BESIII Electronics and On-Line

BESIII Workshop in Beijing IHEPZhao Jing-wei Sheng Hua-yi He Kang-ling

October 13, 2001

Brief Measurement Tasks Technical Strategy Sub-systems Configurations and Software On-Line System

Brief

BESIII’s sub-detectors are: Vertex Chamber Main Drift Chamber TOF plus CCT Counter Electromagnetic Calorimeter MUON Identifier

Electronics will consist of five sub-systems correspondingly.Total channel amount is about 50K~77K.

Measurement Tasks To measure the time information carried by

detector signal. To measure the charge values carried by

detector output signals or signal amplitude. To deliver the information of fired point

position (x,y) in detector cells. To provide the hit information or sum of

analog signals for making trigger decision. To implement data taking and data

formatting and preprocessing and sub-event packing.

To transfer the packed data to On-line computer system via fast switch network.

Technical Strategy

Short bunch crossing (8 ns) Long trigger latency (2.4us) pipeline must be used.

High luminosity (1×1033cm-2s-1).High event rate.

Parallel processing on-board isneeded to make dead time as small as possible.

Technical Strategy

High beam intensity (1100 mA×2)Short lifetime (3-4 hours)Bad noise environment Measures must be taken to make system immune from noise background and RF interference.

Weak signal, especially for VC, EMC and MDC. low noise technique must be

adopted.

Sub-system MDC Tasks

Tasks & technical requirements The charge deposition on sense wire (dE/d

x) Charge range : 8~1500 fcResolution : σQ ≈ 4 fc

The drift time of ionized electrons towards sense wires. (to determine the spatial trajectory of particles and the momentum of particles.) Time range : 0~500ns Resolution :σt ≈ 0.5ns

Hit information to trigger

Sub-system MDC Scheme 1

Based on “Q to T converter + HPTDC”

Wiresignal

trigger

Online

VMEbusQ to T based mainamp

Calibration

CERN HPTDC based TDC

Preamp

Sub-system MDC Scheme 1

Preamp.A transimpedance typeLow noiseLow power dissipation

Main amp.Based on Q to T converter – MQT300A

TDC moduleAdopt CERN HPTDC as a key component.

Advantage for above scheme:Simple system: Use only TDC to measure

both the time and charge.

Sub-system MDC Scheme 2

Based on “FADC and HPTDC”

VMEbusClock

online

Preamp

Trigger

Start

WireSignal

Qmeasurement

T measurement

Calibration

Mainamp

Trigger

Timing

dE/dX

Vth

Sub-system MDC Scheme 2

Charge measurement is based on FADC waveform sampling & Numerical integral.10bit and 40MHz FADC is required.9U VME board and 32 ch./board

Time measurement is based on CERN HPTDC chip9U VME board and 96 or 128 ch./board

Sub-system VC

Charge information Range = 0.22 fc on average

σQ ≤ 20% at 0.22fc Ch. = 300

Hit information to trigger

Sub-system EmC Tasks

Charge measurement

Range : 0.2 fc to 300 fcResolution : q= 0.1 fc

Sub-system EmC Block diagram

Trigger

Post amplifier

V

M

ETrigger L1CTrigger CL1 Trigger L1

CR (RC 2)

∑

calibration

Fan - out

Chargemeasurement controller

Σ

BGO

∑

Preamplifier

Sub-system EmC Brief introduction

20200 BGO crystals Charge-sensitive preamplifier

to receive the signal from photodiode 20MHz FADC to digitize the waveform 15 bit dynamic range is needed. 10 bit resolution is required.

Sub-system EmC Scheme

Preamplifiers are mounted on the BGO crystals. Two signals from each crystal are added together,

and then feeds to post-amplifier for further amplifying and shaping.

FADC samples the signal with 20MHz. The data are pushed to the digital pipeline. The length of the pipeline equals the trigger L1 latency.

Digitized data within 1.5s interval are read out by a peak finding circuit on arrival of trigger L1. The peak value is stored in a buffer for readout by VME.

Auto Range Encode Circuits are employed to expand the FADC dynamic range from 10 bits to 15 bits.

Sub-system TOF Tasks

To provide the information for particle identification by measuring the flight time of the particles.

To correct the flight time by measuring the charge .

To provide hit information to trigger

Sub-system TOF Requirement

Time measurement Number of channels: 320 Range : 0~60ns Resolution : σt ≤25ps

Charge measurement Number of channels : 320 Dynamic range : 2Vmax for TOF 0.2Vmax for CCT Resolution : 2% at 2V for TOF 2% at 0.2V for CCT

Sub-system TOF Block Diagram

Start

10nsL-threshold

H-threshold

L0 trigger

From Online

To Trigger

Pre-amp Splitter

Stop

Signal Driver

HL

Calibration

LL delay

Trigger L1

Q Read-out

Read-out T

Sub-system TOF Charge measurement

The circuitry consists of the Voltage-to-Current converter,integrator, FADC and two FIFOs.

VM

E

BU

S

W R W

40MHz CLK

V/I FADC Peak-finding

FIFO FIFO

Trigger L1

Sub-system TOF Time measurement

TOF time measurement schema is based on TAC plus FADC.

CLK 40M

L0 200ns

Delayvcc

_+

S !QR Q

Tempcontrol

STOP

TACSTART

FADC

Sub-system Muon Tasks

Tasks & technical requirements

To deliver the information of fired point position(x,y) in detector cells.

The hit information to trigger

Sub-system Muon Configuration

Configuration Modules of VME 7 Chains in a module 24 Data of a chain 256 Total data of readout system

10K~30K

Sub-system Muon Diagram of chain

Sub-system Muon Diagram of VME

Configuration and Software Tasks

DAQ L1 Event Rate ≈ 3000Hz Event Length ≈ 6K~10K Byte Read Out Tasks:

protocols & communicationssystem controldata taking Preprocessingtransmission

50K~77K channels will be read out and preprocessed and sent outreduce the “dead-time” in data taking from read out electronics

avoid “bottle-neck” of data flow

Configuration and Software Structure

branch 1 branch n

Configuration and Software Device

Read-Out CrateVME Crate + ADC/TDC modules + ProcessorThere are ~600 channels in each read out crate. ~90 VME crates will be needed.

BranchComputer(Multi-CPU) + Switch(100M) + Crates

Multi-Port network card will be used to the computer.One port is linked to the online computer system via a Gigabit switch, others are linked with the processors of Read-Out Crates via 100M switch. There are 1~6 VME Read Out Crates per branch.There are >16 branches in BESIII read out electronics system.

Configuration and Software Design Consideration

Adopt Commercial ProductPowerPC 、 100M Switch 、 Computer and others

Consider to adopt new technique and future device

Performance/cost ratio The software developing environment

VxWorks and x86 BSP 、 PowerPC750 BSP

On-Line System Tasks

Event rate ~2000Hz after L2 filter ~16MBytes/sec to persistent store Event Builder System

Transport information from readout crate to Online(L2) farm

L2 trigger SystemSoftware trigger. Selects events for storage

Online System Run environment monitoring and controlling Experiment monitoring and controlling Human interface

On-Line System Tasks

Data Storagemass storage and transmission via fast network

Slow control system HV control and monitoring Environmental monitoring Dead time & Luminosity monitoring

Tests

On-Line System Requirements

High performance computer Graphics User Interface to experiment Functional requirement

Configuration and constants of system Execute command to FEE and Farm nodes Error message reports for FEE and Farm nodes Calibration Support Diagnostic Tools Data Monitoring Support

Database and network support

Thanks!