Centering and adjustment unit for a cryostat for mechanical decoupling and thermal centering of massively heavy Ge detectors within a cryostat system

Abstract

Copper cooling finger (4) with a cylindrical taper characterized by: that the taper has a cylindrical shape which allows the plastic ring (3) to fit snugly and flush in the taper and not protrude beyond the rest of the copper cooling finger.

Description

Introduction:

[0001] The core innovation is characterized by mechanical centering by a conical stainless steel ring, which holds an insulation ring, the carbon fiber-reinforced centering star, and the central copper cooling rod in the optimal position over a temperature range of -190°C to +100°C. This ensures the necessary tolerances between the outer shell of the ATC cryostats (aluminum) and the encapsulated detector systems. Description:

[0002] This solution through design and geometry was first used in the ATC cryostat.

[0003] The materials were selected to ensure the position of the copper cooling rod over the entire temperature range from -190°C to +100°C.

[0004] Without this solution, system failures due to ground faults repeatedly occurred during operation, meaning that the operating voltage of up to 5000 V could not be maintained.

[0005] The problem can be described as follows: The linear expansion of the copper cooling finger, which is essential for the heat transfer from the Ge detectors to the cooling reservoir (Dewar for liquid nitrogen, or mechanical cooler), as well as all structural holding parts within the cryostat, which ensure a fixation of the position between cold components (inside) and warm components (outer shell), lead to large changes in the expansion during cooling to operating temperature of approximately -190°C. Therefore, the clearances of approximately 5 / 10 mm between the detectors and the end cap of the entire detector system cannot be guaranteed in conventional designs. This distance is essential to minimize convection (heat loss due to material transport). Direct contact between the inner structure and the outer shell would lead to massive thermal bridges. Typical structure:

[0006] The centering is technically realized as follows: The central copper cooling rod has a taper at the level of the mechanical centering ( Fig. : 4 in the sketch of the section through the copper cooling fingers).

[0007] There, two half-shells are inserted, which together enclose the copper cooling finger ( Fig. : 3). These Teflon half-shells provide electrical insulation between the copper cooling finger and the conical centering ring ( Fig. : 2).

[0008] The conical centering ring ( Fig. : 2) is made of stainless steel. Function:

[0009] During cooling from -190°C to +100°C, the copper cold finger contracts in length, moving the centering ring so that the increasing radius of the centering ring's cone always closes the gap between the copper cold finger and the outer support structure (1). This ensures that the copper cold finger is always centered in the ATC cryostat at any temperature between room temperature and operating temperature. The centered position of the copper cold finger in the ATC cryostat is a key requirement for ATC cryostat operation. Since ATC cryostats can be operated in any spatial orientation, decentration of the copper cold finger must not occur. Such decentration can lead to thermal bridges between the ATC cryostat's external structure and the detector systems in the ATC cryostat's end cap. This can result in: • Increased consumption of coolant (liquid nitrogen LN2) • Mechanical malfunctions of the entire ATC detector system • Electronic malfunctions of the entire ATC detector system • Deterioration of the quality of the measurement data recorded by the ATC detector system

[0010] Such an automatic centering, which uses the temperature dependence of the length contraction in a temperature range of -190°C and +100°C for centering, has not yet been realized in any other cryostat.

[0011] The entire construction and selection of materials ( Fig. : 1-4) is unique and defines the protection claim.

[0012] This overall solution has solved the problem of uncontrolled position changes due to length contraction during cooling from room temperature to the operating temperature of approximately -190°C.

[0013] The solution is used in the ATC cryostat of the AGATA research project.

[0014] There are no comparable solutions for ATC cryostats on the market.

[0015] There are no variants of this solution Inventive step:

[0016] The inventive step lies in the construction of a centering device consisting of a conical stainless steel ring, an insulation ring (thermal and electrical), and a centering star made of (carbon reinforced) glass fiber fabric, which, through its geometry and arrangement, ensures that the necessary tolerances of the arrangement are maintained during cooling to -190°C and during operation.

[0017] The centering ring is mounted and positioned so that the copper cold finger is centered on the detector system's symmetry axis at any temperature. Thermal expansion or contraction of the copper always moves the conically shaped stainless steel ring to a position that ensures centering. Advantages of the invention • Automatic adjustment / centering of the cooled ATC detector systems, especially for high weights, such as the ATC cryostat. • Improvement of mechanical stability while reducing heat transfer from the outside to the inside. • Avoidance of thermal bridges between cold detectors and warm outer skin • Electrical insulation of internal structure and outer skin. Commercial applicability

[0018] The invention is applied in the production of any asymmetric AGATA triple cryostat and is commercially marketed. The invention is suitable for use in comparable cryostats for other applications. Terminology ATC (abbreviation for AGATA Triple Cryostat). The AGATA Triple Cryostat is the system that allows and enables the operation of exactly three highly segmented Ge detectors. The cryostat ensures the required high vacuum, mechanical precision in detector positioning, cooling to below -180 °C, and electrical readout of a total of 111 high-resolution signal outputs. Array A detector array is a combination of many detectors that form a (closed) spherical shell, similar to a soccer ball. This is achieved with a specific number of hexagons and pentagons, which then form the front of the detectors. Dewar The Dewar is a vacuum-insulated storage vessel for liquid nitrogen, similar to a thermos flask. For more complex detector systems that can be suspended flat or upside down in an array, so-called all-layer Dewars are used, whose internal construction prevents the liquid nitrogen from leaking out. LN2 is an abbreviation for liquid nitrogen. The 2 represents the fact that naturally occurring nitrogen is a double molecule. Getter: A getter is a chemically reactive material used to maintain a vacuum for as long as possible. Gas molecules form a direct chemical or physical bond at the surface of the getter and are thereby removed from the volume. A standard getter, for example, is zeolite, an open-pore ceramic that, when cooled to liquid nitrogen temperature, is an effective getter. Grounding English term for earthing, or mass (electrical); earthing is the reference level against which a measurement takes place or a signal is generated. FET (field-effect transistor) is a semiconductor transistor with high sensitivity and low inherent noise while maintaining high gain. When cooled, these components perform particularly well. Ge detector: A detector system made of a high-purity germanium crystal. The Ge detector system is used to measure ionizing radiation. Cryostat Device for cooling and maintaining a high vacuum for thermal and electrical insulation of the Ge detector systems installed in the cryostat. List of designations 1 adjustment star made of carbon reinforced fiberglass 2 Centering ring made of stainless steel with conical outer profile 3 Plastic ring, divided into two half shells. The ring has a U-shaped profile, suitable for the centering ring (2) made of PCTFE or POW. 4 copper cooling fingers with a cylindrical taper, suitable for the plastic ring (3)

[0019] The numbers refer to the Fig. on the sheet drawings

Claims

[1] Copper cooling finger (4) with a cylindrical taper characterized by : that the taper has a cylindrical shape which allows the plastic ring (3) to fit snugly and flush in the taper and not protrude beyond the rest of the copper cooling finger. [2] Plastic ring (3) characterized by : It is split to allow for assembly between the copper cooling finger (4) and the centering ring (2), and the plastic ring (3) has a U-shaped profile to ensure the centering ring fits properly. PCTFE or POW is used as the material. [3] Centering ring (2) characterized by : that it is made of stainless steel and has a conical outer profile that compensates for the change in position of the copper cooling finger (4) due to the thermal contraction during cooling and ensures adjustment.

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