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The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
OUTLINEOUTLINE
•General scientific aspects: Mercury’s General scientific aspects: Mercury’s Exosphere.Exosphere.
•Surface emission: Ion Sputtering and Surface emission: Ion Sputtering and BackscatteringBackscattering
•ELENA Instrument description (part of ELENA Instrument description (part of the BepiColombo/SERENA suite)the BepiColombo/SERENA suite)
Plasma
ionsions
keV ENA
Plasma-airless bodies interaction
Charge-ExchangeCharge-Exchange
SurfaceSurfaceIon-SputteringIon-Sputtering
10s eV ENA
ionsions
SurfaceSurfaceIon-BackscatteringIon-Backscattering
100s eV ENA
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
SW precipitation
(Massetti et al, 2003)
BIMF =(0,0,-10) nT
BIMF =(0,5,-10) nTPdyn=16 nPa
BIMF =(0,5,-10) nTPdyn=60 nPa
Flux(cm
-2 s sr keV)
-1
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Solar wind impact on a surface
An ion impacting (1) on the surface produces different effects:(2) back scattering, (3) neutralization and back scattering, (4) surface ion sputtering(5) electron emission (6) photon emission (7) adsorption (8) chemical sputtering: displacement and change of the surface mineralogy
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
•Reflection•Backscattering
•Ion sputtering•Chemical sputtering.
Solar wind impact on a surface
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Surface Ion Sputtering process
Ion sputtering products depend on:• the composition and the chemical structure of the surface; • the impinging plasma flux.
Surface release of neutrals due to energetic ion impacts
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Back-scattering from the Moon
•The BS energy spectrum goes up to almost 1 keV (Wieser et al., 2009)•The backscattering reflection yield is between 10-20% (Mc Comas et al., 2009)
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Energy distribution of sputtered particles
H escape O escape
Ca escape
Fe escape
Ca O HFe
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Surface release processesDifferent release processes can have different efficiencies as a function of latitude and longitude/LT at Mercury due to surface compositions and mineralogy together with external conditions, as solar irradiance or plasma precipitation. (from Killen and Ip, 1999)
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Generally, the upper part of the atmosphere where the column density is so low (less than 1014 cm-2) that the collision frequency between particles becomes negligible. Exobase is the boundary between collisional and not collisional regimes (Earth case: about 500 km altitude).
In the case of absence of an atmosphere (Mercury case), we refer to surface-bounded exospheres. It is the result of a complex dynamic equilibrium with the surrounding systems, mainly: surface, magnetosphere and outer space. In this case the exobase is considered the surface itself.
Exosphere
The exosphere is the boundary between the planet and the open space. So its investigation is a way to know the mechanisms and interactions acting today as a proxy of what happened in the ancient times.
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Sputtered High Energy AtomsWhy do we wish to detect SHEA (neutrals at energies >10 eV) to investigate the ion sputtering process?Because below 10 eV the ion-sputtering
products mix to other release process, and the particles do not maintain the initial direction (due to gravitational effects) so that the emission location on the surfaces cannot be easily recognized (Milillo et al., 2011).
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
(Environment Simulation Tool@IFSI)The Goldel Age of Solar System
Exploration
Particles released at different energy rangesEnergy range: <0.06 eVEnergy range: 0.06-0.3 eVEnergy range: 0.3-1.5 eVEnergy range: 1.5-10 eVEnergy range: 10-40 eVEnergy range: 40-200 eVSHEA detection provides a map of
plasma precipitation regions and an imaging of particle emission from surface.
Stefano Orsini
Settembre 2012
Instrument package on board BepiColombo/MPO
SERENASearch for Exospheric
Refilling and Emitted Natural
Abundances
Units:ELENA: Emitted Low-Energy
Neutral Atoms
STROFIO: Start from a ROtating FIeld spectrOmeter
MIPA: Miniature Ion Precipitation Analyser
PICAM: Planetary Ion CAMera
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
ELENA is a Time-of-Flight (TOF) system, based on oscillating shutter (operated at frequencies up to a 100 kHz) and mechanical gratings: the incoming neutral particles directly impinge upon the entrance with a definite timing (START) and arrive to a STOP detector after a flight path. In this way the low-energy neutral particles are directly detected, without using elements of interaction.
STOP detector
Shuttering membrane
Position encoder
START section
ToF chamber
ENA flux
Fixed membrane
Parameter ActualEnergy range <0.02- 5 keV (mass dependent)Velocity resolution v/v Down to 10% Viewing angle 4.5ox76o
Angular resolution 4.5ox4.5o (actual)4.5°x2.4° (nominal pixel)
Mass resolution M/M H and heavy speciesOptimal temporal resolution 40 sGeometric factor G 2. 10–5 cm2 sr Integral Geometric factor 6 10–4 cm2 sr
The ELENA Instrument
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
ELENA START Section: shutter system
The shuttering element of the ELENA detector consists in a couple of nano-patterned self standing silicon nitride membranes, one facing the other and separated by a distance between 1 and 5 μm, in order to have the correct number of time of flight channels. One membrane is fixed while the second one is moved respect to the other by means of a piezoelectric actuator, at a frequency up to 50 kHz.
ELENA membranes are of 10x10 mm2 area, 1µm thick Si3N4 with slits of
the order of 200nm and 1,4 mm pitch.
SERENA PM#19, Milan, 22-23 May, 2012
ELENA shutter Static and dynamic High-frequency test
with ion beam
Dynamic case: V=23V: freq=42kHz
Static case: 0-100V (0-6m) piezo elongation : 3 apertures at step 1,4m.
Static test: verifies the 1.4mm pitch of the membranes; it confirms the open/closed condition inside the 24 Volt elongation available.
Dynamic test: up to 52kHz (without damage) in the requested voltage range (DV≤24V). The offset has to be optimized to see the double aperture in the oscillation.
0 20 40 60 80 100
0
500
1000
1500
2000
2500
3000V=24V
Data: Data1_BModel: Gauss Chi^2 = 13517.88693R^2 = 0.98728 y0 123.79287 ±46.18093xc 48.99452 ±0.09244w 7.04025 ±0.25959A 22993.10289 ±1019.78183
C/1
0s
Piezo Voltage (V)
Ion beam He+, 1keV15-02-2012
SERENA PM#19, Milan, 22-23 May, 2012
0 20 40 60 80 100
0
500
1000
1500
2000
2500
3000V=24V
Data: Data1_BModel: Gauss Chi^2 = 13517.88693R^2 = 0.98728 y0 123.79287 ±46.18093xc 48.99452 ±0.09244w 7.04025 ±0.25959A 22993.10289 ±1019.78183
C/10
s
Piezo Voltage (V)
Ion beam He+, 1keV15-02-2012
Static test1keV He+ beam
Dynamic test (10kHz)1keV H beam
Dynamic test (52 kHz)2keV He+ beam
The Goldel Age of Solar System Exploration Stefano OrsiniSettembre 2012
MCP EfficiencyMCP EfficiencyEfficiency measurement for the standard MCP with Hydrogen, Helium and Oxygen at energies from 10 to 1000 eV.
We can observe a good agreement with the only existing data on this argument in the range of 30-1000 eV (Stephen et al, 2000; Peko et al., 2000)
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Time-of-flight resolution for a membrane hole of 200 nm, 0.7 um of amplitude, and 1.5 um of membrane separation (those parameters are
best expectations from technological development) Expected ToF resolution is 1/8.
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Left panel: analytical prediction of countrates for Ion Sputtering signal.
Right panel: Montecarlo simulation of countrates.
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Left panel: analytical prediction of countrates for Ion Back-scattering signal.
Right panel: Montecarlo simulation of countrates.
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
Noise – Background due to the neutral generation of ion-sputtering and back-scattering inside the instrument.
Simulation of SHEA detection at Mercury by
BepiColombo/MPO/SERENA-ELENA
(Orsini et al, 2008)
Thanks to the BepiColombo/SERENA package we will have simultaneous measurements of precipitating plasma (MIPA), circulating plasma (PICAM), and neutral gas composition (STROFIO) and SHEA observation (ELENA), for a complete investigation of the IS process.
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
The Goldel Age of Solar System Exploration
Stefano Orsini
Settembre 2012
IN SUMMARY…..IN SUMMARY…..
•The exosphere of Mercury is the region where the interaction between planet and Solar System environment occurs.
•The SERENA particle suite is designed for observing this region along the BepiColombo MPO Orbit. In particular, ELENA will be able to measure the planet’s surface emission via Ion Sputtering and Backscattering, thus providing an image of the ion precipitation areas, together with an estimate of the soil emitted elements.