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Fuzzy pressure controller for helium bath cryostats
Hanzelka, Pavel ; Jura, P.
Pressure stability of about 10 Pa/h is necessary for precise measurementsof the helium evaporation rate of the low loss cryostats. A pressure controller fulfilling this requirement was designed and tested. It consists ofan absolute pressure sensor, an electronic fuzzy controller and a proportional electromagnetic valve. Computer simulation of the system behaviour was used for the controller tuning. The minimization of the final deviationwas preferred to the reaction speed. The operational properties of the controller were verified at the tests of a helium dewar. The controller was utilised at the development of a small helium cryopump.
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Helium cryopump for electron optical devices design and preliminary cryogenic testing
Dupák, Jan ; Hanzelka, Pavel ; Musilová, Věra
A helium cryopump for electron optical devices was designed and preliminary cryogenic parameters of the first pump sample were tested. Low LHe consumption should enable economical operation of the pump without recycling the evaporated He. The pumping cryopanel is cooled by normal LHe down to 4.2 K. A LN2 bath is utilized for the LHe bath thermal shielding. Two additional heat radiation shields cooled by the vapours of the consumed cryoliquids are installed to decrease the LHe and LN2 losses. Three chevron screens placed between the input office and the cryopanel are used to protect the internal parts against direct heat radiation from the parts at ambient temperature. The chevron systems were replaced by low emissivity screens in the preliniary tests. Predicted low evaporation rates of LHe and LN2 were achieved.
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