SAOA Grazing Incidence X-Ray Telescope(GI-XRT) for Solar-C

Ed DeLuca & Leon Golub
Harvard-Smithsonian Center for Astrophysics

Solar-C Meeting 18-21 Nov. 2008

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Outline GI vs. NI Trade Space Characteristics of the GI XRT for Solar-C High energy imaging of the corona
 Temperature discrimination
 Large dynamic range imaging
 Time resolution
 Integrated science observations– Ubiquitous Reconnection– Ubiquitous Waves– MHD and Plasma Processes
 Conclusions

Nov 19 2008 3SAO

GI vs NI Trade SpaceGISAOPROCON

 Broad temperature response, cansee all of coronal plasma Moderate spatial resolution(0.5” - 0.3”) possible

 Fe XVII available, the mainemission line between 3-8MK

 Images have a large dynamic
range (detector issue) Robust design - energetic photons
are easier to detect

 Need multiple filters fortemperature resolution
 Image stabilization difficult

NI Relatively isolated temperature
response Relatively isolated temperature
response → multiple telescopes

 High spatial resolution (0.1”-0.03”possible) Charge spreading in detector

 Large collecting area possibleNov 19 2008 4

 Need large entrance filters

Coronal Imaging – Dominance of Fe XVII in Active CoronaSAO

Fe line fractions as a function of temperature (solid lines are most recent models, Raymond)Imaging Fe XVII (Fe+16) is critical for following the evolution of magnetic structures before the on-set of instabilities

Note Log Scale

Nov 19 2008 5

Suggested GI-XRT Characteristics: Geometry

 4.0 m focal length– 0.5 arcsec pixel at 10µm size
 25 cm radius (at the intersection of primary and secondary surfaces)– 1.8 deg graze angle at intersection
 40 mm long primary– and 50 mm long secondary to reduce vignetting off-axis
 45 deg wide segment of full circle– optic will be polished as a flat, not cylindrical, piece.
 Wolter-I design– modified for wide field, similar to XRT Flat detector– can be shifted ~0.2 mm forward of on-axis best focus
 F.O.V.: 2kX2k ≈ 1000 arcsec = 16 arcmin– Full Sun if 4kX4k detector available– SAO development program, 8µm pixels, APS sensor, NkXNk
Nov 19 2008 6SAO

GI-XRT Characteristics: Comparison to XRT Optic

Propose a segment of full optic as
indicated above, with larger graze
angle for increased collecting area
(and longer λ diffraction limit).

Nov 19 2008 7SAO

Encircled energy curves for XRT flight
optic, <2 arcsec diameter @ 50% EE.
Figuring optic as a flat will allow
improved performance – better figure,mid-frequency and microroughness.

GI-XRT Characteristics: View of the Optic

Inner thermal baffle
Entrance Aperture
Optic
Mounting bracket

See next slide for detailed view of mirror and mount.
Nov 19 2008 8SAO

GI-XRT Characteristics:
Optical Assembly With Focus Mechanism

X-Ray Telescope

Nov 19 2008 9SAO

GI-XRT Characteristics:
Full Telescope (Conceptual) – Entrance to Focal Plane

Nov 19 2008 10SAO

GI-XRT Characteristics:
Flexures Used for XRT Mirror Mount

For GI-XRT the angled portions would not be needed.
Nov 19 2008 11SAO

GI-XRT Characteristics:
Resolution v. Field Angle for Hinode XRTXRT operates at two positions: best on-axis for small f.o.v.
and ~200 µm forward of best focus for full field imaging.
Nov 19 2008 12SAO

GI-XRT Characteristics:
Telescope Wavelength Response•XRT cut-off (R=10%) is 5.6Å.
•GI-XRT on Zerodur is 12Å.
•With Ir coating, GI-XRT cutoff
is 6.2Å (and no dip at OVII)
Nov 19 2008 13

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GI-XRT Characteristics:
Wavelength Response•XRT cut-off (R=10%) is 5.6Å.
•With an Ir coating there issignificant response around 5Å
for an angle of 1.8 degrees anddown to 3-5Å at 1.35 degrees.
Nov 19 2008 14

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GI-XRT Characteristics:
Entrance Filter Temperature Models

Shown: final heat shield layer with telescope entrance filter installed.
Two cases were run: Five solar constants on Al filter (3.5 mm wide)and Five Suns on larger area, 6 mm wide to allow heat shield motions.
Assumed cooling straps in LL and UR corners, at 20 C.
Nov 19 2008 15

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GI-XRT Characteristics: Results

Worst-case model (larger illuminated area) shows ~3 C rise at worst location.
Total power conducted through straps is 1.1 W.
Nov 19 2008 16

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Coronal Imaging: Analysis FiltersSAO

 We can consider a wheel withseveral positions for X-ray
spectral diagnostics.
 Right: Al entrance filter (from1-300Å) Four thicknesses of Be at focal
plane filters (from 1-30Å).

Be, 9 µm
Nov 19 2008 17

Al, 2000 Å

Be, 2000 Å

Be, 30 µm

Be, 1 mm

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Temperaturesensitivity of XRTFilters.
GI-XRT will havebetter hightemperature
discrimination.

Nov 19 2008 18

Expected Exposure Times for GI-XRT

XRT observations of a quiescent AR in Al/Poly (0.36s) and Thin Be [=9 µm] (2.0s). GI-XRT
has Ageom = 2.5 cm2 , about same as XRT. For linear unresolved features, expect ~same τexp.
Nov 19 2008 19SAO

High Energy Imaging
SAOImaging below from below 5 Å to a diffraction limit of 60-100Å

30 MK

FeXVIIOVII & FeXVII

NeX

MgXII

SiXIII

SXVI
SXV

FeXXV

SiXIV

Fe XXIV: 10.65, 10.66, 10.78, 11.3, 11.45
Fe XXIII: 11.0, 11.74
O VIII: 18.97

Fe XXI: 12.29
Fe XX: 12.82, 12.83, 12.91, 12.93, 12.95
Ni IX: 13.45
O VIII: 18.97
Fe XIX:13.46, 13.50, 13.52
Fe XVIII: 14.22
Fe XVII: 15.01, 15.26, 15.46, 16.79, 17.05, 17.110 MKTesta, 2008

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High Energy Imaging
SAOSpectral Response with an angle of 1.8 degrees and Ir coating

30 MK

Nov 19 2008 21

10 MK

High Energy Imaging
SAOSpectral response with an angle of 1.35 degrees and Ir coating

30 MK

Nov 19 2008 22

10 MK

Temperature Discrimination
SAO

If an integrating detector is used a large set of filters is needed for energy
discrimination.
– Coarse temperature discrimination is possible with 2-3 filters.
– Full differential emission measures can be built using 6-12 filter combinations.
– There is a trade off between high cadence and temperature discrimination
Photon counting detectors give true imaging-spectroscopy– Focal plane filters are needed to prevent flux pile-up during flares.
– See the next talk for details

Nov 19 2008 23(Reeves, 2008)

Magnetic Field Line Mapping
2007-May-02 17:30 UTMDI+SOT/SPPF modelSAO

2007-May-02 11:31 UT

2007-May-02 14:59 UT

KSO/H-alpha

XRT MDI+SOT/SP

Insert Flux Rope

MagnetoFriction

NLFFF Model(Su, etal 2008)

Nov 19 2008 24

Magnetic Field Line Mapping

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Large dynamic range in coronal emission


A key problem with seeing all of the plasma is that the dynamic
range of the image exceeds the dynamic range of the CCD byorders of magnitude.

Active pixel sensors allow (in principle) for separate exposure
times at each pixel.
– An image is built from pixels read at different rates. Consider a 5s integration:in the core of the AR the pixels may be read 20 times (0.25s exposures),while the pixel seeing large loops are exposed for the full 5s. The
accumulated image is then formatted and stored for processing.
– With an APS the cadence can be set based on the physical process being
studied. If a low cadence is acceptable, long integration times can be usedwithout concern for saturated images.
– The Automatic Exposure Control program is built into the detector for thesedevices.

Seeing all of the coronal plasma– Essential for following the topology of complex and dynamic magneticstructures.
– Separating out the hot plasma - using a set of thick filters.
– Observing transitions from closed to open field lines - coronal dimming.

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Integrated Science Observations

Nov 19 2008 27SAO

Integrated Science Observations
Ubiquitous Reconnection– Magnetic requirements for reconnection• Vector Fields in photosphere and chromosphere• Coronal mapping of field lines before during and after reconnection event• NLFFF models– Plasma requirements for reconnection• Identification of pre-reconnection loops• Pre-reconnection plasma properties: density & temperature– Types of reconnection:Sweet-Parker, Petschek, Hall MHD, QSL• Field configurations around reconnection site
• In-flow velocities• Reconnection outflows, exhausts– Particle acceleration• Requirements: When does it occur - (needs Hard X-ray or radio)• Energy contribution: measure energy deposition in the chromosphere• Direct looptop heating:– Plasma acceleration• Jets• Outflows/exhausts– Dissipation processes• Direct heating in closed loops• Micro-flares, nano-flares

Nov 19 2008 28SAO

Integrated Science Observations
 Ubiquitous Waves– Identification of wave types: fill in the K-Omega diagrams for thesolar atmosphere• Transverse oscillations• Intensity oscillations• LOS velocity oscillations– Wave energy, transport and dissipation• Wave amplitude• Wave propagation and reflection• Localized wave heating• Wave initiation

Nov 19 2008 29

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Integrated Science Observations
 MHD and Plasma Processes– MHD stability and instability• The onset of ideal instabilities• Transition to adjacent meta-stable states– MHD topological constraints• Null points in the solar atmosphere• Separators and Quasi-separators• Helicity and energy– Beta ~ 1 plasma• Radiative processes• Magnetic field diffusion• Reconnection

Nov 19 2008 30

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Conclusions
 Broadband X-Ray observations are critical for understanding the coronal
response to photospheric and chromospheric magnetic field evolution.
– The primary coronal emission line if Fe XVII, this can only be imaged with asoft x-ray telescope.
– Hot and super hot thermal plasma is most easily seen in soft x-rays.
Following the rapid evolution of this plasma can only be done with a soft xray telescope.
– Seeing both the bright and faint coronal plasma is possible with a new Active
Pixel Sensors
 Temperature discrimination from 1MK to 50MK is possible with a single
telescope– DEM studies with Hinode/XRT have demonstrated that multi-filter
observations can be used to measure the thermal evolution of coronal plasmas– Photon counting detectors offer the promise of true spectral imaging!
 New mirror designs extend GI capabilities to shorter wavelengths andhigher spatial resolutions– A factor of two increase in imaging will give us a dramatically new look at
the corona– Increased sensitivity to hot and super-hot plasma will allow us to study
fundamental physical processes at work in the corona.
Nov 19 2008 31

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