SPIRE Design Description - Research Services

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Draft SPIRE Design Description Document CVV Level 0 PSW 4.12 Thermal straps 4.12.1 4-K to 10-K Photometer Arrays Heat Switch PS2 PS1 PMW PLW Heat Switch Electronics Prime Filter Prime ES1 ES2 PH2 106 PH1 Spectrometer Arrays SSW Electronics Redundant SLW 300-mK Cooler Filter Redundant Figure 4-48 - 3 He Cooler cryogenic redundancy scheme. The 3 He cooler and the detector boxes require thermal straps from the Herschel Level-0 stage of the cryostat to maintain the correct temperature. These straps are fabricated from Copper and are supplied to SPIRE by the satellite platform. As shown in Figure 4-48, the cooler requires two straps; one connected to the evaporator and one connected to the condenser. These two straps must pass through the cover of the photometer which is a part of the FPU from the CVV. A further strap passes through the cover of the spectrometer to the detector boxes. The
Draft SPIRE Design Description Document temperature immediately outside the FPU is at a temperature of between 10 and 15 K and is therefore radiating strongly in the frequency band of the detectors. A stray light baffle is therefore required to greatly attenuate this stray light from entering the FPU close to the detectors. Two possible ‘Add-on’ Structure Thermal Strap Aramide cable suspension 107 Aramide cable suspension ‘Part of the structure’ Figure 4-49 – Conceptual design of the stray light baffle on the 2-K straps entering the FPU. light baffle on 2-K straps power limits on 2-K strap during recycle (IID-B Ch 5) FIRST Interface SPIRE Interface IID-A (Sect. 5-26) 4.12.2 300 mK Instrument Temperature Requirement Instrument Conductance Requirement L2 Photometer JFET Enclosure T < 15K - TBD L2 Spectrometer JFET Enclosure T < 15K - TBD L1 FPU 4K Optical Bench T < 6K T < 3.5K (at FPU Flange) TBD L0 FPU 1.8K Boxes T < 2K T < 1.75K (at FPU Flange) TBD L0 Cooler Evaporator T < 2K T < 1.75K (at FPU Flange) G>100mW/K @ 2K L0 Cooler Pump T < 2K T < 1.75K (at FPU Flange) G>50mW/K @ 2K For the photometer and spectrometer detectors to operate correctly, they have to be maintained below a temperature of 300 mK during operation. Power is constantly being dissipated within the bolometers due to ohmic heating caused by the bias current and power is being absorbed due to photon thermailization, and conduction from warmer parts of the instrument. This heat needs to be carried away from the bolometers to prevent them from heating up. Two 300-mK straps between the photometer and spectrometer BDAs to the 3 He cooler conduct this heat away. The routing of the photometer 300mK strap is shown in Figure 4-50 and Figure 4-51 shows the routing of the spectrometer strap. The design of these straps is challenging. They have the following requirements: (i) the straps need to be supported rigidly so that the first mode of vibration is above 120 Hz (TBC);
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