Conceptual Design and Modeling of the Toroidal Field Coils Circuit of DTT

Transient Electrical Behavior of the TF Superconducting Coils of Divertor Tokamak Test Facility During a Fast Discharge

“…In order to assemble the TFC circuital model, the inductances matrix has been implemented as a coupling matrix together with the capacitances and the resistances, analytically estimated. Each single TFC circuit has been then modelled as a sub-circuit as well as each FDU: the latter includes the electrical parameters to simulate the operations of its hybrid CBs (mechanical and static switch) and an active discharge by DRs [3]. All sub-circuit just described have been connected in series to each other and to the TFPS.…”

“…As the conductive paint layer and the case are electrically connected to each other and then to ground by means of a resistance, Rcase-to-gnd, the paint-to-case capacitances have not been taken into account, while all other frequency independent capacitances are estimated analytically. All capacities in the toroidal direction (z-axis), Ctor, and in the radial direction (x-axis), Crad, have been estimated by applying the formula of the flat capacitor and the cylindrical capacitor composed of two coaxial and concentric cylinders, respectively (see [3]). The range of the obtained results, in toroidal and radial direction, are reported below:  3 nF < Cturn-turn,tor < 5 nF  0,3 nF < Cturn-paint,tor < 3 nF  5 nF < Cturn-turn,rad< 6,5 nF  0,15 nF < Cturn-paint,rad< 5 nF The broad ranges of the capacitance values come from different position of the corresponding turns and of the outermost turns respect to the conductive paint layer, in both directions.…”

“…of a quench, of a fault or when a failure of the Toroidal Field Power Supply (TFPS) occurs; therefore, the reliability of the FDU is of primary importance as the safety of the superconducting magnets depends on it. In previous works [3] it has been demonstrated how the discharge of the FDU can take place with passive elements (fixed resistors) or with active elements (IGCTs progressively disconnected through the discharge time) allowing a reduction of the maximum voltage of 20%, the reduction of discharge time of TFCs of 72% and the possibility of installing only three FDUs instead of six with considerable advantages from the point of view of thermal and electrical parameters. The model, the mathematical approach and the control system have been simulated with Matlab and extensively described in [3].…”

“…In previous works [3] it has been demonstrated how the discharge of the FDU can take place with passive elements (fixed resistors) or with active elements (IGCTs progressively disconnected through the discharge time) allowing a reduction of the maximum voltage of 20%, the reduction of discharge time of TFCs of 72% and the possibility of installing only three FDUs instead of six with considerable advantages from the point of view of thermal and electrical parameters. The model, the mathematical approach and the control system have been simulated with Matlab and extensively described in [3]. The voltage across each TFC is negligible during the normal operation, but in case of quench it increases very fast and the TFCs must be discharged to avoid their damage.…”

“…For this reason, the operation of the FDU must be as quick as possible once the fault or the quench is identified and the discharge of the magnets must take place in total safety and with maximum efficiency. As it was extensively described in [3], every time that the crowbar (an electrical breaker) is activated to bypass the TFPS, a trigger signal will be send to each FDU. The hybrid Circuit Breaker (CB) of each FDU, composed by a mechanical By-Pass Switch (BPS) and a Static Circuit Breaker (SCB), will connect in series the TFC to the dump resistors (DRs) in order to dissipate the energy associated to the coils magnetic field (Fig.…”