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NAOC, May 14, 2013.

Participants: Pierre Chauveau, Deng Jianrong, Gu Junhua, Hu Hongbo, Liu Zhenan, Olivier Martineau-Huynh, Wu Xiangping

- Presentation of the context for DAQ development (see slides):

  • Monte-Carlo simulations show that a giant radio-array deployed over a mountaineous area (GRAND) could constitute a very sensitive neutrio telescope: preliminary studies indicate that a one-year operation of a 200x200km\x{00b2} array resulting in no neutrino candidate would allow to derivea limit on the cosmic neutrino flux above 10^17eV 10 times better than the present best (IceCube), and 2-3 times better than the best project (ARIANNA).
  • Background rejection would be a key issue in such an experiment: data taking with the TREND-50 array indicate that around 10^13 background events would be recorded on GRAND in a year, while 10 to 100 neutrino events would be expected in the same period of time.
  • Polarization information of the detected radio signal could be a key issue to perform an efficient background rejection. Indeed signal from an extended air shower is polarized linearly, perpendicularly both to the geomagnetic field and the direction of origin of teh shower.
  • It is proposed to deploy a prototype to evaluate quantitativelly the potential for background rejection of this method. The GRAND-proto array would be composed of:
    • 30 antennas with 2 arms measuring respectivelly the East-West and vertical components of the triggering elm wave.The design of this double polar antenna is based on the one developped by the SUBATECH group and adopted by the AUGER collaboration for their radio project AERA.The Xi'An XiDian university would be in charge of their production. The total price for 30 units is estimated around 250 kRMB.
    • 20 scintillators forming an array dedicated to the detection of the EAS particles. A proposal was submitted to NSFC to fund this setup.
  • This hybrid prototype would be deployed along the South-North arm of the 21CMA array. An algorithm based on the polarization information of the detected radio events would be applied in an offline treatment to select EAS radio-candidates. The EAS nature of these candidates would eventually be cross-checked thanks to the scintillators data.
  • DAQ: the output of the 2 antenna arms are digitized at the foot of the antenna (1GSps & 12bits). A commercial GPS provides timing (precision: 25ns). The signals will be sent to the DAQ room through the (already installed) 21CMA optical fibers.

- DAQ status

  • A "version 0" prototype of the GRAND-proto array was developped by the TriggerLab (Lin Haichuan's PhD).
  • On-site tests of this v0 proto were carried out in March 2013. These tests were succesfull, the DAQ recording signals on 2 antennas connected to fibers from pod W1.
  • Several issues still require investigation:
    • Communication between Front-End station & DAQ board could not be established when using fibers from pod E10. Connector issue? This has to be investigated, but succesfull result on pod W1 shows that there is that the principle of using 21CMA fibers for the communication is valid.
    • Trigger rate was limited to 0.5Hz. This is certainly due to the fact that the USB protocol is used for communication between the GPS module and the main board.The max trigger rate limit has to be improved, with a target of 1kHz. This is necessary to be able to perform a comfortable offline study of the radio signals and their polarization characteristics and evaluate with enough confidence the actual rejection potential of the method. It was suggested by Hongbo that we could try to use the polarization info at the trigger level to perform an early background rejection and thus reach a lower trigger rate. This is certainly worth investigating, but will most likely make a marginal difference: valuable polarization features of radio signals can indeed be revealed only by collecting the signal characteristics of severall triggering antennas. To be more precise, linearity of the polarization (one main feature of EAS) can be confirmed only by making sure that all antennas have the same ratio of Vertical/Horizontal amplitudes, while hortogonality of the signal polarization to the shower propagation direction (another string feature of EAS radio signal) can be tested only if this shower direction has been reconstructed. Only in very basic cases (for example a shower coming exactly from the North, in which case there is no vertical componant of the signal) can these features be checked at the indvidual antenna level. In the general case, it is necessary to collect & exchange trigger times and signal amplitude of several antennas before determlining the pattern expected for EAS and defining the corresponding trigger criteria. This is not an option as we want the trigger decision to be kept at the individual antenna level.
    • DAQ should be made more flexible. In particular it should be made possible to define the trigger threshold from remote and distribute it to all (or only some) of the antenna. External trigger (through a trig signal sent on the uplink fiber for exxample) should also be made possible. Also the length of the registered buffer should be adjustable.
    • The mechanical elemnts of the DAQ also require a detailed study. In particular a casing for the electronics has to be developped. It should allow teh system to run over long period of times, preventing dust & humidity to come in, and at the same time maintaining the temperature within the nominal range for the electrionics. Expertise of the SUBATECH people on these issues will be most valuable.

- Next steps

After discussions, it is proposed that:

  • the TriggerLab (Lin Haichuan, Guo Feng?) investigates on the possibility to modify the present DAQ prototype in order to tackle the issues listed above (and in priority the trigger rate limit). On-site tests will be made possible at their convenience.
  • Liu Zhenan will provide an estimate of the cost for the production of 30 DAQ units, so that we can investigate on the possible funding sources as soon as possible.
  • We make all efforts to produce by the end of 2013 a valid unit for the GRAND-prototype DAQ. This would allow the production of 30 units in 2014, and the GRAND-prototype could therefore be in running state before the end of 2014.
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PDFpdf DAQMeeting_14052013.pdf r1 manage 856.5 K 2013-05-14 - 08:36 OlivierMartineauHuynh Slides presented at the meeting
Topic revision: r1 - 2013-05-14 - OlivierMartineauHuynh
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