Date post: | 06-Jul-2018 |
Category: |
Documents |
Upload: | nguyenthuy |
View: | 215 times |
Download: | 0 times |
Bruno Altieri -- SCI-SDX
XMM-Newton
EPIC MOS long term stability &radiation damage effects
EPIC consortium meeting
Palermo, 16 October 2003
B. Altieri
XMM-Newton
2
Bruno Altieri -- SCI-SDX
Talk outline
• Charge Transfer Inefficiency (CTI)
• Energy scale
• Energy resolution
• Bad pixels and CCD damages
• Background
• Radiation environment
• Conclusion
XMM-Newton
3
Bruno Altieri -- SCI-SDX
MOS2 CTI
• reduction of the parallelCTI by a factor 3, at the MOScooling in November 2003
•serial CTI: constant sincelaunch
• very slow degradation rateobserved since
CTI = 1.2 10-5 @ rev 700
-120C-100C
XMM-Newton
4
Bruno Altieri -- SCI-SDX
MOS1 CTI
• MOS1 CTI significantlyworse than MOS2• the worse of all 14 CCDs.
• Improved by a factor 2.2at cooling
No major solar flare sincerevolution 433
-100C -120C
XMM-Newton
5
Bruno Altieri -- SCI-SDX
MOS CTI modeling (CCFs)• 8 time periods defined
• CTI = (a + b δt) . Eα with α(t,CCD) =0.35-0.7
• Slow degradation since cooling now measurable, to be implemented
XMM-Newton
6
Bruno Altieri -- SCI-SDX
CTI degradation rates• CTI degradation rates comparable for all detectors
– Radiation management succeeded in limiting rate of CTI degradation to acceptable levels.
• PN back-illuminated CCDs degrading more shows that a relative low dose ofsoft-protons is reaching the CCDs.
– Soft-protons can only contribute an upper limit of ~20% of the total radiation damage (Smith& Holland)
– proton dose estimated to 106 /cm2 from pn discarded line counter (Altieri,2003), far below theradiation test with 109 /cm2, where no change of properties was seen (Kendziorra, 2000)
• CTI dominated by energetic penetrating radiation (for both BI & FI CCDs)
pn (BI)(150µ m)
beforecooling
aftercooling
BI FI
d(CTI)/dt /year 1.3E-05 1.3E-05 2.0E-06 4.4E-06 1.4E-06
d(CTI)/dt /year /100µ m 8.7E-06 3.3E-05 5.0E-06 1.8E-05 5.8E-06
EPIC ChandraMOS (FI)(40µ m)
ACIS-I(24µ m)
XMM-Newton
7
Bruno Altieri -- SCI-SDX
MOS1 energy scale
• some over-correction,by 5-10 eV
• MOS1 gain could betuned further (<2.10-3)
• No spatial dependenceof the energy scale
6 keV
1.5 keV
XMM-Newton
8
Bruno Altieri -- SCI-SDX
MOS2 energy scale
• slight over-correction inthe past
• temperature dependencegain of the gain notcorrected, but ~1.5% onlyof scientific observationaffected, during eclipseseasons
• MOS2 gain ~OK
1.5 keV
6 keV
XMM-Newton
9
Bruno Altieri -- SCI-SDX
MOS energy resolution• Ground software (SAS) manages to restore most of energy loss, but inevitably
detector energy FWHW widens due to imperfect correction and statisticalnoise of charge trapping.
– Energy resolution rather constant since cooling
140eV@6keV
[email protected] MOS2
6 keV
1.5keV
XMM-Newton
10
Bruno Altieri -- SCI-SDX
Decay of the internal calibration source
Half-life = 2.7 years
longer and longer exposuretimes will be required ...
XMM-Newton
11
Bruno Altieri -- SCI-SDX
MOS bad pixels
Number of hot pixels at >1% recurrence frequency per CCD
• Not an issue for TM bandwidth• Bad pixels have virtuallyvanished since cooling
•No or limited impact of radiation
XMM-Newton
12
Bruno Altieri -- SCI-SDX
Micro-meteoroid events• Two events in revs 108 & 325
• The figure shows a 3d surfaceof E1+E2 over all CCDs, forthe seconds impact.
• The intensity was notuniformly distributed butshows a smooth peak onCCD7 and large spikes onCCD6.
XMM-Newton
13
Bruno Altieri -- SCI-SDX
CCD impact damage• The figure shows the
distribution of new bad pixelsoverlaid with a contour ofE1+E2.
• In exposures following theevent 27 bad pixels appearedon CCD6 and CCD7.
• The new bad pixels coincidewith the location where theenergy was greatest.
XMM-Newton
14
Bruno Altieri -- SCI-SDX
MOS background (1)
XMM-Newton
15
Bruno Altieri -- SCI-SDX
MOS background (2)
XMM-Newton
16
Bruno Altieri -- SCI-SDX
XMM-Newton radiation historyM. Casale
R. Gonzalez
XMM-Newton
17
Bruno Altieri -- SCI-SDX
Earth magnetosphere
XMM-Newton
18
Bruno Altieri -- SCI-SDX
Asymmetry of radiation profile• Asymmetry results from a
combination :– asymmetry of earth magnetic field wrt
rotational axis/center of the earth– asymmetry of the earth’s magnetic field
wrt to solar wind pressure– synchronisation of the XMM orbit with
earth rotation
• The two legs see different regions oftrapped particle belts when at thesame radius.
XMM-Newton
19
Bruno Altieri -- SCI-SDX
Evolution of orbital parameters
• perigee altitude increased from 13.000 to16.000 km
• longitude of ascending node decreased bymore than 90 degrees since launch
• balanced by a 70 degrees increase of perigeeargument
•⇒ rotation of the orbit: perigee tends to aligntoward the equatorial plane.
XMM-Newton
20
Bruno Altieri -- SCI-SDX
Orbit configuration wrt magnetosphere
Winter: low radiation Summer: high radiation
XMM-Newton
21
Bruno Altieri -- SCI-SDX
Modeling the XMM radiation
• Goal:– minimise manual commanding– optimise science window duration– limit failed observation re-planning– avoid spoiled observations in the archive.
• Problem:– radiation trend linked only to the drift of orbital parameters ?
• then how will it evolve after the orbit change manoeuvre ?– or also related to solar cycle ?
• more particles trapped during the solar minimum ?– especially soft-protons in the quasi-trapped region
• Correlation of soft-proton radiation with the pointing direction ?
XMM-Newton
22
Bruno Altieri -- SCI-SDX
Are soft-proton chaotic flares predictable ?
Rev 687
Rev 688
XMM-Newton
23
Bruno Altieri -- SCI-SDX
A simple model to start with?• Advance start of EPIC science
observations :– Perigee Passage + 4 hours, from
revolution ~700 onwards– until Feb. 2004 ?– ==> initial CALCLOSED dropped.
• XMM-Newton: 20-40% affected by soft-proton flaring
• Chandra: <10% ?– Science observations only above
70000km
XMM-Newton
24
Bruno Altieri -- SCI-SDX
Conclusion
• Cooling of the MOS CCDs was highly beneficial– stable properties (energy resolution and scale)– should minimize number of CCFs
• CTI, gain, including redistribution CCFs
• CTI : very simple model implemented SAS (CAL/CCF)– no count rate dependence– over correction of the energy scale,
• Long-term stability prospect
• Need to understand radiation environment trends