Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Reexamination Certificate
1999-12-22
2001-05-15
Doerrler, William (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C062S335000
Reexamination Certificate
active
06230499
ABSTRACT:
TECHNICAL FIELD
The invention refers to a detector device in accordance with claim
1
.
Such detector devices comprising a sensor based on a low temperature effect which is cooled, in a first cooling stage, by way of a pulse tube cooler, have a wide field of operation in analytical applications in which particles, radiation or fields with a high energy resolution and/or a high time resolution are to be examined in any place.
PRIOR ART
For cooling sensors based on a low temperature effect (cryosensors or cryodetectors) cryostats are used in the prior art which comprise a first cooling means and a second cooling means pre-cooled by the first cooling means, the sensor being thermally coupled or interconnected to the second cooling means. For generating a temperature of approximately 4K the first cooling device usually consists of a coupled nitrogen/helium cooler. This cooler is very costly as to the process and the device and requires a lot of space. Furthermore, the required liquid coolant (nitrogen, helium), one the one hand, is expensive and, on the other hand, is not everywhere available. For this reason, the use of sensors which are based on a low temperature effect, is comparatively unprofitable for industrial purposes and therefore unsuitable.
From Info-Phys-Tech No. 6, 1996, from the VDI Technologiezentrum, Physikalische Technologien, a refrigerator in the shape of a pulse tube cooler is known, the pulse tube cooler comprising: a pulse tube at one end at which a cold heat exchanger is provided at which heat is absorbed from outside, and at the other end of which a hot heat exchanger is provided at which heat is released to the outside, a regenerator which serves as an interim heat reservoir, and a pressure oscillator which serves to generate periodical pressure changes, the pulse tube, at the end of which the cold heat exchanger is provided, being connected to the pressure oscillator by way of respective lines via the regenerator so that a periodic shift of a working gas between the pulse tube and the pressure oscillator is made possible.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a detector device having a sensor based on a low temperature effect which can be cooled or pre-cooled with a minimum extent of work as to device and process.
This object is solved by a detector device in accordance with the features of claim
1
.
The detector device according to the present invention comprises a cooling system having first cooling means for providing a first cooling temperature T
K
, said first cooling means comprising a two-stage pulse tube cooler system, in which a first pulse tube cooler pre-cools a second pulse tube cooler; and second cooling means for providing a second cooling temperature T
T
, which is lower than the first cooling temperature T
K
, said second cooling means being pre-cooled by said first cooling means. Furthermore, the detector device comprises detector means for detecting particles, radiation or fields with a sensor based on a low temperature effect, said detector means being thermally coupled to said second cooling means.
By this arrangement a detector device is provided which has a good energy resolution and which, on account of its being of low complexity, virtually can be employed almost everywhere, thus being mobile. Furthermore, the operation or maintenance of the first cooling stage is cost-effective, as the pulse tube cooler merely requires to be supplied with electric power. As a consequence, the staff can be reduced, as no person must be provided for supervising or refilling the coolants.
According to an advantageous aspect, the first cooling means comprises three or more pulse tube coolers. These are preferably located such that they reach, in several successive cooling stages, the first cooling temperature T
K
to which an object to be cooled, i.e. in this case the second cooling means, should be cooled. In particular the term “successive cooling stages” is to be understood such that pulse tube coolers for providing a higher cooling temperature for which they are optimized pre-cool pulse tube coolers for providing a lower cooling temperature for which those are optimized. Principally, the object to be cooled or a plurality of objects to be cooled can be positioned at any cold head (cold heat exchanger) of the respective cooling stages. However, it is advantageous to position the object to be cooled at the cooling stage which provides the lowest temperature, i.e. in a two-stage pulse tube cooler system as described above at the second pulse tube cooler.
According to another advantageous aspect, each of the pulse tube coolers comprises a pulse tube at one end of which a cold heat exchanger is provided at which heat is absorbed from outside, and at the other end of which a hot heat exchanger is provided at which heat is released outwardly. Moreover, the pulse tube cooler has a regenerator serving as an interim heat reservoir, and a pressure oscillator which serves to generate periodical pressure changes. In this case the pulse tube, at the end of which the cold heat exchanger is provided, is connected with the pressure oscillator by way of respective lines via the regenerator so that a periodic shift of a working gas between the pulse tube and the pressure oscillator is made possible. In contrast to other mechanical coolers the pulse tube cooler has the advantageous feature that there is not much vibration.
According to another advantageous aspect the pulse tube, at that end at which the hot heat exchanger is provided, comprises a flow resistance and a container or tank to receive a ballast volume.
According to another advantageous aspect, each of the pulse tube coolers further comprises a secondary line extending from the respective end of the pulse tube at which the hot heat exchanger is provided, to the line provided between the pressure oscillator and the regenerator, and running into this line, the secondary line comprising a variable or variably adjustable flow resistance.
The second cooling means preferably is positioned at or in the vicinity of the cold heat exchanger of a respective pulse tube cooler.
Moreover, the detector device may comprise an absorber which is thermally coupled to a sensor and in which incident particles and radiation interact. The absorber may consist of a dielectric or a semi-conductor or a metal or a semi-metal or a semi-metal alloy or a super conductor or a combination of the individual materials.
As second cooling means a demagnetization stage is preferably used. Furthermore, a
3
He/
4
He-dilution refrigerator or a
3
He-cooler or mechanic cooling means such as a helium compressor cooler, or electric cooling means such as a Peltier element, or a superconducting tunnel diode such as an NIS-diode can be employed.
According to another advantageous aspect of the detector device in accordance with the invention the cooling system is part of a cryostat into which the detector means is incorporated, the cryostat further comprising an entrance port or inlet port for passing the particles and the radiation to be examined from the outer part of the cryostat into the inner part of the cryostat to the detector means. Furthermore, the cryostat may comprise a focussing device such as an X-ray lens or a Wolter arrangement or a Fresnel lens or a focussing tube bundle or electric focussing devices/defocussing devices or magnetic focussing devices/defocussing devices.
The sensors used in the detector device which are based on a low temperature effect, or also cryo-detectors or cryogenic detectors are sensors which measure energy deposited by an absorption of radiation or particles by way of an effect which only or in particular occurs at low temperatures (operational temperature range lower than 20 K, however, preferably lower than <4 K). These temperatures are provided by a heat sink thermally coupled to the detector means which comprises a sensor based on a low temperature effect.
These effects can be:
i) Increase of temperature after deposition of energy (calorimeter) in an absorber (die
CSP Cryogenic Spectrometers GmbH
Doerrler William
Foley & Lardner
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