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Rapid-fire: Electrical circuit may bring Sandia Z to fusion sooner
Posted on Wednesday, April 25, 2007 @ 23:41:14 UTC by vlad
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 An electrical circuit that should carry enough power to produce the long-sought goal of controlled high-yield nuclear fusion and, equally important, do it every 10 seconds, has undergone extensive preliminary experiments and computer simulations at Sandia National Laboratories’ Z machine facility.
Picture: From Siberia, not Area 51: Sandia researcher Bill Fowler tests circuits on an LTD device able to produce large electrical impulses rapidly and repeatedly. Photo by Randy Montoya
Z, when it fires, is already the largest producer of X-rays on Earth and has been used to produce fusion neutrons. But rapid bursts are necessary for future generating plants to produce electrical power from sea water. This had not been thought achievable till now.
How does it work?
An automobile engine that fired one cylinder and then waited hours before firing again wouldn’t take a car very far.
Similarly, a machine to provide humanity unlimited electrical
energy from cheap, abundant seawater can’t fire once and quit for the
day. It must deliver energy to fuse pellets of hydrogen every 10
seconds and keep that pace up for millions of shots between maintenance
— a kind of an internal combustion engine for nuclear fusion.
That’s so, at least, for the fusion method at Sandia National
Laboratories’ Z machine and elsewhere known as inertial confinement.
But, unable to produce fusion except episodically, the method has
been overshadowed by the technique called magnetic confinement — a
method that uses a magnetic field to enclose a continuous fusion
reaction from which to draw power.
The electrical circuit emerging from the technological hills may
change the balance between these systems. Tagged as “revolutionary” by
ordinarily conservative researchers, it may close the gap between the
two methods.
The circuit is easily able to fire every 10.2 seconds in brief, powerful bursts.
“This is the most significant advance in primary power generation
in many decades,” says Keith Matzen, director of Sandia’s Pulsed Power
Center.
The new system, called a linear transformer driver (LTD), was
created by researchers at the Institute of High Current Electronics in
Tomsk, Russia, in collaboration with colleagues at Sandia.
Says Rick Stulen, Sandia Vice President for Science, Technology and
Research Foundations, “This new technology not only represents a
remarkable technical advance but also demonstrates the strong
engagement of Sandia's scientists and engineers in the international
community.”
The large-cherry-lifesaver path to nuclear fusion
The circuit — a switch tightly coupled to two capacitors — is about
the size of a shoebox and is termed a “brick.” When bricks are tightly
packed in groups of 20 and electrically connected in parallel in a
circular container resembling a large cherry lifesaver, the aggregate,
or “cavity” as the physicists would have it, can transmit a current of
0.5 megamperes at 100 kilovolts.
A test cavity in Sandia’s Technical Area 4 has fired without flaw more than 11,000 times.
Because the cavities are modular, they can be stacked like donuts
on a metal prong called a stalk. Arranged in a suitable configuration,
they could generate 60 megamperes and six megavolts of electrical
power, enough (theoretically) to generate high-yield nuclear fusion
within the parameters necessary to run an electrical power plant.
“This is a revolutionary advance,” says Craig Olson, Sandia senior
scientist and manager of the pulsed power inertial fusion energy
program.
The next-generation cavity model, now being tested in Tomsk,
transmits 1.0 megamperes at the same voltage and with the same
rapidity. Five such units have been built; four have been purchased by
Sandia, and one by the University of Michigan. The units cost $160,000
each. They too, according to Sandia scientist and project leader Mike
Mazarakis, who supervised the tests at the Siberian site, are
performing without flaw.
“This is an amazing achievement,” says Sandia Vice President Gerry
Yonas, a former leader at Z and of Sandia’s Advanced Concepts Group.
Advantages of the new technology
Happily for Sandia accountants but sadly to those who love the
widely distributed arcs-and-sparks photo of Z firing by Sandia
photographer Randy Montoya, the new switch eliminates the need for the
hundreds of thousands of gallons of insulating water and oil carried by
the present Z structure. It was over the surface of that water that the
electrical arcing of Z became a phenomenon as much appreciated by
graphic artists as it was loathed by engineers (who saw it as wasted
energy). Also gone will be much of Z’s intricate switching. All were
needed to shorten to nanoseconds the machine’s original microsecond
pulse.
The linear transformer driver produces its 100-nanosecond pulse
from the get-go. It works so well because its design lowers inductances
that ordinarily slow electrical transmission.
It does this in part by
eliminating the huge plates and extensive wiring in the current Z
machine, all of which generate magnetic fields.
In the new system, each brick has almost no wiring. Two capacitors
about the size of small thermos bottles are tightly linked to a switch
the size of a lunchbox. There is little opportunity to generate
magnetic fields that slow the passage of current.
Further, linking the bricks in parallel in a cavity not only adds
currents, but decreases inductances to levels significantly less than
previously possible.
The subsets are then linked in series to add voltages.
This allows a very powerful machine to fire very rapidly, with only a thin layer of oil bathing the rings and rows of switches.
The LTD technology is 50 percent more efficient than current Z
machine firings, in terms of the ratio of useful energy out to energy
in. Z is currently 15 percent efficient to its load (already a very
high efficiency among possible fusion machines).
There is, however, a small matter of cost.
Funding for Z historically has been for defense purposes: Its
experiments are used to generate data for simulations on supercomputers
that help maintain the strength, effectiveness, and safety of the US
nuclear deterrent. Even without its rapid repetition capability, a
powerful LTD machine would better simulate conditions created by
nuclear weapons, so that data from the laboratory-created explosion of
Z firing could be used with greater certainty in computer simulations
regarding nuclear weapons. The US has refrained from actual testing of
nuclear weapons for 15 years.
But fired repeatedly, the machine could well be the fusion machine
that could form the basis of an electrical generating plant only two
decades away. Progress in this arena might eventually require funding
from DOE’s energy arm.
To confirm the new Z concept would take $35 million over five to
seven years to build a test bed with 100 cavities. If successful,
future generations of Z-like facilities would be constructed with LTDs.
Funding thus far has come from two US congressional initiatives
through DOE-NNSA Defense Programs, Sandia’s internal Laboratory
Directed Research and Development monies, and Sandia’s Inertial
Confinement Fusion program.
“It’s like building a tinker toy,” says Matzen. “We think we need
60 megamperes to make large fusion yields. But though our simulations
show it can be done, we won’t know for certain until we actually build
it.”
The device was designed by Tomsk pulsed-power head Alexander Kim
with the switch developed by Boris Kovalchuk; its speed-up from a
microsecond to 100 nanosecond firing was urged by Sandia manager Dillon
McDaniel, and encouraged by Sandia managers Rick Spielman and Ken
Struve; the work was led at Sandia and Tomsk by Sandia researcher Mike
Mazarakis; testing at Sandia was by Bill Fowler and Robin Sharpe; the
Z-IFE fusion energy program at Sandia was initiated and is managed by
Craig Olson.
Recent results on LTD development will be presented at the IEEE
International Pulsed Power Conference and the IEEE Symposium on Fusion
Engineering to be held in Albuquerque in June 2007.
Sandia has filed a patent application on a high-power pulsed-power
accelerator invented by William Stygar that can use an LTD as the
primary power generator to replace the conventional Marx generator.
Source: Sandia National Laboratory
Via: http://www.physorg.com/news96730015.html
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Rapid-fire: Electrical circuit may bring Sandia Z to fusion sooner (Score: 1)
by Henry on Thursday, April 26, 2007 @ 17:07:41 UTC
(User Info | Send a Message) | 'Z is currently 15 percent efficient to its load (already a very high efficiency among possible fusion machines). '
If I understand this right, this means the Z is providing an output of 15%*Ein?
(Ein, of course, is the energy in)
Magnetic Confinement fusion devices are up to a Q-factor of approximately 1, with the JT-60 having theoretically broken the 1.5 barrier.
Self-sustaining fusion requires a Q-factor of infinity, and commercial fusion will require approximately 25-30 to be financially viable.
Perhaps I'm misintepreting it and should see a Q-factor of 1.15, rather than 0.15? |
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