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The Acceleration Grid Power Supply of MITICA is a high power, high voltage power supply devoted to feed the acceleration grids of the full scale prototype of the ITER NBI injector. It is divided in two subsystems: the AGPS – Conversion System (CS) and the AGPS – DC Generator (DCG), procured by different domestic agencies. Numerical simulations have pointed out a voltage ringing at the interface of the two systems, which would generate repeated high overvoltage at the input of the AGPS-DCG, not in compliance with the interface requirements. The phenomenon has been investigated and a solution for the mitigation has been identified based on a suitable low pass RC filter, as a trade-off between simplicity and effectiveness. The filters have been successfully tested directly with the AGPS-CS to demonstrate the reduction of the voltage peaks in the operation condition foreseen for the AGPS.

The ohmic heating system and the poloidal field coils of ASDEX upgrade are supplied by 15 thyristor converter units with an installed apparent power of 600 MVA. To protect the thyristor converters against dc overvoltage arising from abnormal operations and resulting damages caused by the large energy stored in the AUG magnet coils an overvoltage protection system was required. The paper describes the motivation for—and the design and testing of the thyristor crowbar system representing the thyristor converter overvoltage protection system. It will present the layout, analyse the results of measurements obtained during commissioning, compare them to the calculated (design) values and report on the first experience of operation on the AUG coils improving the safety of the equipment.

The power supply of the ASDEX Upgrade (AUG) tokamak consists of 11 thyristor converter modules which feed the poloidal field coils. All converters installed are powered by 10.5 kV flywheel generators starting at a frequency of 110 Hz, running down to 85 Hz during a pulse. For quasi-stationary advanced tokamak experiments with enlarged flat-top phase, the power supply system must be extended. The variable frequency of the pulsed network, fast load changes, together with the different parameters of the load coils require a very sophisticated converter design with reduced reactive power consumption. The paper describes the design and testing of the modular Thyristor Converter Group 6 with neutral control and four quadrant possibilities. It presents the various configurations available for operation on AUG magnetic coils, analyses the results of measurements obtained during commissioning, compares them to the calculated (design) values and reports on the performance achieved in fast four quadrant operation, improving the possibilities of the AUG feedback control of plasma shape and position.

The ASDEX Upgrade (AUG) tokamak requires an electrical power up to a few hundred MVA for a time period of 10–20 s. The power and energy is provided by three separate networks based on flywheel generators. In 1999, during a routine check performed on generator EZ3, it was discovered that coupling bolts of the flywheel generator shaft were deformed. Given that the active load of the generator (∼100 MW) in service is well below the design value of the shaft (∼800 MW), the damages may only be explained by a torsional resonance of the shaft line, itself excited by active power transients from the converter loads. A value of 23.6 Hz was calculated for the first eigen-frequency of the shaft line. Frequencies between 10 and 30 Hz have been identified in the spectrum of the load curves. Since torsional shaft oscillations are characterised by very low damping, torsional resonance can become dangerous even for over-dimensioned generator shafts. Therefore, a novel ‘torque’ measurement system was installed. The paper presents results from calculations and measurements showing that devices capable to measure the stress in the shaft line are essential for generator protection in feedback controlled fusion experiments.

The power supply of the ASDEX Upgrade (AUG) tokamak consists of three pulsed distribution systems (110–85 Hz), each supplied by a dedicated flywheel generator: EZ2 (1.45 GJ/167 MVA) which solely feeds the toroidal field coils, EZ3 (500 MJ/144 MVA) and EZ4 (650 MJ/220 MVA). For quasi-stationary advanced tokamak experiments with extended flat-top phase, the power systems of EZ3 and EZ4 must be connected in parallel, so that full advantage of the installed generator power and flywheel energy can be realised. The variable frequency of the pulsed network, fast load changes (up to 1000 MW/s), together with the different parameters of the generators and saturation effects during pulsed operation, require detailed numerical models for an investigation of the stability limits of a parallel operation of the two machines on one common 10.5 kV busbar. The paper describes the dynamic load requirements of a feedback controlled plasma experiment, the controller development for paralleling two large flywheel generators, the results of system studies with optimised power supply and implications of these results on the technical realisation.

JET has available one of the world's most powerful AC/DC multi-convertor systems, with unique capabilities in terms of delivery of high DC voltages and currents. Whilst the primary purpose of the system is the supply of the loads required for the experimental sessions, there is scope for other uses, in particular for testing of high power electrical equipment. The first successful example of the utilization of these capabilities was achieved with the establishment of a new Test Cell powered by the Toroidal Flywheel Generator Convertor (TFGC). The new facility was used for the test of a prototype Bypass switch manufactured within the ITER programme. The aim was to prove the switch is able to fulfil the requirements concerning contact life and general reliability of the assembly.

The JET neutral beam injection system has proved to be both effective and reliable as a plasma heating device. The ion heating and plasma fuelling characteristics of the system are ideally suited to the production of high fusion performance plasmas while the flexibility in the choice of beam species (H, D, T, 3 He or 4 He) and the ability to inject into almost any JET plasma configuration allows a wide variety of related physics experiments to be carried out. The capability to inject (for the first time) tritium beams was essential to the successful execution of the first tritium experiments in which 1.7 MW of power from DT fusion reactions was generated.

After five years of construction JET started its operation in June 1983. In December plasmas with peak currents of 3 MA were produced. Flat top times of a few seconds were obtained for currents of 2.4 MA. The plasmas were slightly elongated ( ~ 20%) with a minor radius of about 1 m. Line densities (peak values) reached 7 × 10 19 m −2 , electron temperatures on the axis 1.5–2 keV and energy confinement times 0.3 s. The paper describes the state of the machine, the methods employed for impurity control and summarises the experimental results obtained during 1983.