evaluation of the evaluated data...2012/09/04 · equation) with bolsig+ which is based on the...
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![Page 1: Evaluation of the evaluated data...2012/09/04 · equation) with BOLSIG+ which is based on the two-term approximation of the electron distribution function See Hagelaar and Pitchford](https://reader033.vdocument.in/reader033/viewer/2022060711/60773d4058b089524e2629ac/html5/thumbnails/1.jpg)
Y. Itikawa
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At the IAEA Consultants Meeting
7-9 February, 2012, NIFS
my personal experience in data evaluation was reported.
Today
one step further !
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There is no standard method of data evaluation.
→
The result of evaluation (i.e., the recommended data) may be different depending on who evaluates them.
We need
evaluation of the evaluated data
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Examples of attempt:
(1)Consistency of the total scattering cross section
(2)Swarm parameters
(3)Modelling result
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Consistency of
the total scattering
cross section
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QT = Σ Qs S= elastic and all inelastic processes
QT can be measured directly.
We can test
QT (measured) = Σ Qs ?
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0.01
0.1
1
10
100
cross
sec
tion (
10
-1
6 c
m2)
0.001 0.01 0.1 1 10 100 1000
electron energy (eV)
elas
tot
mom transf
rot J=0 2
v=0 1
ion(tot)
diss
ion(diss)
a
B
C
e + N2
vib v=0 1
e + N2 Itikawa, JPCRD 35, 31 (2006)
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Energy (eV) 100 200 500 1000 uncertainty
elastic 5.6 3.5 1.85 1.0 20%
ionization 2.51 2.19 1.36 0.85 5%
dissociation 1.16 0.95 20%
electronic
exc
0.43 25%
sum 9.70 6.64 3.21 1.85
Total
(measured)
8.94 6.43 3.55 2.13 5%
e + N2 (cross sections in 10-16 cm2 )
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e + O2 Itikawa, JPCRD 38, 1 (2009)
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Energy (eV) 100 200 500 1000 uncertainty
elastic 4.78 3.15 1.72 1.10 20%
ionization 2.43 2.28 1.46 0.922 5%
dissociation 0.33 0.29 34%
electronic
exc
0.41 0.26 0.13 0.08 25%
sum 7.95 5.98 3.31 2.10
Total
(measured)
8.68 6.24 3.58 2.08 5%
e + O2 (cross sections in 10-16 cm2 )
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This relation generally holds, when uncertainty of individual cross sections is considered.
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Details
We have no data, or less reliable data, for excitation and dissociation.
Furthermore, a part of excitation
contributes to diss.
→ Double counting ?
But contribution of exc & diss to QT is small. It is not a serious problem.
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The most serious problem is the uncertainty of elastic cross section.
Can we measure the elastic cross section within an uncertainty of 5% ?
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Swarm parameters
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Website for
collecting, displaying and
downloading
electron-scattering cross sections
and
swarm parameters
(mobility, diffusion coefficient,
reaction rate etc)
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Developed and maintained by
the Toulouse group (L.C.Pitchford et al.)
See
S.Pancheshnyi et al.
Chem. Phys. 398, 148 (2012)
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(1)Make an intercomparison of the cross section data sets
(2)Calculate swarm parameters and compare them with experimental values
(with solving the Boltzmann
equation)
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with BOLSIG+
which is based on the two-term
approximation of the electron
distribution function
See
Hagelaar and Pitchford
Plasma Sources Sci. Technol. 14, 722 (2005)
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All the following figures of swarm parameters are provided by Leanne Pitchford.
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0.1 1 10 100
1x1024
1025
Experiments : Nakamura
calculations : Itikawa
µN
(m
. v.
s)-
1
E/N (Td)
N2
1 Td = 10-21 V m2
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0.1 1 10 100
0.01
0.1
1
10
calculations
Itikawa data
Expriment
Crompton
Jory
Crompton 1963
townsend
Naidu
Warren
Fletcher
Wedding
DT
/µ (
eV
)
E/N (Td)
N2
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0.01 0.1 1 10 100 1000 10000
1x1024
1025
1026
Experiments
Nelson
Pack
Herreng
Nielsen
Fleming
Doehring
Naidu
Fromhold
Schlumbohm
Roznerskhi(below 27.5Td)
Roznerskhi(taken 293K)
Mobili
ty (
/m/V
/s)
E/N (Td)
Calculations
Biagi LXCat and Bolsig+
Phelps LXCat and Bolsig+
Trinite LXCat and Bolsig+
Biagi Monte Carlo
Itikawa No Dissoc LXCat and Bolsig+
O2
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0.1 1 10 100 1000
0.1
1
10
Calculations
Biagi LXCat and Bolsig+
Phelps LXCat and Bolsig+
Trinite LXCat and Bolsig+
Biagi Monte Carlo
Itikawa No Dissoc LXCat and Bolsig+
D/
(eV
)
E/N (Td)
experiments
Fleming
Rees
Huxley
Naidis
O2
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Mobility and diffusion coeffcient calculated with Itikawa’s cross sections generally agree with the corresponding measured values, except for some discrepancy at high E/N.
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A part of electronic-state excitation contributes to dissociation. Can we separate that part ?
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In the present calculation, we simply ignore the dissociation process.
We found that
the dissociation has a significant effect in the case of O2,
but much less effect in the case of N2.
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Chemical modelling
with reaction rate data
base
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A wide variety of molecules have been found in interstellar space
→ (Interstellar) Molecular Cloud
→ Formation of stars
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Calculation of synthesis and destruction of interstellar molecules
with solving time-dependent rate equations
→ Molecular abundance (time dependent)
Needs reaction rate coefficients
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V. Wakelam et al.,
Space Sci. Rev. 156, 13 (2010)
Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges
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udfa
(The UMIST Database for Astrochemistry)
420 species, 4573 reactions
www.udfa.net
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OSU model
(Ohio State University, Astrophysical Chemistry
Group)
468 species, 6046 reactions
www.physics.ohio-state.du/~eric/research.html
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KIDA
(Kinetic Database for Astrochemistry)
474 species, 6090 reactions
kida.obs.u-bordeaux1.fr/models
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Comparison with observation
Example:
negative ions (recently observed)
using udfa
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Observation vs model : Molecular abundance In the circumstellar region IRC+10216
Error bars of calculation are due to the uncertainties in the rate coefficients.
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Discrepancy is caused probably by
incompleteness in the chemical network
or
wrong reaction rates of key reactions involving those species
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Intercomparison of models
Example
abundances of H3O+, HCO+,
etc
Kida vs OSU vs udfa
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Molecular abundances in a dense cloud (T=10 K)
Black dotted lines are 2σ error bars of kida results.
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The three different chemical models are consistent with each other, if the uncertainties of the rate coefficients are considered.
But
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Quite a small number of reaction processes have measured or calculated rate coefficients at low temperature.
Then many processes have rate coefficients obtained by a combination of experiment, theory and common sense (chemical intuition !).
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Any attempt of application of the evaluated data can be a chance of the evaluation of them.
In this sense, comments of users are helpful for evaluation of the evaluated data.
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Website of database should have a page for feedback where users can easily contact and send their comments.