KASCADE is an extensive air shower experiment array to study the cosmic ray primary composition and the hadronic interactions in the energy range E₀=10¹⁴−10¹⁷eV. The experiment is situated on site of the KIT, Campus North (the former Forschungszentrum Karlsruhe) (49,1°N, 8,4°E) at 110m a.s.l, corresponding to an average atmospheric depth of 1022g/cm². One of the main results obtained by KASCADE is a picture of increasingly heavier composition above the 'knee' caused by a break in the spectrum of the light components. Conventional acceleration models predict a change of the composition towards heavier components.

The main detector components of KASCADE are the KASCADE array, the Muon Tracking Detector and the Central Calorimeter to measure the hadronic component of the showers.

As an extension of the KASCADE experiment KASCADE-Grande was built in 2003 by reassembling 37 stations of the former EAS-TOP experiment running successfully between 1987 and 2000 at Campo Imperatore, Grand Sasso Loboratories, Italy.

More about KASCADE & KASCADE-Grande.

The KASCADE array consists of 252 scintillator detector stations setup in a regular grid with 13m spacing covering an area of 200x200 m² organized in 16 clusters 4x4 stations each (see figure 'Array Setup') equipped with unshielded and shielded detectors for the measurement of the electromagnetic and muonic shower components simultaneously and independently. Each station contains unshielded liquid scintillation detectors to measure the electron/photon component. Additionally, the outer 12 cluster (marked yellow in the figure) have lead and iron absorber sheets (10cm Pb and 4cm Fe) underneath the e/γ detectors to measure only the muonic shower component (see figure 'Array-Stations').
For electrons the energy threshold is about 5 MeV. Muons, detected below the shielding by in plastic scintillation counters of 3.2m², have a threshold of 230 MeV.
The power supply and the electronic readout of the detectors in the stations are organized in 16 clusters of 16 stations each, except for the four inner clusters, which contain only 15 stations (see figure below). Each cluster is able to take data independently. Data are accumulated in the electronic station of each cluster and transmitted to the data acquisition system (DAQ).
The time resolution of the detector is 0.77 ns. This excellent timing leads to an angular resolution of about 0,1° for the arrival directions of the showers which enables us to search for large scale anisotropies as well as for cosmic ray point sources.

Fig.: 'Array Setup' - Schematic view of the KASCADE array.

Fig.: 'Array Stations' - Schematic view of the Array Detector Stations.

An important part of the information about the mass and energy of the shower inducing primary particle is transported within the hadronic air shower component to ground level. The hadrons and their interactions are vital for the understanding of the shower development within the atmosphere. Therefore, the hadron calorimeter is one of the major components of KASCADE, located in the centre of the KASCADE array.

The main component of the KASCADE Central Detector is an Iron-Sampling- Calorimeter 16×20m² in size. Between the iron absorbers are 9 layers of active media. 8 Layers are equipped with roughly 10.000 liquid ionisation chambers, the 3rd layer from top houses scintillation counters used as Trigger for the components of the central detector and to measure the arrival times of the shower particles.

Below the iron absorber is an additional layer of liquid ionisation chambers located, followed by 32 Multiwire Proportional Chambers used to detect high energetic muons, and a layer of Limited Streamer Tubes.

Fig.: 'Central Detector Setup' - Schematic view of the KASCADE central detector system.

The detector is an iron sampling calorimeter with liquid ionisation chambers as active media. Its size corresponds to the size of the shower core of high-energy air showers. The absorber consists out of several layers of iron with a thickness of 12 cm in the upper part increasing to 24 cm and 36 cm in the lower part, respectively. A 5 cm lead filter on top of the calorimeter serves to suppress the electromagnetic component. The 77 cm concrete ceiling of the detector basement acts as last absorber layer. The absorber corresponds to 1460 g/cm² or 11.4 hadronic interaction lengths. Hadrons up to an energy of about 25 TeV can be absorbed in the calorimeter completely.

More than 10.000 liquid ionisation chambers serve as active components, installed in eight layers between and below the iron absorbers. The ionisation chambers are based on a new detector technology developed at the Institute for Astroparticle Physics of the KIT. The KASCADE hadron calorimeter is the first experiment using warm ionising liquids for a large detector. The chambers achieve a large dynamic range of about 6×10⁴, only limited due to the amplification electronic. Therefore, signals from a minimum ionising particle as well as from hadrons in the shower core can be measured up to primary energies of 10¹⁶ eV without saturation. Due to the fine lateral segmentation and the read-out of the calorimeter in 40.000 electronic channels, hadrons with an energy EH>20 GeV can be measured in the calorimeter. They can be separated from each other when the distance of their shower axis is above 40 cm. The spatial resolution of the calorimeter is about 11 cm and the angular resolution is in the order of 5^o. The energy resolution is 30% for hadrons with 100 GeV decreasing to 15 % for E_had=25 TeV.

Fig.: Hadron tracks as reconstructed in the central calorimeter: shower core - 3 single tracks - 25TeV single hadron

KASCADE-Grande is the extension of the Extensive Air Shower detector array KASCADE, realized to expand the energy range for cosmic ray studies from 10¹⁴- 10¹⁸ eV primary energy range up to 10¹⁹ eV. This is achieved by extending the area covered by the KASCADE electromagnetic array from 200×200m² to 700×700 m² by means of 37 scintillator detector stations of 10 m² active area each. This new array named GRANDE provides measurements of the all-charged particle component of extensive air showers, while the original KASCADE array particularly provides information on the muon content.

Fig.: Grande Layout 37 detector stations at KIT Campus North, Karlsruhe

The Grande array is composed of 37 detector stations installed over an irregular triangular grid with an average spacing of 137 m, thus covering an area of approximately 0.5km². Each detector station includes a total of 10m² of plastic scintillators subdivided into 16 individual modules each viewed from the bottom by a XP3462B photomultiplier for timing and particle density measurements (High Gain PMTs). The four central modules are equipped with an additional PMT of the same type which is operated with a lower high voltage value optimized for high linearity even at large particle densities (Low Gain PMTs).

Fig.: Grande Station Layout, left: half a station; right: sketch of 16 scintillators and PMTs

The Grande array is organized in 18 overlapping trigger clusters. Each cluster includes seven detector stations: six in a hexagonal shape and a central one. The data acquisition is triggered by either a 4/7 coincidence from a cluster (4 stations in a compact configuration, trigger rate: ˜5 Hz) or by a central trigger coming from KASCADE (trigger rate: ˜3.5 Hz). In addition, any full 7/7 coincidence (rate: ˜0.5 Hz) from one of the 18 clusters is transmitted also to KASCADE as a KASCADE-Grande trigger to start KASCADE-Grande event aquisition.

Fig.: Grande Trigger Layout, 18 trigger hexagons

The two examples of Grande Events are screenshots from the Grande Event Display. On the left sides you see the energy deposits in the Grande stations. The warmer the color the higher the energy. On the right sides the corresponding arrival times. As the colours used are normalised to the difference between the first and the last time stamp, it cannot be used as a direct measure for the zenith angles

Fig.: Grande event display, 2 examples

The radio antennas of the LOPES experiment (LOfar PrototypE Station), distributed over the KASCADE detector array, are designed to measure the radio emission of cosmic ray air showers in the frequency range from 40 to 80 MHz. In an offline analysis LOPES is using reconstructed parameters provided by the KASCADE-Grande data processing from the particle detectors such as location of the shower core, shower direction, energy deposited in the particle detectors, reconstructed total number of electrons and muons at ground level.

Fig.: Setup for LOPES-30 radio detector array on the original KASCADE site or close by.

LOPES data taking is invoked by a high energy trigger from KASCADE or by a Grande trigger which leads to an energy threshold of 10¹⁶eV.The capability to digitally form a cross-correlation beam (CC-Beam) with the electric field strength traces of all antennas makes LOPES a radio interferometer. A beam is formed by shifting the electric field strength traces of each antenna accordingly to the arrival time of the radio pulse, in order that the radio pulse of each trace overlaps (Fig. a). After shifting the traces a cross-correlation between them is calculated to form the cross-correlation beam (CC-beam) (Fig. b). The cross-correlation amplitude is a measure for the strength of the air shower induced radio pulse. The CC beam is used for the analysis of the LOPES data as a useful tool to reconstruct the air shower arrival direction, the primary energy, and mass.

Fig.: Example of a LOPES event: electric field strength in individual antennas (different colors) (left) which are calibrated and corrected; cross-correlation and power beam (right).

'COMBINED' is a virtual dectector consisting of the two detector components 'KASCADE' and 'GRANDE' combined in joint analysis methode.
Until now the two components have been analysed independently of each other, although the GRANDE data analyses used the shielded detectors of KASCADE for the reconstruction of the total number of muons. Treating both detectors as one has several advantages over the standalone analyses. For events with the shower core located in the KASCADE array, the main advantage is the increased distance range in which sampling points are available. For showers inside GRANDE the main benefit is the availability of 252 additional detector stations among which three GRANDE stations are located. This results in a more accurate reconstruction of the shower observables.