1. The dynamic range extension system for the LHAASO-WCDA experiment
Cheng LIU
On behalf of the LHAASO collaboration
2017/7/18

2. Outline The LHAASO-WCDA experiment The dynamic range extension system
Motivation
System design
Summary

3. The LHAASO-WCDA Experiment
3 water ponds (78,000 m2 )
3120 cells, with an 8”/9” PMT;
Dynamic range: PEs;
Angular resolution:
Sensitivity: <1.3%
Physics Goal: To survey the northern sky
for γ sources from 100 GeV to 30 TeV.

4. The LHAASO Experiment —— a hybrid air shower detector
Direction
Multi-parameter measurement of air showers
 Identify the composition of the primary particles
Muon
Energy
& Image shape

5. Why do we need the dynamic range extension system for LHAASO
proton
iron
The lateral distributions of the particle density
log10 ( Energy / TeV )
log10( Npe core )
The NPE distribution of the large PMT in the core cell
The dynamic range
of the large PMT
Motivation: To measure the shower cores
from 100 TeV to 10 PeV (~knee region)

6. The dynamic range extension system
1 water pond (22,500 m2 )
900 cells, with 1.5” PMT
Dynamic range: 50 – 500,000PEs

7. 1.5” Photo Multiplier Tube
Candidates：
CR285 (HAMAMATSU), XP3960 (HZC Photonics)
Polarity of HV: Positive
Gain: ~2 × 105
XP3960
CR285

8. The dynamic range base design
The pulse shape of the PMT
Anode
500 mV/bin
Dy7
5 mV/bin
Anode & the 7th Dynode readout
Schematic diagram of voltage-divider circuit
CR285
Typical non-linearity of PMTs
Non-linearity (%)
Dynamic range
Anode
DY7
The requirements of the 4 orders of dynamic range can be reached.

9. the waterproof package design of the large PMT
Waterproof design
Scheme B
Large PMT
PACTAN 6010
Stainless steel
Heat shrink tube
the waterproof package design of the large PMT
Scheme A
Directly measure the Cherenkov light produced in the water
Measure the large signals and the absorption effect of glass can be neglected.

10. Waterproof test system
Prototype test
Waterproof test system
Scheme A
Pressure sensor
RH&T sensor
Scheme B
Pressure tank
Air compressor
The estimate of these two schemes is still in progress

11. Design of charge digitizing module for readout electronics.
Signals from the anode and the dynode of one PMT are digitized by a two-channel ADC after being manipulated by the amplification and shaping circuit.
the digitized signals are sent to the FPGA for digital peaking.
All digitized data is transmitted to DAQ (Data Acquisition) via a simplified White Rabbit protocol.
Design of charge digitizing module for readout electronics.

12. Design of the Charge calibration
Charge calibration system based on an array of LEDs and plastic optical fiber bundle is designed
The LEDs array can be turned on individually or in any combination.
Using the different light emitted by the LEDs array, we can measured the SPE spectrum and the high voltage response of each PMT.
Schematic of charge calibration for small PMTs.

13. Summary
The dynamic range extension system of the LHAASO-WCDA is to precisely measure the shower cores of events at the energy range from 100 TeV to 10 PeV;
900 cells of the WCDA array are planned to add another 1.5 inch PMT at side of the large PMT;
Using all detector arrays in LHAASO, combining the shower cores information, it will be powerful to identify the composition of the primary particles.

14. Thank you

15. Backup

16. LHAASO site

17. WCDA

18. Effective Area & Angular Resolution
At 500 GeV, the effective area can reach 3,000 m2, the angular resolution is 0.6◦ and the energy resolution for -rays is 95%.
The corresponding values are 10,000 m2, 0.4◦, 90% at 1 TeV, and 50,000 m2, 0.2◦, 60% at 10 TeV.
The highest sensitivity is 1.3% of the Crab nebula flux at the energy around 2 TeV.

19. Muon Detector Water Cherenkov detector Underneath soil Eth ~ 1 GeV
Item
Value
Area
36 m2
Detection efficiency
>95%
Purity of N
Time resolution
<10 ns
Dynamic range
1-10,000 particles
Particle counting resolution
1 particle
10,000 particles
Aging (<20%)
>10 years
Spacing
30 m
Number
1171
Muon Detector
Water Cherenkov detector
Underneath soil
Eth ~ 1 GeV