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Thermonuclear IgnitionBy Means of Compact Devices*B. CoppiMassachusetts Institute of TechnologyCambridge, Mass.Scuola Normale SuperiorePisa, ItalyR. Pozzoli and E. SindoniIstituto di Scienze Fisiche dell'Universita di MilanoLaboratorio di Fisica del PlasmaAssociazione CNR-EuratomMilan, ItalyA. TaroniCNEN, Centro CalcoloBologna, ItalyTranslated by Margaret BardwellThe peaceful use of nuclear fusion energy occupies an important placeamong the objectives that science has been pursuing since the 1950s.Realizing this objective would constitute a permanent solution to theworld's energy problems. In fact, in comparison to the exploitation ofnuclear fission energy, which was realized at an economical level manyyears ago, the development of fusion energy will present a considerablysmaller degree of risk and will use a low-cost, practically inexhaustible,easily accessible fuel reserve in the form of deuterium obtained fromseawater.*This article appeared in Italian in Vol. 26, No. 12, pages 573-584, of the monthly journal Energia Nudeare (Milan,Italy). Credit is given to C.I.S.E.. the publisher of Energia Nucleare, for permission to translate and publish thisarticle.
2 COPPI ET AL.For a nuclear fusion reactor it is necessary to bring a mixture ofhydrogen isotopes to a certain critical temperature and keep it confinedfor a sufficiently long period of time. Since the relevant temperature fora fusion reactor is on the order of tens of millions of degrees Celsius, thefuel mixture will be in the plasma state; that is, its atoms are split intoions and free electrons. Thermonuclear fusion can be achieved andmaintained with the mixture at a low density (10 14 —10 15 particles/cm 3 )and confined in a high magnetic field (magnetic confinement), or it canbe achieved with a denser mixture (10 22 particles/cm 3 ) that is broughtto fusion conditions by interaction with beams of laser light or highenergyparticles (inertia! confinement).In this article we shall discuss some of the problems involved inmagnetic-confinement nuclear fusion devices, particularly those devicesthat use reduced dimensions and high magnetic fields (higher than 100kG) to realize "thermonuclear" plasmas; that is, plasmas in which thefusion reaction plays a fundamental role. The experimental possibilitiesof such devices would be significant in developing a prototype fusionreactor.THE IDEAL IGNITION TEMPERATUREThe nuclear fusion reaction attainable in the first magnetic-confinementreactor is the result of an interaction between a nucleus ofdeuterium and a nucleus of tritium, with energy sufficiently high toovercome the Coulomb repulsion of the nuclei. The products of thisreaction are a neutron with energy above 14 MeV and an alpha particle(helium nucleus) with an energy higher than 3.5 MeV:D + T — n + "• (1)(14.06 MeV) (3.52 MeV)The plasma here would be confined in a toroidal magnetic configurationof the tokamak type, as described in Refs. 1-5.Figure 1 shows the process of the energy loss from the alpha particlesproduced in the D-T reaction in a tokamak-type system, as a functionof their energy. Note that the alpha particles initially lose energypredominantly through collision with the electrons and begin to loseenergy in appreciable amounts to the ions only when their energy hasdecreased to levels around 0.5 MeV.If the alpha particles are produced in relevant quantities and areconfined inside the plasma during their deceleration, the energy theydeposit in the plasma makes an important contribution in compensatingfor the various energy losses of the plasma itself. In an actual workingv'
Page 2 and 3: EDITORIALSTAFFEditorDr. Steven Bard
Page 6 and 7: THERMONUCLEAR IGNITIONFigure 1. Alp
Page 9 and 10: 6 COPPI ET AL.fore, in order to stu
Page 11 and 12: 8 COPPI ET AL.desired plasmas by mi
Page 13 and 14: 10 COPPI ET AL.Figure 5. Three-dime
Page 15 and 16: THERMONUCLEAR IGNITION 13plasma com
Page 17 and 18: THERMONUCLEAR IGNITION15Table 1. Ex
Page 19 and 20: THERMONUCLEAR IGNITION 17(see Table
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Page 23 and 24: 22 S. BARDWELLics of the first of t
Page 25 and 26: 24 S. BARDWELLstatistics and obtain
Page 29 and 30: 28 S. BARDWELLof a complicated and
Page 31 and 32: Figure 2. Cylindrical projection of
Page 33 and 34: 32 S. BARDWELLthen uses the energy

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