ASDEX. Photo: IPP
Experiments in ASDEX upgrade were successful
Alexander bock, a plasma physicist at the max planck institute (IPP) in garching near munich, germany, investigated in his doctoral thesis how the kafig of the plasma can be made suitable for continuous operation. He succeeded in driving the 800-kiloampere current in the plasma of auben at the ASDEX upgrade fusion facility.
In a fusion reactor, nuclear fusion, i.E. The fusion of two atomic nuclei into one, takes place in a controlled manner. But a fully functional reactor does not yet exist, because in order to effectively generate electricity in a fusion power plant, the reactor must run continuously, and in the process scientists repeatedly encounter technical and physical obstacles.
The two concepts of fusion reactors
Tokamak is the name for a specific type of fusion reactor. Atomic nuclei and electrons are separated from each other and, as plasma, are electrically conductive and can be influenced by magnetic fields. The hydrogen plasma, which is held in a vacuum by magnetic fields to prevent it from colliding with the cold walls of the vessel, is heated to 100 to 150 million degrees. In order to achieve a permanent fusion reaction, as it occurs for example in the sun, high particle density, temperature and energy confinement time are required, which has not yet been achieved. In order to obtain a stable magnetic confinement of the plasma, the magnetic field must be helically twisted. This is generated in the tokamak by a steady flow of current through the plasma.
It’s different with the stellarator, the alternative concept for a fusion reactor, for example wendelstein 7-X. Here, the twisted magnetic field is generated by super current-carrying coils. With no current flowing through the plasma, there are two advantages. Instabilities related to the plasma flow are prevented and it is possible to work with a stellarator as a fusion power plant, since it is possible to work in continuous operation.
Constant plasma current has been generated for three seconds
At the tokamak, however, scientists such as alexander bock are still working to keep the reactor in continuous operation. In his doctoral thesis, he studied the effects of attempts to create a continuous, rather than pulsating, flow of current through the plasma by means of irradiating high-frequency waves or inserting particle beams. With a partially superimposed current, it is possible to influence the plasma current and thus alter the twisting of the field lines. The bootstrap current that the plasma builds up on its own in response to prere differences can then be used to discharge and extend pulses independently.
The ASDEX upgrade team has now achieved this for the first time in a plasma vessel in the reactor, the inner wall of which is completely covered with tungsten, the metal with the highest melting point. With high plasma prere and good confinement properties, the operation succeeded almost without a transformer. The change in the plasma pulse caused by microwaves and particle beams being injected was noticeable: for three seconds, the 800 kiloampere plasma current remained constant without a transformer. This time could potentially have been extended to continuous operation with better coils. Alexander bock therefore concludes that transformerless operation is possible in ASDEX upgrade and that it is worthwhile to continue the studies on the advanced tokamak.