The Ignitor experiment is designed to achieve ignition conditions by a combination of high toroidal (BT ≤ 13 T) and poloidal magnetic fields. Given the strong central pressures (> 1.5 MPa), in fact, the poloidal magnetic fields need to be particularly high in order to avoid the onset of large oscillations in the central region. The resulting poloidal magnetic field pressure, Bp^2≡(Ip /5√(ab))^2, can be about 30 times that reached at JET .
The main components of the magnetic system are the Central Solenoid (CS) (7 coils), the External Coil Assembly (ECA) (6 coils) and the Press Coils (2 coils). Helium gas is used for cooling the poloidal field coils and the toroidal field magnet.
The IGNITOR poloidal field is generated by an optimised system of 13+13 coils symmetrically located relative to the machine equatorial plane. The poloidal field coils are placed outside the toroidal fields coils.
The central solenoid includes seven coil pairs which are mounted around the central steel post of the machine. The CS is a critical component of the machine because of its temperature gradient and its contributions to the overall mechanical bucking of the toroidal magnet. The primary function of the CS is to produce most of the magnetic flux variation needed to drive the plasma current according to prescribed scenarios. In order to reduce the temperature gradient and the EM forces between coils of the central solenoid, an increased grading of the current density distribution between the turns of the coils has been adopted in the current design, thus obtaining an increased uniformity of the temperature into the coils. Furthermore, the central solenoid is segmented to allow greater plasma shaping. A radial splitting of the CS into two concentric coils has been adopted to maximize the magnetic flux variation while keeping the coils within their thermal and mechanical limits .
1) B. Coppi et al, Nucl. Fusion 41, 1253 (2001)
2) G. Ramogida et al, 48 th Annual Meeting of the Division of Plasma Physics, Philadelphia, US, October 30 –November 3, 2006