A project to detect the radio-frequency pulse associated with extensive air showers of cosmic rays is described briefly. Prototype work is being performed at the CASA/MIA array in Utah, with the intention of designing equipment that can be used in conjunction with the Auger Giant Array proposal

Rosner, Jonathan L

Wilkerson, J F

CERN Document Server

EFI-97-10
hep-ex/9702008
DETECTION OF THE RF PULSE
ASSOCIATED WITH COSMIC RAY AIR SHOWERS 1
Jonathan L. Rosner
Enrico Fermi Institute and Department of Physics
University of Chicago, Chicago, IL 60637
and
John F. Wilkerson
Department of Physics
University of Washington, Seattle, WA 98195
ABSTRACT
Initial results of a project to detect the radio-frequency pulse associated
with extensive air showers of cosmic rays are described briefly. This work
is being performed at the CASA/MIA array in Utah, with the intention of
designing equipment that can be used in conjunction with the Auger Giant
Array proposal.
1 Motivation
As a result of work in the 1960’s and 1970’s [1, 2], some of which has continued beyond
then (see, e.g., [3, 4, 5, 6]), it is recognized that air showers of energy 1017 eV are
accompanied by radio-frequency pulses, whose polarization and frequency spectrum
suggest that they are due mainly to the separation of positive and negative charges
of the shower in the Earth’s magnetic eld [7]. The most convincing data have been
accumulated in the 30{100 MHz frequency range. However, opinions have diered
regarding the strength of the pulses, and atmospheric and ionospheric eects have led
to irreproducibility of results. In particular, there may also be pulses associated with
cosmic-ray-induced atmospheric discharges [8]. There are reports of detection at MHz
or sub-MHz frequencies [3, 4, 5], which could be associated with such a mechanism.
Signals above 100 MHz have also been reported [6].
A study is being undertaken of the feasibility of equipping the Auger array with
the ability to detect such pulses. It is possible that the higher energy of the showers to
which the array would be sensitive would change the parameters of detection. Before
a design for large-scale RF pulse detection can be produced, it has been necessary to
retrace some of the steps of the past 30 years by demonstrating the existence of the
pulses for 1017 eV showers, and by controlling or monitoring some of the factors which
led to their irreproducibility in the past. RF pulses may be able to provide auxiliary
information about primary composition and shower height [2].
1Based on an appendix to proposal for the Auger Air Shower Array
1
In this report we describe the prototype activity at the CASA/MIA site, note
related activities, and set forth some considerations regarding plans for the Auger
project. More concrete plans for RF detection at Auger must await the outcome of the
ongoing work at the CASA/MIA site.
2 CASA/MIA Prototype setup
In order to verify the claim [1, 2] that 1017 eV showers are accompanied by RF pulses
with signicant energy in the 30{100 MHz range, a prototype detector has been set
up at the CASA/MIA site in Dugway, Utah. This section describes the status of that
eort.
2.1 Large-event trigger
A trigger based on the coincidence of several muon \patches" was set to select \large"
showers with a rate of 30 { 50 per hour [9]. The MIA Patch-Sum trigger was sent
into a fan-in/fan-out. From this, the signal was put into a LeCroy 821 Discriminator,
amplied, and sent over a cable to a trailer located just to the east of the CASA array.
The location of the trailer outside the array was dictated by the intense RF noise within
the array determined by surveys taken in 1995.
The electronics was set to trigger at 7 of the eight outermost muon patches. This
was estimated to correspond to a minimum shower energy of about 21016 eV, based on
the rate at 1018 eV of 1/km2/day/sr. At this level good correlation could be established
between trigger pulses and events recorded by the CASA data acquisition system.
2.2 Monitoring of RF noise environment
It was a concern that the RF noise of the local electronics and the presence of an exten-
sive lightning-protection array might dictate the placement of the RF pulse detection
system outside the periphery of the array. The behavior of a single CASA board was
investigated at the University of Chicago. The various clock signals were detected at
short distances (< 1 m) from the board, but a much more intense set of harmonics of
78 kHz emanated from the switching power supplies. These harmonics persisted well
above 100 MHz. At 144{148 MHz, they overlapped, leading to intense broad-band
noise.
A spectrum analyzer, obtained from the now-defunct SSC Laboratory, was used to
make a broad survey of the RF noise at the CASA site in various frequency ranges
and at various locations. Surveys indicated considerable noise within the array, but a
much lower level sitting just outside the array. Consequently, it was decided to set up
a special trailer for monitoring RF pulses just to the east of the array.
2
2.3 Data acquisition
A log-periodic antenna sensitive to 26 { 170 MHz was mounted about 30 meters to the
east of the CASA boundary, at an elevation of about 10 meters to place it just above
the lightning protection grid. A digital storage scope was used to register ltered and
preamplied RF data on a rolling basis. These data were then captured and stored
upon receipt of a large-event trigger.
The experiment was repeated using successively greater amounts of amplication
and narrower band-pass lters. Data were taken using two systems on two separate
computers (at dierent times), allowing for analysis both by Wilkerson and students
at the University of Washington and by Rosner at Chicago. Wilkerson’s data are still
being processed, so the preliminary results to be mentioned below will be based on
Rosner’s analysis.
2.4 Results
The most recent conguration involved feeding the signal from the antenna through
Mini-Circuits BHP-25 and BLP-30 lters, with 6 dB points of 23 and 39 MHz, a Mini-
Circuits ZFL-500LN preamplier with 26 dB of gain, a Mini-Circuits BBP-30 bandpass
lter with 6 dB points 24.5 and 37 MHz, and another ZFL-500LN preamplier. This
conguration was arrived upon after numerous runs in which eorts were made to
minimize noise from sources such as computers, monitors, and the preampliers them-
selves. It was employed for an 8-1/2 hour run during which 305 triggers were received.
Each trigger caused 50 s of RF data, centered around the trigger and acquired at 1
GSa/s, to be saved on a Tektronix TDS540B digitizing oscilloscope. These data were
then passed using a GPIB interface to a Dell XPS200s Pentium computer, where they
were stored for future analysis.
Events were scanned for large positive peaks. Three points each exceeding 15.2
mV on the oscilloscope input were demanded within a window of 10 ns, in order to
eliminate both constant background noise and very-high-frequency transients. If an
event contained such a peak, the largest peak within an associated group of duration
less than 300 ns was then identied and its height was plotted as a function of time
relative to the trigger pulse. The results are shown in Fig. 1(a).
A clear signal is visible in the window between −10 and −5 s relative to the
trigger. The trigger pulse itself requires several s to be formed at the CASA site,
and an additional 2.15 s to propagate to the RF detection trailer. Consequently, the
signal is likely to be due to the prompt RF signal associated with showers.
The pulses within the window from −10 to −5 s in Fig. 1(a) are associated with
showers whose cores nearly all lie east of the center of the CASA array, as shown
in Fig. 1(b). This result is in accord with the rapid decrease of pulse intensity with
distance from the core observed by the Haverah Park group [2].
3
Figure 1: (a) Maximum pulse height as a function of arrival time relative to trigger.
(b) Distribution of cores with respect to center of CASA array for events in (a) between
10 and −5 s.  : 15:2 < Vpk < 20 mV; + : 20  Vpk < 30 mV; fancy points: 30
mV  Vpk. Here (x; y) = core position (east, north) of array center. The antenna was
located at (x; y) ’ (270; 0) m.
2.5 Near-term plans
A total of more than 5000 triggers, obtained under various conditions of ltering,
preamplication, and noise reduction, remains to be analyzed. Preliminary results from
runs in September and December of 1996 indicate that about 1 in 10 of these triggers
may contain information on RF pulses from air showers. Shower sizes, core locations,
and incident shower angles will be correlated with time, duration, and intensity of radio
bursts. Data must also be collected with the CASA detector disabled (leaving only the
MIA trigger), in order to exclude the possibility that signals are due to pulses involved
in CASA data transfer.
A non-imagining Cherenkov light array (BLANCA) has recently been added at the
CASA site. RF data will be collected during at least one period when BLANCA is
active in order to utilize the additional information that BLANCA may provide on
shower energy and primary composition.
Still to be performed are experiments which seek to monitor RF pulses at lower
frequencies and at greater distances from the array. For these pulses, whose strengths
may be correlated with atmospheric electric elds, it is planned to monitor such elds
with the help of a eld mill, which Rosner has recently constructed. A group working
at the AGASA array in Japan [3] has detected pulses associated with large air showers
(typically above 1018 eV) at frequencies below 500 kHz. These pulses are of several
microseconds duration. While they can be associated with cores more than 1 km
away from the antenna, they do not always occur, even for very large showers. It
is suspected that they may be associated with an atmospheric discharge mechanism.
Consequently, once suitable low-frequency lters are found to eliminate signals from
the AM broadcast band and the 284 kHz air trac control beacon at Dugway, a survey
4
of pulses below 500 kHz will be undertaken at Dugway. Simultaneous monitoring of
electrostatic atmospheric electric eld gradients at ground level will provide at least a
rst look at the possibility that a discharge mechanism is involved.
Wilkerson was engaged in projects at Los Alamos whose aim was detection of
electromagnetic pulses, including those possibly produced by cosmic-ray-induced elec-
tromagnetic discharges, with frequencies in the 30 { 100 MHz range. Part of this work
included building hardware for self-triggering on short duration wide-band RF pulses.
Many of the pulse identication, fast-digitization and memory problems are identical
to those for pulse detection at CASA/MIA. Time-frequency plots have been obtained
which are exactly those one would generate in a survey at CASA/MIA. Wilkerson has
also encountered similar requirements for digitization of SNO data. His estimate is
that one can use Maxim MAX 100 A/D chips for less than $1K per channel, but that
feeding their output into memory may well amount to another $1K per channel. Other
references on digitizers have been obtained [10, 11].
Wilkerson has moved his data acquisition system to CASA and has taken data
from the digitizing scope for analysis at the University of Washington. Time-frequency
plots obtained for a day’s data in September, 1996, already showed behavior consistent
with Fig. 1. In the near future the RF pulse detection system will be activated with a
suitable set of lters, in order to detect pulses from air showers without the need for
an external trigger.
In the future the spectrum analyzer obtained by Rosner may of help in detecting
potential sources of interference to RF communications in the Auger project.
3 Related activities
3.1 Status of GHz detection
David Wilkinson, who visited the University of Chicago during the spring of 1995,
has promised to look into the power radiated at frequencies of several GHz, where
new opportunities exist associated with the availability of low-noise receivers. These
techniques have now been implemented in the RICE project [12], which seeks to detect
pulses with frequency components around 250 MHz in Antarctic polar ice.
3.2 Other options
Dispersion between arrival times of GPS signals on two dierent frequencies may serve
as a useful monitor of air shower activity. The possibility of correlation of large showers
with such dispersion events will be investigated.
It may be possible at the CASA/MIA site to monitor commercial broadcast signals
in the 55 - 88 MHz range to detect momentary enhancements associated with large
showers, in the same sense that meteor showers produce such enhancements. Television
Channels 3 and 6, for which no nearby stations exist, oer one possibility.
5
4 Considerations for Auger project
At present we can only present a rough sketch of criteria for detection in the 30{100
MHz range. Data would be digitized at a 500 MHz rate at each station and stored in
a rolling manner, with at least 20 microseconds of data in the pipeline at any moment.
Upon receipt of a trigger signaling the presence of a \large" shower (> 1018 eV), these
data would be merged into the rest of the data stream at each station.
Per station, we estimate the following additional costs, in US dollars, for RF pulse
detection:
Two antennas and protection circuitry: 200 (a)
Mounting hardware: 100 (b)
Cables and connectors: 200 (c)
Preamps: 500 (d)
Digitization and memory electronics: 2000 (e)
Total per station: 3000 (f)
(a) Two military-surplus log-periodic antennas; crossed polarizations. Dierence signal
to be detected.
(b) Highly dependent on other installations at site. Antennas are to be pointed verti-
cally but optimum elevation not yet determined.
(c) Antennas are mounted near central data acquisition site of each station, but su-
ciently far from any sources of RF interference such as switching power supplies.
(d) Commercial GaAsFET preamps and gas discharge tubes.
(e) Subject to prototype development experience. Power requirements not yet known.
(f) The number of stations to be equipped with RF detection will depend on prototype
experience.
The above estimate assumes that one can power the preamps and DAQ electronics
from the supply at each station without substantial added cost. It also assumes that
a \large-event trigger" will be available at each station. A further assumption is that
the dierence signal suces to characterize the pulse. Additional preamplication
and DAQ electronics may be required if this is not so. One consideration may be
the acquisition of antennas robust enough to withstand extreme weather (particularly
wind) conditions.
For detection at frequencies above or below 30{100 MHz, the criteria are not yet
well enough developed to permit any cost estimate.
5 Acknowledgments
We thank Kevin Green for setting up and studying the \large-event trigger," Rachel
Gall for assisting him in this work during the summer of 1996, and Mike Cassidy for
help in all stages of the experiment. Funds provided by the Enrico Fermi Institute and
by the Physics Department of the University of Chicago were instrumental in allowing
this work the be undertaken. Thanks are also due to Jim Cronin, Lucy Fortson, Dick
6
Gustafson, Gerard Jendraszkiewicz, Larry Jones, Brian Newport, Rene Ong, Dave
Peterson, Leslie Rosenberg, Dave Smith, Augustine M. Urbas, and Dave Wilkinson for
help in various phases of this work. J. L. R. is grateful to M. Nagano for hospitality
at the Institute for Cosmic Ray Research in Tokyo, and to him and K. Kadota, F.
Kakimoto, and M. Teshima for discussions. This work was supported in part by the
Louis Block Fund of the University of Chicago.
References
[1] P. R. Barker, W. E. Hazen, and A. Z. Hendel, Phys. Rev. Lett. 18, 51 (1967); W.
E. Hazen, et al., ibid. 22, 35 (1969); 24, 476 (1970).
[2] H. R. Allan, in Progress in Elementary Particles and Cosmic Ray Physics, v. 10,
edited by J. G. Wilson and S. G. Wouthuysen (North-Holland, Amsterdam, 1971),
p. 171, and references therein; V. B. Atrashkevich et al., Yad. Fiz. 28, 366 (1978).
[3] K. Kadota et al., Proc. 23rd International Conference on Cosmic Rays (ICRC-
23), Calgary, 1993, v. 4, p. 262; Tokyo Workshop on Techniques for the Study of
Extremely High Energy Cosmic Rays, Tanashi, Tokyo, 27 { 30 Sept. 1993.
[4] C. Castagnoli et al., Proc. ICRC-23, Calgary, 1993, v. 4, p. 258.
[5] P. I. Golubnichii, A. D. Filonenko, and V. I. Yakovlev, Izv. Akad. Nauk 58, 45
(1994).
[6] R. Baishya et al., Proc. ICRC-23, Calgary, 1993, V. 4, p. 266.
[7] F. D. Kahn and I. Lerche, Proc. Roy. Soc. A 289, 206 (1966); S. A. Colgate,
J. Geophys. Res. 72, 4869 (1972).
[8] R. R. Wilson, Phys. Rev. 108, 155 (1967); R. A. Roussel-Dupre, A. V. Gurevitch,
T. Tunnell, and G. M. Milikh, Los Alamos National Laboratory report LA-12601-
MS, November, 1993.
[9] R. Gall and K. D. Green, UMC-CASA note, Aug. 23, 1996 (unpublished).
[10] M. Atiya, M. Ito, J. Haggerty, C. Ng, and F. W. Sippach, Nucl. Inst. Meth. A
279, 180 (1989).
[11] D. Bryman, J. V. Cresswell, M. LeNoble, and R. Poutissou, IEEE Trans. NS-38,
295 (1991).
[12] RICE Project, D. Z. Besson et al., proposal to National Science Fundation; G. M.
Frichter, J. P. Ralston, and D. W. McKay, \Toward radio detection of PeV neu-
trinos on the cubic kilometer scale," report astro-ph/9606008, to be published in
Neutrino Telescopes (Venice, 1996), Proceedings of the 7th International Sympo-
sium on Neutrino Telescopes, Venice, Feb. 27 { Mar. 1, 1996, edited by M. Baldo-
Ceolin (INFN, Instituto Veneto di Scienze, Lettere ed Arti, 1996); Phys. Rev. D
53, 1654 (1996).
7


Detection of the RF Pulse Associated With Cosmic Ray Air Showers

Abstract

Similar works

Full text

Available Versions

CERN Document Server