The Divertor Cassette Multifunctional Mover (CMM) will carry a 3.5 m long and 9 tons divertor cassette with its end-effector (SCEE) and move it inside the torus. The manipulator arm (WHMAN) operates tools to lock and unlock the cassette divertor. Picture: VTT

Work on the divertor test platform (DTP2) in Tampere, Finland, is in full swing now, after it was inaugurated on January 29th. The divertor is the region in the plasma vessel, which is located nearest to the hot plasma and collects ash, such as helium, which is produced during the fusion process. Its centrepieces are the divertor cassettes, each 3.5 m long, 2.5 m high and weighing 9 tons. The only way to maintain these devices is to build a special machine which moves them remotely.

A prototype of this machine, called Cassette Multi-functional Mover (CMM), forms the heart of DTP2. DTP2 also possesses a full size replica of a section of the ITER divertor region along which the CMM will eventually move. The entire set-up is 20 m long and weighs nearly 100 tons. The design and manufacture of these components has taken four years under the management of Euratom and the Fusion research centres via EFDA. Now it is the responsibility of the Euratom Association TEKES, comprising the Tampere University of Technology (TUT) and VTT, to test the prototypes and develop a fail-safe handling mode for the fi nal ITER device.

Currently, VTT and TUT are very carefully operating each joint of the CMM’s end-effector (see picture), which will eventually move the divertor cassette into the plasma vessel. For each joint, the parameters, which will ultimately be used by the remote controls, are fi ne-tuned. This way VTT ensures that all joints work in absolute synchronisation and in exact positions when fi nally moving the heavy divertor cassette. In a few months time, VTT will install the manipulator arm, which sits on top of the CMM. It will operate the tools to lock and unlock the divertor cassette. When the parameters for each joint of arm and end-effector are fixed, VTT can start operating the CMM from the control room.

Setting up the control room is another VTT task. The control room screens display all of the necessary information, for example, speed and distances of the components and provide an insight into otherwise invisible spots. Invisible spots are a challenge at ITER: Space is tight and only very few cameras can be fitted to monitor the cassette movement. Whenever no camera information is available, pictures created using virtual models must assist the operator placing the device. These models have been developed by TUT.

At DTP2, the CMM is operated using cameras as well as virtual models. The pictures created by the models are compared with the “real” camera picture. Any dimensions that the models display incorrectly, are corrected to ensure that the virtual models are ultimately accurate enough to safely move the divertor cassette. Furthermore, the virtual models are used to fi nd the best operation procedures and to train operators. During the entire testing phase extreme care must be taken. Errors or mishaps would be fatal considering the weight and size of the components. Hence, while humans operate the controls, preset limits to trajectories, velocities and forces ensure safe movements at all times.

VTT is already planning the next steps for DTP2: The divertor region mock up (DRM) will be extended to a larger section of the torus, namely 63°. This is necessary to include an in-vessel mover, called cassette toroidal mover (CTM) in the test programme. The CTM will be designed and built in 2009 and 2010. The ultimate goal of VTT is to develop the entire maintenance sequence, identifypotential risks, verify the operations, find optimum process parameters, and train operators. The insights VTT gains during these tests will result in the final specifi cation of the ITER divertor and its remote handling devices.

An animation, which shows the entire sequence can be downloaded here: