SPASE shack

@ South Pole sunset 2002

Contact Info

Point Source Analysis

SPASE is
supported by
National Science
Fundation

SPASE

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 And Neutrino Detector Array), 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 .