ASDEX UPGRADE

Figure 1:Max-Planck Institut in Garching (Germany)

The history of ASDEX Upgrade
ASDEX Upgrade Parameters
ASDEX Upgrade Milestones
ASDEX Upgrade Objectives

The history of ASDEX Upgrade

The ASDEX (Axially Symmetric Divertor EXperiment) Upgrade tokamak went into operation at Garching (Germany) in 1991. This fusion device, Germany's largest at present, is for investigating crucial problems in fusion research under reactor-like conditions. For this purpose essential plasma properties, particularly the plasma density and the wall load, have been adapted to the conditions that will be present in a future fusion reactor.
The ASDEX Upgrade non-circular tokamak programme has been largely focused to provide the physics basis for ITER. The similarity of ASDEX Upgrade to ITER in its poloidal field coil system and divertor configuration makes it particularly suited to testing control strategies for shape, plasma performance and Magnethydrodynamic (MHD) mode stabilization. Additionally, the similarity in cross-section to other divertor tokamaks is important in determining size scalings for core and edge physics.
With the increasing number of experiments proposed by collaborators within the EU fusion programme, the ASDEX Upgrade Programme Committee was opened to the Associations to take more responsibility for the ASDEX Programme. At present it comprises 9 members from the associations and 8 from IPP. The operation in 2001 was dominated by maintenance and hardware upgrades. In 2002 the operation of ASDEX Upgrade in close connection with the JET programme and in co-operation with the EU Associations will continue.

Figure 1:ASDEX Uprade - Outside

Figure 2:ASDEX Uprade - Inside

ASDEX Upgrade Parameters

Diameter	10 m
Height	9 m
Weight	800 t
Magnetic field	Up to 3.9 Tesla
Plasma major radius	1.65 m
Plasma minor radius	0.5 / 0.8 m
Plasma Components	Deuterium, Hydrogen
Plasma current	2 MA
Pulse length	Up to 10 s
Plasma heating	27 MW
Plasma volume	13 m3
Plasma quantity	3 mg
Plasma temperature	Up to 150 Million degrees
Plasma density	Up to 2 x 1020 particles/m3

Figure 3:ASDEX Upgrade

ASDEX Upgrade Milestones

1991	ASDEX Upgrade went into operation.
1994	Tungsten experiment.
1995	New plasma regime with soft energy dissipation.
1996	The installed divertor II ("Lyra" divertor) permits simultaneous operation with up to 20 MW heating power and a very low heat load on the divertor.
1998	Stationary H-mode discharges with internal transport barrier.
1998	First experiments on Neoclassical Tearing Mode Stabilisation by ECCD.
2001	Hardware upgrades.
2002	Core physics studies for improvement of plasma performance.

ASDEX Upgrade Objectives and Achievements

One of the major problems is incurred by the interaction between the hot fuel and the confining walls. This entails, on the one hand, damage to the wall of the plasma chamber and, on the other, undesirable contamination of the plasma. To counteract these effects, ASDEX Upgrade is being used to investigate a special magnetic field configuration known as the divertor. The divertor removes the outer boundary layer of the plasma and deposits it on collector plates. The incident plasma particles have already cooled down by then, away from the hot core, and are pumped off. This process also rids the plasma of disturbing impurities, which simultaneously safeguards the wall of the plasma vessel and achieves good thermal insulation of the fuel.
The divertor makes it possible to model the plasma edge, so that a favourable influence can be exerted on the central problem areas of plasma physics - plasma purity, plasma confinement and plasma-wall interaction. ASDEX Upgrade is thus providing essential know-how for the next step.

Figure 4:ASDEX Upgrade - Plasma

In addition, modes of operation in which the profile of the plasma current is influenced (advanced tokamak) are investigated for their compatibility with the divertor. For this purpose an auxiliary plasma current is produced with high-frequency waves or particle injection. Depending on the current profile, a transport barrier can form which greatly reduces plasma losses to the outside and improves the values in the plasma core. ASDEX Upgrade will attempt to create such conditions in divertor operation for the first time in quasi-steady state (i.e. for a few seconds).
ASDEX Upgrade can be operated routinely with Neutral beam injection (NBI) heating powers up to 20 MW and injection energies up to 100 keV, which allows studies of the influence of heat deposition on transport and of fast particle effects.
The investigation of high performance plasmas both in conventional H-mode regime and in advanced tokamak scenarios will continue.