ENA detection techniques:Instrument considerations
Elisabetta De AngelisIFSI-INAF Rome, Italy
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008
Outline
• Energetic Neutral Atoms instrument brief history
• Principal ENA generating processes
• ENA instrument schematic
• Low-Energetic Neutral Atoms case
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 2
The detection of ENA:Hystorical survey
• 1950 evidence of ENA in the Earth environment (Doppler shifted emission of H (6563 Å) in an aurora)• 1959• 1961• 1968 1° instrument that detect ENA (in situ). • 1971 failed experiment ( Mars 3/RIEP)• 1975 project not used (slotted disk velocity selector for LENA, J.H. Moore et al, Sp.Sci.Instrum. 1,377 , 1975)• 1982 IMP7,8 – ISEE 1 validation of remote sensing magnetosphere processes with ENA detection• 1985 1° ENA image from ISEE-1 (Roleof et al. JGR 90, 10991,1985)• 1990 ULYSSES (GAS)• 1991 CRRES• 1992 GEOTAIL (MICS)• 1995 ASTRID (PIPPI)• 1995 SAC/B (ISENA)• 1997 CASSINI (INCA)
New millenium
• 2000 IMAGE2000 IMAGE• 2003 MarsEXpress (Aspera3)2003 MarsEXpress (Aspera3)• 2003 Double Star (NUADU)2003 Double Star (NUADU)• 2005 Venus Express (Aspera4)2005 Venus Express (Aspera4)• 2006 Twins2006 Twins
To be launched To be launched
• 2008 Chandrayyan 2008 Chandrayyan • 2008 IBEX2008 IBEX• 2013 BEPI COLOMBO2013 BEPI COLOMBO
} study of ENA investigation possibility
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 3
1. Principal processes The charge exchange process
A generic charge exchange collision between energetic ions and neutral gas atoms can be represented by the following relation
where I1 + represents an ion of species 1, and A is an atom of species 2. The involved species could be the same, e.g., H+
+H→H+H+ (that is, one of the most common process in space plasma, given the presence of a great quantity of protons and Hydrogen). In figure a scheme of the process is showed.
2121 IAAI
ENA energy up to hundred keVENA energy up to hundred keV
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1. Principal processes Sputtering process
max
min
,E
E
iieSi
H dEEEfdE
dRY
dE
d
If we consider the energy distribution of sputtered atoms fs(Ee,Ei) and the sputtering yield Y If we consider the energy distribution of sputtered atoms fs(Ee,Ei) and the sputtering yield Y (Lammer et al., 2003), we can calculate the flux of ENA originated via sputtering processes(Lammer et al., 2003), we can calculate the flux of ENA originated via sputtering processes
where R is the fraction of the considered species in the soil composition. where R is the fraction of the considered species in the soil composition.
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 5
Energy distribution function for sputtered particles of ejected Na
ENA energy of few eV up to hundred eVENA energy of few eV up to hundred eV
2. The ENA instruments
When we speak about an ENA instrument we should always specify the energy range of the instrument, because each design is chosen in order to accomplish a specific energy range. In fact, nowadays a unique detection technique for the entire ENA energy range doesn’t exist. It starts from few eV up to hundreds of keV, and such an extended range is able to acquire different information, useful for different environments. Conventionally, we can consider the ENA separated into three categories, depending on the energy range:
LENA (Low Energetic Neutral Atom) few eV- 1keVMENA (Medium Energetic Neutral Atom) 1keV – 30 KeVHENA (High Energetic Neutral Atom) 30 KeV- hundreds of KeV
The limits of these ranges are not frozen, and often they differ from each other or are partially superposed, but they will help us to distinguish the diverse techniques applied.
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 6
2. The ENA instruments:The IMAGE package
3 different energy ranges3 different solutions
2. ENA instrument schematic
Input Analysis Detection
Task
1. ENA direction
2. Photons rejections
3. Charged particles
deflection
1. Particle
identification
2. Energy analyses
1. Time of Flight
2. Energy resolution
Elements
and
Solutions
1. Sectored collimator to
have needed angular
resolution
2. Rejection techniques:
Filters-gratings-
photons/ENA trajectory
separation
3. Deflection plates
1. Carbon Foil or
conversion surface
generating
secondary electrons
2. Electrostatic
analyser for ionised
ENA
1. Start and Stop
detectors: 1-D, 2-D
MCP; SSD
2. Pulse height signal
or position detection
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 8
2. ENA instrument schematic
ENAPhotons
Charged Particles
Input Analysis Detection
Foil /surfaceESA
Stop/position detector
Time of Flight
Start element
Ions
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 9
e
3. L-ENA caseL-ENA Instrument techniques
A commonly used method to identify neutral atoms is to convert them to ionic one with a subsequent energy analysis of the ions by an electrostatic method.
Some Examples : LENA (Image), NPD (Aspera3-4), Chandrayaan-1, IBEX-Lo → conversion surf
IBEX-Hi → ultra-thin foils
This kind of instruments use an Indirect detection technique.The interaction element introduces uncertainty in terms of angular and energy scattering.
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008
i+ i- n
Trasmission: ultrathin foilTrasmission: ultrathin foil
ENA
Reflection: conv. Surf.Reflection: conv. Surf.
i+ i- n
ENA
In particular interaction in transmission or in reflection with foil or conversion surface has been In particular interaction in transmission or in reflection with foil or conversion surface has been used in the L-ENA instruments.used in the L-ENA instruments.
10
ENA in ultrathin Carbon-foil
Efficienza di ionizzazione : f(H+) = 5% per E=1keV f(H+) = 35% per E=30keV f(H0) = 1- f(H+) - f(H-) ~ 1 - f(H+)
H.O. Funsten, D.J. McComas, B.L. Barraclough,Opt.Eng. 32, 3090 (1993) H.O. Funsten, D.J. McComas, E.E.Scime, Opt. Eng. 33, 349 (1994)
Angular scattering at 1 keV→ >10 degrees
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 11
ENA– Conversion Surface : MgO example
(Scattering of Atoms and Molecules of a Magnesium Oxide Surface, M.Wieser,P. Wurz,K.Bruning, H. Heiland, NIM B,192, pp 370-380,2002)
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 12
L-ENA case
ENAPhotons
Charged Particles
Inpu t Analysis Detection
Stop/position detector
Time of Flight
Foil /surfaceESA
Ions
Start element
A Direct detection technique (without any conversion unit and/or electrostatic analysis) has not yet used in the low energy range for this instrumentation.The unique attempt of this phylosophy : J.H.Moore et al, Space Sci. Instr 1, 377, 1975 a slotted disk instrument with high power consumption, tested but not used for ENA
Shuttering Start system can be the good solution to have a direct Time-of-Flight analysis in the range of the low energetic neutral atoms
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 13
Micro-shuttering techniques:the ELENA example
STOP detector
Shuttering membrane
Position encoder
START section
ToF chamber
ENA flux
Fixed membrane
400 nm 20 m400 nm400 nm 20 m20 m
1. Scanning electron micrographs (SEM) images of one of the samples of Si3N4 membranes manufactured by the Institute of Photonics and Nanotechnology of CNR (Rome, Italy) (Orsini et al, in press)
2. Piezoelectric ultrasonic actuator (compact design, fast response and low power consumption) ranging up to 100 kHz
3. A capacitive based encoder has been studied to control the frequency and the instantaneous displacement of the ultrasonic shutter payload and the shutter phase, together with the alignment of the grids (Di Giulio, Engineering thesis)
The START SECTION
See Di Lellis presentation on Wednesday May1414
Direct detection of L-ENA
PRO• No interactions of ENA with any element preserve
information of energy and direction• Low weight and consumption• Photons can be distinguished from ENACONTRO• Detector efficiency at low energies• Limit on mass resolution• Photons can enter into the entrance with ENA and reach
detector
Joint SERENA-HEWG Conference Santa Fe, May 12-14, 2008 15
Conclusions
• From Scientific point of view the ENA detection has proved a great potentiality and now it promise new goals with the L-ENA detection
• From Technological point of view new solution has been solicited and the under development systems could open new possibilities of investigation.
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