The Pinch Effect Revisited What Appeared to Somejusion Researchers As "Instabilities,"Turned out to Be Self-Organizing Plasma Vortexfilaments
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Click here for Full Issue of EIR Volume 18, Number 7, February 15, 1991 The pinch effect revisited What appeared to someJusion researchers as "instabilities,"turned out to be self-organizing plasma vortexfilaments. Part2 qf a series. In Stockholm, September 1956, at a conference on Electro maintain stability the electrical conductivity of the plasma magnetic Phenomena in Cosmical Physics at a special Satur should be high and remain high that the Bz inside the 110 day morning session following the scheduled conference, pinched plasma column should nqt be permitted to diffuse Igor Golovin gave a description of the Soviet Ogra program and mix rapidly with the Be outsid� the column. The appear and Lev Artsimovitch gave an analysis of the instabilities of a ance of increased Bz outside the pi.,lched column resulted in pinch with an applied axial magnetic field. The U. S. Atomic m 1 instability for long wavelengths, and the deterioration Energy Commission (AEC) was still keeping most of its CTR of =sharply defined magnetic field d�stributions into "diffuse" program under security wraps. volume distributions was definit�ly harmful to stability. The author remembers having a conversation in 1956 Also, the electrical conductivity o(the plasma remained dis with a very highly placed physicist employed in the U. S. appointingly low. CTR program at one of the large U. S. national laboratories . The electrical skin depth in the plasma is a good measure The author opened the conversation by advocating that all of the diffusion distance as a function of time. If finitethermal security classifications on the U.S. CTR be dropped. The conductivity is allowed for, but ra�iation losses are neglect highly placed physicist responded by saying that he agreed ed, it is predicted theoretically that the mean plasma tempera that the classificationshould be dropped "but we should wait ture over a skin depth in from the pinch surface is about for six months until we have some more results." Such a research-inhibiting attitude was undoubtedly born of a pro fessional life lived too long under the protection of security classification. In 1956 at least the United Kingdom and the , U.S.A. agreed to exchange information. where H is the magnetic field amplitude and n is the particle The forthcoming International Atomic Energy Agency density in the undisturbed region of the pinch. Tc is the maxi (IAEA) Atoms for Peace Conference in 1958 at Geneva was mum temperature compatible with pressure balance at densi the occasion for Lewis Strauss [then head of the U. S. Atomic ty n. The classical theory of conduction of electricity in an Energy Commission] to finally declassify the U.S. CTR ef ionized gas states that the electri<tal conductivity varies as fort. Strauss wanted a first class show of U.S. experimental T!/2where Te is the electron tempe�ature. equipment at the Geneva exhibit hall, so most of the U.S. As the Hz and He fields (or the Bz and Be) interdiffuse, experimenters spent months polishing, shipping, and setting the stability of the pinch diminish�s. On the same time scale up the U. S. equipment for the exhibit. One Princeton experi on which the stability is lost the pinch is heated. In making menter estimated that the U. S. experimental program was a practical thermonuclear machine pf the pinch type one must set back nine months, at least, by the show. But then the therefore arrange for the plasma to gain energy fast enough Soviets must also have been set back. It is a pity such a vast to overcome radiation losses, but: not so fast as to destroy effort at a show was spent on the small town of Geneva. If pinch stability in times insufficient for appreciable fusion to the show had been a road show held in New York, London, occur. Paris and Moscow, many more people would have seen it. The experimental results in iboth linear pinches and But apparently the show was not for the people of the world: toroidal pinches (where heat conduction to the electrodes can It was for the U.S. AEC and United Kingdom to impress the be eliminated) are that the plasm� electrical conductivity is Soviet physicists and for the Kurchatov Institute of Atomic distressingly low. This result ocelurs in discharges where, Energy to impress the U.S. and United Kingdom physicists. from the point of view of expec�d energy balance in the Considerable research on efforts at stabilization with the transfer of magnetic energy to the plasma from the calculated use of Bz in linear and circular pinches was reported at the Tr=V3Tc, one would expect the electrical conductivity of the IAEA Geneva conference in 1958. The results added up to a plasma to be high: For example iJl cases where one would somewhat discouraging outlook for the pinch effect as a fu calculate that Tc should be about 3,� electron volts (ev), the sion device. In order for the magnetic field configuration to electron temperature calculated fr.,m electrical conductivity EIR February 15, 1991 Sc�ence & Technology 17 © 1991 EIR News Service Inc. All Rights Reserved. Reproduction in whole or in part without permission strictly prohibited. measurements was Te=lO ev. The electrical conductivity can be measured by the rate of diffusion of the Hz and Ho fields and by the decay time of the shorted pinch current in SchematicFIGURE 6 diagram of the FiIi pov electrode the machine. The interpretation given at the time of these � geometry which producSd 10 0 neutrons in measurements (1955-58) was that if the plasma was ab 1961. sorbing energy from the magnetic field, it was losing that energy equally rapidly by some process such as accelerated I runaway electrons which would encounter the chamber wall. if7 6 Colgate, Furth, and Ferguson, in their 1958 paper at the IAEA conference, point out that in their toroidal stabilized pinch the plasma resistivity is 20 to 100 times as great as the highest resistivity which would be tolerable for a thermonu clear reactor, namely the classical resistivity of a 200 ev plasma. Even if ion temperatures of 100 kev could be pro 4 duced, as long as the electrical resistivity requirement is not met, the containment time will be too short to allow economical operation. Thus they felt that nothing can be done to improve the plasma conductivity, and therefore the 1) capacitor power supply, = 180 microfarad main emphasis of stabilized pinch research should at this 2) ring vacuum discharger C point belong not to the attainment of high plasma tempera 3) cathode tures, but to the understanding of the energy dissipation phe 4) porcelain insulator nomena in the plasma. 5) inner electrode (anode, diameter=480mm) 6) voltage divider And indeed the concept of turbulent heating as a erR 7) cross-shaped slit (A and B) process has been actively pursuedin the U.S.A., United King dom and U.S.S.R. as an extension of this work. A high current is passed through a plasma column containing a Bz field and energy is imparted to the plasma by forcing the current through effect failed to reach its objective. This effort involved some the anomalously high resistivity which the plasma presents to of the best experimentalists and theoreticians in the U. S. A. , the current; it is this anomalously high resistivity which was U.S.S.R., United Kingdom, France, and Sweden. making its appearance in the stabilized pinch experiments. In The leaders of the CTR programs in the various countries vestigators in thisfield claim thatthe anomalously high resistivi eventually decided that a self-pinched plasma column had no ty results from ion-acoustic waves which are excited by an future as a CTR magnetic-containment reactor, and financial instability which results when the electron drift velocity, under support for pinch-effect research came to be drastically cur the influence of the applied electric field, exceeds the ion tailed and in some cases eliminated. On the other hand, the acoustic velocity. In these turbulent heating experiments the Tokamak concept that now dominates CTR planning is a sudden onset of high resistivity is usually accompanied by the kind of Bz stabilized pinch (like SCEPTRE and ZETA) where emission of X-rays, neutrons (in deuterium), and microwaves, the Bo is small compared with the stabilizing Bz (the toroidal similar to what happens in the ordinary dynamic pinch at the current is kept below the "Kruskal limit") and the fields are time of pinching. well mixed. The United Kingdom's SCEPTRE and later the large Although the pinch effect has now completely lost the toroidal ZETA apparatus at Harwell and Culham were stabi CTR center stage to the Tokamak, the pinch effectas a com lized pinches on a large scale (large diameter, approximately plex physical process that can come up with surprises for the 3 meters for ZETA). (See Figure 5, * EIR, Feb. 8, 1991 "The experimenter has been by no means dead! pinch effect revisited," Part 1.) The neutrons which came The next important announcements on pinch effect re from SCEPTRE and ZETA (approximately 1958) were search were made at the IAEA conference on CTR in 1961 shown experimentally to come also from some acceleration in Salzburg. The Soviet group under N. Filippov at the Kur process and not from a thermalized deuteron plasma. ZETA chatov Institute reported results on a pinch produced with the also showed anomalously high resistivity which must have electrode structure shown in Figure 6. The conventional been associated with the same type of turbulence that occurs pinch effect produced between the two "conventional" elec in the turbulence heating experiments and in the stabilized trodes as shown in Figures 2 and 4 [see EIR, Feb.