The Mercury Imaging X-ray Spectrometer (MIXS): Lessons learned for the ATHENA Wide Field Imager

(WFI)

GW Fraser, A Martindale and C Thomas

Space Research Centre, Department of Physics and Astronomy, University of Leicester, UK

On behalf of the BepiColombo MIXS Team

1. BepiColombo ESA/JAXA mission to Mercury, launch July,2016, arrival 20222. MIXS – first true imaging X-ray telescope for planetary XRF

3. Enabling technologies - low mass MCP optics and DEPFET arrays4. DEPFET advantages include: radiation tolerance and high-temp operation

5. MIXS Flight Model delivery scheduled for Q3/20146. MIXS as a “pathfinder” for the Wide Field Imager?

• BepiColombo Science Requirements for the mapping of the elemental composition of Mercury on global, intermediate and local scales dictate two complementary X-ray channels

• Wide field-of-view – Non-Imaging Collimator MIXS-C• Narrow field-of-view – Imaging Telescope MIXS-T• Common detector format – 64 x64 pixel, 300 x 300 micron DEPFET

APS

QM MIXS

MIXS Functional Schematic

MEB MIXS Electronics Box 1660 gFPA Focal Plane Assembly 1330gFEE Front End Electronics 248gDPA Detector Plane Array

Detector Assembly

MIXS Electronic Block Diagram

ATHENA WFI Electronic Block Diagram (Figure 6 of Rau et al.)

Athena WFI (central detector) BepiColombo MIXS-T and -C

256 x 256 DEPFET pixels 64x64 DEPFET pixels100 x 100 microns 300 x300 micronsArray divided north and south Array divided north and southOperating Temp -40 degC Operating Temp -55 to +20 degCGateable (27 bias voltages?) Non-Gateable (25 bias voltages)Maximum Rate (1 Crab equivalent)

350,000 events/s

<150eV FWHM @ 6 keV 140 eV FWHM @-40 degC@6keV

MIXS-C LM6 room temperature switch-on (not gain calibrated 3 peaks)

Offset tracking

Increase of energy with time at start of observation is caused by the MEB tracking the offsets to their operating level after switch on.

MIXS-C QM operating at room temperature

Offset tracking

Noisy pixel identified by OBSW and turned off

Energy (arb.)

Energy (arb.)

Tim

e ( a

rb. A

nd n

on li

near

)

Even

ts p

er b

in

Noisy pixel identified by OBSW and turned off

The noisy pixel in the QM is only visible at room temperature and is turned off by the OBSW after it is identified by autonomous algorithms

Gain, Offset and Noise

X-ray calibration of MIXS FM

Carbon and Oxygen band response

Titanium Self-fluorescence

Stainless steel target

Conclusions

• The BepiColombo MIXS DEPFET focal plane array provides a direct technical precursor, in FM build for an ESA Cornerstone mission, for the ATHENA WFI

• Sensor control, communication and internal calibration have been implemented in a rad-hard FPGA

• Split pixel, hot pixel.. Corrections have been implemented in OBSW• Front End Electronics have been implemented in low-mass, hybrid

components• MIXS DEPFET detectors have been subjected to environmental test

and detailed X-ray calibration and provide a basis for power and mass estimates for the WFI

• TRL 6 now