ACS FM Scientific Measurements

1
ACS FM Scientific Measurements

• SPI Team Meeting, Valencia, 14.10.99
• MPE A. von Kienlin

2
ACS FM Measurement Plan

• Intention of ACS FM measurements
• opportunity for MPE to check if ACS works as
  specified
• important parameters for the later adjustment and
  operation of the ACS will be measured
• Important scientific parameters of the ACS
• energy-threshold calibration
• figure of merit of BGO crystals (light yield)
• determination of the threshold function
• processing time and jitter
• Measurement plan described in SPI-MPE-PL-12-32

3
Important Scientific Parametersof the ACS FM

• Energy-threshold calibration of all detection
  chains using ?-ray sources (241Am, 22Na,
  ...)
• measurement will be performed using the automatic
  stepping method
• the VCU-UT .log files will be processed with an
  analyzing program of MPE which is able to display
  and to fit the spectrum ? energy calibration
• Determination of the figure of merit (light
  yield) for each BGO-crystal
• the measured light yield is not a fundamental
  crystal property ? it is a
  figure of merit
• dependent on crystal packing, and geometry,
  irradiation position and direction
• this figure of merit is a significant performance
  value for test checking (vibration, TV
  tests)

4
Important Scientific Parametersof the ACS FM

• Determination of the threshold function
• probability for a ?-event of known energy to
  exceed a fixed energy- threshold level as a
  function of energy ? can be deduced from
  measured integral spectra
• Measurement of the processing time and jitter
• determination of the processing time between the
  logical signal of a tagged ?-ray source and the
  VCU-UT veto output (overall processing time)
• the timing measurement is performed using a TAC
  (as for EM)
• the processing time and jitter is evaluated from
  the time spectrum (position of peak and width of
  distribution)

5
Procedure for theACS FM Scientific Measurements

• It is planned to split the ACS FM scientific
  measurements into different parts ?
• in order to keep the ACS delivery date to
  CNES ? MPE proposes an FM scientific measurement
  procedure which can be adapted easier to the
  tough ACS integration time schedule
• 3 levels of measurement procedure
• ACS FM measurements on detection-chain level
• (BGO-module FEE VCU) 3 h/chain ? ? in
  total 54 h/subassembly
• ACS FM measurements with each subassembly
• (UCR, LCR, SSA, LVS) 4 days each ?
• FM measurements on ACS level ? (complete ACS)
  3-4 days ?
• in current time schedule not foreseen
• measurements on UVS level ?, measurements at
  SPI-FM level ?
  

6
Concept of ACS FM Measurements

• Due to the redundant interconnection of the BGO
  modules with FEEs
• output of two BGO crystals is added in one FEE
• problem different light yields of neighbouring
  crystals (sometimes more than 50)
• important knowledge of the the light yield for
  one BGO/1xPMT/FEE channel
• measurements with one PMT disconnected before the
  final integration
• advantage of procedure on chain level connection
  and disconnection of PMTs is easy
• measurement with both PMT connected on
  subassembly level overlay of single
  measurements

7
Procedure for ACS FM Measurements on chain
level (BGO, PMT, FEE, VCU)

• Connecting left PMT of BGO unit to assigned FEE
  (right PMT disconnected)
• Acquisition of energy spectra with left chain
• Measurement of processing time and jitter with
  left chain

• Functional tests with left chain (overrange veto,
  oscillation suppression, ..)
• same measurements with right PMT

energy-threshold calibration, figure of merit
(BGO), processing time and jitter for all half
chains
8
Procedure for ACS FM Measurements on
subassembly level (UCR, LCR, SSA, LVS)

• BGO unit with both PMTs connected
• energy spectra
• processing time and jitter
• Complete subring
• adjustment of the delays of all BGO chains
• measurement with all units connected together in
  one subring
• Complete subassembly (UCR, ...)
• adjustment of the delays of the 3 subrings to a
  common UCR delay
• measurement of energy spectra, processing time
  and jitter of the complete subassembly
• functional test of burst mode

• UCR Test with each UCR subring
• 6 detection units connected together

9
FM Measurements with the complete ACS

• Adjustment of the delays of all ACS subassemblies
  (UCR, LCR, SSA, LVS)
• Test of the ACS overall processing time and
  jitter (tagged sources)
• Simultaneous acquisition of energy spectra of all
  ACS-FEEs using different ?-ray sources (241Am,
  57Co, 203Hg, 22Na, 54Mn)
• Overall ACS dead-time measurement, if possible
• General test with the ACS
• test of all VCU features
• investigation of crosstalk effects

10
MPE preparations for ACS FM Measurements

• Tagged ?-ray sources for timing measurements ?
  suitable for thermal vacuum (TV) - tests
• PMT
• NE 110 plastic scintillator cylinder
• surrounded with ? - active foil (241Am or 60Co)
• temperatures from -10?C to 60?C
• HV (10-6 Torr)

11
MPE preparations for ACS FM Measurements

• Support for the measurements on chain level

12
Preparation of ACS FM measurements at
DSS - Friedrichshafen
FM-VCU
Detector module
FM-FEE
13
Preparation of ACS FM measurements at
DSS - Friedrichshafen
FM-FEE
? - telescope
FM-PMTs
? - ray source
tagged
BGO-crystal
14
Preparation of ACS FM measurements at
DSS - Friedrichshafen
UCR wooden mock-up
VCU-UT
VCU-UT command screen
VCU-UT data display
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MPE preparations for ACS FM Measurements

• ROOT analyzing program (ROOT - macro LightYield
  from R. Georgii)
• reads the VCU-UT .log hex-file of the automatic
  stepping method
• transforms the integral into differential
  spectra
• determines the figure of merit for a BGO crystal
  using a peak-fit routine (from width)
• Test of ACS FM measurement procedure at DSS, July
  14-15
• measurement setup
• Ref1-FEE (FEE00) connected to BB-VCU and VCU-UT1
• using EM-LED module
• stimulation of PMT with L-LED signals _at_ 300 keV
• energy-threshold calibration
• automatic stepping method implemented in the VCU
  software ?

16
Results of FM-Preparation Tests performed atDSS,
July 14-15
UCR

• Output of ROOT- macro LightYield.C
• ? Light Yield 13 pe/100 keV

FEE0 stimulated with LED module
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ACS FM Scientific MeasurementsTime Schedule
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ACS FM Scientific MeasurementsTime Schedule

• chain level
  subassembly level
• SSA 6.12. - 14-12. (6 days) 29.12. -
  4.1. (5 days)
• LCR 10.12. - 18.12. (6 days) 8.12. -
  13.1. (5 days)
• UCR 20.12. - 28.12. (6 days) 21.1. -
  26.1. (5 days)
• LVS
  27.1. - 7.2. (10 days)
• ACS ?