How did we get to this point? The scatter in the points in Fig. 8.1 tells a story. In the short term, progress has been sporadic, with fits and starts caused not only by problems of physics, but also by problems of funding and politics. Glimpses of the history of fusion research can be found in popular books by physicists Amasa Bishop [1], Hans Wilhelmsson [2], McCracken and Stott [3], and Ken Fowler [4].

Less technical coverage of people and politics is given in books by journalists Joan Lisa Bromberg [5] and Robin Herman [6], and in an article by Gary Weisel [7]. Here is a nutshell account.

In the USA, three groups started research on controlled fusion in 1951-1952: one at Livermore, California, headed by Richard F. Post; one at Los Alamos, New Mexico, headed by James Tuck, and one at Princeton, New Jersey, headed by Lyman Spitzer, Jr. It was obvious that the hydrogen bomb reaction was a source of a huge amount of energy, if only it could be released slowly in a controlled way. It was not obvious how to do it. All agreed that trapping and holding a hot plasma would be necessary. Dick Post proposed to use magnetic mirrors, which we shall describe in Chap. 10. Jim Tuck proposed to use pinches (Chap. 7), in which the entire magnetic field is generated by plasma currents. These devices suffered, of course, from the kink instability, which was not known at that time. Tuck had the foresight to name his machine the Perhapsatron. At Princeton, Lyman Spitzer, an astronomer, designed the figure-8 torus, which he named, of course, a Stellarator. A little later, a fourth program started at Oak Ridge, Tennessee, based on another mirror machine, the DCX. This group emphasized experiments which ran continu­ously (hence DC) rather than in pulses, and eventually included the curiously named ELMO Bumpy Torus. In England, the initial efforts concentrated on pinches, particularly the toroidal pinch, which is a torus like a tokamak, but with a poloidal confining field produced by a large toroidal current. In Russia, research began at the Kurchatov Institute in Moscow with a small torus which they named the Tokamak, invented by Igor Tamm and Andrei Sakharov. Other nations did not join in until after the first milestone, the Geneva conference of 1958, when these secret programs were declassified and revealed.

In the years before that, the US program grew rapidly with the enthusiastic support of Atomic Energy Commission chairman Lewis L. Strauss. The program was named Project Sherwood after the name of James Tuck, reminiscent of Friar Tuck of Sherwood Forest. Strauss kept the program classified and well funded with the aim of beating out the UK and the USSR in achieving fusion. Sherwood confer­ences were held yearly, and there were some memorable occasions. In 1956, the meeting was hosted by Oak Ridge at Gatlinburg, Tennessee, and most attendees found out for the first time the meaning of “dry town.” Even without lubrication, Lyman Spitzer regaled the group with his rendition of songs by Gilbert and Sullivan, which he sang from memory. In 1957, the meeting was in Berkeley, California, and a movie theater had to be taken over in the day time and secured for the classified meeting. By sheer coincidence, the movie that was playing that week was “Top Secret.” From 1952 to 1954 James van Allen, who discovered his famous radiation belts, built the B-1 stellarator at Princeton, a machine which the newly hired young experimentalists inherited in 1954.

Meanwhile, Spitzer had assembled a strong theoretical group, whose magnum opus was the elegant paper An energy principle for hydromagnetic stability problems, published in 1958 [8]. This paper by Bernstein, Frieman, Kruskal, and Kulsrud did more than anything else to establish plasma physics as a respectable new field in the eyes of all physicists. A calculational method based on minimization of energy was given that could predict the boundaries of stable MHD operation even in toroidal machines with complicated magnetic geometries. This tool allowed experi­mentalists to build machines that were stable against the Rayleigh-Taylor and kink instabilities, among others, that were discussed in Chaps. 5 and 6.

The 1958 Atoms for Peace conference was organized by the IAEA (International Atomic Energy Agency), formed in 1957 by the United Nations. Based in Vienna, Austria, the IAEA has sponsored the plasma physics and controlled fusion confer­ence every two years since then. A large contingent from Project Sherwood was sent to Geneva, flying across the Atlantic on propeller planes. Preceding the team were tons of display equipment managed by the Oak Ridge experts. Not only were there models such as the figure-8 stellarator shown in Fig. 4.18, but actual operating machines were also transported, including the power supplies and control equip­ment needed to make them work. No expense was spared. England also put on a large and splendid exhibit, featuring their toroidal pinch, the Zeta. Meanwhile, the USSR exhibit featured the Sputnik, which they had just launched to open the space age. Their fusion machine, the tokamak, was secondary. The tokamak on exhibit looked like a formless, dark, unrecognizable piece of iron and was not made to work. This was how the tokamak age began. But the gauntlet was thrown by the USA, the UK, and the USSR; and the race was on.

At the Geneva conference, the British team announced that neutrons character­istic of fusion reactions had been observed in Zeta. This would have been the first demonstration of fusion created by hot plasma. Unfortunately, it was found that these neutrons came from energetic ions striking the wall, not from the thermal ions in the body of the plasma. As explained in Chap. 3, ion beams cannot produce net energy gain; that requires a thermonuclear reaction. The Brits had been careless and had stumbled. It was an embarrassing moment for their leaders, Peter Thonemann and Sebastian “Bas” Pease, two gentlemen who were the best friends one could have. The idea of a toroidal z-pinch (zed-pinch to Englishmen) has survived, however, as a possible advanced alternative to the tokamak, aided by a brilliant theory by their countryman, Bryan Taylor.

The 1960s saw progress on many fronts. The most important was the announce­ment in 1968 by Lev Artsimovich, the driving force of the Russian effort, that the confinement time was 30 times longer than the Bohm time and record-breaking electron temperatures had been achieved in their T-3 tokamak. Recall that Bohm diffusion, caused by microinstabilities, was limiting confinement times to the millisecond regime, so this was important progress if it could be believed. The scientific community was skeptical, since Russian instruments were compara­tively primitive. In 1969, an English team headed by Derek Robinson flew to Kurchatov with a laser diagnostic tool that the Russians did not have. They measured the plasma in the T-3 and found that the Russian claims were correct. The tokamak had to be taken seriously. Soon thereafter, research tokamaks began appearing at General Atomics and several universities in the USA, as well as in many locations in Western Europe and Japan. Even the venerable Model C stellarator at Princeton was converted to a tokamak in 1970. In retrospect, the invention of the tokamak was a lucky break. Its self-curing feature of sawtooth oscillations was not foreseen, nor were the gifts from Mother Nature listed in Chap. 7. The cures for Bohm diffusion could have been laboriously found in any of a number of magnetic bottles, some of which may turn out to be more suitable for a reactor than a tokamak. It was concentrating on a single concept, the first promising one, that advanced the tokamak to its present status.

Throughout the 1960s, the Princeton group whittled away at the Bohm diffu­sion problem, clarifying the microinstabilities responsible for that enhanced loss rate. Much of this work was basic experimentation done in linear machines, which did not suffer from the complicated field lines of stellarators and tokamaks. In the USSR, Mikhail Ioffe at his institute in St. Petersburg invented the “Ioffe bars.” These were four bars carrying current to form a magnetic well (“minimum-B”) configuration in a mirror machine, thus stabilizing the most troublesome insta­bility in those confinement devices. Though mirror confinement is outside our scope here, the minimum-B concept is also used in tokamak configurations. These results, as well as the ones from the T-3 tokamak, were presented in the memorable IAEA meeting of 1968. After the technical sessions in Moscow, Artsimovich led the entire conference to a big party in Novosibirsk, the science city deep in Siberia. The party was held at a large artificial lake made by cutting down trees and covering the stumps with water. Long picnic tables were set up on the shores and food served with Russian hospitality. It seemed that the tables for 60-second chess games must have stretched for 100 yards. Here, plasma physicists from many countries got acquainted on a personal level. It was the beginning of international cooperation and competition.

Another milestone was announced at the Novosibirsk meeting when the General Atomics group showed the picture of Fig. 8.8, which completely surprised the Russians. Had the Americans trumped them with the resources to build a torus large enough to hold a person standing up? Actually, it was not a tokamak or stellarator

but an “octopole,” spelled “octupole” when another one was built at the University of Wisconsin by Don Kerst. It had four current-carrying rings suspended by thin wires within the plasma, creating a magnetic well. The plasma was absolutely stable in such a magnetic field, and the classical diffusion rate, caused by collisions alone, was observed for the first time [9]. Being a pure physics experiment, the octopole did not require a large, expensive magnetic field, and it was not the advanced fusion machine that the Russians had feared. Internal conductors would not be practical in a real reactor.

The 1970s was a period of euphoria, with Artsimovich predicting scientific breakeven by 1978, and Bob Hirsch, then head of fusion research in the Atomic Energy Commission, pushing for an even earlier date. The prospect of an infinite energy source evoked such lyrical epithets as “Prometheus Unbound!”. With the difficulty of magnetic confinement recognized, the importance of controlling fusion was compared with that of inventing fire. Funding started to increase when James R. Schlesinger became AEC chairman on the way to the CIA and Defense. Support for fusion energy was further escalated by the oil crisis of 1973, when a speed limit of 55 miles per hour was mandated throughout the USA. The dramatic increase in the fusion budget is shown in Fig. 8.9, reaching a peak of almost $900M annually in 2008 dollars. Championed by Representative Mike McCormack (D-WA), Congress passed the Magnetic Fusion Engineering Act of 1980, which laid out the plans and the budget needed to build a demonstration reactor DEMO by the year 2000. The Act was never funded as passed. Tired of promises that fusion would be achieved in 25 years regardless of when the question was asked, Congress began cutting the fusion budget. Ed Kintner took over the fusion office from Hirsch in 1976 and had to reorganize priorities to fit available funds. Many alternative

approaches to magnetic confinement still existed at that time,2 and they should be explored while keeping the tokamak as the flagship, while critical engineering tests are made. Nonetheless, several large projects ultimately had to be canceled, includ­ing the Fusion Materials Test Facility and MFTF-B, the world’s largest supercon­ducting magnet built for mirror fusion. That fusion would always be 25 years in the future was made a self-fulfilling prophecy by the decrease in funding.

Curiously enough, the peak in funding in Fig. 8.9 follows a similar graph of the price of oil at the time.3 Unfortunately, this did not happen in the oil crisis of 2008, since other energy alternatives such as solar and wind power were available, and the USA was at war in Iraq. The dissolution of the Soviet Union in 1991 had a major effect on the willingness of Congress to support fusion. The threat of being outdone by the Russians was no longer there, and the attitude was to let the friendly nations which are more dependent on foreign oil bear the main expense. As a result, the USA, which had been the world leader in fusion development, slowly lost its preemi­nent position to the UK and Japan.

The peak funding levels of the 1970s nonetheless enabled the start of the billion-dollar machines that set milestones two decades later. The TFTR at Princeton4 began construction in 1976 and ran from 1982 to 1997. This was a big step because it was the first machine made to run with DT rather than helium or deuterium. Once tritium is introduced, the DT reaction would produce 14-MeV neutrons, which would activate the stainless steel walls. Massive shielding would be required, and maintenance could be done only by remote control. By 1986, TFTR had set records in ion temperature (50 keV or 510,000,000°C), plasma den­sity (1014 cm-3), and confinement time (0.21 s), but of course not all at the same time. In 1994, a 50-50% DT mixture was heated to produce 10.7 MW of fusion power. This is only about 1% of what a power plant would give and occurred only

in a pulse, but it was the first demonstration of palpable power output. Before it was decommissioned, TFTR also demonstrated bootstrap current and reversed shear, effects described in Chap. 7.

Close on the heels of the TFTR, western Europe built an even larger machine, the Joint European Torus, JET, also capable of using DT fuel. Designed in 1973-1975 and constructed in 1979, it has operated from 1983 until now. It was funded by the countries of Euratom and is now operated under the European Fusion Development Agreement, with participation of over 20 countries.5 Currently, the world’s largest tokamak with a major radius of 3 m, it is also powered impressively with a mag­netic field of 3.45 T (34.5 kG), total heating power of 46 MW, and a toroidal current of 7 MA. It set a record with a pulse of 2 MA that lasted 60 s. In 1997, JET announced a new world record with DT fuel, producing 16 MW of fusion power and keeping 4 MW going for 4 s. JET is being modified for experiments in support of ITER, the large international project described at the end of this chapter.

The third large tokamak of this era is Japan’s JT-60, which started operating in 1985. It plays a leading role in researching the effects on the forefront of tokamak science, such as reversed shear, H-modes, and bootstrap current. Much of this is too technical for this book, but JT-60 has set some world records which are easy to understand. In 1996, it achieved the highest fusion triple product. Recall that the triple product is, more exactly,

Triple product = hTit e,

where te is the energy confinement time. The value achieved was 1.5 x 1021 keV s/m3, close to the value needed for energy breakeven, and only about seven times less than that required for a reactor. Of course, this was in a pulse and not in steady state. In 1998, JT-60 set a record for Q, the ratio of fusion energy to plasma heating energy, at Q = 1.25. However, since JT-60 was not designed to handle tritium, the experiment was done in deuterium and the result extrapolated to DT. The highest ion temperature of 49 keV was also reported in JT-60. The machine excelled in long pulses, running steadily for as long as 15 s, or for 7.4 s while the bootstrap fraction was 75%. Perhaps most impressive was the production in 2000 of a plasma with zero current over 40% of the minor radius. The current in an outer shell held the plasma even though there was no confinement in the current hole. This is exactly the profile that is suitable for operation with a large bootstrap current fraction.

By focusing on these three machines, we have had to omit the great contributions of other large machines such as DIII-D and ASDEX, as well as those of hundreds of smaller tokamaks built to study particular effects. Though not tokamaks, there are also large machines of the stellarator type, such as Wendelstein 7 in Germany and the Large Helical Device in Japan. No large tokamaks had been built since the turn of the century until two Asian machines went online in 2007: the KSTAR in Daejeon, Korea and the EAST (Experimental Advanced Superconducting Tokamak) in Hefei, China. You can guess what KSTAR stands for. Both of these machines use superconducting coils cooled by liquid helium, requiring a second vacuum system to keep the coils cold. The development of large superconductors is an important step toward a fusion reactor.

As can be seen in Fig. 8.9, the US fusion budget steadily declined in the 1980s and 1990s. Construction of large machines had been completed; there was no oil crisis or competition from the USSR; and people were disillusioned about the pros­pect of ever achieving fusion. In particular, members of Congress were reluctant to support a project that could not be completed in their terms of office. Major sources of funding shifted to countries which have very limited fossil fuel reserves, and the USA slowly lost its lead at the forefront of fusion research. In 1995, a Fusion Review Panel headed by John P. Holdren and Robert W. Conn submitted a report6 to President Clinton’s Commission of Advisors on Science and Technology on a requested evaluation of the fusion situation. The Panel estimated that progress to a demonstration reactor by 2025 would require annual funding levels averaging $645M between 1995 and 2005, with at peak of $860M in 2002. Should budgetary constraints not permit this level, alternate scenarios were also given. At a realistic level of $320M/year, the best that could be done was to maintain the expert com­munity in plasma science and fusion technology while expanding international participation. With this devaluation, the Magnetic Fusion Energy Program was changed to the Fusion Energy Sciences Program. The restructured program was presented to the DOE Office of Energy Research by the Fusion Energy Advisory Committee, chaired by Conn, in 1996 [13]. As seen in Fig. 8.9, the budget has been maintained the $300M level since that time, partly through the efforts of Undersecretary for Science Raymond Orbach under President Bush. With DIII-D, the largest tokamak extant in the USA, the level of fusion science and innovation nonetheless leapt forward with many intermediate-sized devices in universities and with advances in computation and theory.

It was in this period that burning plasma became the catchword, and planning for a large international tokamak to achieve this, the ITER, began. The success story of the negotiations deserves its own section. This is presently our best chance to move forward in making our own sun. Meanwhile, we need another scientific interlude to clarify the uncertainties that still exist in fusion science.