Ion pump for cryogenic magnet apparatus

Abstract

Ion pumping modules without ion pump magnets are disposed within evacuated spaces located within the fringing fields of cryostatic housed high field magnets. Improved vacuum conditions are obtainable both within superconducting magnet cryostats and for evacuated auxiliary apparatus proximate the magnet cryostat, particularly where such auxiliary apparatus is sensitive to RF noise.

Description

FIELD OF THE INVENTION [0001] The invention relates to the field of vacuum ion pumps and particularly pertains to vacuum pumping applications with cryostat housed magnets. BACKGROUND OF THE INVENTION [0002] Vacuum ion pumps have been well studied over a period of more than 40 years, are the subject of a vast literature and have proven to be successful commercial products for maintenance of high vacuum. A review of such apparatus may be found in M. Hablanian, High Vacuum Technology: A Practical Guide, pp. 360-372, (Marcel Dekker, Inc., 1990). [0003] Although ion pumping apparatus is not limited to a particular geometry, the vacuum ion pump ordinarily includes an anode formed from an array of close packed, axially symmetric (tubular) metal elements and a cathode surface normal to the axis of the tubular array and spaced apart from the anode. (“Tubular” includes hexagonal, rectangular, circular, square and other cross sections for the purposes of this work.) The cathode(s) and anode(s)...

AI Technical Summary

Benefits of technology

[0009] The present invention, in a first embodiment, achieves vacuum ion pumping in and close to a magnet cryostat with a vacuum ion pump that utilizes the fringe field of the cryostat-housed magnet. Such vacuum ion pump represents a less expensive and less weighty pump than prior art vacuum ion pumps. In one embodiment the elements of the pump form internal structure within the space to be evacuated, such as within the evacuated volume of the magnet cryostat, disposed in a region thereof where a significant component of the fringe field is oriented substantially parallel to the axis of the anodes. In a variation of this embodiment, the pump is located outside the main structure of the magnet cryostat with gas communication to the evacuated region, but in sufficient proximity to regions of the fringe field where the orientation and intensity is sufficient for vacuum ion pump operation. In yet another embodiment, another evacuated volume, in close proximity to the cryostat structure but independent thereof, is maintained at a desired vacuum. An example of the latter embodiment is a dewar enclosing the cooled RF coil of an NMR apparatus where such dewar is located in the bore of the cryostat and the supporting apparatus housing a suitable cathode / anode array is necessarily located proximate one end of that bore intercepting a substantial fringing field of the magnet. The latter embodiment is especially advantaged over conventional mechanical pumping for this purpose because the issue of vibration isolation from such mechanical pump is avoided, and the particular pumping properties of the vacuum ion pump aid in suppression of RF noise in the acquisition of NMR data.

Problems solved by technology

The fringe field of such apparatus is a source of possible damage or anomalous behavior to some instrumentation, credit cards and possibly dangerous to human beings with pacemakers or defibrillators implanted.

It is apparent that the thermal performance of the cryostat is adversely affected if the gas pressure in the evacuated region should rise to the point that such higher pressure supports non-radiative mechanisms for heat transport, compromising the function of the cryostat.

Mechanical pumps pose a problem in that the vibration spectrum must be carefully suppressed to prevent introduction of artifacts into the NMR spectrum.

Sorbs do not enjoy a very long useful life and must be renewed or re-activated.

It is also known that dewar housed RF coils for NMR studies are a source of pressure dependent RF noise triggered by high power RF pulses.

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