Horizon antenna GRANDproto 3D antenna (CODALEMA butterfly Need to - - PowerPoint PPT Presentation

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Horizon antenna GRANDproto 3D antenna (CODALEMA butterfly Need to - - PowerPoint PPT Presentation

Feb 02, 2024 431 likes •629 views

Start point: Horizon antenna GRANDproto 3D antenna (CODALEMA butterfly Need to favor very inclined air showers (near 90) detection antenna designed by Take advantage of ground reflections D. Charrier) Benchmark antenna or Size S

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SLIDE 1

Horizon antenna

Need to favor very inclined air showers (near 90°) detection → Take advantage of ground reflections Size S 25-100 MHz h=9 m Size S/2 50-200 MHz h=4.5 m Start point: GRANDproto 3D antenna (CODALEMA butterfly antenna designed by

  • D. Charrier)
  • r

(equivalent gain pattern) Benchmark antenna In the long run:

  • Study alternative design
  • Frequency bandwidth optimization (in collab.

with A. Balagopal)

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SLIDE 2

Antenna gain pattern

G(q,j): unloaded butterfly antenna X-arm response to q,j wave @ 50 MHz NEC4 simulation wih infinite ground (“sandy dry”) hypothesis → G = 0 @ q >= 90°, huge gradiant (<-18dB between 80 & 90°), effect of infinite ground simulation Symmetrical pattern for j > 90°

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SLIDE 3

Infinite ground Soil Mesh over soil

Antenna gain pattern

Effect of a realistic ground (simulation) G > 0 @ q >= 90° SKALA antenna, H plane, 150 MHz (from SKA paper)

https://arxiv.org/ftp/arxiv/papers/1512/1512.01453.pdf

q

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SLIDE 4

Antenna orientation

a,b, angles of ground normal vector (=antenna pole) in GRAND frame computed from topography with 30 m step data

  • Antenna X-arm and Y-arm // to ground
  • Projection of X-arm and Y-arm on XY plane along NS & EW

X-arm Y-arm

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SLIDE 5

Antenna orientation

If antenna pole is not put ^ to ground → arms are not // to ground → antenna response does not differ much for q in 80-90° 75 MHz 125 MHz 175 MHz 18° tilt ^ to ground

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SLIDE 6

GRAND frame to antenna frame

  • Hyp. : all radio emission comes from Xmax position

→ calculation of Xmax direction in antenna frame (qant,jant) to apply antenna response

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SLIDE 7

Antenna voltage response

Vpp EW Vpp NS~0 Vpp UP V=Leq(n,q,j).E Leq: equivalent length of antenna connected to a circuit RLC (300 W, 6.5e-12 F, 1e-6 H )

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SLIDE 8

Events selection

Stationnary noise @ 50-200 MHz

  • Ground: T ~ 290 K black body
  • Sky: LFmap (galaxy..) T(direction, LST)

Atmosphere T ~ 0 K

  • Tot: Vrms ~ 15µV

→ Selected air shower event if Pessimistic (conservative) hyp. 8+ antennas with Vpp > 10 Vrms(noise) Optimistic (agressive) hyp. 5+ antennas with Vpp > 3 Vrms(noise) & antennas are selected if not isolated: distance to 1+ other selected antenna(s) < 2 antenna array step Vpp > 10 Vrms Add noise + digitization of V

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SLIDE 9

t events simulation

Hotspot 500 m step antenna array ~ 10 000 km² Decay positions of t (weighted by Waxman-Bahcall 1/3 nt flux) 20 000 (detectable) t events are simulated, between 1017 to 1021 eV

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SLIDE 10

antenna array ~ 10 000 km² antennas in the 3° light cone holes ↔ mountain shadowing

  • 25 m

EW

  • 75 m

antennas with a computed voltage additional holes ↔ qant (Xmax ) > 89.5° array step = 500m

t event example

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SLIDE 11

Ground slope affects voltage

a = zenithal angle (deg) of ground normal vector qant = Xmax zenithal angle in antenna frame Vpp = f(qant) & qant = f(a) Vpp (µV) Big differences of a for nearby antennas: calculation of a from 30m step topography not accurate → Limitation for Vpp computation accuracy

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SLIDE 12

Optimistic hyp. 1000 m step array

t events simulation

Number of antennas per shower Not in moutain shadow With a computed voltage Which triggers on Vpp condition

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SLIDE 13

Exposure

Agressive = Optimistic hyp. Conservative = Pessimistic hyp. As expected, conservative hyp. (8+ antennas with Vpp > 10 Vrms(noise) ) cuts a lot of low energy events, but keeps half of high energy events Preliminary study and new study compatible

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SLIDE 14

Exposure

Agressive = Optimistic hyp. Conservative = Pessimistic hyp. 500 m step array: density = 4 ant / km² Density *4 Exposure ~*2 1500 m step array density = 0.44 ant / km² Density /2.3 Exposure ~/2 100m step array: density = 1 ant / km²

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SLIDE 15

t detection rate

  • Prelim. study optimistic: 2.8 yr-1

500 m light cone: 7.568 +-0.097 yr-1 500 m optimistic: 2.975 +-0.032 yr-1 500 m pessimistic: 0.807 +-0.008 yr-1 1000 m optimistic: 1.490 +-0.021 yr-1 1000 m pessimistic: 0.299 +-0.004 yr-1 1500 m optimistic: 0.720 +-0.009 yr-1 1500 m pessimistic: 0.118 +-0.001 yr-1 t detection rate (yr-1) =  exposure (1 yr) * flux * dE flux = Waxman-Bahcall, 1/3 nt = 2e-4 /3 * E-2 GeV-1.m-2.sr-1.s-1

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SLIDE 16

t detection rate (decay positions)

antenna array ~ 10 000 km² Optimistic hyp. 1000 m step array

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SLIDE 17

t detection rate (directions)

downgoing upgoing To South To South To North Optimistic hyp. 1000 m step array

  • We might get more upgoing events with a proper ground in the simulation
  • f antenna response
  • t events mainly come from North (they travel towards South) because

Southern ridge of Tianshan mountains act as target for neutrino decays

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SLIDE 18

Conclusion & to do

  • Results of new simulation compatible

with preliminary simulation

  • Improvements on exposure depend on

antenna design and its fair simulation

  • Comparison with a flat array to quantify topography effects
  • Comparison with a real topography array but with vertical antennas to quantify

the effect of the antenna response

  • Simulation for arrays in the whole Western China (to be done for March 2018)
  • Find a way to simulate antenna response with a realistic ground (HFSS?)

To do Conclusion