Laboratory Experiments for Studying the Emission of Nitrogen and Air
description
Transcript of Laboratory Experiments for Studying the Emission of Nitrogen and Air
Laboratory Experiments for Studying the Emission of
Nitrogen and Air
Andreas Ulrich, Andrei MorozovTechnische Universität München
Fakultät für Physik E12
4th Air Fluorescence WorkshopMay 17-20, 2006, Prague - Pruhonice
I) Excitation of dense gases with low energy electron beams
II) Shape of the excited volume
III) Correlation of quenching rate constants k and p‘ values
IV) Intensity ratios of N2 emission bands (experiments in Chicago and Garching)
V) Improvements
Vacuum Gas
Membrane
I) Excitation of dense gases with low energy electron beams
Typical parameters:
Electron energy: 15 keV
Beam current: 10 μA average
Pulses: 5 ns minimum
Gas pressure: 0.1 – 2 bar
Membrane: 300 nm SiNx
0 10 20 30 40 50 60 70 80 90 1000
10
20
30
40
50
60
70
80
90
100
Al, "Lenard"2650 nm
SiNx
300 nm
Ti, 1.1 mg/cm2
2439 nm
Tra
nsm
. (%
)
E (keV)
Experimental setup
Motivation for using low energy electrons for N2 emission studies:
High fluorescence yield at low energy
Copied from DPG-presentation 2006: Andreas Obermeier
Steel tube
Glowing gas
Silicon wafer with entrance
foil Z
Y
X
Ne, 250 hPa Ne, 500 hPa Ne, 1000 hPa
0 2 4 6 8 10 12 0 2 4 6 8 10 12 0 2 4 6 8 10 12 Distance, mm Distance, mm Distance, mm
II) Shape of the excited volume
The shape can be modelled using the program: „casino“ (P. Drouin, A. R. Couture, R. Gauvin, P. Hovington, P.
Horny, H. Demers, Univ. de Sherbrooke, Quebec, Canada (2002))
This will be important for absolute emission measurements using low energy electron beams!
III) Correlation of quenching rate constants k and p‘ values
Rprod.
τ0 τc
QpRT
pVknk
ratesQuenching
p
pI
Qp
Definition
QpI
pEfI
Qp
R
RRR
Rf
ratioBranching
exc
rad
collcollrad
rad
:
'1
1
1'
:
1
1
)(
11
1
1
1
:
0
0
0
The two approaches:
0 50 100 150 200 250
1
10
100
1E3
Inte
nsity
, co
unts
Time, ns
0 10 20 30 40 500,00
0,01
0,02
0,03
0,04
0 10 20 30 40 500,00
0,01
0,02
0,03
0,04
337 nm (0 0)
Rat
e, n
s-1
N2 pressure, hPa
R = a + b×P
a = (227.8 ± 6.6) ×10-4 ns
-1
b = (43.6 ± 2.5) ×10-5 ns-1 hPa-1
R = a + b×P
a = (236.1 ± 6.7) ×10-4 ns
-1
b = (41.9 ± 2.5) ×10-5 ns-1 hPa-1
357 nm (0 1)
Rat
e, n
s-1
N2 pressure, hPa
time spectra pressure dependence
the connection
Nagano et al. astro-ph/0303193 v3 26 Aug. 2003
qkp
0
' 1
Example:
N2 2P-Band, v=0 and v=1, 337 and 316nm
τ0 = 41.7ns (for both v)
kq = 1.2×10-11 cm3/s and
kq = 2.5×10-11 cm3/s, respectively
Results in
p‘ = 74.6 hPa and
p‘ = 35.8 hPa, respectively (10% error)
Morozov et al. Eur. Phys. J. D 33, 207 (2005)
In contrast to:
p‘ = 151.7 hPa and
p‘ = 88.3 hPa, respectively (10% error)
Nagano et al. astro-ph/0303193 v3 26 Aug. 2003
?
Potential reasons for the discrepancy:
Systematic errors ?
Collisional mixing of the vibrational levels ?
See: J. M. Calo and R. C. Axtmann, J. Chem. Phys. 54, 1332 (1971)
C, v=0, 1
B, v=0, 1, etc.
Non radiative quenching
Collisional quenching of v – levels by N2
Radiative transition
A model worked out by Andrei Morozov showed an increase of the p‘ value for the 337nm (v‘=0 to v=0) transition from 79.36 to 91.95 hPa using the data given in the publication by Calo and Axtmann. (I(p) modelled with and without coll. quenching of v levels and then fit using the regular formular.)
10
111
1
1000
'1
1
1
1
1
:mod
EFE
p
pI
pQpQ
pQF
EFEpQ
I
elExtended
d
v=0
n=1
τ0 Q1p τ1 Q1dp
Q1p
First test of the influence of vibrational relaxation via collisions:
Classical model, new model with vibrational relaxation, data from new model fit with classical model
Intensity ratios of nitrogen emission bands
Spectral response of McPherson 218. Preliminary measurements:
Black:W Strip-lamp
Blue:W Strip- lamp + UG11
Red:D2 Lamp
280 300 320 340 360 380 400 420 4400.0
0.2
0.4
0.6
0.8
1.0
1.2
S
ensi
tivity
(re
l. un
its)
(nm)
Spectral response of the „Rome“ spectrometer
Measured with a calib. halogen and a Hg pen-ray lamp, respectively
Spectrum of air recorded using electron beam excitation, McPherson model 218 VUV monochromator and photon counting:
Comparison of spectra of laboratory air excited by 10 keV photons (photoelectrons) and 10 keV electrons (APS Chicago and e- beam Graching)
Comparison of spectra of laboratory air excited by 10 keV photons (photoelectrons) and 10 keV electrons (APS Chicago and e- beam Graching)
Detail:
Comparison of the weakest and strongest lines analysed (Garching data):
Relative intensities of N2 emission bands:
Comparison of Chicago and Garching data with literature values
Relative intensities of N2 emission bands:
Comparison of Chicago and Garching data with literature values
Log – scale:
Analysis of the same Garching- data, two persons independently
Improvements:
We have bought a 100 W calibrated halogen lamp (LOT / Heraeus)
We will borrow a new calibrated D2 from GSI-Darmstadt (Plasma physics group)
Measurements of the absolute photon flux will be performed
Pressure dependences should be measured for the ~10 keV electrons
Acknowledgement !
Many thanks to Paolo Privitera, Hans Klages and all their coworkers for inviting me to participate in the Chicago experiment and KfA-Karlsruhe for paying for the trip.
Thanks to Reiner Krücken and MLL for supporting my trip to this conference.
I want to thank Jochen Wieser (TuiLaser/Coherent) for his help with the experiments and the apparatus, in particular the very stable power supply.
Thank you for your attention