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Using CompactRIO and LabVIEW to Monitor and Control a Compact Spherical Tokamak for Plasma Research, Tokamak Solutions, UK

Xilinx Employee
Xilinx Employee
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By Dave Wilson, Academic Marketing Director, National Instruments



Demand for electricity is increasing at a rate of 5% per year worldwide, which creates a pressing need for fusion energy generation. Annual global expenditure on fusion energy R&D is about £2 billion (about $3.4 billion), and any serious scientific effort requires a tokamak for fusion research. Tokamak Solutions develops small spherical tokamaks used as neutron sources and as plasma research instruments in 300 plasma research centers around the world.


ITER is an international nuclear fusion research and engineering megaproject that is currently building the world's largest experimental tokamak nuclear fusion reactor in the south of France. It will cost about $15 billion. Small tokamak research reactors cost only a few million dollars. (Tokamaks are not devices recently legalized in Colorado and Washington State. Tokamak is a Russian acronym for "toroidal chamber with axial magnetic field.”)


A tokamak uses magnetic fields to confine a hydrogen plasma into the shape of a torus. This is accomplished by combining a toroidal field, which orbits the vertical axis of the torus, and a poloidal field, which encircles the central axis of the torus. Confining plasma with magnetic fields is necessary as plasmas can reach temperatures of millions of degrees. That means the plasma can’t touch anything physical.


Tokamak Solutions’ ST25 uses eight 1-farad capacitors switched by IGBTs (insulated-gate bipolar transistors) to provide the kiloampere current needed to produce a toroidal confinement field of 0.2 teslas. The poloidal field coils and hydrogen-injection solenoid coils are supplied by separate high-voltage capacitor banks. The injection solenoid squirts hydrogen from a piezoelectric valve into the toroidal field at 10 Hz, precisely synchronized with the electrical discharges from the capacitor banks driving the containment coils. The plasma is ionized and sustained with 2.45GHz microwaves generated by a 3 kW magnetron. The system induces a ten to 20 kA plasma current.



Tokamak Solutions ST25 Reactor.jpg



NI’s LabVIEW and LabVIEW FPGA software and FPGA-based CompactRIO hardware handle the plasma control and data acquisition. Two NI CompactRIO devices run separate parts of the system. The first CompactRIO controller collects data from voltage loops and coils mounted around the tokamak vessel. The collected data describes the plasma’s condition and position within the vessel. The CompactRIO controller also digitizes signals from photodiodes that measure plasma duration and intensity using an FPGA-based NI PCIe-1433 frame grabber and the NI-IMAQ drivers to collect high-speed video of the plasma at more than 1,000 frames/sec.


A second CompactRIO controller networked to the first manages the synchronization of the capacitor-bank discharges into the confinement coils via the IGBTs and keeps the plasma discharge stable. The second CompactRIO controller also manages hydrogen injection into the plasma chamber. The speed necessary to acquire waveform data, process signals, and react to control the plasma discharge required the use of LabVIEW FPGA to meet microsecond timing requirements of this real-time system.


The ST25 took less than six months to design and build, and the working prototype yielded promising results in a very short time.


Note: This project was a finalist in the NI Engineering Impact Awards 2014 competition, in the Advanced Research category. The entry was submitted by Paul Apte, Tokamak Solutions, UK.