Tianshan Radio Experiment for Neutrino Detection (TREND) was an antenna array devoted to the autonomous radio-detection of high energy cosmic rays deployed at the Tianshan Mountains in the XinJiang province of China. It includes 50 antennas for a total area of 1.2 km2. It is the first experiment that showed that autonomous radio detection of air showers is possible with a high background rejection outside of polar areas (Ardouin et al. 2011).
It is the first construction stage of GRAND, aiming at testing whether radio detection of air showers is possible with a high efficiency and a significant background rejection. It consists of 35 radio stations deployed at the same site as TREND. The GRANDProto35 antennas contain an additional vertical arm that allows to sample three polarization directions. This stage uses a fast data acquisition system (DAQ) allows recording of all transient signals under standard background conditions at the array site, which will significantly enhance the air-shower detection efficiency compared to TREND. To cross-check the efficiency of the antennas, GRANDProto35 includes an autonomous surface array of particle detectors, co-located with the antenna array. This array is composed of 24 scintillators and a separate DAQ chain and trigger logic. Offline comparison between the scintillator and radio detector data will confirm the radio detection efficiency and evaluate the noise level in the recorded radio date. GRANDproto35 started to be deployed in summer 2018.
GRANDproto300, the engineering stage of GRAND, will provide experimental validation of our simulations of radio detection of horizontal showers. It will span an area of 100‑300 km2, consisting of 300 antennas, with a square grid layout with a 1 km inter-antenna spacing. GRANDProto300 will be the largest self-triggered radio array for air-shower detection targeting cosmic rays in the range 1017-1018 eV. Up to 105 cosmic-ray events are expected in the first two years of operation. In addition, by using the correlation between the number of muons in a shower and the depth of shower maximum, GRANDproto300 will achieve a precise measurement of the mass composition. GRANDProto300 will be in a privileged position to study the transition between galactic and extragalactic cosmic rays. The spectrum and mass composition of cosmic rays obtained with GRANDProto300 will be compared to results from previous experiments in order to confirm that very inclined air showers can be detected and accurately reconstructed using radio, hence validating an important step towards further stages of GRAND.
It is the first large element of the full GRAND array. GRAND10k will be the first radio array that is sensitive to UHE neutrinos. It will consist of 10,000 antennas deployed over an area selected for its suitability for the detection of neutrino‑initiated air showers — a hotspot. Located on the southern rim of the Tian Shan mountains, GRAND10k would yield a integral sensitivity to UHE neutrinos of 7.2 10-9 GeV cm-2 s-1sr-1 after 3 years. GRAND10k will also be large enough to detect giant radio pulses.