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Solar power mirror arrays for radio astronomy Olaf Wucknitz, Alan - - PowerPoint PPT Presentation

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Solar power mirror arrays for radio astronomy Olaf Wucknitz, Alan Roy wucknitz@mpifr-bonn.mpg.de aroy@mpifr-bonn.mpg.de Scintillometry Conference, Bonn, 7th November 2019 Solar power mirror arrays for radio astronomy Solar Power Mirror

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SLIDE 1

Solar power mirror arrays for radio astronomy

Olaf Wucknitz, Alan Roy

wucknitz@mpifr-bonn.mpg.de aroy@mpifr-bonn.mpg.de

Scintillometry Conference, Bonn, 7th November 2019

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SLIDE 2

Solar power mirror arrays for radio astronomy

  • Solar Power Mirror Arrays
  • Phased array feeds
  • Test case J¨

ulich

  • Simulations of test observations
  • Issues, plans
  • Prospects
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SLIDE 3

Gemasolar as SKA? (Alan Roy, Ivan Camara, Olaf Wucknitz, …)

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SLIDE 4
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SLIDE 5

Gemasolar Basics

Solar field: 2650 heliostats, each 120 m2, total 304 750 m2, equivalent to 620 m diameter single dish Tower height: 140 m Heat-Transfer Fluid: Molten salts (sodium + potassium nitrate) Receiver inlet temp: 290 °C Receiver outlet temp: 565 °C Turbine capacity: 19.9 MW Construction cost: 230 M€ (5 M€ from EU FP5, 80 M€ loan EIB) Timeline: 2007 begin, 2011 online Electricity sales: 110 000 MWh/yr = 30 M€/yr Ownership: Torresol Energy, subsidiary of consortium: 60 % SENER Grupo de Ingeniería (private company, Spain) 40 % MASDAR (alternative energy company of Abu Dhabi)

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SLIDE 6

The Solar power array problem

  • many mirrors, different delays
  • signal spread over larger area
  • cannot catch the signal with one big feed
  • PAF

⋆ sample focal area ⋆ re-align phases ⋆ scale with signal strength

  • ptimal weights from speckle pattern
  • Need to test concept!
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SLIDE 7

Some large facilities

[ https://en.wikipedia.org/wiki/Solar_power_tower ] collecting areas Ivanpah 2.6 km2 [ https://solarpaces.nrel.gov/ ] Ashalim 1.1 km2 Crescent Dunes 1.2 km2 Gemasolar 0.3 km2 J¨ ulich 0.018 km2 (> 2× Effelsberg)

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SLIDE 8

Solar Tower J¨ ulich: 150-m equivalent

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SLIDE 9

Solar Tower J¨ ulich: Experimental platform

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SLIDE 10

Practical issues

  • heat (use dedicated tower?)
  • RFI
  • mirrors: do they reflect radio waves?

⋆ expectation: must be thicker than skin depth ⋆ ca. 0.5 – 2 µm for 10 – 1 GHz ⋆ metal mirrors (Gemasolar) okay ⋆ J¨ ulich: 0.2 µm ⋆ actually seems to work!

  • can we predict speckle pattern?
  • beamforming techniques
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SLIDE 11

Technical setup for test in J¨ ulich

  • tripole antennas (Uppsala, Onsala)
  • simple uncooled receivers, mostly OTS parts
  • Rubidium/GPS clock
  • DBBC3 for sampling (512 MHz bandwidth,
  • max. 6 channels)
  • Mark 6 or dedicated server for recording
  • correlate with Effelsberg for calibration (VLBI)
  • record, correlate, beamform, analyse
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SLIDE 12

Representative mirror positions for J¨ ulich

200 150 100 50 50 100 150 200 east [m] 50 100 150 200 250 300 north [m]

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SLIDE 13

Parameters

  • field size ca. D = 300m
  • 2150 mirrors, each 3.2×2.5m2
  • distance to receiver ca. L = 150m (ca. 50 m height)
  • assume 1.5 GHz (20 cm)
  • ‘focus’ size ca. 10 m
  • approximate speckle size

⋆ 0.2 m size ⋆ 1 MHz in frequency ⋆ 10 sec in time ⋆ 0.04 deg on sky

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SLIDE 14

Speckle image for J¨ ulich experimental platform

4 2 2 4 x [m] 3 2 1 1 2 3 z [m]

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SLIDE 15

Speckle dynamic spectrum for single feed

100 200 300 400 500 600 700 time [sec] 1500 1510 1520 1530 1540 1550 freq [MHz]

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SLIDE 16

Instrument response

  • mirror rm, focus/PAF element f p
  • time t and frequency ν generally omitted
  • delays

c τpm = |rm −f p|−θ·rm

  • voltage response for signal E(t)

⋆ time domain Vpm(t) = gpmE(t −τpm) ⋆ freq. domain Vpm = E gpme2πiντpm

  • total voltage response

Vp = E Bp Bp = ∑

m

gpme2πiντpm

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SLIDE 17

Beamforming theory

  • fit of field E per t,ν

Efit =

∑

p

Bp Vp

∑

p

|Bp|2

  • power estimate from all t,ν

Sfit =

∑

tν

  • ∑

p

Bp Vp

  • 2

∑

tν

  • ∑

p

|Bp|22

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SLIDE 18

Beamforming result: one antenna element, one sample

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.5 1.0 1.5 2.0 2.5 3.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

no position from one sample

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SLIDE 19

Beamforming result: 5 antenna elements, one sample

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

5 elements spread over ∼ 5m

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SLIDE 20

Beamforming result: 20 antenna elements, one sample

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

20 elements spread over ∼ 5m

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SLIDE 21

Beamforming result: 100 antenna elements, one sample

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

100 elements spread over ∼ 5m

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SLIDE 22

Beamforming result: one antenna element, 100 samples

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

10 times (∆t = 10sec), 10 frequencies (∆ν = 1MHz)

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SLIDE 23

Beamforming result: one antenna element, 2500 samples

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

50 times (∆t = 10sec), 50 frequencies (∆ν = 1MHz)

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SLIDE 24

Beamforming result: one antenna element, 10000 samples

20 10 10 20 x [arcmin] 20 10 10 20 y [arcmin]

beam map

0.0 0.2 0.4 0.6 0.8 1.0 400 200 200 400 U [m] 400 200 200 400 V [m]

FT of beam

10 20 30 40 50

100 times (∆t = 10sec), 100 frequencies (∆ν = 1MHz)

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SLIDE 25

Alternative beamforming

  • formal result

Efit ∝ ∑

p

Bp Vp Bp = ∑

m

gpme2πiντpm

  • reorder

Efit ∝ ∑

m

  • ∑

p

gpme−2πiντpm Vp

  • c τpm = |rm −f p|−θ·rm
  • split delay

Efit ∝ ∑

m

e2πiν θ·rm/c ∑

p

e−2πiν |rm−f p|/c Vp two-stage delay beamformer (optical/analog?)

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SLIDE 26

Summary

  • solar power array radio telescope may actually work
  • PAF is essential, big PAFs not trivial
  • J¨

ulich: tests in preparation

  • many practical issues to consider
  • multi-beaming provides huge field of view
  • true Square Kilometre Array within reach !?
  • advanced beamforming, only cross-corr?, polarisation
  • build dedicated optimised array?
  • synergy with interstellar scattering/scintillation

see backup slides from Alan Roy (scintillometry 2016)

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SLIDE 27

Model Mirror Locations

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SLIDE 28

Dynamic Spectrum: Amplitude

80 MHz

(1400 MHz to 1480 MHz)

12 min

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SLIDE 29

Dynamic Spectrum: Phase

80 MHz

(1400 MHz to 1480 MHz)

12 min

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SLIDE 30

Secondary Spectrum

10 μs 1.1 Hz

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SLIDE 31

Ivanpah Solar Power Facility (USA)

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SLIDE 32

Cerro Dominador (Chile)

[ https://cerrodominador.com/ ]

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SLIDE 33

Some Google maps links

https://en.wikipedia.org/wiki/Solar_power_tower

  • J¨

ulich

https://maps.google.de/maps?ll=50.915,6.387778&t=h&z=15

  • Gemasolar

https://maps.google.de/maps?ll=37.558,-5.329&t=h&z=15

  • Crescent Dunes

https://maps.google.de/maps?ll=38.233,-117.366&t=h&z=15

  • Ivanpah

https://maps.google.de/maps?ll=35.57,-115.47&t=h&z=13

  • Cerro Dominador

https://www.google.de/maps?ll=-22.771,-69.485&t=h&z=15

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