Abstract ASDEX Upgrade Research Articles

Plasma surface interaction with tungsten in ASDEX Upgrade

ASDEX Upgrade pursues the progressive increase of W coated plasma facing components. At present, the central column, the upper passive stabiliser loop, the complete upper divertor, the baffles at the lower divertor, as well as six tiles of one guard limiter at the low field side are W coated, representing about 65% of the total surface area. W erosion at these guard limiter tiles exceeds the erosion found at other main chamber components by more than one order of magnitude, and spectroscopically determined erosion yields indicate a strong contribution from fast particles. Upper single null discharges do not show an obviously increased W content compared to discharges run in the lower C based divertor.

Replacement strategy for ASDEX upgrade’s new control and data acquisition

ASDEX Upgrade is being equipped with a new real-time plasma control and data acquisition system and a novel time system. Major components were implemented and installed. While much work for performance optimisation and application programming remains to be done, commissioning of the new system parallel to experiment operation is being prepared. Commissioning of the new system will be done step-by-step. To facilitate testing the old and new control systems share all input signals. Switching between old and new system can be performed within 60 min: 23 fibre optics for output of actuator commands and input triggers must be connected to the active system and minor modifications done to interface the machine protection. Commissioning phases include background listening, technical discharges and full plasma operation. With the strategy chosen we minimize risk to the machine and reduce interference with ongoing experiment campaigns.

Integrating discharge control and data acquisition at ASDEX Upgrade

ASDEX Upgrade is being equipped with new plasma controllers and advanced diagnostics. These will be integrated into a distributed system, exchanging process data and plasma state information via a real-time network. Infrastructure tasks on dedicated nodes represent a functional framework for embedding of applications. Any type of hardware or operating systems may implement these, as long as the general rules on I/O timing and signal exchange methods are observed. To avoid temporal uncertainties in the measurement process a new time system was designed. Time becomes a measurement quantity sampled with data and process values.

Power supply and protection system for plasma stabilisation in the ASDEX upgrade tokamak

ASDEX Upgrade is a diverter-type tokamak commissioned in the spring of 1991 at IPP, Garching. The highly elongated plasma (elongation factor = 1.6) requires a sophisticated plasma stabilisation system for both horizontal and vertical position control. A system of passive and active coils serves as a means of stabilising the plasma. The two active coils are powered by two 4-quadrant thyristor convertors at a power level of about 30 MVA. A digital computer study has shown that a 4-quadrant, phase-controlled thyristor convertor can stabilise the plasma position of ASDEX Upgrade. In this study, an exact model of the power supply system was used. A thyristor breaking system prevents the active coils from being overcharged by currents induced in the active coils in the event of a fast plasma disruption, where the plasma current of 2 MA decays within several milliseconds. A pyrobreaker serves as a back-up solution if the thyristor protection system fails. This supply and protection system was installed in 1989 and was tested with a dummy load until May 1990. These tests have shown satisfactory results. The final acceptance test with the original load were done in the spring of 1991.

The ASDEX Upgrade toroidal field magnet and poloidal divertor field coil system adapted to reactor requirements

ASDEX Upgrade is a tokamak experiment with external poloidal field coils that is now under construction at IPP Garching. It can produce elongated single-null (SN), double-null (DN), and limiter (L) configurations. The SN is the reference configuration with asymmetric load distributions in the poloidal field (PF) system and the toroidal field (TF) magnet. Plasma control and stabilization require a rigid passive conductor close to the plasma. The design principles of the coils and support structure are described.