@ South Pole sunset 2002
Point Source Analysis
(Bird's Eye View of the SPASE2 Array)
SPASE is a large-area air shower array established at the geographic South
Pole for the detection of cosmic rays with primary energies above 50 TeV.
At these energies, the flux of events is too low to measure on considerably
smaller short duration balloon flight experiments or more expensive satellite
experiments. The array is situated on the Antarctic Plateau near the U.S.
Amundsen-Scott South Pole Station. The unique advantages of this location
are the very high altitude (~10,000 ft) which minimizes the atmospheric
overburden, the circumpolar nature of potential astrophysical sources,
all of which remain at a constant zenith angle, and the existence of the
world's largest muon and neutrino telescope,
AMANDA (the Antarctic Muon
below the array. SPASE is supported by the Office of Polar Programs of the
National Science Foundation.
The South Pole Air Shower Experiment began in 1987. SPASE-1 was
turned on December 21, 1987 under the direction of Alan Watson (Leeds)
and Martin A. Pomerantz (Bartol). The project was a joint effort
of the Bartol Research Institute
of the University of Delaware
and the cosmic ray group of the University
of Leeds. SPASE-1 operated for 10 years until it was removed at the end of
1997. SPASE-1 consisted of 16 one sq. meter scintillator detectors at 14
locations on a 30 meter triangular grid. enclosing an area of 6200 sq.
meters; The primary purpose of SPASE-1 was to search for point
sources of ~100 TeV gamma-radiation.
Construction of AMANDA began in the 1990's. As AMANDA came into operation the
SPASE-1 detector was used as a survey device to provide
independent information about the location of AMANDA modules.
A new, larger array SPASE-2 was laid out in 1995, consisting of 120
scintillator modules spread over an area of roughly 16,000 sq. meters,
with the express purpose of working in coincidence with AMANDA. The
aerial photographs above show the array as it appeared on 10 December
1995 just after deployment was completed. Cables for 15 of the stations
were laid out in February, 1995 and are therefore not visible. The
building in the center contains the high voltage supply for the photomultipliers
and the data acquisition electronics. The other building is a temporary
Jamesway building that was used for deployment operations.
These modules are clustered in 30 stations, each consisting of 4 detector
modules containing a hexagonal scintillator of 0.2 m2 viewed
by a photomultiplier. This picture shows the station 16
as viewed from the deck of the central building, with stations 12, 17 and 18 in the
distance. The structure of each station and inside the detector can be seen in this
picture. In addition to the 120 scintillator
modules, the Leeds group positioned nine
air-Cerenkov telescopes (VULCAN) within and surrounding the array to measure
the Cherenkov light generated by showers as they penetrate Earth's atmosphere. The
SPASE2 DAQ electronics is in the
SPASE2 electronics tower.
One of the biggest advantages of having SPASE at the South Pole is its
proximity AMANDA. The SPASE array measures the number of charged particles
in the shower that reach the surface, while (for showers heading in the
right direction) the AMANDA detector provides a measure of the number of
high energy muons which penetrate deep into the icecap. For these same
events, during dark periods in the winter, the VULCAN telescopes measure
the lateral distribution and intensity of Cherenkov light at the surface
which is correlated with the height of interaction of the primary particle.
By measuring as many shower parameters as possible we hope to determine
the primary composition of cosmic rays over this crucial energy range to
help understand the sources and acceleration sites of such particles.
The South Pole Air Shower Experiment ended as a separate project on 30
June 2004. The SPASE-2 detector array is now incorporated into
the IceCube project
as part of its surface component, IceTop .
Last modified 08/03/2004