Max-Planck-Institut für Plasmaphysik Garching · Greifswald

ASDEX Upgrade fusion device Design: Graphisches Atelier Fenke, Munich Atelier Fenke, Design: Graphisches Title: The plasma vessel of ASDEX Upgrade, The “Axial-SymmetricASDEX Upgrade, Divertor ITER Experiment” and DEMO ASDEX Upgrade, a Divertor and plasma boundarycreated from layer CAD data tokamak-type fusion device, has been in operation at Max Planck (Graphic: Tilmann Lunt) InstituteBecause for Plasma the construction, Physics in Garching equipment since and 1991. important plasma Transferring the proven divertor operation to larger facilities such The propertiesresearch is areaimed adapted at developing to a future a power power plant plant, that generaASDEX- as ITER or a power plant is not without problems. The tightly tes energyUpgrade from isfusion particularly of atomic suitable nuclei –among as takes the place facilities in the ofsun. the bundled plasma particles flowing into the divertor transport a lot The fuelEuropean is an ionised fusion low-density programme hydrogen for preparing gas, athe “plasma”. operation To of of energy to the divertor plates. ASDEX Upgrade has come up ignite the ITERfire of international fusion, the plasmaexperimental must bereactor confined and thein planningmagnetic with potential solutions: the area affected can be suitably shaped fields forand aheated DEMO to temperatures demonstration above power 100 plant.million Investigationsdegrees. and enlarged to reduce the peak load. To prevent the entire energy for DEMO – for example, on the thermal insulation of the hitting the divertor plates in the form of fast plasma particles, part plasma, on the stability of the plasma confinement, and of it has to leave the plasma in a gentle way as radiation, i.e. light on particle and power removal – essentiallyIn thedetermine plasma vessel the rays. These may be emitted by impurities,The tokamak for example principle noble gases, experimental programme of ASDEX Upgrade. It is drawn up injected into the plasma boundary layer. A cushion of cold neutral by a European programme committee. Research scientists hydrogen gas can also protect the divertor plates. from all over Europe use the device for their experiments.

Fusion research currently is focused on two types of devices, View into the plasma the tokamak and the stellarator. PlasmaBoth confinementare being studied at IPP. ASDEX Upgrade is of the ASDEXtokamak-type Upgrade – islike used most forof the systematicallyfusion devices studying in operation different today. plasmaTwo states. superimposed It was demonstrated, magnetic for instance,fields thatconfine the conditions the plasma at ina the plasmaring-shaped edge stronglyvacuum influencevessel: one the behaviouris a ring-shaped of the plasma field core. produced This makesby external it possible magnet to coils optimise and and Essential data of ASDEX Upgrade the plasmathe other core is from the fieldthe boundary of a current Size of the device diameter 10 metres; and toflowing improve inside confinement. the plasma In itself. height 9 metres particular,The combinedin the so-called field H regime,produces the Weight 800 tons a transporttwisting barrier of the at fieldthe plasma lines edgenecessary Major plasma radius 1.65 metre improvesfor confiningthe thermal the insulationplasma. A third Plasma cross-section width 1 metre; height 1.6 metre of thefield, plasma. a vertical In the fieldmeantime, produced a by Plasma large externalnumber ring-shapedof sample discharges coils, defines  composition hydrogen, deuterium have beenthe plasma developed. shape Together and the withposition  volume 14 cubic metres newlyof developed the current computerin the plasma. codes,  quantity 3 milligrams Photo: IPP, Bernhard Ludewig they allowThe reliable current predictions is induced for a in Magnetic field up to 3.9 tesla fusionthe power plasma plant. by a transformer Plasma current up to 1.4 million ampere coil located in the axis of the plasma ring. Owing to this Discharge time 10 seconds transformer a tokamak does not Plasma heating run in a continuous, but in a  neutral particle heating 20 megawatts  ion cyclotron heating 6 megawatts pulsed mode. However, since this  electron cyclotron heating 6 megawatts is unfavourable for power plant Plasma temperature up to 150 million degrees operation, methods are being investigated to generate the current Plasma density up to 2 · 1020 particles per m3 in continuous operation. Energy confinement time up to 0.2 second Photo: IPP ASDEX Upgrade, ITER and DEMO Divertor and plasma boundary layer Ports for Transformer coil heating, diagnosticss Because the construction, equipment and important plasma Transferring the proven divertor operation to larger facilities such and pumps Support structure properties are adapted to a future power plant, ASDEX as ITER or a power plant is not without problems. The tightly ixtract Graphic: IPP, Photo: IPP, Volker Steger Volker Photo: IPP, Upgrade is particularly suitable among the facilities of the bundled plasma particles flowing into the divertor transport a lot European fusion programme for preparing the operation of of energy to the divertor plates. ASDEX Upgrade has come up the ITER international experimental reactor and the planning with potential solutions: the area affected can be suitably shaped for a DEMO demonstration power plant. Investigations and enlarged to reduce the peak load. To prevent the entire energy for DEMO – for example, on the thermal insulation of the hitting the divertor plates in the form of fast plasma particles, part plasma, on the stability of the plasma confinement, and of it has to leave the plasma in a gentle way as radiation, i.e. light on particle and power removal – essentially determine the rays. These may be emitted by impurities, for example noble gases, experimental programme of ASDEX Upgrade. It is drawn up injected into the plasma boundary layer. A cushion of cold neutral by a European programme committee. Research scientists hydrogen gas can also protect the divertor plates. from all over Europe use the device for their experiments.

View into the plasma

About 180 staff members from science, engineering and technology work on Plasma confinement ASDEX Upgrade. About 100 scientific guests come each year for working visits lasting several weeks. ASDEX Upgrade is used for systematically studying different plasma states. It was demonstrated, for instance, that the conditions at ASDEX Upgrade fusion device the plasma edge strongly influence the behaviour of the plasma core. Plasma ASDEX Upgrade is intended to investigate crucial problems This makes it possible to optimise Divertor plates in fusion research under power plant-like conditions. For this the plasma core from the boundary purpose, the arrangement of the magnet coils, the shape of the and to improve confinement. In Plasma vessel Magnet coil particular, in the so-called H regime, plasma and essential plasma properties have been adapted to the Vertical field coils conditions that will be present in a future power plant. a transport barrier at the plasma edge An important component is the divertor: to protect the vessel improves the thermal insulation Schematic sketch of ASDEX Upgrade against particles from the plasma and, conversely, the plasma of the plasma. In the meantime, a against impurities from the wall, a special magnetic field directs large number of sample discharges the outer boundary layer of the plasma – and with it particles have been developed. Together with and energy from inside the plasma – away from the hot centre newly developed computer codes, to specially equipped, cooled sections of the vessel wall, the they allow reliable predictions for a divertor plates. This safeguards the wall and provides good fusion power plant. Extended plasma pulses thermal insulation of the plasma. At the same time, the disturbing impurities – in a burning plasma this would include the “fusion One disadvantage of tokamak devices is their pulsed mode of ash”, i. e. helium – can thus be removed from the plasma. operation. Therefore, various methods are being investigated to To investigate the interaction between plasma and wall under drive the current in the plasma without a transformer, for example realistic conditions, ASDEX Upgrade can still do without a by feeding-in high-frequency waves or injecting fast particles. burning plasma and full power plant size. It is sufficient to simulate Pressure differences in the plasma can also generate an additional only the plasma boundary layer, i.e. the outer ten centimetres of a plasma current, the so-called “bootstrap current” – all of which are power plant plasma. To achieve a wall load like in a power plant, ways towards a continuously operating tokamak. With a suitably up to 30 megawatts of heating power are available to heat the shaped current profile, an additional barrier can be created for heat plasma. Photo: IPP transport inside the plasma, which improves thermal insulation. Plasma instabilities

The interaction of the plasma particles with each other and with the magnetic field may cause various instabilities inside the plasma that act like a short circuit for heat transport and impair energy confine- ment. ASDEX Upgrade is successfully doing research into elimina- ting or mitigating these instabilities.

Objectives of ASDEX Upgrade Investigating the core issues of fusion under conditions similar to those in power plants, particularly in preparation for the ITER international experimental reactor and a demonstration power plant:  particle and energy transport in the plasma  plasmas with improved thermal insulation  physics of plasma boundary layer and divertor  plasma instabilities  wall materials

Material for the vessel wall

Carbon has proven to be particularly resistant in sections of the vessel wall that are exposed to particle and energy flows from the plasma. However, since this material binds hydrogen, a power plant using carbon would lose too much fuel. Uniquely in the world, the plasma vessel of ASDEX Upgrade was therefore cladded with tiles made of the metal tungsten. The successful experiments made tung- sten the reference material for a demonstration power plant.

You want to learn more about ASDEX Upgrade and the state of research? Visit us: www.ipp.mpg.de/visitors

Max Planck Institute for Plasma Physics (IPP) Boltzmannstrasse 2 85748 Garching near Munich Tel. ++49 89 3299-01 e-mail: [email protected] www.ipp.mpg.de

ASDEX Upgrade interactive panorama:

www.sonnenmaschine.eu Munich Atelier Fenke, Design: Graphisches