global eor experoments
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Global EoR Experoments. Ron Ekers , CSIRO CAASTRO Global EoR Workshop Uluru, 17 July 2013. Summary. Strategy for technically difficult experiments Either masochists or people who don’t know any better! NB the Crick and Watson story on DNA structure Global HI EoR v imaging HI EoR - PowerPoint PPT PresentationTRANSCRIPT
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Global EoR Experoments
Ron Ekers, CSIRO
CAASTRO Global EoR WorkshopUluru, 17 July 2013
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Summary
Strategy for technically difficult experiments– Either masochists or people who don’t know any better!– NB the Crick and Watson story on DNA structure
Global HI EoR v imaging HI EoR– Statistical v direct detection
CORE ZEBRA SARAS Other global HI experiments
– EDGES, BIGHORNS, COREII, DARE, Pulse calibration Epoch of (re)combinationJuly 2013 2
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Global HI EoR prediction Pritchard et al, Nature 468, 772 (2010)
Z =
6.3
Peter Shaver
conjecture
(200/65)2.5=17
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The 21cm EoR challenge
Global T ~30mK in few MHz– S/N easy – can reach a few mK in few hours
T/T < 10-4 to10-5
Calibrate the complex gain Minimize the number of unknowns that can couple to EoR Remove the forgrounds Remove the additive constant
– Correlation receiver» Eliminate LNA additive noise
– Position switching» T now very small so large antenna and long integration times » Correlation interferometer» Arrays
• Statistical detection• Direct detection
Zero spacing interferometerZero spacing
interferometer
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From CoRE to ZEBRA
CoRE (Chippendale)
ZEBRA SARAS
ZEBRA II
Calibratable receiver
CSI
RO
RR
IM
RO
July 2013 5
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COREfrequency independent antenna beam
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Global EoR system RRI Bangalore
Ravi Subrahmanyan
Ron Ekers
Peter Shaver
A. Raghunathan
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Zebra – fat dipole v1
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ZEBRA Global EoR Experiment
ZEro-spacing measurement of the Background RAdio spectrum
Partially reflecting resistive screen
Virtual zero spacing interferometer
Removes all additive errors
Modulate screen ?
Subrahmanyan, EkersPatra
Partial reflector/transmitter
X
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The space beam-splitter: a resistive wire mesh
Need a space beam-splitter before the antenna A lossless screen (e.g. a conducting grid)
– transmitted & reflected waves are orthogonal Resistive wire mesh
– Thickness of wire < skin depth– Frequency independent– Re-radiated fields no longer cancel the incident field on
the far side of the wire screen Lumped resistance on scale <<
– Practical solution instead of resistance wire
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Building resistive screen
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The Resistive Screen
copper wire + lumped resistors
resistor value = free space impedance/2
3x4 metres
holes to reduce wind loading
Roll up for transport
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ZEBRA – interferometerfirst CMB correlation 20 Jan 2011
3.4m
1.5m separation Max sky coverage at zero spacing
26% Contributions to correlated output
– Global sky signal– Screen radiating– 1.5m interferometer sky
correlation» One path through screen» Both paths miss screen
Ferrite absorber
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ZEBRA at Gauribidanur
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Zebra correlated output
Baseline ripple – changes with LST– Repeats each day– Multipath scattering of galaxy foreground signal– Shifted location …….
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SARAS receiver evolution
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SARAS receiver
Patra & Subramanyan, EA (2013) 88-175MHZ Differential correlation spectrometer Digital correlator well separated from
receiver Minimize number of parameters in
solution (11) Solve for multipath propagation from
internal reflections Eg noise from receiver input
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SARAS internal reflections
Short connections to keep broad bandwidth Long connections to decrease coupling
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SARAS internal reflections
Short connections to keep broad bandwidth Long connections to decrease coupling
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SARAS waterfall plot
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Pulse calibration ?
Pulse injected at Parkes vertex
Pulse reflected from Parkes focus
Inject and integrate short (sec) pulses Calibrated noise spectrum Understand & calibrate reflections Nipanjana Patra, Paul Roberts
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Pulse calibration
Band limited pulse with -20db reflection Pulse repetition rate 106 Hz Accuracy 0.05%
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Other Global EoR Experiments
WSRT: – Lunar occultation
EDGES: Rogers & Bowman– Polynomial fits Δz > 0.06– Absolute calibration of components for wider bandwidths
BIGHORNS: Sokolowski, Tremblay, Wayth, Tingay ⑫– Low rfi site, high stability
Core II: Bannister, Chipendale, Dunning ①– Precision self calibrating receiver
DARE– Go to moon to avoid ionosphere and rfi
July 2013 23
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Estimates of the sources of error and their magnitude expressed as the residuals to fits with increased numbers of parameters along with the bias in EOR estimation
Parameters of 10 parameter solution:1] EoR signature (30 mK, 50@145MHz)
2] scale (assumes spectral index of -2.5)
3] constant (ground emission)
4] frequency -2 (ionosphere emission)
5] frequency -4.5 (ionosphere absorption)
6] Magnitude of antenna S117] Magnitude of LNA S118] S11 phase error9] S11 delay error10] temperature scale
Estimate of errors using simulations – for more details see EDGES memo 99
Rogers & Bowman (EDGES memo #99)
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BIGHORNS Sokolowski, Tremblay, Wayth,
Tingay ⑫– Low rfi site, high stability
Dynamic spectrum normalised by the median
Dynamic range 2%– Required 10-4
Day
200MHz
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CORE2: A global EOR experiment with a self-calibrating receiver on two antennas
CORE2: A global EOR experiment with a self-calibrating receiver and two antennas| Keith Bannister | Page 26
CORE2-MONO60 Degree beamOptimised for frequency Independence and low RFI and
CORE2-DISH5 Degree beamOptimised for foreground removal
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The Richness and Beauty of the Physics of Cosmological Recombination
well defined quasi-periodic spectral dependence
photons are coming from redshifts– z 1300−1400– i.e. before the time of
the formation of the CMB angular fluctuations
Chluba & Sunyaev A&A, 458, L29 (2006)
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Observing
All sky so dish size is not relevant Needs a wideband spectrograph in 2-10 GHz range Can measure multiple independent patches of sky
– Many dishes/receivers Need lowest possible Tsys Can integrate over all oscillations
– Spectral dependence is accurately predicted
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Sensitivity Required
Need ΔT/T = 10-8
Tsys = 25K Δν = 1010 Hz 2 pol 100 antennas Time = 1month (3.106 sec) ΔT/T = 25/(√(1010 . 2.100.3.106 .)) = 10-8 !