One
wonders if there has been a net improvement. Hopefully, other ways
can be found to achieve these goals.
But there may be other, far
better ways to achieve fusion: The recent Innovative Confinement
Concepts workshop at University of Maryland was the most exhilarating fusion
conference I've attended in decades. Presentations that justified
jobs were minimal. Instead, a host of new and promising ideas were
presented, some extremely clever. But these ideas must be enthusiastically
supported in order to be fleshed out, particularly to determine what is
needed to turn them into credible fusion reactors.
The tokamak has done better
than other approaches in part because of a universal scaling law:
taue/$ = constant. I believe we would be astonished at the progress
that could be made if these clever ICC ideas got the support they deserved.
At least 10% of the fusion budget should go into these ideas. It's
a risk, but one well worth it, even at the cost of cutting back slightly
on flagship programs.
If we put all of our fusion
eggs into the low-beta tokamak basket, we risk going the way of the nuclear-powered
airplane. But if we look for new and better ways of doing fusion,
we will, at the least, attract younger minds who can carry on after we're
gone. At the most, we may find something that is easier, cheaper,
and actually commercially viable.
Lastly, a word about hybrids:
we must tread carefully. To introduce fissile material could taint
the perception of fusion, now the holy grail, in the minds of legislators,
the public, and the media. We risk losing much of the enthusiasm
for fusion, and for marginal gain. Having a tritium separation facility
is one thing. Having a fissile material processing plant is quite
another.
Dr.
Rick Nebel
In general, I support a burning
plasma experiment. I plan to go to Snowmass and going into the meeting
I have no preconceived notions as to what that device should be. I have
one question that I would like the proponents of each device to answer.
We have tried to take the
burning plasma experiment step 8 times in the last 20 years (ETF, FED1,
FED2, TFCX, CIT, BPX, TPX, ITER). Each time we've failed. Each time we've
sacrificed part of our program and come up empty. Why is this time any
different? What is fundamentally different about any of these devices which
will allow them to actually be built and operate rather than be just another
paper tokamak?
I don't want to repeat the
past. I think our political problems are at least as formidible as our
technical and structural problems. I would like to see the proponents of
these devices present a credible plan for addressing these problems.
tel 505.662.2469
bourquelosalamos.com
Los
Alamos National Laboratory