No experiment has yet entered the burning plasma regime, and the physics in this self-heated regime remains largely unexplored. Table 2.1 presents a comparison of some critical parameters expected for a burning plasma experiment in the International Thermonuclear Experimental Reactor (ITER) device with the values achieved to date in D-T experiments. A burning plasma experiment would address for the first time all of the scientific and technological questions that all fusion schemes must face. Such an experiment is the crucial element missing from the world fusion energy science program and a required step in the development of practical fusion energy.

Scientific advances in the 1990s significantly improved designs for a burning plasma experiment. Tokamaks are the most advanced magnetic-confinement configuration. They alone have established a scientific basis that can be projected to burning conditions with reasonable confidence. Thus, a burning plasma experiment will take place of necessity as a tokamak.

TABLE 2.1 Comparison of Design Characteristics of the International Thermonuclear Experimental Reactor (ITER) with Achieved Conditions in Deuterium-Tritium (D-T) Experiments to Date

Parameter

ITERa Pulsed

ITERa Steady State

TFTRb (D-T)

JETc (D-T)

Radius (m)

6.2

6.4

2.5

3.0

Plasma volume (m3)

831

770

38

153

Normalized pressure (percent)

2.8

2.8

1.1

2.6

Normalized confinement (H98y,2)

1.0

1.6

1.3

1.6

Pressure-driven current fraction (percent)

10

48

26

10

Magnetic field strength (T)

5.3

5.2

5.6

3.5

Fusion power (GW)

0.5

0.36

0.011

0.016

Q (fusion power/power supplied)

10

6

0.27

0.64

NOTE: The normalized pressure is the ratio of the average plasma pressure to the vacuum magnetic pressure at the horizontal midpoint of the plasma.

aFrom “ITER Technical Basis,” available online at http://www.iter.org/ITERPublic/ITER/PDD4.pdf. Accessed June 1, 2003.

bFrom “TFTR Machine Parameters,” available online at http://w3.pppl.gov/tftr/info/tftrparams.html. Accessed July 1, 2003.

cFrom “Report on JET Activities,” available online at http://www.jet.efda.org/pages/rep-of-activ.html. Accessed June 1, 2003.



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