FOT ACIS Training

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FOT ACIS Training

1. HW and SW Overview
2. Flight Operations
3. X-Ray CCD Basics
4. Radiation Damage and Contamination
5. Science Examples with ACIS (pretty pictures)

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Overview of ACIS HW and SW

• ACIS HW, MAIN COMPONENTS
• DEA, Detector Electronics Assembly - analog
  electronics to clock the CCDs and process analog
  data, contains video boards for the CCDs MIT
• DPA, Digital Processing Assembly - contains
  Back-End Processors (BEPs) and Front-End
  Processors (FEPs), processes digital data from
  the from DEA (CCDs) and SW commands MIT
• DH, Detector Housing - contains CCD focal plane
  (FP), optical blocking filter (OBF), proton
  shield, collimator Lockheed-Martin and Lincoln
  Laboratories
• PSMC, Power Supply and Mechanism Controller -
  power supplies, door and valve controllers,
  connection to the ISIM RCTU, processes HW
  commands
• Lockheed-Martin
• Radiators - Warm (connected to DH) and Cold
  (connected to FP) radiators Lockheed-Martin

3

ACIS Flight SW

• ACIS BEPs controls all science functions which
  CCDs are on, which video boards are on, which FEP
  is connected to which CCD, ACIS TLM formats, etc.
• Normal commanding entails only ACIS SW
  commands, in fact we have not sent a HW command
  to ACIS since 15 July 2004 (a Warm Boot) ! This
  means the weekly Chandra load contains only SW
  commands.
• ACIS SW commands are of variable length, the
  parameter block is the most important, it
  contains about 150 commands
• Flight SW has been patched several times since
  launch, the latest version is loaded by
  SOP_ACIS_SW_EVHCC3X3_CATL (4/15/2004)

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ACIS HW Diagram
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ACIS HW Diagram Exploded View
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ACIS Detector Housing
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ACIS Engineering Unit Door Mechanism
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ACIS Focal Plane Support Drawings
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ISIM at Ball with SIs
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ACIS CCDs, FEPs, VB Connections
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ACIS PSMC Interfaces
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ACIS DPA Interfaces
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ACIS Focal Plane
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ACIS Paddle Design
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HW Design and Lifetime Issues

• DEA - 10 video boards (VB), one VB hard-wired to
  one CCD, the loss of one VB would result in the
  loss of that CCD
• DEA - A/D converters may experience long-term
  degradation due to radiation exposure
• DPA - FEPs multiplexed to the CCDs, any FEP can
  process data from any CCDs
• DPA - FEP0 anomaly has been of no consequence
  since we started assigning FEP0 last
• DPA - both side A and side B of the DPA must be
  powered on to clock 6 CCDs
• Radiators - cooling capacity is less than
  pre-launch predictions, have difficulty
  maintaining -120 C, more on this later
• CTI - CTI of the FI CCDs may increase to the
  point at which the CCDs are no longer useful for
  scientific observations
• Contamination - contamination may increase to
  the point at which science observations are more
  seriously impacted than now

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ACIS Mass
Weight (lbs)
Detector Assembly 20.8
Venting Subsytem 8.7
Support Assembly 124
Thermal Control and Isolation 5.4
Radiators 10.2
Sun Telescope Shades 16.0
PSMC 32.7
PSMC Cables 9.1
SIM Mounted Cal Source 4.3
Total Weight 254

• total weight from Observatory to SI ICD
  (CM07a), email from Bill Mayer
• Email from Bill Mayer, all other weights from
  May 1997 Monthly Report

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Flight Operations

• OPERATIONAL CONFIGURATIONS
• Only three general ones thankfully, Normal
  Science,Thermal Standby, Radiation
  Shutdown because there is so much margin in the
  spacecraft power budget

Mode DPA A 1DP28AVO 1DPICACU DPA B 1DP28BVO 1DPICBCU DEA A 1DEA28AVO 1DEICACU DA htr B 1DAHBVO 1DAHBCU Total
Normal Science (6 CCDs) 40 W 35 W 57 W 5 W 137 W
Thermal Standby 40 W 35 W 26 W 5 W 106 W
Radiation Shutdown 12.5 W 8 W 26 W 5 W 51.5 W

• DPA A B On DEA A on, DEA B off, DA Htr side B
  On, this is normal
• DEA A power consumption will vary depending on
  the number of active CCDs
• DEA current monitor is noisy must integrate to
  get an accurate reading
• Cold Radiatior (1CRABT) at -127.3 C, Warm
  Radiator (1WRABT) at -82.0 C
• ACIS Ops web page http//asc.harvard.edu/mta/RT/a
  cis/www/acis-mean.html displays realtime data,
  average 10 samples, computes power

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Flight Operations

• Radiation Environment
• The pre-launch concern was high energy protons
  (Egt10 MeV), hence the heavy proton shield around
  ACIS
• The unfortunate discovery post-launch was that
  low-energy protons (100 keV) reflected off of
  the mirror with a small but not negligible
  efficiency
• The solution was to translate the SIM to the
  HRC-S position for every perigee passage
• Low energy protons outside of the belts also
  produce damage
• EPHIN only measures protons from 5 MeV and up,
  the spectrum of the protons varies from one solar
  event to the next, sometimes the low and high
  energy protons both go up dramatically, sometimes
  only the low energy protons go up significantly
• Use ACE to monitor the 112-187 keV protons on
  the way, use GOES P2 channel (4-9 MeV) to better
  predict EPHIN P4 GM rates
• Use EPHIN P4GM, P41GM, and E1300 as SCS107
  triggers P41GM for hard proton events, P4GM for
  softer proton events, E1300 as a failsafe
  detector out of the belts
• HETG is assumed to provide a factor of 5
  attenuation for 100 keV protons and the LETG a
  factor of 2

THE SIM MUST BE AT HRC-S (-99616) FOR EVERY
PERIGEE PASSAGE !!!!!!
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Flight Operations

• Operational Issues and Concerns
• Perigee passages - the SIM must be at HRC-S and
  the video boards powered down
• RADMON MUST be enabled if ACIS is in the focal
  plane
• Unsafe ACIS Response - procedures developed,
  SAP_UNSAFE_ACIS_PHASE1 and SOP_UNSAFE_ACIS_PHASE2.
  Should we schedule a separate meeting to review
  these procedures in detail ?
• FP temperature regulation - it has become more
  difficult over the course of the mission to
  maintain -120 C on the FP. Analysis is under way
  to determine if this is caused by earth in the
  ACIS radiator FOV or Sun on the ACIS radiator
  shades or both. One option it to turn off the
  ACIS DH heater, this would require significant
  analysis from FOT Thermal for approval.
• Multiple Limit Sets - ODB, Greta, SOT MTA, ACIS
  Ops, ODB needs to be updated, other three sets
  have the latest limits
• PSMC gets warm for pitch angles between 45-60,
  (1PIN1AT, 1PDEAABT), raised the limits for
  these values to the ground qualification limits
  in February 2005, need to get the ODB updated
• DPA-A shutdown anomaly - occurred twice on
  October 26, 2000 and December 19, 2002, most
  likely due to a SEU in the ISIM RCTU
• Threshold Crossing Plane Latchup - occurred three
  times over the life of the mission. Last
  occurrence was Nov 5, 2001. We now power-cycle
  the FEPs before

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Flight Operations

• Operational Issues and Concerns (continued)
• observations which compute a new bias. This
  wont prevent the latchup from occurring but it
  will reset the memory chip so that subsequent
  observations wont be affected.
• Large ACIS commands - ACIS PBs are much larger
  than most spacecraft commands. The loads cannot
  put another command directly after the ACIS PB
  command because the OBC will not complete
  processing the PB in time. The risk is that the
  load will hang.
• THREATS to ACIS
• SIM at the incorrect position
• Spacecraft attitude is incorrect so that the Sun
  is on the ACIS radiator or the HRMA
• Any future ACIS HW commanding. SW commanding
  should be innocuous.
• An ACIS bakeout.
• Contamination damages the instrument, perhaps the
  OBF
• PSMC gets warm enough that a component fails

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ACIS FP Cooling Tests to Date
Date Duration (ks) Min Temp (C)
2005070 43 -121.86
2004201 101 -121.58
2003133 114 -121.96
2003130 54 -121.64
1999354 46 -123.09
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Issues for the FOT SOT in 2005

• PSMC heating, we may have to reduce the duration
  of observations at pitch angles between 45 and 60
  degrees
• BAKEOUT !!!!!
• Analysis of FP heating, we need to understand
  what the effect is and if there is anything we
  can do to limit the heating
• We may have to study the feasibility of turning
  off the ACIS DH heater to provide more margin on
  the FP

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X-Ray CCD Basics

• An X-ray photon interacts with the CCD by
  liberating electrons in one or a few pixels
• The electrons are held in the pixel by the
  electric fields in the CCD, until it is time to
  be read out when the fields are varied to clock
  or push the charge out the readout amplifiers
• The number of electrons is proportional to the
  original energy of the X-ray photon, thus the
  position and energy of the photon can be measured
• ACIS CCDs were manufactured at MIT Lincoln
  Laboratories. They are 1024X1024, 24um pixel,
  frame-transfer CCDs, meaning there is a 1024X0124
  pixel imaging region and a 1024X1024 pixel
  framestore region
• ACIS has 8 Frontside-Illuminated CCDs and 2
  Backside-Illuminated CCDs
• ACIS allows the CCDs to be clocked in a Timed
  Exposure mode or a Continuous Clocking mode.
  Full frame requires a 3.2s static integration
  time.
• ACIS also allows subarrays, spatial windows, and
  different events filters
• ACIS flight SW detects events and reports only
  those pixels with charge from X-ray events, other
  pixels are not telemetered. Hence, X-ray CCDs
  are usually operated in the photon-counting
  mode.
• ACIS has several different telemetry formats for
  reporting information about each event. It also
  has a mode specifically designed for FMT 1 when
  the HRC is the prime instrument.

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ACIS Timed Exposure Mode Clocking
Image to Framestore Transfer 41us
Framestore Readout 3.2
Integrate for 3.2s
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X-rays in ACIS Full Frames
I3, subassembly O-K (0.525 eV)
I3, subassembly Cu-K (8.09 keV
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Initial Damage of the ACIS CCDs

• ACIS-S was at the launch-lock position,
  launch on DOY 204 (1999)
• First measurements of internal Fe-55 source were
  nominal on DOY 210
• ACIS Door was opened on DOY 220 and Aft
  Contamination Cover of the HRMA was opened on DOY
  223
• Measurements of calibration sources on Forward
  Contamination Cover (FCC) were nominal on DOY 224
  (see Elsner et al. SPIE 2000)
• FCC opened late on DOY 224, first light with
  ACIS, first unprotected perigee passage on DOY
  225
• ACIS-S at focus for 5 perigee transits, ACIS-I
  for 3 perigee transits, and ACIS-S/HETG for 2
  perigee transits
• Large increase in CTI discovered on DOY 250, DOY
  257 was the last unprotected perigee transit
  and DOY 260 was the last ACIS-S/HETG perigee
  transit

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Radiation Damage of the ACIS CCDs

• The CTI increase was caused by low-energy (100
  keV) protons, which scatter off of the mirror
  surfaces to the focal plane.
• All 8 FI CCDs exhibit a large increase in CTI,
  damage is restricted to the imaging region,
  framestore regions are unaffected.
• Neither of the BI CCDs shows any damage.
• No increase in the dark current of the FI CCDs.
• Irradiation of flight-like CCDs with 100-150 keV
  protons produces similar damage.
• Prigozihn et al. (2000) identify 4 types of
  traps, two with timescales of tens to hundreds of
  ms, one with hundreds of ms, and one on the order
  of several seconds
• Kolodziecjzak et al. (SPIE 2000) simulated the
  scattering of protons off of the HRMA and
  transmission to the focal plane, they conclude
  that it is plausible but their model
  underpredicts the damage by a factor of 3-4 and
  preliminary ground measurements indicate the
  scattering efficiency is not high enough

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Spectrum of 1E0102-723 No or little degradation
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Spectrum of 1E0102-723 Significant degradation
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Operational Response

• ACIS is always moved out of the focus of the
  HRMA before radiation belt transit.
• A 10 ks pad has been added on either side of
  the radiation belts.
• Data from other satellites with sensitivity to
  low-energy protons have been incorporated into
  the Chandra alert system.
• On-board thresholds for safing have been
  adjusted.

Mitigation Techniques

• Operate the CCDs as cold as possible, currently
  -120 C.
• Develop a phenomenological correction for the
  effects of CTI, improve the quality of the data
• perhaps use new modes in the future which will
  report additional information for each event
  which could lead to a better correction for CTI

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CTI Correction at Al-Ka (1.5 keV)
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CTI Correction at Mn-Ka (5.9 keV)
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Average ACIS-I CTI
Grant (MIT)
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Average ACIS-S3 CTI
Grant (MIT)
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ACIS Contamination Brief Description of the
Problem
Problem A layer of contamination is building up
on the ACIS Optical Blocking Filter
(OBF). Impact The contamination layer reduces
the transmission of X-ray photons through the
OBF, thereby reducing the number of photons which
reach the CCDs. This decreases the effective
area of the High-Resolution Mirror Assembly
(HRMA) and ACIS system. The effective area
is defined as the combination of the collecting
area of the HRMA, the transmission of the OBF,
and the detection efficiency of the CCDs. The
detection efficiency is defined as the
probabilty of detecting a photon which strikes
the detector. This effect is energy-dependent,
affecting low energies most. The decreased
sensitivity results in

• longer observing times to achieve the same
  science objective ( 15)
• loss of some science programs because they are
  no longer feasible (15)

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Comparison to Level 1 Requirements (Detection
Efficiency)

• Level 1 requirements on the ACIS instrument
  detection efficiency are greater than 5 between
  0.4 0.7 keV, 20 between 0.7-1.0 keV, and 50
  between 1.0-8.0 keV
• The decrease is due solely to the additional
  absorption of the contamination layer

• At the current rate of increase in the thickness
  of the contamination layer, the level 1
  requirement will not be met at 0.4 keV around
  November 2005

Bandpass Level 1 Req. Launch
Value 6/2004 Value
0.4- 0.7 keV gt 5 gt29 gt7
0.7-1.0 keV gt 20 gt59 gt35
1.0-8.0 keV gt50 gt50 gt50
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Contamination, Bakeouts CTI Increase

• Contamination was expected on ACIS during the
  mission since ACIS contains the coldest surfaces
  internal to the spacecraft
• The pre-launch plan was to bake ACIS out at
  regular intervals to minimize the buildup of
  contamination

• There have been two ACIS bakeouts to room
  temperature in the mission, both early in 1999.
  The first bakeout was part of the ACIS door
  opening procedure. The CCDs were functioning
  nominnally before and after this bakeout.
• The CCDs suffered radiation damage from
  low-energy protons (100 keV) in August and
  September 1999. Further damage has been
  minimized by moving ACIS out of the focus of the
  HRMA during radiation belt passages.
• The second room temperature bakeout was an
  attempt to anneal the CCDs (to reverse some
  of the effects of the radiation damage).
  Unfortunately, the CCD performance got worse
  after the second room temperature bakeout (CTI
  increased by 30).
• This leads to the expectation of increased CTI
  for another bakeout.

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Mitigation Options

1. Accept degradation, relax the level 1
   requirements on detection efficiency
2. Bakeout to remove the contamination

Proposed Bakeout Scenario

• Heat the ACIS detector housing (DH) from -60 C
  to 20 C
• Heat the ACIS focal plane (FP) from -120 C to
  20 C
• DO NOT Heat the Science Instrument Module (SIM)
  surfaces surrounding the ACIS aperture from -10 C
  to 10 C
• Maintain the hot phase of the bakeout for 1
  orbit (150,000 s)

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Risks Associated with Bakeout
Definition Risk to the spacecraft or instrument
health safety, and/or to the science mission.

• Thermal cycling results in a HW failure in the
  ACIS instrument
• Damage to the OBF
• CTI increases by a larger than anticipated amount
• Unexpected change in contamination
• 4a) contamination increases in thickness
• 4b) contamination returns quickly
• 4c) contamination migrates to another
  spacecraft system
• Thermal cycling has a negative impact on the
  spacecraft

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Risk Assessment
RISK MITIGATION IMPACT PROBABILITY
1. HW failure due to thermal cycling Assessment by ACIS engineering team, HW design, previous bakeouts Moderate Possible degradation Very low
2. OBF Damage Ground tests at NGST on spare flight OBFs Moderate Loss of science Very low
3. Larger than anticipated CTI increase Ground irradiation tests on spare flight CCDs Low Loss of science Very low
4. Undesirable change in contamination Simulations of bakeout, materials testing Moderate Loss of science Low
5. Thermal cycle has adverse effect on spacecraft Assessment by Chandra FOT and NGST Low Possible misalignment Very low
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Benefits of the Bakeout

• Restore the HRMAACIS effective area to close to
  launch values and restore the original margin
  against the level 1 requirements
• Provide an additional 2.8 Million seconds of
  observing time per AO, which will be 54
  additional Chandra observations per AO
• Restore classes of targets with soft spectra
  which are not currently feasible (such as
  supersoft sources, neutrons stars with soft
  spectra)

Costs of the Bakeout

• The bakeout and calibration observations will
  take 1 Million seconds. Given that the
  contaminant accumulation is slowing in time and
  we have gone 5 years without a bakeout, we expect
  that we would not desire another bakeout for at
  least another 5 years.
• The likely CTI increase of the FI CCDs will
  impact observations of extended objects on the I
  array through degraded spectral resolution
• The delay in some analyses until updated
  calibration products are available

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External Calibration Source Mn-L complex/Mn-K vs
Time
Grant (MIT) Analysis
Tennant, ODell (MSFC) Functional Form
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E0102 Spectrum vs. Time
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E0102 Count Rate vs. Time
DePasquale (SAO)
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Optical Depth vs. Time based on the Mn-L
complex/Mn-K
Vikhlinin (SAO)
Bottom of S3 CCD
Middle of S3 CCD
Contaminant is thicker along the edges of the I
and S array OBFs, thinnest in the middle.
Contaminant has reached over 80 of its maximum
depth.
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Material Investigation (from Kelly Henderson and
Marty Mach)

• Several materials were tested in an attempt to
  identify the contaminant
• GCMS was performed to determine the elemental
  ratios of the outgassing products for materials
  used on Chandra
• None of the materials tested had ratios similar
  to that of the ACIS contaminant
• None of the materials tested indicated
  fluorocarbons in the outgassing products, except
  Braycote, which evolved a very small amount
• It was suggested that radiation could enhance the
  outgassing rate of Braycote and other materials
• Braycote 601 grease irradiated w/ 27Co60 gamma
  radiation was more volatile and the only material
  that liberate fluorocarbons per GCMS and VODKA
  tests
• Most of the materials tested spanned the
  retention time (similar boiling point range) of
  the Braycote 601 grease. It was therefore chosen
  as the model compound

CONCLUSION The contaminant is most likely a
mixture of several materials and not just one
material.
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ACIS Optical Blocking Filter
ACIS-I OBF Al/Polyimide/Al 1200A/2000A/400A ACIS-S
OBF Al/Polyimide/Al 1000A/2000A/300A
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Thermal Models of the ACIS Instrument
Purpose In order to model and understand the
bakeout, one must know the temperatures of all
the surfaces the contaminant might encounter.
Modeling provided by Neil Tice at LMA, ACIS
thermal engineer pre- and post-launch Collimator
primary surface which the contaminant will
interact with on its way out of the instrument
during the bakeout Detector Housing upper
portion probably contains the majority of the
contaminant by mass and the OBFs are installed in
the DH OBFs significant temperature gradient
across the filters In order to model the bakeout,
the temperatures of the relevant surfaces in ACIS
must be known for 1) Normal operations, FP -120
C, DH-60 C 2) Bakeout conditions, FP 20 C,
DH20 C
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Tice (LMA)
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ACIS Filter Temperatures for Standard Conditions
Tice (LMA)
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Geometric model
OBA vent
SIM focus structure
SIM translation table
Optical bench (OBA)
ACIS collimator
Snoot
OBA stove pipe
ACIS camera top
ACIS OBF
TRASYS model by NGST/ H. Tran et al.
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Integrated Science Instrument Module (ISIM)
Translation Table
Focus Assembly
Top Hat Stove Pipe
ACIS Aperture
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Contaminant Path of Travel
ACIS Location
OBA Vent Locations
Contaminate Migration Path
Optical Bench Assembly (OBA)
Integrated Science Instrument Module (ISIM)
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10.DOP de-rated TOBF Mass column
ODell Swartz (MSFC)
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
NOMINAL
DE-RATED
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1.0DOP de-rated TOBF Mass column
ODell Swartz (MSFC)
NOMINAL
DE-RATED
1 ACIS OBF 2 Camera top 3 ACIS snoot 4 ACIS
collimator 5 SIM trans table 6 SIM focus
struc 7 OBA stove pipe 8 Optical bench 9 OBA
vent
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Limits on vaporization rates
ODell Swartz (MSFC)
Min to vent 0.2 g in 1 orb5?10-3 mg cm-2 s-1 _at_
Tcoldest
Min to clean OBF in 1 orb2?10-3 mg cm-2 s-1 _at_
TOBF-bake
Upper limit at OBF center1?10-7 mg cm-2 s-1 _at_
TOBF-ops
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Conclusions From New Simulations

• If the contaminant has a volatility of less than
  0.1 X DOPs volatility, a one orbit 30 C bakeout
  will not move a significant amount of the
  contaminant
• If the contaminant volatility is within an order
  of magnitude of DOPs volatility, a significant
  amount of the contaminant will vaporize and
  migrate to the cold surfaces at the top of the
  ACIS collimator and the SIM. The contaminant
  will then migrate very slowly back to the OBF and
  it may be years before a significant amount
  re-accumulates on the OBF
• If the contaminant volatility is an order of
  magnitude higher than that of DOP, a significant
  amount of the contaminant will vaporize and
  migrate to the cold ACIS collimator and SIM
  surfaces. The contaminant will then migrate back
  to the OBF such that after 1 year, the thickness
  will be 1/3 of the original thickness.

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Work Still to be Done (January 2005)

• ACIS team will conduct irradiation tests,
  analyze the results, and refine the prediction
  for the effect of another room temperature
  bakeout on the CTI
• The working group will prepare another briefing
  for the Chandra project and seek approval for the
  bakeout

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Orion Nebula
Orion Nebula, X-ray
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E0102 Chandra and ROSAT Images
Gaetz et al. 2000
Hughes et al. 2001 t 1000 yr
1 arcmin
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CAS-A ACIS S3 50ks
Gotthelf et .al 2001
t 350 yr
4 arcmin
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Cas A
1 Million second true-color Image of Cas-AGreen
ContinuumBlue FeRed SiHwang et al.(2004)
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Cas A
Cas-A The Movie
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• Crab Nebula (Mori et al 2002), compliments of
  Hester/Mori/Gaensler
• Wisps move outwards at 0.43c (similar
  features seen in optical/radio)
• Inner ring quasi-stationary
• Knots brighten over 6 months

Crab Nebula (0, 3, 6, 9, 12, 15, 18, 21 weeks)
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SN1987A Chandra and HST
Image Chandra Contours HST Burrows et al. 2000
2 arcsec
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SN 1987A, Montage
SN 1987A Montage
Burrows et al. 2000
ATCA 8 GHz
HST
ACIS 2000 Jan 17
ACIS 1999 Oct 6
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G292.01.8 A SNR Like They Outta Be
Hughes et al. 2001, Park et al. 2002, Camilo et
al. astro-ph/0201384
0.5-2.5 keV
2.5-8.0 keV
8 arcmin
t 1600 yr
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Summary of Advances in SNR Research with Chandra

• Resolve the X-ray emission into smaller and
  hopefully, physically meaningful regions
• Allow a detailed correlation with high
  resolution radio and optical data.
• Separate the outer blastwave from the ejecta so
  that one can use the outer blastwave for
  dynamical studies
• Discovery of new compact objects, some
  traditional pulsars, others perhaps a new class
  of objects Central Compact Objects.
• Discovery of new synchrotron nebulae.
• In the future, proper motion studies of
  shockfronts and bright knots.

High Angular Resolution is the Key !!!!!
We owe our gratitude to the thousands of
engineers and technicians who built AXAF/Chandra
!!!