PACS Photometer 1
PACS IBDR 27/28 Feb 2002
PACS PHOTOMETER
J.L AuguèresL.Rodriguez
CEA/DSM/DAPNIAService d’Astrophysique
PACS Photometer 2
PACS IBDR 27/28 Feb 2002
Development Status (1)
• Bolometers at LETI:– CQM run available (DC+RC & 2K buffers).
• BFPs:– Design finalised, Kevlar suspension validated.– Mounting tools:
• Design, detailed design, fabrication completed.• Mounting procedure validated (some tuning from experience)
– Test BFPs (used for bolometer test & selection):• Detailed design finalised.• A few sets available, additional sets under fabrication.• 1st (blue type) BFP integrated and under test at LETI.
– CQM Mechanic:• Design finalised, detailed design almost completed.• Optical filters: specified, design started but requires validation.
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Main differences between SPIRE & PACS Bolometer arrays
VrRc
Rb
MU
X
address
300 mK 2 K
SPIRE arrays Problems•MUX function perturb the high impedance bolometer bridge.•MOS 1/f noise dominant.•Correlated noise show sensitivity to RF.•MUX only 8->1
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Main differences between SPIRE & PACS Bolometer arrays
PACS arrays Solutions•Cold readout circuit under the pixel reflector: low capacitance.•MUX now 16->1 •MUX function after the readout.•Large readout MOS to reduce 1/f noise.•Blind pixels to remove all perturbations.•We added 2 impedance adaptation stages:-BU @ 2K,-BOLA @ 130K. To cope with thermal budgets
MU
XVr
Rc
Rb
300 mK 2 K
Buffer Unit
addressVrRc
Rbhe
ate
r
BO
LA
heater
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BOLOMETER FOCAL PLANE
The detector unit: A 16 x 16 pixel array+ two rows of blind pixels…
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BOLOMETER FOCAL PLANE
…attached by the 0.3K-2K ribbon cableto the buffer unit…
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BOLOMETER FOCAL PLANE
8 arrays butted on the common carrier @ 300mK cooled by the strap…
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BOLOMETER FOCAL PLANE
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BOLOMETER FOCAL PLANE
…under the 300 mK filter.The Buffer Units are assembled by 4
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BOLOMETER FOCAL PLANE
The 0.3 K stage suspended by Kevlarwires on the 2K structure…
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BOLOMETER FOCAL PLANE
Two half shells close the bolometer assembly…
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BOLOMETER FOCAL PLANE
...and a cone with air gap filter achieve the stray light rejection.
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Development Status (2)
• PhFPU:– I/Fs
• with PACS FPU (almost) validated.• S/C I/F: Connectors: OK, 2K straps: Outstanding issues.
– 4K & 2K Structures.• Design completed.• Detailed design started (goal end of Feb. 02).• Call for Tender process started (SMs & CQM Models).
– Cooler:• Design, detailed design of STM, CQM, FM & FS
completed.• Manufacturing of 2 STM + 2 CQM parts completed.• Mounting ongoing.
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PHOTOMETER ASSEMBLY
The 2K structure holds the Blue and Red BFPs…
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PHOTOMETER ASSEMBLY
…is insulated from the 4 K stage by stainless steel tubes…
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PHOTOMETER ASSEMBLY
The 4 K structure is mechanically interfaced with the remaining partof the instrument
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PHOTOMETER ASSEMBLY
The cooler is mounted on the bottom,the RF filter boxes are bolted on the rear side.
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PHOTOMETER ASSEMBLY
The cooler straps are finally located.
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PHOTOMETER ASSEMBLY
A black painted metal blanketachieve the stray light rejection.
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BUDGETS
Mass Budget
Blue BFP = 630 gRed BFP = 520 g2 K Struc. = 550 g4 K Struc. = 2720 gCryocooler = 1700 gRF Filters = 1260 g
Total = 7380 g
Thermal Budget
2 K Stage = 5 mWElect. = 3.3 mWCond. = 1.7 mW
4 K stage = negative
0.3 K Stage = 12 µW
Cryocooler = 800 J/cycle
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Development Status (3)
• Cryogenic Test Facilities:– BFP Test facilities: Designed to test BFP individually, they
consist in: 1 cryostat equipped with 0.3K cooler and optical bench + 1 acquisition system.
• 2 identical facilities installed respectively at Saclay and LETI.
• Currently they are equipped with simplified optical benches.
– PhFPU Test facility: Designed to test a fully assembled PhFPU, it consists in one cryostat equipped with simplified optical bench.
• Specified.• Detailed drawing of cryostat almost completed.
– Irradiation test facility:• Cryostat ordered at IRlab.
– FTS spectrometer test facility:• Manufactured. Currently in acceptance tests.
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BFP & PhFPUTest facilities
LH
eL
N2
LH
eL
N2
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TESTS PROGRAM AND COLD FACILITIES
BFP test facility
PhFPU test facility
Irradiation test cryostat
Spectrometer
Filters measurements
check none none yes
Spectral responsivity none none none yes
Responsivityyes check yes check
Noise performances yes yes yes yes
Gamma ray total dose no no yes no
Protons and heavy Ions no no yes no
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TESTS RESULTS
Tests on bolometer arrays started only two weeks ago after unexpectedDelays on ribbon cables delivery.We started by functional tests: Pixel multiplexing, electronic chopping,blind pixel differential mode including tests on background compensationHeater.
16 pixels
Chopper on
Multiplexing imposes to drive signals of 40 frames/s x 16 pixels x 2 (chop) =1280Hz
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TESTS RESULTS: differential mode
Without heating the blindpixels
Heater on300 mV on heaters
350 mV on heaters
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BOLA is currently a « relay »: it adapts the output impedance of the BU to cope with the expected cablecapacitance in a given 2 K power consumption.
BOLA ISSUE
MU
X
VrRc
Rb
300 mK 2 K
Buffer Unit
addressVrRc
Rbhe
ate
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BO
LA
Warmelectronics
14 meters ?!
BOLA is still today the baseline!
h ea te r
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Bandwidth measurementsin function of dissipated Power and output capacitance
100 1000 10000 Hz
100 1000
100 1000
Without capacitor
+1 nf
+2.2nf
6 mW2.5 mW
1.25 mW
BOLA ISSUE
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TESTS RESULTS• FUNCTIONNALITY:
– Detector array measured is completely functional.– Responsivity (V/W) is not available because test filters are still
to be measured and mounted.– Evaluation of multiplexing on noise increase currently
explored.– Buffer Unit performances are compliant with noise
specifications.
CONCLUSIONSThe detector system is a complex set up. It is completely
functional. We already notice some minor problems: - diode protection on BU for the 300 mK stage to be removed,- modify geometry of even/odd MOS transistors (threshold
slightly different).
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PhFPU Models (1)• SMs:
– CEA SM:• Consists in flight representative 2K & 4K mechanical structures
equipped with dummy mass models of the BFPs and a Cryocooler SM.
• Goals: Validation of the mechanical concept.
– KT SM:• Consists in a flight representative 2K & 4K mechanical
structure equipped with dummy mass models of the BFPs and of the Cryocooler.
• Validation of: the mechanical I/F with the instrument, the mounting procedure, the mechanical concept.
• SOAM (Structure and Optical Alignment Model)
– Consists in the KT SM refurbished with optical marks.– To be used to perform Warm & Cold Alignment with the
instrument.
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PhFPU Models (2)
• CQM:– Fully representative Flight Model.– Performance restrictions:
• Blue Channel: 8 functional arrays, 2 @ performances.• Red Channel: 2 functional arrays, 1 @ performances.
• FM:– Fully compliant.
• FS:– Spare BFPs & Cryo-cooler.
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AIV & QA
• AIV:– Full PhFPU Models AIV diagram available.– AIV means identified (already available or
development/procurement planned).
• QA:– QA organisation operational at SAp, LETI and SBT
• PA plans, Doc. Management,
– PhFPU QA Documentation:• DML (currently in draft)• DPL (currently in draft)
– Bolometer evaluation:• Evaluation plan available
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PROBLEM AREAS (1)
• Current lack of Bolometer Complete Test results:– Problem:
• The 1st blue BFP has been successfully integrated at LETI . We started measurements in an incomplete test bench, with some minor problems in stray light rejection, and 300 mK operation (new double stage 3He/4He cooler).
– Solution: • The tools needed to measure the performances will be validated and
implemented in the fore coming weeks.• cryogenic issues are under investigation.• additional SAp staff support test at LETI.
• 2K Buffer characteristics:– Problem:
• Encouraging results have been obtained from preliminary tests at LETI and at Sap. Today, uncertainties on the stray capacitance of the wires and allocated 2K power budget prevent to remove BOLA.
– Solution:• BOLA is still the baseline and to remove it, is a system issue (we will have to take
in account the EMI susceptibility).
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PROBLEM AREAS (2)• Optical filters:
– Problem: • filter housing design uneasy due to filter material behaviour.
– Solution:• Asking for samples of filter material to UC for housing
prototyping at SAp.• UC is investigating housing solutions as well (together with
SPIRE opt. filter design).
• Cooler electrical insulation:– Problem:
• Detector insulation from the instrument mechanical ground (today only through the cryo-cooler).
– Solution:• Several solutions under investigation.
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PROBLEM AREAS (3)
• Cold (4K) Vibration Tests:– Problem:
• Cold vibration cannot be carried out at PhFPU level.
– Solution:• Cold Qualification at instrument level.
• Procurement of Ribbon cables:– Problem:
• Provision relies on only one company.
– Solution:• Looking for other sources.
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SCHEDULE
Milestones Date
Blue & red QM, FM, SP + 2 cones + optical baffle delivery to MPE 10/04/2002
Optical filters delivery to SAp 06/05/2002
Blue & red black painted cones delivery from MPE 06/05/2002
SM KT PhFPU delivery to KT 29/07/2002
SM KT PhFPU delivery from MPE for refurbishment 02/09/2002
SOAM PhFPU delivery to MPE 30/09/2002
Cryo-cooler SM delivery from SBT 06/06/2002
PhFPU SM CEA available 18/07/2002
Cryo-cooler CQM delivery from SBT 23/09/2002
PhFPU CQM delivery to MPE 10/03/2003
Cryo-cooler FM delivery from SBT 22/07/2003
FM PhFPU delivery to MPE 23/02/2004