Implementation of the Spherical Tokamak MEDUSA-CR: Stage 1

Full text: The low aspect ratio Spherical Tokamak (ST) MEDUSA (Madison Education Small Aspect Ratio Tokamak) is currently being recommissioned at the Instituto Tecnológico de Costa Rica, after it was donated by the University of Wisconsin-Madison, USA. The main characteristics of this magnetic confinement device are described as follows. plasma major radius of R_o < 0.14 m, plasma minor radius a < 0.10 m, plasma vertical elongation 1.2, toroidal field at the geometric centre of the vessel B_t < 0.5 T, plasma current I_p < 40 kA, n_e(0) < 2 x 10²⁰/m³, central electron temperature T_e(0) < 140 eV, discharge duration is < 3 ms, top and bottom rail limiters, and natural divertor D-shaped ohmic plasmas. Training students and researchers is the main goal as for ST MEDUSA-CR, to merge knowledge between physics and engineering in order to address relevant concepts for spherical and conventional tokamaks. Currently diverse topics are being addressed in the first engineering stage of the MEDUSACR. For the vacuum system design there has been developed a corresponding documentation process of the implementation and testing vacuum, also it is present a new design of the vacuum vessel made of stainless steel. The design of the new injection system, entirely developed to accomplish the spherical tokamak's requirements has been successfully tested. The electric current control of the coils presents a possible upgrade to converting ST MEDUSA-CR to AC mode. Additionally, a MHD equilibrium simulation for the original configuration of the device has been performed using a code named Fiesta; which was facilitated by Geoffrey Cunningham from Culham Centre for Fusion Energy (CCFE). (author)