Perhapsatron

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The Perhapsatron was an early fusion power device based on the pinch concept in the 1950s. Conceived by James (Jim) Tuck while working at Los Alamos National Laboratory (LANL), he whimsically named the device on the chance that it might be able to create fusion reactions.[1]

The first example was built in the winter of 1952/53, and it quickly demonstrated a series of instabilities in the plasma that plagued the pinch concept. A series of modifications followed which attempted to correct these problems, leading to the ultimate "S-4" model. None of these proved fruitful.

History

Early fusion efforts

Scientists at

atomic bomb
"trigger" was used to provide the required temperatures.

Capturing that energy on a smaller industrial scale would not be easy, since plasma at that temperature would melt any physical container. As plasma is electrically conductive it was obvious that it could be contained magnetically, but the proper arrangement of the fields was not obvious. Enrico Fermi pointed out that a simple toroid would cause the fuel to drift out of the "bottle".[3] Several arrangements were studied, notably the stellarator developed around 1950.

Z-pinch

Main article: Z-pinch
Dark metal tube crushed inward
The Lorentz force created by a lightning strike crushed this hollow lightning rod and led to the discovery of the pinch technique.

An alternate approach was the "pinch" concept, developed in the

magnetic bottle approaches, in a pinch device, the required magnetic field was created by the plasma itself. Since the plasma is electrically conductive, if one were to run a current through the plasma, it would create an induced magnetic field. This field, through the Lorentz force
, will act to compress the conductor. In the case of a plasma, the force would collapse it into a thin filament, "pinching" it. Since the current had to be very large, pinch devices made no attempt to confine the plasmas for extended periods. They would attempt to reach fusion conditions quickly and then extract power from the resulting hot products.

The pinch technique was patented in 1946 by

Oxford University, he arranged funding for an experimental device and started assembling it. Before it was complete, he was lured to the US by a job offer at the University of Chicago (Illinois).[5]

Other teams in the UK continued their efforts. Thomson passed his concepts on to Stanley (Stan) W. Cousins and Alan Alfred Ware (1924-2010[6]), who assembled a linear pinch device using old radar equipment, and started operations in 1947. Follow-on experiments used large banks of capacitors to store energy that was quickly dumped into the plasma through a solenoid wrapped around a short tube. These experiments demonstrated a number of dynamic instabilities that caused the plasma to break up and hit the walls of the tube long before it was compressed or heated enough to reach the required fusion conditions.[3]

After a short time in Chicago, Tuck was hired by Los Alamos to work on the

hydrogen bomb),[5] where he was put on the task of calculating the nuclear cross section of the deuterium-tritium fusion reaction. This work continued to pique his interest in fusion power, and he spent some time through 1951 considering the problem.[7]

At Los Alamos, Tuck acquainted the US researchers with the British efforts. By this point

U.S. Atomic Energy Commission (AEC) to fund his design. Tuck was skeptical of Spitzer's enthusiasm and felt his aggressive development program was "incredibly ambitious".[8] Tuck proposed a much less-aggressive program based on pinch. Both men presented their ideas in Washington, D.C. in May 1951. In July, Spitzer received $50,000, and Tuck was sent away without funding.[8] Not to be outdone, Tuck convinced Norris Bradbury, the Los Alamos director, to give him $50,000 from the discretionary budget.[3]

Still unconvinced that the concept would work on the first attempt, he called this approach, with

Stanislaw Ulam's input, the Perhapsatron.[7][9] Tuck assembled a small team, and using scrounged parts and the budget money, built the first Perhapsatron in 1952/53.[3] The Perhapsatron used a toroidal tube made in the local glass shop. In the middle of the toroid was a large iron core from a transformer
, which was used to induce current into the gas.

The Perhapsatron quickly displayed the same problems as the British experiments. No matter how slowly the current was added, once it reached a critical point the instabilities arose. In 1954, Martin David Kruskal and Martin Schwarzschild published a critical paper on the issue, which suggested that all Z-pinch devices were inherently unstable.[10] Tuck proposed the addition of a second, steady, magnetic field running longitudinal along the tube, a concept he called "adding a backbone to the plasma". Several modifications to the Perhapsatron were made to test variations on these concepts, but none proved fruitful.[11]

Z-pinch goes out of favor

The failure of Perhapsatron was followed by the failure of other pinch devices. Another team at Los Alamos had been working on another fast-pinch machine known as Columbus that used electrical fields instead of magnetic, producing the same results. Meanwhile the much larger

theta-pinch concept.[11]

Tuck never restricted himself to the pinch concept, and he spent considerable effort on other concepts, which led to joking within Los Alamos about his apparently unfocused work.[12] Over the years he led development of several other concepts, including the picket-fence reactor, new pinch concepts, and work on mainstream devices.

References

  1. ISBN 0-7503-0310-7
    . Accessed October 8, 2010.
  2. ^ Phillips, pg. 64
  3. ^ a b c d e Phillips, pg. 65
  4. ^ Herman, pg. 40
  5. ^ a b c Bromberg, pg. 20
  6. ^ "UTPhysicsHistorySite". Archived from the original on 2022-05-29. Retrieved 2022-05-29.
  7. ^ a b Bromberg, pg. 25
  8. ^ a b Bromberg, pg. 21
  9. ^ Herman, pg. 41
  10. S2CID 121125652
    .
  11. ^ a b Phillips, pg. 66
  12. ^ Bromberg, pg. 58

Bibliography

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