Fall 2011

Don Holly, PSL’s Physicist and the latest on the Madison Symmetric Torus

The Madison Symmetric Torus (MST) produces hot plasma for research in plasma physics and fusion power generation, the energy source of the sun. Located in the Physics Department of the University of Wisconsin-Madison, the MST project is operated by the UW Plasma Physics Group and is funded by the Department of Energy and the National Science Foundation.

PSL Physicist Don Holly reports that MST’s versatile new Toroidal Field Programmable Power Supply is now operating at its full design voltage and he has begun design of a similar, but even more powerful, Programmable Supply for MST’s poloidal field.

The two power supplies will generate the two magnetic fields that confine and heat the plasma in the MST fusion research device.  The new supplies will provide unprecedented flexibility and control, allowing MST researchers to optimize heating and to minimize loss of the plasma, important objectives in developing a fusion energy source.

The Toroidal Field Supply consists of 32 identical high-power modules connected in a series-parallel arrangement to provide a desired output waveform of up to 1800 V at 25,000 A.  This supply has been in operation for some time, but it has only recently achieved its full design voltage.  A major step was rewiring MST’s toroidal field transformer to better match the new supply.  The modified transformer connections also resulted in improved toroidal field uniformity.  Experience has shown that some experiments would benefit from even more precise control of the toroidal field, so Holly is currently designing a more sophisticated microprocessor-based control unit for the toroidal supply.

Holly estimates that the poloidal supply will require 96 modules similar to the modules in the toroidal supply, and will produce about 2500 V at 55,000 A. Because it will run at higher voltage, the poloidal supply will require improved voltage isolation techniques.

Since the new supply is divided into a larger number of modules, it can provide not only more output power, but a finer level of control. “Supplies which use such a large number of high-power modules are very uncommon, and careful design is needed to keep all the modules working together,” says Holly, “but that’s what is needed to deliver the required power with the required time response and precision.”  He adds that experience gained in using the smaller toroidal supply will help minimize the cost and shorten the construction and testing time for the poloidal supply.

 

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