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ENEA - Fusion division

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You are in: Home » Research Activities » FTU Management » Machine » Liquid Nitrogen

Liquid Nitrogen sub-plant of FTU

The liquid nitrogen plant serves to cool the FTU windings to the cryogenic temperature of -192°C so as to considerably lower the values of Ohmic resistance and, consequently, obtain high magnetic field values.
The plant (called LN2 in the following) was built by RIVOIRA and consists basically of:

  • three RIVOIRA storage tanks, with a capacity of 30,000 litres, each one operating at a pressure of 2.5 bar;

  • two cryogenic pumps fabricated by the French company of CRIOSTAR, lubricated with the same liquid nitrogen, each one with a flow rate of about 30 m3/h;

  • two evaporators which operate alternately to avoid saturation during operations at high gas flow;

  • tanks, valves and the typical equipment of a standard hydraulic plant.
View of out-door part of Liquid Nitrogen sub-plantView of out-door part of Liquid
Nitrogen sub-plant (tanks)

At the start of operations, the FTU machine (i.e., the vacuum chamber + magnets + support structure) is cooled from room temperature to -180C. This operation is performed very slowly (about 4 days) and is done by using appropriate injectors to trickle liquid nitrogen inside the cryostat which encloses the machine. Once the whole machine has reached -180C, the copper windings are cooled further to a temperature of -190C. This cooling is carried out by means of one of the two cryogenic pumps. At the end of cooling, the second pump is used to send gaseous nitrogen under pressure inside the cooling channels of the windings so as to eliminate any residual liquid nitrogen, which could create unexpected evaporation with a dangerous increase in pressure when a plasma shot takes place.
At this point, experimentation can begin with the plasma shots.

Between one plasma shot and the next, the magnet windings have to be cooled because they heat up, on average, by about 35C.

Another important operation of the LN2 plant is to constantly send a flow of gaseous nitrogen inside the cryostat enclosing the FTU machine. This flow serves to keep the cryostat in slight overpressure (20 mm H2O) to avoid air from the outside penetrating the cryostat and giving rise to ice formation due to the humidity contained in the air.
The LN2 plant also provides gaseous nitrogen flows to the FTU diagnostic instruments, where required.