D-3He burning, second stability region, and the ignitor experiment

The Ignitor experiment has been designed to achieve fusion burn and ignition conditions in a high-density deuterium-tritium (D-T) plasma with a compact high magnetic field confinement configuration. The recent addition of a powerful system of radio-frequency heating to the design of Ignitor allows the investigation of physics issues relevant to advanced D-3He reactors and the second stability region for finite-β plasmas. To maximize the production of D-3He power, a lower density regime is considered (e.g., n0 ≅ 3 x 1020 m-3) than that found to be optimal for D-T ignition (n0 ≅ 1 x 1021 m-3). This allows a relatively large population of 3He nuclei at high energies ≥ 0.65 MeV to be produced by a high density of injected power at the 3He ion cyclotron frequency (up to 18 MW injected in the plasma column of volume ≤ 10m3). The investigation of second stability region access can be carried out in relatively low magnetic field and plasma current regimes with the added benefit that the duration of the plasma discharge can be extended over relatively long times. In fact, the Ignitor magnets can be brought down to an initial temperature of 30 K by gas-helium cooling. The low aspect ratio (≅2.8) and elongated plasma cross section of Ignitor make it suitable to reach both finite-β conditions and interesting plasma regimes at the same time. The Candor concept is the next step in the evolution of the Ignitor program. Candor is capable of producing plasma currents up to 25 MA with toroidal magnetic fields BT ≅ 13 T. Unlike Ignitor, Candor would operate with values of βp around 1.5 and with the central part of the plasma column in the second stability region. 40 refs., 16 figs., 7 tabs