A cryostat assembly comprises a liquid coolant containing vessel; a mechanical cooler having at least one cooling stage located above the vessel; and a channel for conveying gaseous coolant from the vessel to the cooling stage where the coolant is condensed in use and then returns through the channel to the vessel. In one aspect, the cleaning behavior of a print head can be used for reflecting health status of the print head, so survival state of a print head can be determined according to cleaning behavior of the print head. Next, a median filter replaces the degree of picture quality degradation for the each block with a median of the degrees of picture quality degradation among the neighboring blocks of the each block. The metal layer exhibits a function as an electrically conductive layer. The air-bridge includes an electrode contact terminal to be connected with the source electrode or the drain electrode and an aerial circuit line for connecting the electrode contact terminal with a contact terminal of the bonding pad, the widthwise cross sectional area of the electrode contact terminal being equal to or less than that of the aerial circuit line. The station is characterized in that the stretching rod is driven by a single tubular electric linear motor the stator of which is mounted on the cylinder and the armature of which is connected to the stretching rod.