THEMIS End of Prime Mission ReviewESA- 1 UCB, November, 19 2009 ESA Plasma Instrument End of Prime Mission Review Dr. James McFadden and Dr. Charles Carlson.

THEMIS End of Prime Mission Review ESA-1 UCB, November, 19 2009

ESA Plasma InstrumentEnd of Prime Mission Review

Dr. James McFadden and Dr. Charles CarlsonUC Berkeley SSL


Requirements and Specifications

Measurement

• The ESA instrument measures 3-D electron and ion energy distribution functions over the Energy range 10 eV to 30 keV. Typical energy sweep has 16 or 32 energy samples• A full 4-pi distribution measurement is produced during each spin• Sweep rate of 32/spin gives dense sample of 3-D particle distributions• Raw measurements are compressed to selectable “reduced distributions” and moments

Implementation

• Ion and electron “top-hat” electrostatic analyzers have 180 degree field of view• Field of view is divided into 8 electron and 16 ion elevation bins• Plasma analyzers have hardware programmed functions: sweep rate, sweep waveform, energy range, data collection rates. These functions are set by command.• Higher level data formatting and computed products are carried out in the ETC board.• Energy sweep is exponential with programmable starting energy and step ratio

ESA Plasma Instrument continues to operate nominally producing high quality data products with no anomalous behavior.


Block Diagram

• Electronics functional design is identical to FAST (with ACTEL upgrades)• Three circuit modules plug together for efficient assembly and test• MCP pulse amplifiers are Amptek A121 with programmable gain• All discrete logic, counters, and HV DAC drivers are Actel FPGAs• HV supplies are a mature design built at UCB SSL


ESA efforts to facilitate data analysis

• ESA data is available within 24 hrs after collection

• ESA instrument performance is described in two publications : McFadden, J.P., Carlson, C.W., Larson, D., Angelopoulos, V., Ludlam, M., Abiad, R.,

Elliott, B., Turin, P., Marckwordt, M. (2008), The THEMIS ESA plasma instrument and in-flight calibration, Space Sci. Rev., doi: 10.1107/s11214-008-9440-2.

McFadden, J.P., Carlson, C.W., Larson, D., Bonnell, J., Mozer, F., Angelopoulos, V., Glassmeier, K.-H., Auster, U. (2008), THEMIS ESA first science results and performance issues, Space Sci. Rev., doi: 10.1007/s11214-008-9433-1.

• Detailed instrument parameters are available on the THEMIS ESA web page: http://themis.ssl.berkeley.edu/esa_table.shtml

• Data products are describe on the THEMIS ESA web page: http://themis.ssl.berkeley.edu/modes_dataproducts.shtml

• Sources of non-ideal response in ESA data are described on the THEMIS web site: http://themis.ssl.berkeley.edu/non_ideal.shtml


REQUIREMENT ESA DESIGN

IN-1. The Instrument Payload shall be designed for at least a two-year lifetime

Compliance. All 10 ESAs functioning nominally after 2.5 years.

IN-2. The Instrument Payload shall be designed for a total dose environment of 33 rad/year

(66 krad for 2 year mission, 5mm of Al, RDM 2)

Compliance. No evidence of radiation degradation of the detectors or of the electronics.

IN-3. The Instrument Payload shall be Single Event Effect (SEE) tolerant and immune to destructive latch-up

Compliance. No SEEs or latch-ups of the ESA sensors.

IN-7. No component of the Instrument Payload shall exceed the allocated mass budget in THM-SYS-008 THEMIS System Mass Budget.xls

Compliance. No mass budget problem.

IN-9. No component of the Instrument Payload shall exceed the power allocated in THM-SYS-009 THEMIS System Power Budget.xls

Compliance. No power problems during 2.5 years.

IN-13. The Instrument Payload shall survive the temperature ranges provided in the ICDs

Compliance. No observed anomalies during eclipse.

IN-14. The Instrument Payload shall perform as designed within the temperature ranges provided in the ICDs

Compliance. No ESA temperature problems.

Mission Requirements



IN-16 The Instrument Payload shall comply with the Magnetics Cleanliness standard described in the THEMIS Magnetics Control Plan

Compliance. ESA complied and experienced no magnetic problems.

IN-17 The Instrument Payload shall comply with the THEMIS Electrostatic Cleanliness Plan

Compliance. ESA complied and experienced no electrostatic cleanliness problems.

IN-18 The Instrument Payload shall comply with the THEMIS Contamination Control Plan

Compliance. ESA complied and experienced no contamination problems.

IN-19. All Instruments shall comply with all electrical specifications

Compliance. ESA complied and experienced no electrical problems.

IN-20. The Instrument Payload shall be compatible per IDPU-Instrument ICDs

Compliance. ESA was compatible and experienced no communication problems with the IDPU and ETC. ETC table loading problems were resolved during commissioning phase prior to first tail season.

IN-21. The Instrument Payload shall be compatible per the IDPU-Probe Bus ICD

Compliance. ESA was compatible.

IN-23 The Instrument Payload shall verify performance requirements are met per the THEMIS Verification Plan and Environmental Test Spec.

Compliance. ESA performance met the Verification Plan and Environmental Test Specification.

IN-24 The Instrument Payload shall survive and function prior, during and after exposure to the environments described in the THEMIS Verification Plan and Environmental Test Specification

Compliance. ESA survived all pre-launch testing and continues to function nominally.

Mission Requirements



IN.ESA-1. The ESA shall obtain partial moments of the 3D plasma electron and ion distributions in the magnetotail plasma sheet

Compliance. ESA partial moments are demonstrated to exceed science requirements.

IN.ESA-2. The ESA shall measure differences in velocity and ion pressure between probes in the magnetotail plasma sheet

Compliance. ESA provides the ETC board with plasma measurement data sufficient for computing the required moments.

IN.ESA-3. The ESA shall measure ion and electron distributions that are associated with the current disruption process

Compliance. ESA continues to measure 3-D distributions in the tail and throughout the magnetosphere, magnetosheath and solar wind.

IN.ESA-4. The ESA shall be capable of measuring ion moments and differences of those moments in the magnetosheath and solar wind.

Compliance. The ESA capability to accurately measure moments in the magnetosheath was demonstrated in the ESA instrument papers.

Science Requirements



IN.ESA-5. The ESA shall measure ions and electrons over an energy range of 10eV to 30 keV

Compliance. Satisfied by design.

IN.ESA-6. The ESA energy sampling resolution, dE/E, shall be better than 25% FWHM for ions and electrons

Compliance. Capability exceeds dE/E<25%, but implementation varies. Typical sampling resolution is ~31% for better dynamic range.

IN.ESA-7. The ESA shall be capable of measuring i+ and e- energy flux of 10^4 to 10^9 keV/cm^2/s/Str/keV


IN.ESA-8. The ion ESA geometric factor shall be attenuated in the solar wind to avoid saturation.

Compliance. High fluxes of solar wind ions are accommodated by small area anodes. Testing shows detectors do not saturate however dead-time corrections are needed.

IN.ESA-9. The ESA shall supply partial energy moments at one spin time resolution.


IN.ESA-10. The ESA shall have a 180 deg. elevation FOV with a minimum angular resolution of 22.5 deg.


IN.ESA-11. To resolve the solar wind, the ESA shall have a FOV with enhanced resolution of ~ 6 deg.


IN.ESA-12. The ESA shall produce measurements of particle distributions over the entire 4pi steradian field of view in one spin period.


IN.ESA-13. ESA calibration shall ensure <20% relative flux uncertainty (not including statistical uncertainty) over the ranges defined above.

Compliance. In-flight relative calibrations indicate relative flux errors are<5%.

Performance Requirements


ESA Moment Accuracy

ESA data demonstrated to be accurate in when ESA energy range contains all significant plasma.

Ne=Ni

Pressure balance demonstrated across the magnetopause.


Bow Shock and Foreshock

Good density agreement in sheath & foreshock where ions are hot.


Solar Wind Measurements

Solar wind mode allows the THEMIS ESAs, which were not optimized for the intense solar wind ion flux, to perform adequately, without saturation as demonstrated by Ni=Ne.

With corrections for s/c charging, solar wind electrons are accurately measured as demonstrated by agreement between components of Vi and Ve.


Cross Calibration with EFI

eSSTeESAiSSTiESA

Ni Ne

Vx Vy Vz

Vll Vperp

Ex -VxBx

Ey -VxBy

Ez -VxBz

Ex Ey Ez

Bx By Bz


ESA and SST combined

Accurate density measurements

Errors in electron velocity measurements due to density fluctuations


MCPs monitored monthly

ESA’s MCP detectors have been monitored monthly since the commissioning phase to test for any degradation and to maintain proper gain.

The tests toggle the preamplifier threshold between the nominal value of ~30 fC to a value equal to the nominal gain (~160 fC). Variations in counts that are less than a factor of 2 demonstrate good MCP detector gain.

MCPs show little evidence of any average degradation. MCP bias voltages have not required changes for a year.

Ions

Electrons


Intense Solar Wind Ions

Concern existed that intense solar wind ions might saturate the MCP detectors and degrade response.

Detector threshold is toggled from nominal values through increasing threshold level to reveal actual MCP gain.

These tests show that MCPs signals decrease in amplitude, but not enough to impact detection at nominal threshold.

Solar wind electrons with nominal MCP full threshold toggle test provide a baseline for comparison.

Ions

Electrons


Bremsstrahlung Background

Energetic electrons measured by the SST detectors produce X-rays that contaminate the ion ESA measurement.

Moment calculations without removal of this background will overestimate ion density (green). Simple background removal algorithms (black) help, but still do not provide good agreement with electron density (red).

Ions

Electrons


eSST Determines iESA Bgnd

We estimate background using both the eSST and iESA data.

Cross fitting these two estimates allows corrections due to changes in response with time.

Using eSST rather than iESA estimate eliminates removal of real counts at low energy.

Ions

Electrons

Background

Density after background subtraction


ESA Non-ideal Behavior

ESA data is not perfect and the THEMIS web site and instrument papers outline sources of non-ideal response.

For example, even with accurate density measurements, errors in electron velocity measurements may be present due to density fluctuations on the time scale of the spacecraft spin period.


Electron ESA MCP degradation

Response after first tail season.

Another minor source of non-ideal behavior was discovered after the first tail season, when the eESA experienced high count rates at low energy due to photo-electrons from the axial booms.

This change in detector response necessitated modifications to the ground software and added several months to the in-flight calibration effort.

Such changes were necessary in order to get accurate electron moments, especially in the solar wind.

Response before first tail season.


ESA Lessons Learned

• Analyzer concentricity essential to good measurements and can be easily achieved with a good design.

• Tuning the analyzers to have identical energy sweeps greatly simplifies data analysis and in-flight calibrations.

• Coast phase with close proximity of multiple satellites greatly simplifies cross calibration of instruments.

• Fast signal amplifiers (short dead-time) are essential for ESAs on magnetospheric missions.

• Multiple data products that complement each other greatly simplify data analysis and in-flight calibration efforts.

• Built in test electronics simplifies in-flight instrument monitoring.• Leakage fields through analyzer grids can impact sensor response• MCP droop in intense solar wind not important.• Two electron sensors looking in opposite directions are essential for

accurate Ve measurements when density fluctuations are present.• Ebanol-C is better than Gold Black for UV rejection.• Combined plasma measurements (ESA+SST) are required for

correct plasma moment calculations.


Publication History and Data Maturity

THEMIS Papers utilizing ESA Data: • 2008 – 2 ESA instrument papers published• 2008 – 22 science papers published• 2009 – 26 papers published to date• 2009 – >16 papers submitted

Data Analysis Software• ESA raw and level 2 data available within ~24 hrs of collection. • Data analysis tools available to all, regular improvement to software.• Level 2 data is regenerated after significant changes to software.• Data will continue to improve with age like a good bottle of wine.

The ESA team will continue to assist the science community, facilitating access to ESA data and evaluating proper use of these data, when possible, within our limited resources.


Summary Performance

ESA Prime mission requirements• No failures or anomalies during prime mission• ESA met all mission and science requirements• ESA met or exceeded all performance requirements• ESA team has provided software and calibrated data • Over 50 papers with ESA data published

ESA Current Status• No noticeable degradation of HV sweep supplies• MCPs have >1kV head room for future bias voltage increases if

needed• No increase in background noise since launch• In-flight calibrations correct for low-energy localized degradation

of electron detectors• No significant localized degradation for ion sensors exposed to

intense solar wind fluxes.


Future Improvements

ESA Data Work in Progress• Bremsstrahlung X-ray background subtraction • GF corrections for eESA low energy MCP degradation• New software algorithms for more accurate moments• New software algorithms to handle glitches in s/c potential• Algorithms to calculate density based on s/c potential

ESA Planned Developments• Scattered electron background subtraction• Composition estimates based on Ne/Ni differences• S/C potential estimates of density • More accurate dead-time corrections for solar wind ions

THEMIS End of Prime Mission ReviewESA- 1 UCB, November, 19 2009 ESA Plasma Instrument End of Prime Mission Review Dr. James McFadden and Dr. Charles Carlson.

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