Initial Transport Studies in the Spherical Tokamak Pi3 at General Fusion Inc

The Spherical Tokamak Pi3 is a relatively new device in operation at General Fusion Inc. aiming to guide the Fusion Demonstration Plant (FDP) to be constructed at Culham Laboratory campus, UK[1].

The Pi3 plasmas are formed exclusively via coaxial-helicity injection (CHI) and last ~20ms. The plasma is close-fitted to an Al spherical vacuum vessel of 1.00m inner radius and 50mm thickness, acting as a flux-conserver. The wall is regularly coated by lithium using 4 heated evaporators.

Typical of Pi3 plasmas in early phases of discharge (~3ms) are: R_o=0.67m, a=0.37m, A=1.8, k=1.7, δ~0.4, B_T(R_o)=0.23T, I_p =300kA, n_e(bar)=4.3x10¹⁹m^-3, T_e(0)=170eV and T_i(bar)=230eV.

Equilibrium reconstruction is performed by Corsica code using constraints from poloidal pickup coils inside of the vessel and polarimeter signals.

Results of the thermal energy confinement time tauE and the thermal diffusivity Chi will be presented. The former is calculated (with corrections of dW_th/dt) from kinetics and power balance associated with the Monte Carlo method. Initial results from kinetics in medium plasma densities (N_G=0.6) show tauE=3.8ms, close to the expected from the ITER97-L-mode scaling: 5.2ms.

[1] M. Laberge et al., in this conference