Approach to ignition in the Ignitor experiment

The scientific objectives of the Ignitor experiment can be achieved owing to the high magnetic field and plasma current planned. The physics projections are here supported by an analysis, carried out by the free boundary 1 1/2-D code JETTO, of the plasma evolution during the current ramp up and hat-top phases. The most advanced operating scenario that is envisaged for the machine is considered, while taking the technological constraints of the project into account. The plasma shape and position are checked to agree with the reference magnetic configurations. The density values are always much lower than the Greenwald limit, and the avoidance of disruption boundaries in the (l(i), q(Psi)) diagram is assured. The influence of the density profile growth on the overall performance is analysed under different assumptions. The results show that ohmic ignition could be reached even assuming transport diffusion coefficients that account for energy confinement times close to the 'ITER89P' scaling, provided that the ramp-up phase is carefully programmed. The density is the main parameter with which to control the path to ignition, but some other items need attention, such as the plasma shape and dimensions, the current density profile and the impurity content. Even when ignition is not achieved globally, a central ignited core is present.