LHAASO-WCDA Design & Performance Zhiguo Yao for the LHAASO Collaboration IHEP, Beijing 2011/08/17.

LHAASO-WCDADesign & Performance

Zhiguo Yao for the LHAASO CollaborationIHEP, Beijing

2011/08/17

LHAASO-WCDAWater Cherenkov Detector Array

ofLarge High Altitude Air Shower

Observatory

Physics Motivation

All Sky Survey: Multi-Wavelength

TeV Sky Survey

>0.20 Crab unit northern sky: MILAGRO; ARGO-YBJ.

Only patches along the galactic plane (including the Cygnus region):

H.E.S.S.; VERITAS; MAGIC.

We eager to have a more sensitive ALL SKY MAP!

MILAGRO ARGO-YBJ

AGN Flares: IACT or Ground Array? IACT could do following-

up observations after receiving alerts from other wavelength: But, more fails than

successes; And the sample is biased; And < 1/2 of the flares

occur in their duty circle.Ground particle detector

array with improved sensitivity could do a better job!

Cen A

Project Overview

Charged Particle Array

DetectorArray

Water CArray

Wide FOVC-TelescopeArray&

Core DetectorArray

Physics Goals of LHAASO-WCDA Technique:

Ground particle detector array at the high altitude LHAASO; 100 GeV – 10 TeV: water Cherenkov technique WCDA.

Main goals of WCDA: Sky survey for VHE extragalactic sources, and their flares; Long time monitoring variable sources; High energy emissions from GRBs;

Cosmic ray physics, such as anisotropy;

Solar flares & IMF;

Dark matter; …

Technical Design Details

Detector Cell

Originally designed for HAWC;Water are partitioned into 55 m2 cells by black

curtains;Water depth 4.5 m;A 8”PMT placed at the bottom, looking upward.

Detector Configuration: 4 Sub-arrays

¼ array: Octagonal pond inscribed a

rectangle of 150150 m2; Side length: (2-1)150 m = 62 m; Area: 2(2-1)150150 m2 = 18640

m2; 25-4 = 21 clusters; 4 groups per cluster; 9 EDs per group; EDs are partitioned by curtains; Total ED PMTs: 720 (8”).

Water Purifying & Recirculation

Tiny holes are punched along the pipes;

Water is injected at the bottom of the pond, and drawn out on the top;

Recirculation speed: 1 pond water per month.

UV lamps in 185 nm are very essential, as it can destroy the dissolved organic carbon (TOC)!

Trigger Level 1 – group trigger: When a PMT is fired, the slave

station produces a signal of 100 ns. For a group, the signals are summed. At any rising edge of the pipe line clock, if the sum is equal to or greater than 3, and the sum is falling after a rising change, send a digital signal containing the sum (hit multiplicity) and group ID to the master station.

Level 2 – station trigger: When the master station receives a group signal, extend it to

700 ns. At any rising edge of the pipe line clock, if there are group triggers satisfying one of the following condition, produce a station trigger:

a: 1(M9); b: 1(M7) + 1(M3); c: 1(M6) + 1(M4); d: 2(M5); e: 1(M5) + 2(M3); f: 3(M4) + 1(M3); g: 2(M4) + 3(M3); h: 6(M3).

We are also working on another approach: triggerless system.

Time Calibration

LED array + double-fiber system: Long & short fibers; 1 pair of LED arrays per cluster; Two fibers can cross-check

themselves; Exchange long fibers for two

nearest PMTs from two neighboring clusters for cross calibration;

A cluster exchanges fibers with at least two neighboring clusters;

LED pulses can be generated in the master station and sent from the trigger / synchronizing cables.

See poster: ID-0771

Charge Calibration

Make use of the SPE measurement: Obtain the gain.

Make use of cosmic muons: Put down a shading pad above

the PMT; Measure charge distribution of

cosmic muons; Find and fit the second peak of

the distribution; 20 minutes (e.g., every 10 days)

running with shading pad can reach a precision of 2%!

e

15cm

See poster: ID-1123

WCDA Sensitivity

For known stable sources. For flares.

OptimizationsCell size;Number, type, size of PMTs;Layout of the array;Out-triggers;Altitudes (there are several viable candidate

locations in Tibet);…

These studies will use experimental data (from prototype or engineering array) as input.

Some Technical Parameters

Characteristics: On Time Measurement

Arrival time of PEs to a PMT: Pulse width (0-90% PEs) for 90% PMTs:

<13 ns; Same thing for large zenith showers:

< 18 ns. Sensitivity:

With / without 1 ns jitter: no big difference.

Multiple hits: About 50 kHz counting rate of noise; Early arrived noise of a fired PMT may

cause recording a wrong time; Electronics shall be able to record

multiple hits if they are separated by 100 ns.

It is not a big issue with modern electronics.

Characteristics: On Charge Measurement

PE distribution (gammas from CRAB): 1 PE: 43%, 2 PE: 18%; nPE>2000: 210-4 (710-4 , E>5 TeV).

Sensitivity: No difference between nPEmax=50000 and

nPEmax=2000; Slight difference between nPEmin=1 and

nPEmin=2.

For R5912, with the dynode + anode (or two dynodes) readout, we have achieved the dynamic range of 1-6000 PEs with nonlinearity < 5%!

Characteristics: On DAQ & Data Storage

¼ array: Trigger rate: 16 kHz; Data rate: 94 Mbps; Data volume: 1 TB/day.

R&D Status: Prototypes

2 layers of 1 m1 m Scintillators

1 layer of 1 m1 m Scintillator

5 m

7 m

WCDA PrototypeSetup in the very beginning

Results: Water & Rate

See NIM A644 (2011) 11-17

Results: Second Peak

Hamamatsu R5912 EMI 9350KB

Hamamatsu R5912

EMI 9350KB

Hamamatsu R5912

See NIM A644 (2011) 11-17

R&D Status: Engineering Array

Engineering Array of WCDA

Engineering Array

Later: permaflex coating will be used to replace PE plastics.

We have succeeded in potting / sealing 11 PMTs in a very cheap way (<200 yuan!)

See posters: ID-0261, 0732

First Test Results 9 PMTs:

CH1, CH2: with charge calibration covers (shading pad);

CH4: not immersed into the water;

Water depth 30 cm above the photo

cathodes.

Summary

Summary & Outlook

Water Cherenkov detectors have good performance in surveying the whole sky for extragalactic sources, complementary to next generation IACTs;

The experiment union (LHAASO-WCDA & HAWC) in East and West doubled the observation time on any sources in northern hemisphere, to realize the best monitoring of their emissions.

LHAASO-WCDA is conceptually designed; R&D is still in the very beginning stage but progressing smoothly.

The LHAASO project has a big chance to be financially supported in next 2 years, and we wish it can be successfully built by 2016;

The first version of technical design report (TDR) of LHAASO is expected to be released by the middle of next year.

Thank You!

Scientific Problem: Gamma Rays

SNRs

Cold Dark

Matter

Pulsars

GRBs

Test of the speed of light invariance

cosmologicalg-Ray Horizon

AGNsOrigin of CRs

Microquasars

Possible Source of UHECRs

VHE Gamma Astronomy: Techniques IACT: HESS, VERITAS, MAGIC, …

Better angular resolution; Fair background rejection; Low duty cycle; Narrow FOV.

More focused on deep observation.

Ground particle detector array: AS, Milagro, ARGO-YBJ, … Reasonable angular resolution; Ordinary background rejection; Full duty cycle; Wide FOV.

More oriented on all sky survey and flares detection

WCDA: Configuration Optimizations

WCDA Sensitivity @ Big Pond + MD

For known stable sources. For flares.