Instruments
Instruments In Brief
The Planck scientific instrument complement comprises two instruments, LFI, a radio receiver array covering the lower frequency range, and HFI, a bolometric detector array covering the higher frequencies. The instruments share a common telescope. Principal Investigator consortia provide the instruments and telescope.
| Planck Principal Investigators | | LFI | Nazzareno Mandolesi, Istituto di Tecnologie e Studio delle Radiazioni Extraterrestri, (Bologna, Italy) | | HFI | Jean-Loup Puget, Institut d'Astrophysique Spatiale, (Orsay, France) | | Telescope | Hans-Ulrik Norgaard Nielsen, Danish Space Research Institute, (Copenhagen, Denmark) |
Low Frequency Instrument
The Low Frequency Instrument (LFI) is designed to produce high-sensitivity, multi-frequency measurements of the microwave sky in the frequency range 27 to 77 GHz (wavelength range 11.1 to 3.9 mm).
| LFI Performance Goals | | Centre frequency (GHz) | 30 | 44 | 70 | | Bandwidth (GHz) | 6 | 8.8 | 14 | | Beamwidth (arcminutes, FWHM) | 33 | 24 | 14 | | Detector technology | High electron mobility transistor (HEMT) radio receiver arrays | | Detector temperature (K) | ~ 20 | | Cooling technology | H2 sorption cooler | | Average ΔT/T1 per pixel* | 2 | 2.7 | 4.7 | | Average ΔT/T2 per pixel* | 2.8 | 3.9 | 6.7 | | Flux sensitivity per pixel* (mJy) | 13 | 19 | 25 | | | | * A pixel is a square whose side is the full width, half maximum (FWHM) extent of the beam. These sensitivity figures are calculated for the average integration time per pixel. The integration time will be very inhomogeneously distributed over the sky and will be much higher in certain regions. | | 1Sensitivity (1 σ) to intensity (Stokes I) fluctuations, measured in thermodynamic temperature units × 10-6, relative to the average temperature of the CMB (2.73 K), achievable after two sky surveys (14 months). | | 2Sensitivity (1 σ) to polarised intensity (Stokes U and Q) fluctuations, measured in thermodynamic temperature units × 10-6, relative to the average temperature of the CMB (2.73 K), achievable after two sky surveys (14 months). |
High Frequency Instrument
The High Frequency Instrument (HFI) is designed to produce high-sensitivity, multi-frequency measurements of the diffuse sky radiation in the frequency range 84 GHz to 1 THz (wavelength range 3.6 to 0.3 mm).
| HFI Performance Goals | | Centre frequency (GHz) | 100 | 143 | 217 | 353 | 545 | 857 | | Bandwidth (GHz) | 33 | 47 | 72 | 116 | 180 | 283 | | Beamwidth (arcminutes, FWHM) | 9.2 | 7.1 | 5 | 5 | 5 | 5 | | Detector technology | Spider bolometer arrays,
neutron transmutation doped (NTD) germanium thermistors | | Detector
temperature (K) | ~ 0.1 | | Cooling technology | H2 sorption cooler + Joule-Thomson cooler + 3He/4He dilution cooler | | Average ΔT/T3
per pixel* | 2 | 2.2 | 4.8 | 14.7 | 147 | 6700 | | Average ΔT/T4
per pixel* | | 4.2 | 9.8 | 29.8 | | | | Flux sensitivity
per pixel* (mJy) | 9 | 12.6 | 9.4 | 20 | 46 | 52 | | | | * A pixel is a square whose side is the full width, half maximum (FWHM) extent of the beam. These sensitivity figures are calculated for the average integration time per pixel. The integration time will be very inhomogeneously distributed over the sky and will be much higher in certain regions. | | 3Sensitivity (1 σ) to intensity (Stokes I) fluctuations, measured in thermodynamic temperature units × 10-6, relative to the average temperature of the CMB (2.73 K), achievable after two sky surveys (14 months). | | 4Sensitivity (1 σ) to polarised intensity (Stokes U and Q) fluctuations, measured in thermodynamic temperature units × 10-6, relative to the average temperature of the CMB (2.73 K), achievable after two sky surveys (14 months). |
Measurement Results
The measurements made by the two instruments will be combined and used to produce a full-sky map of the anisotropies in the Cosmic Microwave Background (CMB) with unprecedented precision. This map will in turn be used to derive a wealth of cosmological information, including an accurate determination of the values of the main parameters that characterise the large-scale structure and evolution of the Universe.
Telescope
The telescope design is an off-axis tilted Gregorian system, offering the advantages of no blocking of the optical path combined with compactness. The eccentricity and tilt angle of the secondary mirror and the off-axis angle obey the Dragone-Mizuguchi condition, which allows the system to operate without significant degradation over a large focal plane array, while simultaneously minimizing the polarization effects introduced by the telescope. The baffling system is composed of two elements. The shield element is a large, self-supporting and roughly conical structure covered with multi-layer insulation (MLI), which surrounds the telescope and focal plane instruments. Together with the optical bench, it defines the optical enclosure. It has two important functions, reducing the level of straylight (which at the chosen orbit is in large part due to the spacecraft itself) and promoting the radiative cooling of the optical enclosure towards deep space. The baffle element consists of one half of a conically shaped surface that links the focal plane instruments to the bottom edge of the sub-reflector. The function of the baffle is to shield the detectors from thermal radiation originating within the optical enclosure.
| Telescope characteristics | | Type | Off-axis tilted Gregorian | | Primary mirror | 1.9 × 1.5 m, off-axis paraboloid | | Secondary mirror | 1.1 × 1.0 m, off-axis paraboloid |
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Introduction |
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Last Update: 27 Feb 2009
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