PACS

1. PACS Test Cryostat, OGSE and MGSE • Gerd Jakob • MPE AIV

2. Test Equipment and OGSE: Overview AIV

3. PACS test cryostat specifications • Two liquid helium reservoirs: 70l for 4.2K and 13l for 1.7K level • 90l liquid nitrogen for thermal shielding • Optical bench diameter 1060mm, covered by 4.2K thermal shield with 900mm available height for PACS FPU + test optics • Hold time of each temperature level ~48 hours with full PACS operation (goal) • Specified mechanical, optical and electrical interfaces to PACS FPU and test equipment • 2 FIR windows for calibration sources input and for optical alignment checks • 2 window shutter/filter mechanisms at 77K shield • Cryogenic filters at 77K and 4.2K shields to provide predicted Herschel telescope background • Representative cryogenic harness with ~1100 wires + 227 shields for FPU, ~124 wires + 20 shields for cryostat and test equipment • Specific mounting rack for different cryostat operation positions, e.g. 30° tilt for cooler recycling; 90° tilt for shield mounting and cryostat transport. • Provide clean instrument environment, payload integration in cleanroom class 1000 AIV

4. Test cryostat status FPU integration evacuation operation with 20°tilt • Cryostat built at Cryovac GmbH;MPE’s design specifications fulfilled • Cryo harness built, integrated with cryostat and tested by MPE in cw31/03 • Several cryo tests performed:-hold time 77K level ~57h-hold time pumped 1.7K level >60h, lowest temperature 1.4K-hold time 4.2K level ~56h, but only without 4.2K-shield! • Cryostat failed last acceptance test with 4.2K-shield in cw 42/03 • Optical bench temperature too high (6,3K); 4.2K LHe-tank hold time ~24 hours (48h goal); shield temp. 25K • Heat dissipation on 4.2K level ~1W higher than without 4.2K-shield • Investigations on a presumable thermal link ongoing; modifications and amendments in progress • Delivery to MPE for optical alignment of test optics with STM after successful acceptance test, end Nov.03 optical bench dia.1060mm cryostat transportation PACS cryostat in different positions: Overall height ~2400mm, Mounting rack ~1400mm x 2100mm AIV

5. Test optics and Herschel telescope simulator specifications • Herschel telescope simulator test optics to be integrated with test cryostat, aligned to PACS FPU and operated at 4.2K • Image quality goal: 3µm wave front error (PACS), field distortion less than 1 blue photometer detector pixel for the total chopped PACS field of view • Design of a complex opto-mechanical imaging and baffling system, internal and external calibration sources • Provision of FIR background based on Herschel telescope temperature of 70K-90K • 3 cryogenic mechanisms for different internal and external calibration source selection • 2 internal calibrated cryogenic blackbodies • TUFIR wavelength calibrator in combination with an internal integrating sphere • TUFIR input in combination with a point source simulator • External blackbody, extended or with point source simulator • Water vapor absorption cell for initial wavelength calibration AIV

6. Test optics schematic and design 3D design of test optics and Herschel telescope simulator AIV

7. Test optics status • Herschel telescope simulator test optics designed, built and assembled at MPE • Rigid tripod structure with optics base plate and stray light reducing housing to be integrated with test cryostat • Interfaces to cryostat, calibration sources and test equipment complete • Test optics harness parts under final assembly • Temperature sensors, positions sensors and read outs implemented • Test equipment available • Integration of 10 mirrors, integrating sphere, mechanisms and optical alignment is ongoing • Optical alignment accuracy goal of test optics to PACS FPU within +/- 1 arcmin by means of a minimum of 3 cryogenic tests to be performed in test cryostat AIV

8. Test optics status ctd. • FIR black coating according KT72-process applied to test optics housing and components • 7 temperature sensors on motors, pupil P1, mirrors, structure • Thermal I/F and cooling straps for PACS FPU manufactured and available • The MPE developed cryo torquer motor was successfully operated at 4.2K • Motor life time test with gear box successful at 4.2K • Chopper wheel performance test at 4.2K to be repeated with reduced friction of angular ball bearing in order to achieve the goal for chopping frequencies up to 2Hz • Flip mirror mechanisms to be tested at 4.2K in combination with motor/gear • Alignment and integration is performed in cleanroom class 1000 Test optics and PACS FPU STM Cryo flip mirror Mechanism1 assembly with gear box and cryo torquer motor AIV

9. Internal calibration source: cryogenic blackbody • Design and manufacturing of 2 identical cryogenic blackbodies for absolute flux calibration and background; devices selected or chopped by test optics chopper wheel • 18mm opening of cavity adapted to test optics pupils P4 and P5 • FIR coating acc. KT72-process applied • Operational temperature range 4.2K – 80K • Typical temperatures of 10K – 60K can be stabilized within 35 minutes by a heaterpower of 100mW with controller LS370 • Power dissipation typically 12.5mW at 30K and 35mW at 50K • Absolute temperature accuracy +/-20mK at 20K and +/-35mK at 50K with integrated calibrated temperature sensor CX-1070 and contr. LS370 • Thermal stability requirement of <+/-1.25mK at 30K and <+/-5mK at 50K feasible • Status: final assembly ongoing, test equipment available, tests at cryogenic temperature to be performed during test optics alignment checks MPE design of a cryogenic blackbody AIV

10. External calibration source: TUFIR and I/F • TUFIR (tunable high resolution coherent FIR radiation source) used for final wavelength calibration and spectral ghost detection • I/F implemented in test optics design;input through cryostat windows 1 and 2; selected by cryo-mechanisms • Window 1:-4.2K-aperture for 300K background reduction-f/4.4 light cone for TUFIR beam collection-integrating sphere dia. 80mm for homogenous illumination of pupil P3 and for filling the telescope simulator beam-background heater to simulate Herschel telescope temperatures of 70K-90K • Window 2:-point source mask in combination with TUFIR located in external focus F2; PACS chopped field of view completely covered-Herschel telescope background simulated by attenuation filter sets on different temperature levels • Status: test optics I/F available, TUFIR I/F to be defined Test optics with integrating sphere, 4.2K-aperture and background heater for TUFIR input through cryostat window1 AIV

11. External calibration source: blackbody • External blackbody in combination with scannable point source simulator for point spread function and grating alignment investigations • Design of X/Y translation stage and point source simulator finished • Scanning area covers the complete field of external focus F2 • Reproducibility goal 20µm • Point source simulation pattern to be PC controlled and synchronized with PACS data read-out • Calibrated blackbody source and controller available, temperature range 300K – 750K, maximum cavity opening dia. 25mm • Hot plate alternatively foreseen • Status: manufacturing has been started Schematic of external blackbody set-up (above) and 3D design with point source mask on X/Y translation stage, aligned with cryostat window2 AIV

12. External calibration source: water vapor source • Design of a water vapor absorption cell for initialwavelength calibration • 300mm absorption pathlength and typical watervapor pressure of10-25mbar provide appropriate absorptionlines in the PACSwavelength range • Alternative gas CO foreseen • Hot plate provides background, temperature range 300K – 600K • Alignment with external focus F2 at test cryostat window 2 • Status: final design finished end of Nov.03 schematic of the water vapor source set-up (above) and 3D design of absorption cell aligned with cryostat window 2 AIV

13. Mechanical ground support equipment MGSE Hoisting device for PACS FPU available, used for STM integration 06/03 Crane with fine drives installed in MPE PACS cleanroom class 1000, 07/03 Pumping unit available, containing oil free vacuum and helium pumps,pressure gauges,gas flow meters and vacuum assembly; 10/03 AIV

14. Mechanical ground support equipment MGSE ctd. PACS FPU class 1000 transportation container with shock absorber, shock and tilt indicators, venting ports; design complete, manufacturing starts 11/03 AIV