Clamp-on flow measurement in cooling circuits independent of magnetic field influences

Four KATflow 150 with Profibus DP interface in high-temperature application of a fusion reactor

Fusion energy offers the possibility of carbon-free, unlimited energy and the liberation of humanity from the constraints of our Earth's limited resources. We are pleased that Katronic's non-invasive clamp-on ultrasonic flow measurement technology is making a small contribution to the operation of an ambitious experimental research facility, the Wendelstein 7-X, a so-called stellarator, in Greifswald, Germany. Together with the Tokamak project ITER in southern France, these long-term projects are intended to build a bridge into the future to the first fusion power plants of tomorrow. Key to the success of the flowmeter application was the Katronic equipment's  immunity to the massive magnetic fields that are key in the containment of the high energy plasma involved in fusion power.

The Wendelstein 7-X facility is ring-shaped with a diameter of about 14 m and is based on the stellarator principle, in which only external coils generate the twisted magnetic field used to confine the hydrogen plasma required for nuclear fusion. The required plasma temperatures are generated, among other things, by an ICRH (Ion Cyclotron Resonance Heating) system. For this purpose, radio waves in the short-wave range are radiated into the plasma via an antenna, where they are absorbed - similar to a microwave - and thus increase the temperature of the plasma up to 150 million °C. This very high temperature, the particle density and sufficient thermal insulation of the plasma from the environment are the three necessary conditions for a successful laboratory fusion experiment with a stellarator magnetic field.

The installation environment of this ICRH antenna includes eight water-cooled cooling circuits. These are essential technical components to prevent the antenna from overheating during ongoing fusion experiments. The water temperature in the 8 mm inner diameter pipes is 150° C at 26 bar maximum pressure, and the water flow rate of all circuits is 5.4 m³/h. For flow measurement, tests were first carried out with variable area flowmeters. However, the magnetic field influence of the stellarator coil system was too strong, so that this technique did not prove successful. The scientists involved in the Wendelstein experiments at LPP-ERM/KMS, the Max Planck Institute for Plasma Physics (IPP) and Forschungszentrum Jülich then had to find a solution that did not have this problem. Due to the deionized water used in the cooling circuits, a second selection criterion was to find a flow measurement system that works independently of the media conductivity.

The KATflow 150 stationary clamp-on flowmeter from Katronic finally met all the technical requirements placed on a new flow measuring system. All components of the measuring unit were to be non-magnetic, which was guaranteed with the plastic housing of the flow measuring unit and the stainless steel housing of the sensor technology used. Furthermore, no direct contact with the medium was allowed, which was ensured by the transducer mounting using clamp-on technology, and realized measurements through the pipe walls of the stainless steel lines installed in the cooling circuits.

The total of four installed flowmeters of type KATflow 150 prove themselves very well in this high-temperature application (flow measurements of deionized water at 150° C). Via the Profibus DP interface requested by the customer in each unit, the measurement data can be transmitted at 4 Mbit/s. Thanks to the combined temperature measurement, scientists are now able to read and evaluate the power dissipation and energy of the radio wave radiation, in addition to verifying the flow rate required for cooling the ICRH antenna.

Project partner:

Laboratory for Plasma Physics, Ecole Royale Militaire-Koninklijke Militaire School (LPP-ERM/KMS), Trilateral Euregio Cluster (TEC), Brussels

Forschungszentrum Jülich GmbH, Institut für Energie- und Klimaforschung - Plasmaphysik, Trilateral Euregio Cluster (TEC)

Forschungszentrum Jülich GmbH, Zentralinstitut für Engineering, Elektronik und Analytik

Max-Planck-Institut für Plasmaphysik (IPP), Greifswald