The large cathode is mounted in an aluminium vacuum chamber of 1.5 m diameter, 2.5 m length with double walls and internal water cooling. There are 20 sideports and 10 end ports for diagnostic tools, power and water feedthroughs. The vacuum chamber is surrounded by 10 watercooled coils producing a uniform, axial dc magnetic field of up to 100 G, limited by the present size of the power supplies. The coils can be energized individually so as to vary the magnetic field configuration from a uniform field to a mirror or a cusp. Safety circuits are installed which switch off the cathode in case of loss of vacuum or cooling.
Pneumatic valves isolate the chamber from the vacuum pumps in case of accidental leaks.
Due to extensive interlocks the machine can operate without human supervision. It runs continuously day and night since the thermalization time does not allow daily turn on and off. In typical week-long data runs the plasma parameters are stable to within 3 digits. Diagnostic probes are inserted through radial and axial ports. Some of them are equipped with vacuum locks which permit the exchange of probes without loss of vacuum in the main chamber.