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14 COPPl ET AL.plays an important role can determine if these modes constitute aserious problem.From this point of view, the surest way to approach ignition conditionsis to use plasmas with the highest possible densities. But underthese conditions the plasma tends to become strongly subject tocollisions and, thus, closest to regimes in which the above-mentioned"classical" processes dominate. This is, in fact, one of the guidingcriteria for Ignitor experiments.Based on calculations now completed, an Ignitor device couldapproach true ignition if no new mechanism of energy loss should arisein the regime between ideal and true ignition. Since nothing is knownexperimentally about plasmas under such conditions, and the theory isnot well developed, it is obvious why there is interest in the Ignitordevice to conduct experiments in such plasma regimes.HIGH-MAGNETIC-FIELDEXPERIMENTAL DEVICESOne prototype compact experimental device is the Alcator, which wasdeveloped and built at the Massachusetts Institute of Technology in1969.' Another type of compact device was built at Frascati in 1971-1972 and has the capability of achieving plasma currents of ~1 MA. Athird device, the Alcator C, was built at MIT and came on line in 1979.The Alcator C is very similar to the Alcator but has larger dimensionsand, like the Frascati tokamak (FT), was designed to achieve a totalcurrent of 1 MA. The characteristics of these three devices are shown inTable 1.It is useful to recall some of the objectives achieved by the Alcatorprogram:The indication that energy confinement time is increased with anincrease in the plasma density. The increase in plasma density isachieved by injecting neutral gas into the plasma vessel at an appropriaterate, called "gas puffing." Notwithstanding the small dimensionsand low cost of the Alcator, therefore, a value of the m confinementparameter (the product of the density and the energy-confinementtime) greater than 10 13 sec/cm 3 was obtained for the first time. Later, in1977, the Alcator achieved the recorded value of 3 x 10 13 sec/cm 3 .The indication that the purity of the plasma (defined as the concentrationof deuterium or hydrogen nuclei relative to the concentration ofother ions, for example, oxygen) increases when the density isincreased. Subsequently, the Alcator obtained record density values inthe first pure plasma under conditions of thermonuclear interest.The control of instabilities, which tend to destroy the plasmacolumn, by means of programming the plasma density and currentduring the discharge. It was thus possible to achieve currents of 300 kA
THERMONUCLEAR IGNITION15Table 1. Experimental Devices with Deuterium PlasmasMaximumMaximummagnetic Minor radius Major radius plasma Year deviceName field (kG) (cm) (cm) current (MA) came on lineAlcator A(U.S.)10010540.3-0.51972Frascati torus(Italy)100218311977Alcator C(U.S.)1401764]1979Maximum temperature (millions of degrees)Figure 8. Toroidal experiments now in operation and projected, represented in the plane m,T.Note the two principal lines of approach to ignition: on the left, which has Alcator A as itsprototype, are compact devices characterized by high particle densities and currents; on the rightis the large-volume device approach.
Page 2 and 3: EDITORIALSTAFFEditorDr. Steven Bard
Page 4 and 5: Thermonuclear IgnitionBy Means of C
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: THERMONUCLEAR IGNITION 13plasma com
Page 19 and 20: THERMONUCLEAR IGNITION 17(see Table
Page 21 and 22: THERMONUCLEAR IGNITION 19increase o
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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