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Cryostat for optical measurements in temperature range 80 - 300 K
Dupák, Jan ; Hanzelka, Pavel
A liquid nitrogen bath cryostat of classical concept was designed, manufactured and tested. A 0.4 litres vacuum-insulated inner vessel is suspended on a thin-wall neck. The specimen folder equipped with a temperature sensor and a heating winding is connected to the bottom of the inner vessel by means of a low-conductivity stainless steel tube. Copper foil strips of different cross-section areas are used to span this tube so that the entire thermal resistance between the vessel and the specimen holder can be adjusted in wide range. The rate of the specimen cooling can be changed this way. Using methods that consider both the non-linear dependence of thermal properties of materials and the influence of heat radiation, evaluations of the specimen cooling rate for different magnitudes of the thermal resistance have been made. Nitrogen consumption in various cryostat regimes was calculated too. These predicted values were compared with the experimental ones.
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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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Electromagnetic fields effects on biological and other objects
Jelínek, Josef
Cryogenic and superconductivity is not only involved in creation of static magnetic fields for physics, medicine but also for AC systems-generators, motors, transformers, power lines and finally for high frequency systems at some extent. All these applications are commonly beneficial but electromagnetic filed (EMF) exposure may sometimes lead to adverse health effect. This article reviews possible adverse health effects for completeness in the whole range of 0 Hz - 300 GHz according to International EMF WHO Project, (static fields, 50 Hz power, HF systems-radio, TV, radar, mobile phones) with some levels recommendation and standards. The last chapter is devoted to nonbiological EMF effects e.g. on computers, magnetic data and medical implants.
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