This magnetic confinement experiment has been built from some components of the ex-tokamak TORTUR (supporting structure, vacuum chamber, copper shell, transformer, toroidal magnetic field coils, radio-frequency generator, and condenser banks) which was de-commissioned by the Association EURATOM/FOM in 1988.
The other components of the tokamak, as well as its diagnostics and control and data acquisition system, were designed and constructed by physicists, engineers and technicians of the Association EURATOM/IST.
The main geometrical parameters of ISTTOK are indicated in Table 1.
Table 1 – Geometrical parameters of ISTTOK
The ISTTOK construction started, officially, on January 1st, 1990, date on which the contract of association EURATOM/IST enter into force. The operation of this experiment in an inductive regime started on February 1991.
Typical ISTTOK discharges are characterized by the parameters referred to in Table 2.
2 – Internal parameters of the ISTTOK plasma
Copper shell. This component envolves the toroidal chamber, has a thickness of 1.5 cm and is internally covered by an 1.5 mm insulating layer (up to 12 kV). Its functions are: (a) – to support the vacuum chamber and (b) – to suppress the plasma column position fluctuations (T<2ms).
Vacuum system. This system is composed by a magnetic levitation turbo molecular pump (500 l/s) supported by double stage rotary pumps. Both ionisation and capacitance manometers measure the residual (~ 5*10 -9 torr) as well as the work (2 * 10 -4 torr) pressure.
Iron core transformer. This component has a primary winding of 2x20 spires in the central post and an auxiliary winding with 20+10 spires in the external post, allowing the variation of the transformer ratio between 10:1 and 70:1. The flux swing is 0.22 Vs.
Toroidol magnetic field solenoid. The toroidal magnetic field, up to 2.8 T, is obtained by a set of 24 water cooled coils. Due to a power limitation (1 MW) ISTTOK is operated at low magnetic field (0.5 T).
Vertical and horizontal magnetic field solenoid. The vertical and horizontal magnetic fields are produced by toroidal windings with 2x6 (horizontal field) and 4x8 (vertical field) spires inserted between the main toroidal coils and the copper shell.
Condenser banks. The discharges are made by using two condenser banks: a fast and high voltage bank (1 mF, 5kV) for the pre-discharge and a slow and high energy bank (0.5 F, 500 V) to assure that the discharge may continue until the saturation of the transformer iron core.
Gas injection system. It is constituted by several electromagnetic and pneumatic valves that allow the filling of the vacuum chamber and by a piezoelectric valve for additional gas injection in a pulsed regime.
Vacuum chamber conditioning system. This system conditions the vacuum chamber by converting impurities (Oxigen, Carbon, etc) in pumpable c omponents (H2O, CH4) through tokamak discharges. Luminiscent discharges are made by radio-frequency power (3 MHz, 200 W) delivered to the tokamak limiters. Inductive discharges are made by feeding the primary of the transformer by an alternating voltage (50 Hz) during small periods, under a pulsed regime
Recently, the ISTTOK scientific programme has been based on: (i) study of the influence of external biasing on the plasma confinement and stability; (ii) operation on alternating plasma current regimes; (iii) testing of the liquid metal limiter concept; (iv) study of the fluctuation induced transport and their driving mechanisms; (v) development and upgrade of diagnostics.
Study of the influence of external biasing on the plasma confinement and stability
Tokamak operation in alternating current regimes
Testing of the liquid metal limiter concept
Study of the fluctuation induced transport and their driving mechanisms
Development and upgrade of diagnostics