The tokamak: 1955?80

摘要: The name tokamak (derived from the Russian for 'toroidal-chamber-magnetic') is applied to axially symmetric toroidal systems in which plasma confined by a strong magnetic field Bt , produced an external solenoid, together with weaker poloidal Bp, mainly current Ip flowing itself. combination of two fields produces nested surfaces composed helical lines. Equilibrium field, whilst serves suppress main magnetohydrodynamic instabilities, provided 'safety factor' q = aBt/RBp sufficiently large, where and R are minor major radii, respectively. also provides 'Ohmic' heating plasma—the only mechanism operative almost all early experiments. Particle orbits tokamaks fall into classes: there 'passing' particles that travel completely around torus, following lines quite closely; magnetically 'trapped' back forth along those parts lie on outer-major-radius side undergoing reflection region higher inner side. In both cases, conservation canonical angular momentum, follows axisymmetry ideal configuration, implies particle's excursion away surface cannot exceed its gyroradius evaluated Bp. this sense, configuration confines 'all' particles; reactor, 3.5-MeV alpha-particles will be exceeds about 3 MA.