1. Simulations as a tool for higher mass resolution spectrometer: Lessons from existing observations
1G. Nicolaou, 1M. Yamauchi, 1,2H. Nilsson, 1M. Wieser, 3A. Fedorov, 1D. R. Castillo and 2L. Berčič
Motivation
ESCAPE: M5 Mission
Science Objective: How and at what rate is Earth slowly losing its atmosphere to space? Determine escape mechanisms
High resolution measurements:
Distinct ion species and their isotopes
Requirement
1Swedish Institute of Space Physics (IRF), Kiruna, Sweden
2Luleå University of Technology, Kiruna, Sweden
3Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS/Universite de Toulouse, Toulouse, France

2. Simulations as a tool for higher mass resolution spectrometer: Lessons from existing observations
1G. Nicolaou, 1M. Yamauchi, 1,2H. Nilsson, 1M. Wieser, 3A. Fedorov, 1D. R. Castillo and 2L. Berčič
Heritage
ICA (Rosetta) and IMA (Mars Express/ Venus Express):
Examples of successful separation of H2O, O, O2 and CO2
Modifications
NOIA (ESCAPE proposed mission)
Geometrical modifications-Electrostatic Analyser
and magnets shape/size
1Swedish Institute of Space Physics (IRF), Kiruna, Sweden
2Luleå University of Technology, Kiruna, Sweden
3Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS/Universite de Toulouse, Toulouse, France

3. Lessons from observations
Simulations as a tool for higher mass resolution spectrometer: Lessons from existing observations
1G. Nicolaou, 1M. Yamauchi, 1,2H. Nilsson, 1M. Wieser, 3A. Fedorov, 1D. R. Castillo and 2L. Berčič
Lessons from observations
Unwanted effects: Sector and mass channel cross-talk, contamination, noise
More to be considered
Different detector design
Understand the nature of contamination → how to remove or avoid
Better calibration on response → mass/sector sensitivity knowledge
1Swedish Institute of Space Physics (IRF), Kiruna, Sweden
2Luleå University of Technology, Kiruna, Sweden
3Institut de Recherche en Astrophysique et Planetologie (IRAP), CNRS/Universite de Toulouse, Toulouse, France

4. ICA/IMA design and principle
The Ion Composition Analyser (ICA) on ROSETTA and the Ion Mass Anylyser (IMA) on MEX/VEX
ICA/IMA design and principle
Credit : E. Behar
(Left) ICA/IMA instrument cross section. Ion trajectories through the instrument are shown. (middle) azimuth sectors orientation and (right) elevation direction detected during the elevation scans

5. Mass detection Deflectors: Elevation selection ESA: E/q selection
Magnets: m/q selection
The MCP is “divided” in 16 azimuth sectors and 32 mass rings:
For the same E/q heavier species land closer to the center

6. Simulations of ICA/IMA response
Goal: to achieve as realistic simulation as possible
SIMION: 3-d ion tracing software
The actual flight model design files are used
Studied: position of different species in the MCP
Purpose:
compare with flight data
Extrapolate to low energies
Modifications for better performance
a) Instrument design in SIMION software, b) cross section of instrument and c) top vie if MCP in SIMION ion tracing software

7. Compared to calibration
ICA calibration:
available for one sector
few species
Energies>300eV
ICA simulation:
Cannot resolve sector differences
Uniform response
“Perfect” magnets

8. Directions for improvement
Geometrical modifications for better mass peak separation (introduced by Nicolaou et al.,2016)
a) Cross section of a simplified ICA-IMA like design with spherical ESA and a modified designed with toroidal ESA, and longer magnets. Trajectories of different species through the magnets are also shown. b) top view of the detector for the two designs. The distributions show better seperation for the modified model.

9. Proposed instrument: Nitrogen-Oxygen Ion Detector (NOID)
Instrument for ESCAPE proposal (ESA’s M5)
Based on ICA/IMA design (geometrical modifications only)
More to be consider: narrower sectors, magnets of different shape, MCP of different shape (Nicolaou et al., 2016)

10. Flight data: Lessons we learned
Mass peaks can be successfully fitted to the IMA-MEX data:
From Castillo et al., 2017
Gaussian fitting does not work all the time!!!

11. Flight data: Lessons we learned
ICA data is more challenging:
Broader signal
Many possible species from the comet
Many heavy species are recorded in low E/q
Strong mass bin and azimuth cross talk
Limited calibration (not at all <300eV/q)

12. Flight data: Lessons we learned
Challenges
Mass rings (bins) cross talk
Inactive mass rings (give no signal)
Non uniform background

13. Flight data: Lessons we learned
Non-uniform response
Noise analysis
Energies where no-signal is expected would give ideally uniform background
Not the case
Each anode has different sensitivity?

14. Flight data: Lessons we learned
Azimuth sectors cross-talk:
Selected periods when solar wind beam illuminates specific sector
Find extremely correlated signal in other sectors
Quantify the cross-talk and remove (already done for protons)

15. Flight data: Lessons we learned
“ghost” counts: particles scattered over the mass anodes
“ghost” counts pollute the information of ion mass
ICA Data
IMA (MEx)Data
“ghost” counts have been removed in order to fit the IMA data mass peaks
Not “clean”
“clean”

16. Conclusions
Preliminary geometrical modifications of the existing design are promising for higher mass resolution
Flight data indicate more problems:
mass/azimuth cross-talk
Contamination
Non uniform response (diff. efficiency of sectors and anodes)
Directions of improvement:
Re-design sector/anode system
Understand the contamination
Calibrate the response in more detail

17. Thank you