ROOM
91
Space Science
mighty trans-Antarctic mountains from the
nearest research stations, nine stations are
currently in operation to test the feasibility of the
detection concept.
Every station is equipped with log-periodic
dipole antennas. The antennas are highly sensitive
and directional, meaning that they are more likely
to detect a signal coming towards their front than
towards their rear. These antennas are placed front
first in the snow on top of the ice enabling them to
monitor the ice underneath for neutrino interactions.
The detection concept benefits from its location on
the ice-shelf and having an ocean underneath, as the
interface between ice and water acts as a mirror for
radio emission. This configuration allows ARIANNA
to simulate a detector with a large field of view, thus
helping to overcome the problem of trying to pinpoint
the location of neutrino sources in the sky.
Nine stations are certainly not enough to
see cosmogenic neutrinos but they do act as
pathfinders to prove that the technology will work.
The stations rely only on solar and wind power
and, during the endless day in the polar summer,
the stations are up 24 hours a day collecting data.
Winter is another matter, however, as the
operations are not quite stable and a perfect
balance has to be found using cold-resistant
batteries that buffer energy from wind-generated
power during the windy periods. What sounds
perfectly straightforward in normal conditions is
not quite that straightforward in Antarctica. The
wind-turbines need to be sturdy enough to survive
hard Antarctic storms and sensitive enough to
create sufficient power from a small breeze to
allow for continuous operations. On top of that,
extreme temperatures put a strain on batteries and
detector moving parts, and with a site that is totally
inaccessible fromMarch through to October, it is not
hard to imagine what other problems that brings.
In spite of this, once operational, the stations
use very little power. With less than 5 watts, the
stations are able to digitize the detected radio
waves at up to 2 billion samples (Gsamples) per
second and a sophisticated chip searches for
coincidences between signals crossing a defined
amplitude threshold in different antennas.
Currently the stations are equipped with long-
range wifi and satellite communication via the
Iridium network, commonly used for telephone
connections in polar regions.
While the long-range wifi allows for a high
through-put of data, it is more expensive, power-
consuming and limited in operation during bad
weather. Satellite communication is more reliable;
however, it is limited to binary short-burst
messages, essentially text messages, which restricts
the amount of data that can be sent.
Still, the ARIANNA site has proven to be so radio-
quiet that there are very few false positive triggers and
the text messages have proven to be sufficient to get
all data out in real-time. The stations autonomously
connect to a server in the United States to check
whether new instructions are available and then
send their data at a given time-interval. This method
ensures that there is virtually no human interaction
needed - an important feature for an array that is
planned to consist of more than 1000 stations and will
operate for more than five years.
Deciphering the good from the bad
Since the pilot-stage array of ARIANNA is
comparatively short, there are no neutrino reports
Overview of the
position of ARIANNA.
Two stations in the field.
While it is highly unlikely for
anything but an elementary
particle to cause a flash of light
in dark ice, every electrical
machine creates radio emission
ARIANNA
Anna Nelles/ARIANNA
