Large Area X-Ray Proportional Counter (LAXPC) Payload

Large Area X-Ray Proportional Counter (LAXPC) Payload design & testing

Shah Parag B. (On behalf of LAXPC Payload Team)

Department of Astronomy & Astrophysics Tata Institute of Fundamental Research

17th December 2014

Outline of presentation

LAXPC instrument overview.

Payload functional requirements to meet all the Scientific Objectives of the mission.

Electronics subsystem design goals & challenges.

Functional overview of electronics.

Design, development & testing of LAXPC packages.

Satellite bus interfaces & payload control.

Qualification tests of payload.

Reviews

17h December 2014 2

ASTROSAT

LAXPC

UVIT

SSM

CZT

SXT

17h December 2014 3

Large Area X-ray Proportional Counter (LAXPC)

17h December 2014 4

LAXPC Instrument Overview Non-imaging Instrument designed and

developed at TIFR Mumbai.

Consist of three identical units recording data

independently and simultaneously.

Field of View – 1 degree by 1 degree

Time Resolution – 10 microseconds

Spectral Band – 3 to 80 KeV

Three Modes of Operations (BBC – Broad Band

Counting, EA– Event Analysis and FC – Fast

Counter)

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The instrument consists of 3 identical detectors with total effective area of about 6000 cm2 and gas volume of about 66 litres each

A 50 micron thick aluminized Mylar window with a FOV of 1ox1o

Fill gas - xenon + methane mixture at a pressure of 1520 torr

Multi layer and multi cell geometry with 60 anode cells and 28 anti cells (~ 1.4 km of wire)

Brief description

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Anode Frames

Detector Housing and Back Plate

Collimator Housing

Window Support Collimator (WSC)

Field of View Collimator (FOVC)

Gas-filling system, onboard calibration

source and onboard gas purification

Detector system

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Electronics Functional Requirements

Generate Stable & command selectable High Voltage for detector operation.

To collect and analyse charge generated due to X-ray photon interaction with gas molecules in the detector.

Detector background reduction : Only accept events, which are qualified through (a) Level Discrimination (b)Mutual coincidence & (c) Anti coincidence.

Ability to handle event rates varying from as low as detector background levels ~200 to as high as ~20000 events per second.

Capacity to time tag each qualified x-ray event accurately.

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Design Goals • Three Independent and modular electronics systems for 3 LAXPC Detectors.

• All three detectors to use a common and accurate time reference.

• To ensure high reliability and adequate safety measures against single-point failures.

• To have adequate redundancy built into the electronics to overcome any failure of critical processing components.

• Payload health monitoring & operational control.

• Independent electrical interfaces to satellite buses (Power, Tele-Command & Telemetry) for all the sub-systems.

• Optimum design in terms of power consumption , package size, weight and resources utilisation like onboard storage memory.

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Design Challenges

Limited availability of analog as well as digital devices with Space grade qualification.

Tight power, weight and volume budgets.

Harsh operating environment in space :

a) Severe shocks & vibrations generated during takeoff.

b) Rapid temperature variance in orbit : -10°C to +50° C.

c) Exposure to cosmic radiation.

Stringent EMI & EMC requirements to ensure minimal interference to other payloads as well as to satellite control & operation.

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LAXPC Engineering Specifications Low level Energy Threshold : 3 KeV (~ 0.24V pulse from CSPA).

High level Energy Threshold : 80 KeV (~ 6.4V pulse from CSPA).

Detector Energy Resolution : ~ 11% @ 22 KeV (~ 190 millivolts).

Resolution in measuring Pulse Height: 10 bit effective in 0-10V dynamic range ADC. (~ 10 millivolts).

Time variability Analysis : Temporal data generation by Broad Band Counters (BBC) for different layers.

Real time tagging of each qualified events.

System Time Base Generation (STBG) system resolution of 10 sec.

Absolute Time accuracy : within 4 sec of UTC (SPS provided).


LAXPC Electronics Front-end electronics including Charge Sensitive PreAmplifiers (CSPAs), HV generator and command control interfaces for HV unit, fast count rate mode electronics, TM/TC & Power interfaces to satellite bus. Signal processing electronics includes event selection logic, pulse height analyzer, count rate monitors, time tagging systems, House keeping data electronics, interface electronics and power distribution system. System Time Base Generator electronics to provide common and accurate time reference with 10 microsecond resolution for entire LAXPC payload.


LAXPC Flight Packages

LAXPC

DETECTOR 1

AS-LX-DT-10

LAXPC

DETECTOR 2

AS-LX-DT-20

LAXPC

DETECTOR 3

AS-LX-DT-30

PROCESSING

ELECTRONICS 1

AS-LX-EL-10

PROCESSING

ELECTRONICS 2

AS-LX-EL-20

PROCESSING

ELECTRONICS 3

AS-LX-EL-30

S. T. B. G.

AS-LX-EL-40

PURIFIER

ELECTRONICS

(XPDE)

AS-LX-EL-50

LAXPC payload has 8 flight packages. Three Detectors, Corresponding Processing Electronics, Common STBG package, & XPDE package


High Precision Timing with LAXPC

•Worked out a detailed scheme to get an Satellite Positioning System (SPS) for ASTROSAT and to use Pulse Per Second (PPS) signal & achieve high accuracy over the long period of 5 years while using standard low cost low power TCXO to get required timing resolution. •other X-ray instruments also gets STBG time sync pulse and thus very good timing co-relation between each of the ASTROSAT science payload.

• The LAXPC Time synchronization scheme successfully implemented and provides a continuous & accurate correlation between a) Instrument Time b) UTC time & C) Satellite OBT time. • Achieved all the required parameters in terms of precision and stability. • Event timing resolution of 10 µsec is achieved.


STBG / SPS / BMU time sync scheme and STBG charterisation

15 17h December 2014

LAXPC STBG (FM & FSM)







Detector Front-End Electronics


CSPA waveforms


Detector Front-End Electronics



LAXPC Data Modes

Event Analysis Mode : High resolution Time Tagging of each qualified event's arrival to 10 microsecond accuracy along with its pulse height and layer ID.

Broad Band Counting Mode: Analyse the rate of occurrence of events in various energy bands with selectable BIN period (8 msec to 1024 msec).

Fast Counter Mode: Generates event rate data for top layer of detector in 4 different energy bands with fixed BIN period of 160 microsec.

Self test / Calibration Mode.



LAXPC Data generation rates. Serial

No.

Operating

Mode

Highest

Event rate

Number of Bytes

/ event or per

BIN

Fastest

Integration /

BIN Period

Maximum Data

generation Rate.

1 Time Tagging

(EA)

20,000 per

second

5 Bytes - 20K x 5 = 100K + 2K

= 102 Kbytes /sec

2 Broad Band

Counting (BBC)

- 64 Bytes 8 msec or 125

frames /second.

64 x 125=

8 Kbytes/sec

3 Fast Counter

(FC)

- 5 Bytes 160 μsec 5 x 6250 = 31

Kbytes/sec


LAXPC Electronics


Satellite Bus Interfaces

Power Interface

Tele-command Interface

Low Bit-rate Telemetry (LBT) Interface

High Bit-rate Telemetry (HBT) Interface


Power Requirements

Normal Operation mode : All three detectors & corresponding signal processing electronics powered on. (Total power : 67W)

Purification mode : One of the detector purifier system powered on. All other packages of LAXPC powered off. (Purification Power : 50W)

System Time Base Generator always remains on.

LAXPC packages draw power from 2 different RAW buses to provide protection against single point failure.


Pulse Commands 17 Pulse Commands are required for each LAXPC front

end and processing electronics. In addition to this 8 Pulse Commands are required for the System Time Base Generator (STBG) package.

A total of 59 pulse commands are used for the operation of the LAXPC payload.


Data Command for LAXPC LAXPC require 1 data command interface for each of

the payload chain.

Thus a total of 4 command channels are required for the LAXPC payloads.

Each 16 bit command is internally decoded in the respective package.


Low Bit-rate Telemetry to BMU

Used for transmitting payload health monitoring and other housekeeping data.

Serial transmission with 40KHz clock and P/S (Parallel / Serial), ALE (Address Latch Enable) & Channel Address data.

Each of the LAXPC package has independent LBT interface with Bus Management Unit.


High Bit-rate Telemetry (SSR Interface)

FPGA

DELI, BBC

LVDS

BDH Channel

•Each LAXPC chain sends data in serial burst of 2048 bytes at various rates, which are then formatted into interleaved packets of 2160 bytes, RS encoded and transferred to SSR on Channel 4 (Q2) as 8 bit parallel @ 8.8Mhz • Individual payload data is segregated and processed on ground to generate Level 1 and Level 2 products.


First LAXPC Flight Detector being shipped to ISAC. March 2012


Second LAXPC Flight Detector being shipped to ISAC. Jan 2013


Third LAXPC Flight Detector being shipped to ISAC. September 2013


Qualification & Test sequence Initial Bench test

EMI/EMC test

Vibration test

Thermovac test

Purification

Pre calibration Gain Equalisation

Full chain Calibration

Final Bench test

Baking prior to AIT handover in clean room

Interface test to satellite buses on open panel

Disassemble mode test


EMI/EMC tests Conducted Emissions on Primary Power lead (CE03 -15

kHz to 50 MHz)

Conducted Susceptibility Tests on Primary Power lead Sine Susceptibility (CS01, CS02 - 30 Hz to 50 MHz)

Spike Susceptibility (CS06 – limited to 10V peak as per QA request)

Radiated Emission Test (RE02 Electric Field - 14 kHz to 18 GHz)

Radiated Susceptibility Test (RS03 Electric Field - 20 MHz to 18 GHz)

Radiated Susceptibility Test on spot frequencies ( 2.245GHz,8.125GHz and 8.3GHz)


LAXPC Full chain: Detector + PE & STBG on EMI/EMC Table


LAXPC Detector on vibration table


Thermovac Test Setup

•Inside Chamber assemblies, cables and harness

– DT-10 detector with X-Y source motion assembly on top

•Test bench setup close to chamber –Full Chain setup (PE-60 (FSM) , STBG-70 (FSM) & XPDE-50)

•Outside chamber Equipment, GCS, Cables and harness

•Electrical Interconnection Verification with chamber door open prior to start

•X-Y Source motion jig setup and verification

•Performance verification with chamber door closed


LAXPC Payload Thermal Cycles


Thermovac test of LAXPC


LAXPC Detector On-board Purification

On-Board Purification for Flight Detector and Leak test


DT-10 Spectrum (28/10/2013) Am241 source.


DT-10 Spectrum (20/11/2013)

After 120 minutes Purification in Vacuum post Thermovac qualification. Am241 source.


AS-LX-DT-10 Purification post thermovac


LAXPC Detectors in AIT


Review & clearances

Design reviews - hardware :

Software design review /FPGA review etc :

Test results review & clearance : Payload science data review


Thank you

Documents

Large Area X-Ray Proportional Counter (LAXPC) Payload