Planck Pre-Launch Status Papers - APC - UniversitÃ© Paris Diderot ...

More documents

Recommendations

Info

M. Bersanelli et al.: <strong>Planck</strong> pre-launch status: Design and description of the Low Frequency Instrument30 GHz44 GHzload load load2020200.030.10.150.10.0370 GHz0.50.350.250.15150.05150.05150.10.075100.07510100.01660.01660.030.01665550.0010.0010.001 0.0010.01660.01660.050.050 0.1sys00 5 10 15 200 5 10 15 20 25 30sys0.0010.0010.5 0.1 0.0300.01660 10 20 30 40sysFig. 7. Curves of equal f k (in Hz) on the plane T load (K, thermodynamic temperature), T sys assuming thermodynamic sky temperature of 2.7 K.Each panel refers to a different frequency channel. The dashed contour refers to values for which the knee frequency is equal to the spin frequency( f spin = 0.0166 Hz). The graphs also show the range of typical LFI noise temperature values (grey area) and the nominal reference load temperature(4 K – double horizontal line).In Eq. (12) a is the proportionality constant of the square-lawdetector diode, and G and I are the effective power gain andisolation of the system:G ≃ 1 4 g2 B (g2 F 1+ g 2 F 2+ 2g F1 g F2 )I ≃ 1 4 g2 B (g2 F 1+ g 2 F 2− 2g F1 g F2 ), (13)where g B is the voltage gain of the BEM in the considered channel.In Eq. (12)thetemperatureterms,(T sky1 −˜T sky = +L feed L OMT˜T load = T loadL 4K+)1T physL feed L OMT(1 − 1L 4K)T phys , (14)represent the sky and reference load signals at the input of thefirst hybrid, where L 4K is the insertion loss of the reference horn,and T phys ≃ 20 K is the front-end physical temperature.Fig. 8. Example of uncalibrated data stream from one of the 44 LFI detectors(LFI19M-00, at 70 GHz) recorded during instrument level tests.The upper and middle panels show the data for the sky and referenceload inputs, while the lower panel shows differenced data stream withoptimal gain modulation factor.3.3.2. Knee frequency and gain modulation factorFor a radiometer with good isolation (>13 dB), as expected inawell-matchedsystem,itfollowsfromEq.(12) thatthepoweroutput is nullified forr = ˜T sky + T noise˜T load + T noise· (15)In this case the gain fluctuations are fully suppressed and the radiometeris only sensitive to the 1/ f noise caused by noise temperaturefluctuations, which only represents a small fraction ofthe amplifiers instability. For an optimal choice of the gain modulationfactor, the resulting knee frequency is given by( ) A(1 − 2 r)Tsysf k ≃ ∆ν∝ (1 − r) 2 . (16)T sky + T sysThus, in principle, for small input offsets ˜T sky ≃ ˜T load very lowknee frequencies can be obtained. Figure 7 displays expectedknee frequencies for parameters typical of the LFI channels asafunctionofnoisetemperatureandreferenceloadtemperature,assuming ideal gain and phase match. For T load ≈ 4Kweexpectf k to be an order of magnitude lower than for T load ≈ 20 K.This was the driver for implementing reference loads at 4 K atthe cost of some complexity in thethermo-mechanicalinterfacesin the focal plane. It can also be shown (Mennella & Bersanelli2001) thatthesamevalueofr that minimises the radiometersensitivity to 1/ f noise is also effective in reducing the susceptibilityto other systematic effects such as back-end temperaturevariations.It is essential that the gain modulation factor r be calculatedwith sufficient precision to reach the required stability.Simulations and testing show that the needed accuracy rangesfrom ±1% (30 GHz) to ±0.5% (70 GHz). This accuracy canbe obtained with different methods (Mennella et al. 2003), thesimplest being to evaluate the ratio of the total power outputvoltages averaged over a suitable time interval, r ≃ ¯V sky / ¯V load .In Fig. 8 we show, as an example, the data streams from one ofthe 44 LFI detectors with the two total power signals and differenceddata. The LFI telemetry allocations ensure that the totalpower data from both the sky and reference load samples will bedownloaded, so calculation of r and differencing is performedon the ground.Further suppression of common fluctuation modes, typicallyof thermal or electrical origin, is obtained by taking the noiseweightedaverage of the two detectors associated to each radiometer(Mennella et al. 2010) aswellasinthedifferencingof the main and side arm radiometers signals when analysingdata for polarisation (Leahy et al. 2010).Page 9 of 21
A&A 520, A4 (2010)Fig. 9. Schematics of the LFI showing interconnections and details of the DAE and REBA main functions and units.3.3.3. Noise temperatureThe LFI radiometer sensitivity is essentially independent of thetemperature of the reference loads. From Eqs. (5) and(12) itfollows that, to first order, the radiometer sensitivity is√2δT =τ · ∆ν (T sys + T sky ) √ 1 + η L , (17)whereη L =(T N,B /G F ) 2(T sys + T sky )(T sys + T load ) , (18)and T N,B is the noise temperature of the back-end, and G F thegain of the front end. For parameter values typical of LFI, wehave η L < 10 −3 ,sothatthedependenceofthenoisetemperatureon T load is extremely weak. The advantage of cooling the referenceload to 4 K, therefore, rests solely on better suppression ofsystematics, not on sensitivity.4. LFI configuration and subsystemsThe overall LFI system is shown schematically in Fig. 9. Inthissection we provide an overview of the instrument units and mainsubsystems. More details on the design, development and testingof the most critical components are given in companion papersthat are cited below.4.1. The front-end unit4.1.1. Focal plane designThe disposition of the LFI feeds in the focal plane is driven byoptimisation of angular resolution and by recovery of polarisationinformation. In addition, requirements need to be met onproper sampling of the sky and rejection of crosstalk effects.The central portion of the <strong>Planck</strong> focal plane is occupied bythe HFI front end, as higher frequency channels are more susceptibleto optical aberration. The LFI feeds are located as close aspossible to the focal plane centre compatible with mechanical interfaceswith HFI and 4 K reference loads (Fig. 10). Miniaturiseddesigns for the FEMs and OMT are implemented to allow optimaluse of the focal area. The 70 GHzfeeds,mostcriticalforcosmological science, are placed in the best location for angularresolution and low beam distortion required for this frequency(Sandri et al. 2010).AkeycriterionforthefeedarrangementisthattheE andH planes as projected in the sky will allow optimal discriminationof the Stokes Q and U parameters. The polarisation informationis obtained by differencing the signal measured by the mainarm(R0) and side-arm (R1) radiometers in each RCA, which areset to 90 ◦ angle by the OMT. An optimal extraction of Q and Uis achieved if subsets of channels are oriented in such a waythat the linear polarisation directions are evenly sampled (Leahyet al. 2010). We achieve this by arranging pairs of feeds withtheir E planes oriented at 45 ◦ to each other (Fig. 11). With thePage 10 of 21
Page 1 and 2:
A&A 520, E1 (2010)DOI: 10.1051/0004
Page 3 and 4:
ABSTRACTThe European Space Agency
Page 5 and 6:
A&A 520, A1 (2010)Fig. 2. An artist
Page 7 and 8:
A&A 520, A1 (2010)Fig. 4. Planck fo
Page 9 and 10:
A&A 520, A1 (2010)Fig. 6. The Planc
Page 11 and 12:
A&A 520, A1 (2010)Table 4. Summary
Page 13 and 14:
A&A 520, A1 (2010)three frequency c
Page 15 and 16:
A&A 520, A1 (2010)Fig. 12. The left
Page 17 and 18:
A&A 520, A1 (2010)Fig. 14. Left pan
Page 19 and 20:
A&A 520, A1 (2010)flux limit of the
Page 21 and 22:
A&A 520, A1 (2010)- University of C
Page 23 and 24:
A&A 520, A1 (2010)57 Instituto de A
Page 25 and 26:
A&A 520, A2 (2010)Fig. 1. (Left) Th
Page 27 and 28: A&A 520, A2 (2010)Fig. 3. (Top)Twos
Page 29 and 30: A&A 520, A2 (2010)Table 2. Predicte
Page 31 and 32: Table 3. Predicted in-flight main b
Page 33 and 34: A&A 520, A2 (2010)materials. Theref
Page 35 and 36: A&A 520, A2 (2010)Fig. 11. Comparis
Page 37 and 38: A&A 520, A2 (2010)Table 5. Inputs u
Page 39 and 40: A&A 520, A2 (2010)Fig. 16. Three cu
Page 41 and 42: A&A 520, A2 (2010)Table 7. Optical
Page 43 and 44: A&A 520, A2 (2010)Fig. A.1. Dimensi
Page 45 and 46: A&A 520, A2 (2010)5 Università deg
Page 47 and 48: A&A 520, A3 (2010)Horizon 2000 medi
Page 49 and 50: A&A 520, A3 (2010)Fig. 1. CMB tempe
Page 51 and 52: A&A 520, A3 (2010)Ω ch 2τn s0.130
Page 53 and 54: A&A 520, A3 (2010)Fig. 6. Integral
Page 55 and 56: A&A 520, A3 (2010)Table 2. LFI opti
Page 57 and 58: 3.3.1. SpecificationsThe main requi
Page 59 and 60: A&A 520, A3 (2010)Fig. 11. Schemati
Page 61 and 62: A&A 520, A3 (2010)features of the r
Page 63 and 64: A&A 520, A3 (2010)Fig. 13. Level 2
Page 65 and 66: A&A 520, A3 (2010)Fig. 15. Level 3
Page 67 and 68: A&A 520, A3 (2010)GUI = graphical u
Page 69 and 70: A&A 520, A3 (2010)23 Centre of Math
Page 71 and 72: A&A 520, A4 (2010)In addition, all
Page 73 and 74: A&A 520, A4 (2010)Table 2. Sensitiv
Page 75 and 76: A&A 520, A4 (2010)Fig. 2. Schematic
Page 77: A&A 520, A4 (2010)Fig. 6. LFI recei
Page 81 and 82: A&A 520, A4 (2010)Table 4. Specific
Page 83 and 84: A&A 520, A4 (2010)Fig. 15. DAE bias
Page 85 and 86: A&A 520, A4 (2010)Fig. 19. Picture
Page 87 and 88: A&A 520, A4 (2010)Table 10. Main ch
Page 89 and 90: Table 13. Principal requirements an
Page 91 and 92: A&A 520, A5 (2010)DOI: 10.1051/0004
Page 93 and 94: A. Mennella et al.: LFI calibration
Page 105 and 106: D.1. Step 1-extrapolate uncalibrate
Page 107 and 108: A&A 520, A6 (2010)DOI: 10.1051/0004
Page 109 and 110: F. Villa et al.: Calibration of LFI
Page 121 and 122: A&A 520, A7 (2010)DOI: 10.1051/0004
Page 123 and 124: M. Sandri et al.: Planck pre-launch
Page 126 and 127: A&A 520, A7 (2010)Fig. 8. Footprint
Page 128 and 129:
-30-40-30-6-3-20A&A 520, A7 (2010)0
Page 130 and 131:
A&A 520, A7 (2010)Table 4. Galactic
Page 132 and 133:
A&A 520, A7 (2010)Fig. A.1. Polariz
Page 134 and 135:
A&A 520, A8 (2010)inflation, giving
Page 136 and 137:
A&A 520, A8 (2010)estimated from th
Page 138 and 139:
A&A 520, A8 (2010)ways the most str
Page 140 and 141:
unmodelled long-timescale thermally
Page 142 and 143:
A&A 520, A8 (2010)Fig. 5. Polarisat
Page 144 and 145:
A&A 520, A8 (2010)Table 3. Band-ave
Page 146 and 147:
A&A 520, A8 (2010)where S stands fo
Page 148 and 149:
A&A 520, A8 (2010)Fig. 11. Simulate
Page 150 and 151:
stored in the LFI instrument model,
Page 152 and 153:
A&A 520, A8 (2010)Table 5. Statisti
Page 154 and 155:
A&A 520, A8 (2010)comparable in siz
Page 156 and 157:
A&A 520, A8 (2010)Table B.1. Main b
Page 158 and 159:
A&A 520, A8 (2010)Bond, J. R., Jaff
Page 160 and 161:
A&A 520, A9 (2010)- (v) an optical
Page 162 and 163:
A&A 520, A9 (2010)Fig. 2. The Russi
Page 164 and 165:
A&A 520, A9 (2010)Table 3. Estimate
Page 166 and 167:
A&A 520, A9 (2010)Fig. 7. Picture o
Page 168 and 169:
A&A 520, A9 (2010)Fig. 9. Cosmic ra
Page 170 and 171:
A&A 520, A9 (2010)Fig. 13. Principl
Page 172 and 173:
A&A 520, A9 (2010)Fig. 16. Noise sp
Page 174 and 175:
A&A 520, A9 (2010)Table 6. Basic ch
Page 176 and 177:
A&A 520, A9 (2010)with warm preampl
Page 178 and 179:
A&A 520, A9 (2010)20 Laboratoire de
Page 180 and 181:
A&A 520, A10 (2010)Table 1. HFI des
Page 182 and 183:
A&A 520, A10 (2010)based on the the
Page 184 and 185:
A&A 520, A10 (2010)Fig. 6. The Satu
Page 186 and 187:
A&A 520, A10 (2010)5. Calibration a
Page 188 and 189:
A&A 520, A10 (2010)Fig. 16. Couplin
Page 190 and 191:
A&A 520, A10 (2010)217-5a channel:
Page 192 and 193:
A&A 520, A10 (2010)10 -310 -495-The
Page 194 and 195:
A&A 520, A11 (2010)DOI: 10.1051/000
Page 196 and 197:
P. A. R. Ade et al.: Planck pre-lau
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
A&A 520, A12 (2010)Table 1. Summary
Page 204 and 205:
arrangement was also constrained by
Page 206 and 207:
A&A 520, A12 (2010)frequency cut-of
Page 208 and 209:
A&A 520, A12 (2010)Fig. 9. Gaussian
Page 210 and 211:
A&A 520, A12 (2010)the horn-to-horn
Page 212 and 213:
A&A 520, A12 (2010)Fig. 15. Composi
Page 214 and 215:
A&A 520, A12 (2010)Fig. 19. Broad-b
Page 216 and 217:
A&A 520, A13 (2010)DOI: 10.1051/000
Page 218 and 219:
C. Rosset et al.: Planck-HFI: polar
Page 220 and 221:
Page 222 and 223:
of frequencies and shown to have po
Page 224 and 225:
Page 226 and 227:
show all

Planck Pre-Launch Status Papers - APC - UniversitÃ© Paris Diderot ...

Create successful ePaper yourself

Delete template?

Save as template?