Device for loss-free cryogen cooling of a cryostat configuration

Abstract

A cooling device (7) for re-liquefying cryogenic gases, comprising an outer jacket (8) which delimits a vacuum chamber (9), and a cryocooler cold head (10) installed therein, which has at least two cold stages (11, 12) and is at least partially surrounded by a radiation shield (13) is characterized in that at least two cold stages (11, 12) of the cold head (10) are separately individually connected in a heat-conducting manner to a heat-transferring device (14a, 14b) which can be inserted into the neck or suspension tubes (3a, 3b) of a cryostat (1) for keeping at least two different cryogenic liquids (18a, 18b). The cooling device can be easily retrofitted into existing cryostat configurations, in particular, those containing superconducting magnets and without (or with minimum) adjustment to permit operation with no or little cryogen loss, even if several cryogens are used.

Description

[0001] This application claims Paris Convention priority of DE 10 2004 037 173.3 filed Jul. 30, 2004 the complete disclosure of which is hereby incorporated by reference. BACKGROUND OF THE INVENTION [0002] The invention concerns a cooling device for re-liquefying cryogenic gases, comprising an outer jacket which delimits a vacuum chamber, and a cryocooler cold head installed therein, which has at least two cold stages and is at least partially surrounded by a radiation shield. EP0905436, EP0905524, WO03036207, WO03036190, U.S. Pat. No. 5,966,944, U.S. Pat. No. 5,563,566, U.S. Pat. No. 5,613,367, U.S. Pat. No. 5,782,095, U.S. Pat. No. 2002 / 000283, US2003 / 230089 e.g. describe cooling of a superconducting magnet system with no or little cryogen loss using a cryocooler. [0003] The e.g. two-stage cold head of the cryocooler is usually installed in a separate sleeve assembly which is under vacuum (described e.g. in U.S. Pat. No. 5,613,367) or directly in the vacuum chamber of a cryostat (...

AI Technical Summary

Benefits of technology

[0012] A cooling device of this type offers the following advantages: Existing cryostat configurations, and in particular those which contain superconducting magnets can be retrofitted without (or with only minor) adjustments, to permit operation with no or little cryogen loss requiring only little extra hardware even if several cryogens are used. The cryostat must not be re-engineered. The additional heat input into the cryostat produced by the device is small and can be predicted quite precisely when properly engineered. The heat-transferring devices in which the cryogens are liquefied are designed such that they can be introduced in a contact-free manner into the neck or suspension tubes of the cryostat configuration. The evaporating gas is liquefied in a thermodynamically effective manner, since the vapor is not overheated and therefore need not be cooled down to the liquefying temperature. The cryocooler cold head is placed at such a distance from the magnetic center of a superconducting magnet arrangement in the cryostat that disturbances on the magnet arrangement caused by the magnetic regenerator material are less severe than if the cold head were directly integrated into the cryostat. Conversely, the function of the cryocooler is also less impaired by the magnetic field of the magnet arrangement. If the cryocooler fails or must be switched off for maintenance work, the cryostat configuration still functions, e.g. for cooling a superconducting magnet arrangement. This ensures high operational reliability. Moreover, the user can freely select the mode of operation (conventional or without cryogen loss).

[0031] In an alternative and preferred manner, the cooling device may be mounted outside of the cryostat e.g. on the room ceiling or on a separate stand. In this case, the cryostat configuration does not have to bear the weight of the cooling device. This can increase the mechanical stability of the cryostat configuration.

Problems solved by technology

The design and construction of the cryostat becomes more demanding and complex and installation of the additional sleeve which receives the cryocooler cold head generates additional heat input into the cold head.

Finally, an unstable state occurs when the cryocooler fails, and the temperatures of cryostat components such as e.g. the radiation shield continuously change until a new balanced state is reached.

In a magnet system for high-resolution nuclear magnetic resonance (NMR) spectroscopy, this can preclude NMR measurements, since the shim state of the magnet constantly changes or, in the worst case, the magnet runs dry and quenches.

This would considerably increase the number of devices, the investment, and the operating costs.

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