During experiments on the TMX, it was found to everyone's surprise that the law introduced by Lyman Spitzer in the 1950s was not holding; in TMX at least, electrons on any single magnetic line were found to be in a wide variety of speeds, which was entirely unexpected.
Post at the Lawrence Livermore National Laboratory in the US. With the formation of Project Sherwood in 1951, Post began the development of a small device to test the mirror configuration.
In 1952 they were able to demonstrate that plasma within the tube was confined for much longer times when the mirror magnets at the end were turned on.
At the time, he referred to this device as the "pyrotron", but this name did not catch on. ===Instabilities=== In a now-famous talk on fusion in 1954, Edward Teller noted that any device with convex magnetic field lines would likely be unstable, a problem today known as the flute instability.
In October 1955 he went so far as to state that "it is now becoming clear that in the case of the mirror machine at least these calculations do not apply in detail." In Russia, the first small-scale mirror ("probkotron") was built in 1959 at the Budker Institute of Nuclear Physics in Novosibirsk, Russia.
In October 1955 he went so far as to state that "it is now becoming clear that in the case of the mirror machine at least these calculations do not apply in detail." In Russia, the first small-scale mirror ("probkotron") was built in 1959 at the Budker Institute of Nuclear Physics in Novosibirsk, Russia.
In 1960, Soviet researchers introduced a new "minimum-B" configuration to address this, which was then modified by UK researchers into the "baseball coil" and by the US to "yin-yang magnet" layout.
In 1960, Post and Marshall Rosenbluth published a report "providing evidence for the existence of a stability confined plasma...
where the simplest hydromagnetic theory predicts instability." At a meeting on plasma physics in Saltzberg in 1961, the Soviet delegation presented considerable data showing the instability, while the US teams continued to show none.
These generally worked by changing the shape of the magnetic field so it was concave everywhere, the so-called "minimum-B" configuration. At the same 1961 meeting, Mikhail S.
The tandem mirror concept, developed in the US and Russia at about the same time, offered a way to make energy-positive machines without requiring enormous magnets and power input. By the late 1970s, many of the design problems were considered solved, and Lawrence Livermore Laboratory began the design of the Mirror Fusion Test Facility (MFTF) based on these concepts.
In December 1972, Dean met with the mirror team and made a series of demands; their systems would have to demonstrate an nT value of 1012, compared to the current best number on 2XII of 8x109.
But as experiments continued through 1973, the results were not improving as expected.
The result was 2XIIB, the B for "beams". While 2XIIB was being set up, in November 1974, Fowler received a letter from Ioffe containing a series of photographs of oscilloscope traces with no other explanation.
After considerable concern from the researchers that this would be impossible, Dean backed off to 1011 being demonstrated by the end of 1975. ===DCLC=== Although 2XII was nowhere near the level needed by Dean's demands, it was nevertheless extremely successful in demonstrating that the yin-yang arrangement was workable and suppressed the major instabilities seen in earlier mirrors.
Ioffe's photographs demonstrated that DCLC was being seen in Soviet reactors and that warm plasma appeared to stabilize it. 2XIIB reactor started real experiments in 1975, and significant DCLC was immediately seen.
When the results were seen, they were described as "sunlight was breaking through the clouds and there was the chance that everything would be all right." ===Q-enhancement and tandem mirrors=== In July 1975, the 2XIIB team presented their results for nT at 7x1010, an order of magnitude better than 2XII and close enough to Dean's requirements.
This problem became known as "Q-enhancement". In March 1976, the Livermore team decided to organize a working group on the topic of Q-enhancement at the October 1976 international fusion meeting in Germany.
The final design was presented and approved in January 1977.
Construction of what was then the largest experiment at Livermore was completed by October 1978.
Through late 1978 when the teams began to actually consider the steps in scaling up the TMX, it became clear that it simply would not hit the required goals.
By July 1979, experiments were demonstrating that TMX was operating as expected. ===Thermal barriers and MFTF=== Even before the tandem mirror concept emerged, what was by this time the Department of Energy had agreed to fund the construction of a much larger mirror known as the Mirror Fusion Test Facility, or MFTF.
In January 1979, Fowler stopped the work, stating that some improvement would have to be found. A solution was soon found.
By this time, the Princeton Large Torus had come online and was setting record after record, prompting Hirsch to begin planning for even larger machines for the early 1980s with the explicit goal of hitting breakeven, or Q=1.
While this huge machine was being built, TMX would be modified to test the concept. On 28 January 1980, Fowler and his team presented their results to the DOE.
The proposal was accepted and construction on both systems began, with TMX shutting down in September 1980 for conversion. ===TMX-U fails, MFTF is mothballed=== TMX-U began experiments in July 1982, by which time parts of Boeing 747-sized MFTF were being installed at Building 431.
The proposal was accepted and construction on both systems began, with TMX shutting down in September 1980 for conversion. ===TMX-U fails, MFTF is mothballed=== TMX-U began experiments in July 1982, by which time parts of Boeing 747-sized MFTF were being installed at Building 431.
The machine was completed in 1986, but by this time, experiments on the smaller Tandem Mirror Experiment revealed new problems.
It was investigated at the Oak Ridge National Laboratory until 1986. == History == ===Early work=== The concept of magnetic-mirror plasma confinement was proposed in the mid-1950s independently by Gersh Budker at the Kurchatov Institute, Russia and Richard F.
If the rates seen in TMX-U were typical, there was no way MFTF would come remotely close to its Q goals. Construction on MFTF, already budgeted, continued and the system was declared officially complete on 21 February 1986, at a final price of $372 million.
The DOE also cut funding for most other mirror programs as well. ===After 1986=== Magnetic mirror research continued in Russia, one modern example is the Gas Dynamic Trap, an experimental fusion machine used at the Budker Institute of Nuclear Physics in Akademgorodok, Russia.
Clarke later lamented that the decision to cancel the project was very difficult, "It would have been so much easier if I had a technical failure to point to." It sat unused for several years on the off chance that operational funding would be provided, but it never was and the machine was ultimately scrapped in 1987.
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