PROGRESS REPORT
on
CONTROLLED FUSION RESEARCH*
by
M. H. BRENNAN
October, 1972
School of Physical Sciences The Flinders University of South Australia Bedford Park, South Australia 5042
'rReport prepared for the Australian Atomic Energy Commission. 1. INTRODUCTION
In this report a survey is made of the international research programme directed towards the development of a controlled thermonuclear fusion reactor. The report is based on observations made during an overseas trip which included attendance at a meeting of the international Fusion Research Council and the Fifth European Conference on Controlled Fusion and Plasma Physics. The itinerary for the trip, which was from 13th August to 28th September, 1972, is included as Appendix A to this report.
In order to provide a basis for evaluating the fusion research programme a brief summary is given in Section 2 of the basic requirements for a fusion reactor. In Sections 3 and k of the report brief summeries are given of the main features of the Council meeting and the Fifth European Conference. The current state of fusion research is reviewed in Section 5° The final Section of the report includes a discussion of the present and near-future international fusion research programme, and some comments on the Australian programme.
2. THE FUSION REACTOR
2.1 The Scientific Problem
The most favourable nuclear reaction for the release of nuclear energy from the fusion of light elements is the deuterium-tritium reaction (D-T reaction). This reaction has a cross section, at energies of -100 keV, of several hundred times that for the D-D reaction (deuterium-deuterium). In addition, considerably more energy is released per interaction. We therefore concentrate our attention on the D-T reaction; it may be possible, at a later stage, to develop a reactor based on the D-D reaction.
The reaction involved is
1H2 + 1H3 -*- aHe" + n1 + (17.6 Mev) .
Approximately 14 Mev of the released energy is carried away by the neutron. The deuterium fuel is, of course, available from sea water; the total energy available is sufficient to satisfy the world's electrical energy requirements - 2 -
for -JO years. The tritium fuel is, of course, not available naturally and is therefore produced in the reactor system, using a lithium blanket, which also serves as a neutron moderator and is a component of the heat exchange system.
In order to achieve the high particle energies required, the fuel (a 50/50 mixture of deuterium and tritium) must be heated to a temperature of ~2 x 108 K, corresponding to a value of kT of 20 keVc At these high temperatures, the atoms of the fuel are all ionized and the gas is in the plasma state.
In addition to the temperature requirement, the plasma particles must be contained in the reaction region for a sufficiently long period to allow nuclear interactions to take place, so that there is a net release of energy. Detailed calculations show that the break-even condition can be expressed as the Lawson criterion:
ni > 101** cm"3 s , where n is the particle density (cm"3) and T is the confinement time (seconds).
The scientific feasibility of nuclear fusion as an energy source thus requires heating a plasma to a temperature of ~20 keV and achieving a particle confinement time greater than that given by the Lawson criterion.
2.2 Confinement and Heatinc Schemes
The basic confinement and heating conditions may be met, in principle, In many ways. In some systems, such as the stellarator, these two conditions may be satisfied more or less independantly; ?n the 0-pinch they are inextricably connected.
The Lawson criterion allows a wide range of densities to be used in achieving fusion conditions; we may use th.s fact to classify the various confinement schemes into two broad categories:
Low density (n~ 101* -1017 cm"3 T Z 1 - 10"3s) High density (n~1020 -1026 cm"3 T Z 10"6 - 10"12 s) . - 3 -
2.2.1 Low Density Systems
The low density systems can again be divided according to two criteria: the magnetic field configuration - open or closed - and the ratio, (3, of plasma pressure to magnetic field pressure The major low density confinement systems are classified according to these two criteria in Table i.
\« - nkT
Low (< 0,1) High (> 0.1) Confining ^v field X.
Open Mirror machine Straight 6-pinch
Closed Stellarator, Diffuse pinch. torsatron Toroidal 6-pinch, Tokamak high-B stellarator Internal conductor Astron
Table I Major types of low density confinement systems
Mirror machine: The simple magnetic mirror system is macroscopically unstable against the magnetohydrodynamic (MHD) instability. Stability has been achieved against this instability by creating a "minimum-B1' configuration In which the magnetic field increases in all directions away from the central plasma region. Plasma production and heating have been achieved mainly by energetic particle injection, adiabatic compression, and r.f. heating. The major difficulty in these devices is the loss of particles along the magnetic field lines, through the mirrors. This may have two serious consequences: (a) the loss of energetic particles may represent too high a loss rate in a reactor system; - i» -
(b) The non-Maxwellian nature of the resulting velocity distribution excites a variety of microscopic instabilities which may prevent the achievement of the required confinement times.
Straight 0-pinch: in the 6-pinch, a rapidly rising axial magnetic field (B ) induces
a surface current (L) in a low density pJasma,, The resultant jflB force rapidly compresses and heats the plasma, Confinement is achieved by the high axial magnetic field. The major loss mechanism is axial diffusion. Reactor conditions would require a length of several kilometres and very large electrical power output (1010 - 1011 watts).
Stellarator, torsatron: ^A in the stellarator and related toroidal devices, particularly the torsatron, containment of the plasma is achieved by a magnetic field of complex geometry, consisting of closed nested toroidal surfaces, produced entirely by currents flowing in external conductors In the case of the stellarator, toroidal coils producing a large toroidal field, B , and helical windings produce the required field configuration. In the torsatron the required field configuration can be produced In a single set of variable pitch helical windings.
A major feature of the stellarator is that heating and confinement are separated functions Thus, stellarator plasmas have been heated in a variety of ways, The most important of these, from the reactor point of view, are: (aj Neutral particle injection — a beam of energetic neutral particles is injected into the plasma (as is done in the mirror machines); (b) Turbulent heating — large currents induced in the plasma create sma'i scale turbulence which aids in the transfer of energy to the plasma; (c) Radio frequency heating — plasmas exhibit a number of natural resonances and energy transfer from waves to particles can be very efficient in the vicinity of some of these resonances.
Tokamak: i.»Cf^ • -vrccoJ in the Tokamak the plasma is both heated and confined by currents flowing parallel to the major circumference of the torus. The self magnetic field, BQ, of this current, an externally-generated toroidal field, B , and - 5 -
induced wal currents, or a small magnetic field parallel to the major axis of the torus, produce the required field configuration.
Supplementary heating will probably be required: this may be achieved by any of the methods used for stellarator heating, in addition, adiabatic compress1on of the plasma, in principle, can be accomplished very simply and economically by moving the plasma (using the plasma current and a small transverse magnetic field) to a position of smaller major diameter; this moves the plasma to a region of higher magnetic field (because of the radial dependence of the large toroidal field) , thus compressing and heating it, interna^ conductor systems: Systems with internal current-carrying conductors are unlikely to be of interest for a reactor. However, they continue to provide valuable Information on plasma confinement and stability in easily variable magnetic field configurations.
Astron: in the Astron a relativistic charged particle layer creates a dosed- Hne magnetic field configuration which !s capable, in principle, of heating and confining a plasma at reactor conditions. Currently, research is being conducted with relativistic electrons; favourable results would justify serious consideration being given to this approach.
Diffuse pinch: in the Tokamak and stellarator the poloidal field is very much smaller than the toroidal field (B„/B ~ 0.1) and the 3-value is relatively o Z smallo A large expenditure is therefore required to produce the toroidal field. A more economically attractive approach (at least in this regard) is the general class of high-3 devices. The diffuse pinches, screw pinches, and belt pinches, are variants of configurations that are Mhigh-&, current
carrying toroidal devices". In these devices Bfl~B -- the magnetic field y z has a very high shear and 3 may be as high as ~0.5. Zeta was the first major device of this type. — ^^u»«^ "r1"? Plasma heating in these devices is achieved by the large axial currents or by fast compression. - 6 -
Toroidal 9-pinches, high-8 stellarators: The stellarator configuration is limited to very low (3-values. It may however be possible to achieve a stable configuration, at higher B, using more complex field configurations and, possibly, feedback stabilization. Examples of such devices are ISAR T-1 (Garching) which is a toroidal 6-pirich in which a combination of helical windings U=1 and £=2) may be able to provide an equilibrium configuration, in a similar, and larger device (SCYLLAC), the Los Alamos group is investigating feedback stabilization on a toroidal sector.
Other approaches: This rather oversimplified classification scheme omits a number of possible devices. The two most important of these are:
(a) Gas blanket confinment — the systems so far discussed rely entirely on magnetic fields to confine the hot plasma. Some encouraging results have been achieved, primarily in Sweden and the Netherlands, with systems in which the hot plasma is in contact with cold neutral gas; there are some indications that thermal losses to this blanket might not be as severe as was originally thought and that plasma stability might be improved by the presence of the dense, neutral gas in contact with the plasma.
A closely related approach is under investigation at Columbia University where a hot, dense, shock-heated plasma will be confined by a combination of an appropriate magnetic field configuration and contact, necessarily through a neutral gas layer, with the containing vessel walls.
(b) Plasma focus -- this is a medium density device (n~1019 cm"3) which has points of similarity with the fast pinch systems. In the focus a rapidly collapsing, current-driven plasma can generate large fluxes of neutrons. The origin of these neutrons is, however, not clear; present indications are that they are not thermonuclear, but come from the acceleration of particles under the action of very high fields produced by the rapidly changing circuit inductance. - 7 -
2.22 High Density Systems
The Lawson criterion may be satisfied by creating a hot very dense plasma with correspondingly short confinement time. Three such systems are currently being investigated.
Relativistic electron beams: Very large energy fluxes are available in a relativistic electron beam. It may prove possible to heat a small solid pellet with such a beam. Only very preliminary theoretical and experimental work has been performed up to the present; a major difficulty will be the need to focus the high-current beam down to a very small cross-section.
Laser-produced plasma: A high-power laser beam incident on a solid pellet will create and heat a plasma. Recent calculations suggest that it may be possible to so shape the laser pulse that, for a highly spherically symmetric incident beam, compression of the pellet to densities 10u times the original solid density may be achieved. At these densities (~ 1026 cm"3) the required confinement time is so short that particle inertia will be sufficient to enable the Lawson criterion to be met. Laser pulses of IMJ energy and of ~10"9 s duration will be required
High magnetic field 0-pinch: The conventional straight 6-pinch has proved to be highly stable and high densities and temperatures are relatively easily obtained. However, fusion reactor conditions would require a machine of several kilometres length. A great reduction in length could be achieved if the plasma density could be raised significantly (to 1019 - 1020 cm"3), thus permitting a shorter confinement time and hence a much-reduced length (of about 20 m). Such high densities require a correspondingly high magnetic field of approximately 3 Megagauss (300 Tesla).
Magnetic fields of such magnitude have already been produced by using a 6-pinch coil to compress a conducting cylinder which, in turn, compresses a field of modest size (~ 20 kG) to several magagauss. The same coil can also be used, in principle, to compress a plasma contained within the conducting cylinder, A particularly interesting feature of the scheme is the possibility - 8 - of using lithium as the conducting cylinder - the collapsing plasma thus "carries" the lithium blanket in with it.
A proposed American device of this type 2.3 Reactor Technology In the previous Section we dealt with the question of scientific feasibility of the fusion reactor and listed the major scientific lines of approach. It is obviously essential to include, in the evaluation of a proposed reactor system, technological and economic considerations; it may well be the case, for example, that although scientific feasibility as defined in Section 2.1 may be achieved by a particular system, technological or economic considerations rule out the system as a viable power producing reactor. (We will refer to this possibility for the laser-produced plasma in Section 5.) The important technological and economic factors to be considered vary considerably as we move from the low density systems through to the high density systems. First, the low-3 Tokamaks and Stellarators may both be able to run continuously, whereas the high-$ devices and high density devices are clearly pulsed — sometimes with very small duty cycles. Clearly, heat exchange, wall loading from energetic neutron fluxes, magnetic field coil construction details and coats, will differ greatly for this wide range of plasma conditions. Detailed consideration ef these various questions has been under way for only a very short period. At this stage, the 1ow-B toroidal systems have been most thoroughly investigated and reference design systems are available for assessment. - 9 - 3, INTERNATIONAL FUSiON RESEARCH COUNCIL MEETING The International Fusion Research Council is a ten-nation committee established by the International Atomic Energy Agency to advise it on inter national co-operation in controlled fusion research. The countries represented on the Council are Australia, France, Federal Republic of Germany, Italy, Japan, The Netherlands, Russia, Sweden, United Kingdom and United States of America. The Council meetings are also attended by a representative of the European Community organization EURATOMo The Council meets annually and, on this occasion, met on 20th August in Grenoble, France. The major items of business discussed by the Council are summarized in the following sections. 3.1 Reports on National Research Programmes Each delegate presented a brief survey of his nation's controlled fusion research programme. The delegates from EURATOM, Russia and the United States also presented review papers on the national programmes at the Conference; these will be available in the proceedings of the Conference. A brief outline of each delegate's report is given below, with emphasis on major areas of activity and major devices* A discussion of results is presented in Section 5» Australia (M. H. Brennan) : A copy of the presentation of the Australian programme is included as Appendix B to this report. In this presentation I briefly reviewed the programmes of the three major research groups (Canberra, Flinders, and Sydney) and emphasized the broad and basic nature of the fusion research being carried out in Australia. France (M. Trocheris): The French programme is conducted at two centres — Fontenay-aux-Roses and Grenoble. In the last two years the programme has swung heavily away from open, mirror systems towards closed, low-$ systems. The Fontenay programme is dominated by the construction of a Tokamak device (TFR) which will have supple mentary heating by neutral beam injection. A Tokamak and a Stellarator are planned for Grenoble, with the objective of studying transit-time magnetic - 10 - pumping. Both laboratories have a number of small experiments in progress; the major areas of interest are neutral beam injection sources, wave propagation and r.f. heating and instabilities. In addition, a laser-produced plasma programme is carried out at Lemeil. Germany (G. von Gierke): The two major fusion research laboratories in Germany are at Garching and Julich. The laboratory at Garching, with a staff of about 120 professional | scientists and engineers, is the world's largest fusion research laboratory. The Garching programme covers most of the possible closed confinement systems. Major devices include 0-pinches, screw pinches, stellarators (they have under construction a very large stellarator, Wendelstein Vil, of 2m major radius, and 36 cm minor radius), and a Tokamak (also under construction). An internal conductor multipole is under construction for containment studies. R.F. heating methods are also under study. Dense plasmas are covered by work with a laser-produced plasma; a major feature of interest is the laboratory's recent success in developing a high-power pulsed iodine laser which may be of considerable interest in this field. Relativistic electron beams are also under consideration for dense plasma production. The Julich programme covers four major areas — diffuse pinches (with fast compression and, more recently, non-circular cross section), high-B stellarators and 6-pinches, plasma focus, and r.f. heating. Italy (B. Brunelli) : Two major projects are planned for Frascati — a Tokamak with similar dimensions to the Fontenay machine, but with a high maximum magnetic field (100 kG), and a 1 Megajoule plasma focus. (This device will be a joint effort by Culham, Frascati and Julich.) A small toroidal screw pinch is also in operation, in Padua. Japan (K. Husimi): The total Japanese effort is comparable with Germany's, with major I groups at Nagoya University and the Japan Atomic Energy Research Institute. In addition, there are a number of smaller university groups funded by a special grant for fusion and plasma research from the Ministry of Education (MY 100 for 1972, MY 200 for 1973 and'197*0'. The programme is characterized by the diversity of relatively small experiments concerned with basic plasma physics. -li lt is now intended to build a large toroidal facility at Nagoya, with a 100 MW generator for magnetic field production. The Netherlands (C. M. Braams): The major fusion laboratory is at Jutphaas, where three major areas are under investigation — screw pinches (a large device, SPICA, is under construction), gas blanket confinement, and turbulent heating. Russia (E. P. Velikhov): The Russian programme is more diverse than any other national programme; despite their very significant success with the Tokamaks, they firmly believe that at this stage there is no clear and unique path to fusion; their programme J thus has a very strong emphasis on exploring the basic scientific questions 1 relevant to the many possible approaches. > Four major approaches to controlled fusion are under investigation. Low-3 toroidal systems are being studied with Tokamaks and stellarators; a large Tokamak (T-10, costing~$10M) is under construction and will be completed in 1375; some attention is also being given to optimizing the current shape and the plasma cross-sectional shape in Tokamaks. Magnetic mirrors are under investigation in a number of machines, notably PR-6 and Ogra III; the Russians appear to be more optimistic about this approach than other workers. Work is in progress on the four major forms of heating in low-3 systems — particle injection, r.f. heating, adiabatic compression, and turbulent heating. Finally, several fast pulsed systems are under investigation; the laser-produced plasma experiments are most advanced, but considerable work has also been done on electron beam heating and the high magnetic field 6-pinch. Sweden (B. Lehnert): The Swedish programme has four major aspects: densities of ~ 1020 m"3 are chosen for study since plasmas at these densities are impermeable to neutral gas, confinement schemes are based on magnetic fields having a main poloidal component, internal ring systems are being developed with magnetically shielded supports, and plasma preparation and heating is achieved primarily by the application of electric fields transverse to the confining magnetic field. United Kingdom (R. S. Pease): The fusion programme in the United Kingdom is conducted almost wholly at the Atomic Energy Authority's laboratory at Culham. A major review - 12 - of the programme is currently in progress. Two major points for consideration are Culham's role in the EURATOM programme following entry into the Common Market and the not unrelated question of a large toroidal device, similar in size and cost to the Russian Tokamak, T-10. (Such a device is also under consideration by the European community; it seems most unlikely that two large machines will be built in Europe!) The U.K. programme centres on closed systems in the low to medium-^ range. No significant work is in progress on I laser-produced, or other, fast plasma systems, or on open systems. The programme thus centres on several devices of moderate size, including stellarators, a Tokamak and a multi-purpose screw pinch. Work is also in progress on fast shock heating, on turbulent heating, and on neutral injection. United States of America (R. W. Gould): The American programme is carried out at four major national research laboratories and at a number of A.E.C.-supported universities. There is significant, and growing, support from private industry, particularly from the electricity supply companies. Four major approaches are being investigated. Five Tokamaks are in operation, or under construction; the four heating methods mentioned earlier are all being pursued fairly rigorously. High-8 pinches are under study at Los Alamos; feedback stabilization of the toroidal sector of Scyllac (the toroidal 6-pinch) will shortly be attempted, following encouraging results on the linear machine. The mirror machine programme is continuing, but at a somewhat reduced level of funding. Finally, considerable research is being done on • laser-produced plasmas; most of this work is closely tied to the defence work J on high-power lasers. Recently, funding of $13M (U.S.) has been approved for the construction of the Princeton Large Torus, a Tokamak device of similar size to T-10. Completion is planned for late 1975/early 1976. 3.2 Fusion Power and the Environment The Council had before it the report of an ad hoc consultants group set up to consider the radioactive problems posed by fusion energy. The consultants had recommended "that further engineering studies of fusion reactors should be made before the environmental effects of fusion power are considered in detail". - U - After some discussion, it was agreed that it was desirable to pursue this question further and that member countries should be invited to comment / on their present and planned research activities on the environmental (particularly radioactive) impact of fusion power. The Nuclear Safety and Environmental Protection Division of the IAEA will be asked to collate and comment on the replies, before forwarding them to the Council. 3»3 Fusion Reactor Technology The larger member nations all reported a significant increase in research effort on various aspects of fusion reactor technology. Further growth in this area will be required during the 1970's to provide a suitable basis for reactor design studies. Attention was drawn to conferences and schools on fusion reactor technology planned for Grenoble (October, 1972), Erice (September, 1972 and 197*0, and Austin (April, 1973)* It was agreed to recommend that the IAEA hold a Working Group/Symposium on Reactor Design Studies at a time to be determined (probably 197*0. 3»fr Conferences It was agreed to recommend that the IAEA consider holding one or two meetings on computational plasma physics or dense plasmas as part of the Trieste theoretical physics series. The Russian delegate announced that the next European Conference on Controlled Fusion and Plasma Physics would be held in Moscow, commencing / 30th July, 1973' The Council agreed to hold its next meeting immediately M prior to this date. / /'^ ^ ** t*y***J /£> - 14 - k. FIFTH EUROPEAN CONFERENCE ON CONTROLLED FUSION AND PLASMA PHYSICS The Fifth European Conference was held in Grenoble, France, from 21st to 25th August, 1972, This Conference has developed as a major international conference and is timed to complement the IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research, which are held every three years. Approximately 370 participants attended the Conference. As Australia's sole representative I was pleased to note that the Conference President included Australia in his opening remarks as one of the "overseas" countries partici- pating in the Conference. A useful feature of the Conference was the relatively large number (19) of invited papers, These will be published as Vol. II of the proceedings. The approximately 180 contributed papers will be available as Vol. I; the contributed papers were presented in four parallel sessions. The invited and contributed papers covered all important aspects of the current controlled fusion research programme. Rather than attempt to summarize the conference here, the major results are included in the review presented in the next Section. 5. THE PRESENT STATUS OF NUCLEAR FUSION RESEARCH The proceedings of the Fifth European Conference on Controlled Fusion and Plasma Physics will provde an excellent review of the present status of nuclear fusion and research; only some of the salient features will be presented here, in what necessarily must be a somewhat subjective selection and assessment of the very wide range of possible reactor systems. Mirror machine: Instabilities resulting from the non-Maxwelllan nature of the velocity distribution (arising from particle loss through the mirrors and from neutral particle injection, when used) appear to be an almost insurmountable obstacle. Certainly, the results from the Livermore machine, 2X M, at high injection energies are not very encouraging. The Russians believe, however, that these problems may be less serious at higher temperatures and densities. - 15 - Research on these devices has been drastically curtailed except for basic plasma and heating studies where the simplicity of the device enables detailed measurements to be performed relatively easily. Stellarator: After many years of frustrating disagreement between theory and experiment, recent work at Culham on Proto-Cleo has shown excellent agreement between the experimentally observed confinement times and the theoretical predictions, over a wide range of plasma conditions. Similarly, excellent agreement has been obtained with the Gulf General Atomic multipole. The essential feature of this relatively new situation is a much improved theory for plasmas confined in toroidal configurations, in particular, the theory includes the effects of particles trapped in small local magnetic traps which arise from the complex magnetic field geometry, indeed, this theory predicts the existence of a self-induced plasma current which, under reactor conditions, would make a stellarator look more like a Tokamak (which, of course, has an externally induced plasma current). No experimental evidence for such a current has been found, at this stage. Further, substantial progress with stellarators probably awaits the commissioning of Cleo, at Culham, and the larger stellarator, Wendelstein VII, at Garching. In parallel with this is the development and assessment of the various plasma heating schemes mentioned in Section 2. Much of this aspect of the programme wi11 be carried out in smaller toroidal and linear devices. Tokamak: Although the performance of the Tokamak is clearly superior to the stellerator at the present time, there are many features of its operation that are poorly understoodo In particular, the origin of the disruptive instability, which prevents high density operation, is not known; the current distribution and hence the detailed magnetic field configuration is not known; the role of trapped particles is not clearly understood; the role of neutral gas re-cycling is not clear. Despite these deficiencies much progress has been made in the last two years and plasma conditions have moved much closer to the Lawson criterion; temperatures of ~2 keV have been achieved in plasmas of density -lO13 -id1* cm" for confinement tJmes of -20 ms (nt~1012 cm"3 s). During the last few months - 16 - r»f\ heating and ad;abat*c compression experiments at Princeton have shown very encouraging results: in the r.f, heating experiments modest power inputs, accompanied by plasma heating, have been achieved without significant particle loss; in the adiabatic compression experiments on ATC, a small Tokamak device, the plasma has been compressed by about s-x times in density with an accompanying three-fold increase in temperature Neutral injection will shortly be investi gated as a "pre-heat" phase on ATC, These encouraging results have led to decisions to build larger Tokamaks in Russia (T—10) and the United States (PLT); a large torus is also under consideration at Culham ana in Europe, As an example of such a device, PLT will have a major radius of ^30 cm5 a m.nor radius of 45 cm, a magnetic field of 50 kG, and a plasma cu.-ent of up to 1.6 MA, it will be powered by the existing 200 MW generator system. These dimensions, fields and currents are only a factor 2-3 less than those proposed for a full scale reactor capable of generating 2000 MW(e) Diffuse pinches: The development of cne diffuse pinch is in some respects at a less advanced stage than the low-3 Tokamak and stellarator systems. In particular, the devices tend to be generally smaller than the low-B systems and comparison between theory and experiment is not so detailed. An important factor which is rapidly changing this situation is the development of computer programmes capable of simulating the plasma behaviour in some detail. Some of the larger, or more interesting devices, include toroidal screw pinches at Jutphaas (Spica), in Japan (Asperator) and at Garching (Isar IV and T-X), the multipurpose High Beta Toroidal Experiment at(Culham), and the recently completed shock heated toroidal z-pinch ac Los Alamos (ZT-1). In several of these devices temperatures of ~1 keV at densities of ~1016 cm"3 have been achieved, corresponding to $-values of -0,3 - 0.4, and values of nx~ 1010 cm"3 s. These results are encouraging, particularly in view of the comparatively small size of the devices,, Several larger devices (for example Isar T-X, which has a 1 MJ capacitor bank) are currently under construction. Toroidal 6-pinches, high-3 stellarators: The very encouraging results obtained with straight 9-pinches have led to the development of a number of toroidal 0-pinches which can be considered as high-B stellarators. No detailed results are as yet available on the - 17 - confinement properties of these systems. However, experiments on curved sectors with combinations of helical fields and with dynamic stabilization Indicate that confinment times can be markedly improved by these methods. Plasma heating in toroidal systems: We have already commented on the successful adiabatic compression experiments at Princeton. Particle injection experiments are planned for commencement in the next six months on several of the Tokamaks and stellarators either in operation or under construction. Very little basic experimental or theoretical work has been done on the instabilities that are likely to be generated. A substantial revival of interest has been shown in r.f. heating, particularly in the low frequency range around the ion cyclotron resonance and the lower hybrid resonance. Much of this interest results from the discovery of parametric instabilities at these frequencies and the high coupling efficiencies that appear possible. At very high power levels other instabilities may also provide efficient plasma heating. There is a clear need here for a variety of fundamental experiments to provide a proper basis for evaluating r.f. heating as a potential component of a reactor design. High density systems: Although technologically speaking the high magnetic field 0-pinch Is the most straightforward, most attention and funding has been directed towards the laser-produced plasma as a possible pulsed reactor system. The Russian group at the Lebedev Institute appears to be the most advanced experimentally — they have a 200J',5ns neodymium-glass laser system which has so far produced outputs of up to 106 neutrons/pulse. In evaluating this result and its relevance to the fusion reactor requirements (see Section 2) it is important to note that there is evidence of very energetic electrons (-100 keV compared with a plasma temperature of ~2 keV); these high energy electrons may be a sign of potentially disruptive instabilities; at the higher power levels required for a reactor, non-linear processes may well make the plasma a good reflector, rather than a good absorber of the laser radiation. Finally, the energy output of the IMJ laser reactor system will be approximately 10 MJ (to allow for the 10% overall efficiency). This small explosion, equivalent to about 3 lb of TNT, will - 18 - produce approximately 0.3 c worth of electricity. Assuming, somewhat optimistically, that the IMJ system could be built at a total cost of $1M it would require some 3 x 106 shots to recover the capital cost of the system — 10 years at a rate of one shot every second. 6 CONCLUSION The most obvious single characteristic of the controlled fusion research programme is the great diversity of approaches under active investigation; potential reactor systems range from the low-$ stellarators and Tokamaks, which could operate continuously, to the fast, pulsed, high-density laser system — a range covering densities from 1011* -1026 cm"3 . It is possible, that significant new approaches, such as the high magnetic field 6-pinch, will further broaden the scope of research over the next few years. In addition to this breadth, the very encouraging Tokamak results have led to the construction of large devices whose size approaches, within a factor of 2-3, the size of a power generating reactor. Major questions of a techno logical nature, such as the provision of superconducing magnet coils for the low-3 toroidal systems, are also beginning to form part of the programme. We can confidently expect the present, diverse progamme to continue | well into the late 1970's and possibly into the early 1980's; certainly, until j i results from the large devices under construction give us more confidence in | i the scaling laws for the various devices and, hopefully, until we have a clearer | theoretical understanding of their operation, in addition, during this period, j we would hope to see the various small scale experiments yield useful information! i on plasma heating, plasma instabilities and stabilization, and indeed the whole range of basic plasma properties. The Australian programme clearly has a role to play in this development; we have a responsibility, as a developed country, to play a part in the programme, and we must ensure that sufficient expertise is developed in Australia to \ evaluate, and ultimately use, the results of nuclear fusion research. These two requirements, coupled with the present diverse nature of fusion research, appear to be best met by a continuation of the present approach in which the universities, and in particular the three major laboratories at Canberra, Flinders and Sydney, co-operate to achieve a coherent and useful national programme. 1 APPFNDIX A 1972 OVERSEAS TRIP ITINERARY 13 August Depart Sydney 15-17 August Max-Planck-InstItut for Plasmaphysik, Garching, Germany 18-19 August Centre de Recherches en Physique des Plasmas, Lausanne, Switzerland 20 August International Fusion Research Council meeting, Grenoble, France 21-25 August Fifth European Conference on Controlled Fusion and Plasma Physics, Grenoble, France 29 August Institut fur Plasmaphys!k der Kernforschungsanlage, Julich Germany 30-31 August Fom-instituut Voor Plasma-Fysica, Jutphaas, The Netherlands I September Departement de la Physique du Plasma et de la Fusion Controlee, Fontenay-aux-Roses, France h September Physics Department, Imperial College, London 5 September Department of Engineering Science, Oxford University 6-7 September Culham Laboratory, Abingdon II September School of Engineering and Applied Science, Columbia University, New York 12-14 September Plasma Physics Laboratory, Princeton University, Princeton, N.J. 15 September Physics Department, University of Maryland, College Park, Maryland 18 September Centre for Plasma Physics and Thermonuclear Research, University of Texas, Austin, Texas 19 September Department of Electrical Engineering, Texas Technical University, Lubbock, Texas 20 September Plasma Physics Group, University of California, Los Alamos Laboratory, Los Alamos, New Mexico 21 September Radiation Laboratory, University of California, Berkeley, CalIfornia 22 September Institute for Plasma Research, Stanford University, Stanford, California 25 September Engineering and Physics Departments, University of California at Los Angeles, Los Angeles, California B1 APPENDIX B NUCLEAR FUSION RESEARCH IN AUSTRALIA* There are three major research groups engaged in fusion research in Austral la: (a) The Australian National University (A„N.U.) group led by Dr. A. H. Morton. (b) The Flinders University group led by Professor M. H. Brennan. (c) The Sydney University Wills Department of Plasma Physics led by Professor C. N. Watson-Munro. The total number of qualified scientists and engineers involved in these three groups is approximately 35, with an annual expenditure (see Table l) of $^30,000. The work is financially supported by the universities themselves, by Australian industry, by the Australian Research Grants Committee, and the Australian Atomic Energy Commission through the Australian Institute of Nuclear Science and Engineering, which also finances a biennial Plasma Physics Conference. Related work in plasma physics and atomic collision phenomena is undertaken in the A.A.E.C. and in a number of universitie. In addition, a high power laser facility is under construction at the A.N.U. Research Programme The main experimental devices and research programmes of the three major groups are detailed in the sheets submitted for the "World Survey of Major Controlled Fusion Facilities" (copies, with minor amendments, attached). The present programme is concerned primarily with three major areas. Toroidal confinement is studied in the Canberra LT-3 machine; the early work on the Ware-pinch phenomenon has been extended to include more detailed measurements of plasma parameters; the machine is currently being modified to permit a wider range of plasma parameters to be studied. *Report prepared for International Fusion Research Council, Grenoble, August, 1972. B2 The Flinders and Sydney groups have been concerned with various r.f. heati ng methods; these include work on ion and electron cyclotron waves, large amplitude torsional and compressional waves; the Flinders group has recently begun work on magnetoacoustic resonance heating and ion-ion hybrid resonance heating. Shock waves have been studied at each laboratory; a major by-product of this work is the present programme of research on plasma centrifuges at Sydney University. Supporting work on basic plasma physics and diagnostics is undertaken by the major research groups and at the other universities, in particular, a wide range of laser diagnostics has been developed and a number of wave propagation experiments are in progress. Future Developments It is expected that the three groups will continue at approximately the present level of activity during the next year, with continuing work on toroidal confinement, r.f. heating, and (at a somewhat reduced level) shock heatingc Two major new activities are planned: the Canberra laser facility will be used to study the inertia! confinement of super-dense plasmas; the Flinders University group will commission a fast z-pinch facility for studies of the stability and r.f. heating of a high-3 plasma. B3 TABLE I Annual Expenditure on Fusion Research in Major Australian Research Groups (1971/1972) Staff $k Key personnel 16 75* Support staff (professional)** 18 60 (technical) 15 75 Equipment and stores items 150 Administration and general over head 90 TOTAL ANNUAL EXPENDITURE $430,000 *50% of total salary **Includes postgraduate students B4 May, 1972 Australia/Canberra LT*-3 Type and Purpose of Device Tokamak-1ike device, similar to LT-1 but generally operating with primary and toroidal field circuits separated. Used for investigation of plasma instabilities. Key Personnel: A. H. Morton, K. G. Srinivasacharya, C. F. Vance. Main Characteristics Vacuum chamber: R • 40 cm, r - 10 cm, no limiter. Cu Shell: r = 11.25 cm, 1.25 cm thick. Toroidal field: up to 14 kG. Plasma current: up to 33 kA, 1.6 ms to peak value. Major Results 1) Typically n .5x 1013 cm"3, T ~ 200 eV. 2) Runaway electrons in outer regions of contracted plasma having energies up to 100 KeV. 3) Plasma conductance does not increase continuously with toroidal field, possibly because of field irregularities. Future Plans A considerable expansion of activities .s envisaged including the conversion of machine to LT4, with R ~ 48 cm, r ~ 13 cm, 350 kJ primary condenser bank, 35 kG toroidal field powered by homopolar generator. *Liley Torus B5 May, 1972 Australia/Flinders (FPS-1, FPS-2) FUNDERS PLASMA SOURCES Type and Purpose of Device Pulsed, linear devices with provision for magnetic mirrors, used for studies of plasma heating by various types of waves. Key Personnel: M. H. Brennan, I. R. Jones, A. L. McCarthy, E. L. Murray. Main Characteristics Vacuum chamber: 10 cm diameter, 100 cm long (FPS-1) 290 cm long (FPS-2) Magnetic field: Pulsed axial field up to 10 kG, with provision for mirrors (FPS-2 only) Plasma production: 200 kW, 15 MHz oscillator for iow densities (~1013 cm"3), ax>a1 discharge or ionizing shock wave for high densities (1015 -1016 cm"3). Major Results 1) Detailed study of ionizing shock structure has revealed substantial radial variations in density and temperature. 2) Excellent agreement between theory and experiment has been obtained for anomalous skin effect in absence of magnetic field. Experiments in progress with magnetic field. Future Plans 1) Magnetoacoustic resonance heating. 2) Ion-ion hybrid resonance. 3) Effects of non-uniform density and magnetic field on ion cyclotron waves. B6 May, 1972 Australia/Sydney SUPPER* MACHINES Type and Purpose of Device Pulsed, cylindrical laboratory sources for studies of: (a) Ion cyclotron and other forms of radio frequency heating. (b) Shock heating with various MHD-waves. Key Personnel: C. N. Watson-Munro, D. D. Millar, J. A. Lehane, R. C. Cross, L. C. Robinson, W. B. Smith, I. S. Falconer, G. F. Brand, B. W. James. Main Characteristics Supper I Supper 11 Supper 111 Supper IV Supper V Length: 80 cm 170 cm 10 cm 250 cm 50 cm Radius: 7.5 cm 10.7 cm 10.7 cm 10.7 or 10 cm 7.5 cm Magnetic field 1 kG (max.): 10 kG 10 kG 25 kG 15 kG (Supper I - IV have provision for mirrors) Plasma Reflex preparation: (Supper I-IV) 1013 -1016 cm"3 by crossed fields discharge or axial discharge. Wave studies, Main purpose: Diagnostic Shock and Plasma Shock b) and development ion centrifuge heating ce cyclotron harmonics heating Major Results 1) One megawatt of energy into plasma at 9.2 MHz, close to ion cyclotron frequency. 2) Shock heating experiments reported at Novosibirsk, 1968 and by Bighel and Watson-Munro [Nuc. Fusion 12, 193 (1972)]. ^Sydney University Plasma Physics Experimental Rigs.