Design and optimization of Electromagnetic

particle Detectors (EDs) in LHAASO-KM2A Xiangdong Sheng, Jia Liu, Jing Zhao

on behalf of the LHAASO collaboration

Institute of High Energy Physics, CAS

August 17, 2011

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Outline

• Introduction

• Design and optimization of ED prototypes Design of the size of Scintillator tile with fiber readout Long-term stability of the candidate scintillators Selection of the PMTs Suitable module power supplies ED’s assembly

• Conclusion

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1. Introduction

KM2A aims at,

• Discovery of the Galactic CR sources

• Survey of the northern sky, exploring the origin of galactic cosmic rays

• Cosmic ray physics

Electromagnetic particle detector

(ED)

Muon detector (MD)

5137 EDs and 1209 MDs, Compose one square Kilometer extensive air shower array (KM2A) (Φ1020m);

Obtain the highest sensitivity (1%ICrab) at the highest Gamma ray energy. (Shuwang Cui, ICRC2011 Poster ID: 776)

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2. Design and optimization of ED prototypes

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Key points, Suitable photo-electrons obtained in photocathode,

20p.e. (1 particle)~80000p.e. (4000 particles)Suitable scintillation light transmission paths and low fluctuation;

Time resolution < 2ns

Candidate scintillators, KEDI type, ST-401 type (~40% Anthracene) and ET9903kB type PMTs, R11102 type ones are applied for the tests, as well as BCF92 WLS fiber of Φ1.5mm.

(1) Design of the size of Scintillator tile with fiber readout

The following processes, scintillation light generation, its transmission and collection and the conversion at PMT’s photocathode, are considered.

Scintillator samples (Tiles), length: 25cm;width: 5cm (KEDI), 15cm (KEDI), 25cm(KEDI, ST-401); thickness: 1.0cm (KEDI), 1.5cm (KEDI), 2cm (ST-401)holes-making: 5, 8 (only for KEDI) (25cm×Φ1.5mm each)grooves: 8 (ST-401), 25cm×1.6mm×1.8mm( or 2.5mm )

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Length : 25cm suitable for time resolution; Width : slowly variation (exceeding 15cm) Np.e. (increase); Time resolution (worse); Depth: < 2cm

Scintillator covered with a layer of Tyvek sheet; ~ 90% : Fiber coated an aluminium layer; > 40% : Fiber-scintillator coupling (BC600 to

air) Deeper grooves has a little superiority

~ 20% : coupling with air;~ 10% : coupling with BC600;

>30% : Fiber-PMT’s window coupling with silicon oil than with air

In case of incoming single particle, Experimental results show the scintillation light collection efficiency affected by different factors.

Time resolution : ~ 1.5ns

A GEANT4-based simulation package have been developed, which results are consistent with the testing ones, which benefits the design and optimization greatly, combining with the tiles testing results.

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Scintillator size:• 25cm× 25cm× 2cm;• 8 grooves (25cm×1.6mm×1.8mm

each) 8 WLS fibers (150cm long and

Φ1.5mm) Fiber-Scintillator coupling with air One ET9903kB PMT applied

< Np.e. > ~ 21 p.e.

Scitillator size: • 25cm× 25cm× 1.5cm;• 8 holes (25cm×Φ1.5mm

each) 8 WLS fibers (150cm long and

Φ1.5mm) Fiber-Scintillator coupling with

air One ET9903kB type PMT is

equipped

< Np.e. > ~ 16 p.e.

Two present optimization sizes of scintillator tiles

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(2) Long-term stability of the candidate scintillators

Two accelerated ageing experiments are done to obtain the critical times (when the light output has decreased by 20%) of the candidate scintillators. (See Tianfu Zhou’s poster, ID 267) High and low temperature aging

experimentIn simulation environment box:

iterative variations: -30℃ ～40 ;℃

Record the iterative times and assume one time means 2 days.

ST-401 scintillator : ~ 9 years;KEDI scintillator : ~ 15 years.

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(3) Selection of the PMTs

HAMAMATSU R11102 type and Electron Tubes (ET) 9903kB type are suitable PMTs. (See Bin Zhou, Chao Hou, ICRC2011 poster ID 261)

Linearity : ~ 3.6 orders of magnitude (<5% non-linearity)

Uniformity : (better than 80%); Operating gain : ~ 105.6; Low gain variation affected by

geomagnetic field : (<10%);

ET 9903kB type PMT

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(4) Suitable module power supplies

To keep the PMTs’ operating gain variation within ±5% at YBJ site, it needs each module power supply with temperature coefficient less than 0.01%/ºC and ripple index less than 0.01%.

Ration variation Vs. the temperatures

Three kinds of candidate module power supplies have been validated to be eligible. (See Shaoru Zhang, ICRC2011 poster ID: 642)

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Each ED consist of 4×4 scintillator tiles, while 128 WLS fibers in total will guide the scintillation light to one PMT’s photocathode. Here, each PMT is equips with a module power supply;

Scintillator Tiles, one PMT and a set of power supply are packed in one aluminium/plastic box (one black box). On the top of the box, a layer of LEAD convertor with 5mm thickness are used to increase the detection efficiency, which is of benefit to improve angular resolution and position resolution of KM2A.

(5) ED’s assembly

Based on the present designs, some ED prototypes will be assembled by the end of this year with two kinds of scintillator tiles, respectively. Now the corresponding works are doing, such as the tests of scintillator tiles, PMTs and power supplies.

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3. Conclusion

Good progresses on the design and optimization of ED have been made. Here, some characteristics or performances of Scintillators, PMTs and power supplies have been studied in detail.

Based on the present designs, some new ED prototypes will be assembled this year.

It still needs more efforts to obtain the final optimization of ED.

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Thank you!