Detection of Radio Transients: ���Digital Requirements from Cosmic Ray Experiments

John Kelley

Radboud University Nijmegen, Netherlands

Lunar Radio Explorer Workshop, ESTEC 28 April 2010

Auger Engineering Radio ArrayAERA

Jörg R. Hörandel, Radboud University Nijmegen for

Auger Engineering Radio ArrayReview, Malargüe, April 2009

1.Introduction

2.Physics case

3.Site layout

4.Antennas

5.Electronics

6.Communications

7.Power harvesting and EMC

8.DAQ

9.Risk analysis

10.Management

Introduction

•  Goal: impulsive radio transients on the moon –  cosmic ray emission in regolith (Askaryan effect) –  other sources? (talk by O. Scholten)

•  Radio cosmic ray detection on Earth –  emission mechanism different, but pulses similar

–  experience with triggering, background rejection –  modest power budget

04.28.2010 J. Kelley, LRX Workshop ESTEC 2

Radio Emission from ���Cosmic Ray Air Showers

•  Primary cosmic ray interacts and causes cascade of particles in atmosphere (or in the moon)

•  Broadband radio pulse –  width ~50 ns –  due to interaction with Earth’s

magnetic field

•  Emission is coherent up to 100 MHz –  RF power scales as (energy)2

•  Trigger on bandwidth-limited pulse

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s]µtime [2.4 2.5 2.6 2.7 2.8 2.9 3 3.1 3.2

vo

lta

ge

[m

V]

-80

-60

-40

-20

0

20

40

60

80EW

NS

pole 1

Radio Detection Station

•  Prototype array in Argentina –  at the Pierre Auger Cosmic Ray

Observatory

•  Autonomous, solar power

•  LPDA antenna –  two polarizations –  to 30-80 MHz bandpass filter

•  Local digitizer and trigger –  four channels

•  Multi-station coincidence via central DAQ

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Auger Engineering Radio Array

•  AERA: Auger Engineering Radio Array

•  20 km2 extension to southern Auger site

•  Phase I: 20 stations, June 2010 (total: 150)

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found to be within a factor of two or better. Presently, the predictions for the radio-detectorarray are at this level of precision. Further cross checks on the predicted results have beenmade by other means of parameterizations using, e.g., world data on radio measurements.

While we are using RDAS for answering the design questions of the proposed radio detectorarray, a task force is integrating the radio software into the Auger Offline framework (see section7). With this effort it will be possible to simulate and reconstruct all three detector systems,surface detector, fluorescence detector, and radio detector, within one framework, allowing forcross checks and combination of complementary shower information.

5 Site layout

It is proposed to set up the radio antenna array at the site of the AMIGA array. The situationis outlined in Fig. 11. For reference, tank names of the surface array are indicated. The largehexagon indicates the position of the AMIGA infill array (water-Cherenkov detectors) and thesmaller hexagon represents a possible infill to the infill array. These arrays are located in thefield of view of the HEAT fluorescence telescopes (the latter are just outside the left border ofFig. 11). In the map the position of the CRS, an abandoned train station, a high voltage powerline, and a fence are indicated.

fence

power line

fence

popo

trainstation

CRSHEAT

Figure 11: Layout of the proposed antenna field.

Baseline parameters for the antenna array are about 150 antennas distributed over an areaof approximately 20 km2. It is assumed that the construction will be divided into three stages,starting with about 22 antennas in a prototype cluster, followed by further 52 antennas, andfinally 85 antennas. In the map, the locations of the antennas are marked as red boxes. Boxeswithout border correspond to stage 1, black borders to stage 2, and white borders to stage 3.To record large event numbers over the whole energy domain (E > 1017.2 eV), the configurationincludes several antenna spacings. Regions with high antenna density should be to the left-handside of the area, close to the HEAT fluorescence telescopes.

Different layout scenarios have been investigated and detailed in Ref. [32]. The proposed

27

The Site

• ~20 km2

• ~150 antennas

• operation together with infill/HEAT/AMIGA

• three antenna spacings to cover efficiently 17.2 < lg E < 19.0

• three deployment stages (22 + 52 + 85 antennas)

• CRS: central container for DAQ & workshop; solar power2

Digital Electronics (NIKHEF and RU)

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GPS receiver (timestamping) Cyclone III FPGA (triggering & readout)

4 channel, 200 MHz 12b ADCs DC/DC conv.

(shielded)

XScale-based PC ���card (buffering, comms)

Ethernet

serial interface

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Triggering in FPGA

•  Main challenge: impulsive RFI

•  Time-domain pulse analysis

•  Basics –  threshold trigger –  baseline integration / subtraction

•  Enhancements –  (max, min) number of threshold crossings –  time between crossings –  veto period before pulse –  pulse height vs. number of crossings –  dynamic noise levels –  …

•  Complexity: 3K logic gates / channel

•  Optional(?) narrowband rejection –  FFT filter iFFT –  digital notch filters (e.g. LOFAR)

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signal  threshold  

noise  threshold  

baseline  

Tper  

Tcmax  

Tprev  

1820 1840 1860 1880 1900 1920 1940 1960 1980 2000 2020

1700

1800

1900

2000

2100

2200

2300

2400

2500

Graph

hFFT0Entries 1024Integral 1.587e+06

0 10 20 30 40 50 60 70 80 90 100

10

210

310

410

hFFT0Entries 1024Integral 1.587e+06

hFFT0

OK   reject  

Comparison with Lunar Requirements

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AERA   Moon   Notes  

Trigger  rate   >100  Hz   30  Hz   OK;  can  also  relax  trigger  

Frequency  range   30-­‐80  MHz   10-­‐200  MHz   Faster  sampling:    see  below  

Background   Man-­‐made  RFI  

?   With  self-­‐shielding,  OK?  

Power   9W      35%  ADCs    15%  FPGA    15%  CPU      etc.  

1-­‐2  W?   CPU  hard  or  so[  core  (buffering,  comms,  compression?)  

Low-­‐power  digi`zer  (e.g.  ATWD  /  Labrador):  switching  cap.  array,  >  1Gs/s,  O(10  mW)  /  channel