Download Ball plasmoid - McCall Research Group

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Outline
• Introduction and
Motivation
• Ball Lightning
• Ball plasmoid
characteristics
• Adjusted
parameters
• Optical Emission
Spectroscopy
• Spectral Analysis
and Fitting
• Conclusions
• Future Work
http://drevol.com/en/blog/Nikola-Tesla-158-years-birthday-009
Tesla, N. Colorado Springs Notes: 1899-1900, Nolit, Beograd, Yugoslavia, 1978
Ball Lightning
• Sphere of light
• Up to 1m diameter
• Lasts many seconds
• Difficult to observe in
the field
• One documented
observation to date
• Formation / Lifetime
• Laboratory analogue:
Ball plasmoid
Image courtesy of the Wikimedia Commons
Cen, J.; Yuan, P.; Xue, S. Phys. Rev. Lett. 2014, 112, 035001
McNally, J. R. Preliminary Report on Ball Lightning, No. 3938; Oak Ridge National Laboratory: Oak Ridge, TN, 1966
Ter Haar, D. Phys. Scr. 1989, 39, 735
Endean, V.G. Nat. 1976, 273, 753-755
Wu, H. C. Sci. Rep. 2016, 6, 28263
Hardware
Discharge Characterization:
105 ms
99 ms
150 ms
200 ms
300 ms
10 cm
Detachment
1. Pre-initiation
a.
b.
Buildup
2. Buildup
a.
b.
Switch
Closes
Switch closes
Current begins to
flow (< cathode
spot threshold)
More current
begins to flow
Plasma forms at
electrode
3. Detachment
a.
Preinitiation
Plasma detaches
from electrode and
becomes plasmoid
i.
Buoyancy
OES Experiment: Whole Plasmoid
• Ocean Optics S2000: 200-500 nm, 0.5 nm resolution
- better efficiency in the blue/violet/UV
• Ocean Optics Jaz: 250-800 nm, 0.7 nm resolution
- better efficiency in the red
- measurements made with optical fiber
• Wavelength and intensity calibration with external sources
• Internal trigger: continuously fire when signal across chip is > 2% dark spectrum
Spectrometer
OES Experiment: Height Resolved
• Series of equal-sized
holes oriented
vertically
•
Spectrometer
0-40 cm
• “Field of view” of
spectrometer (fiber)
is larger than hole
Spectral Assignment
http://www.bristoldynamics.com/activity/laser-spectroscopy-and-pgopher/
• Use NIST Atomic Spectral
Database to assign atomic
transitions
• Use SPECAIR to “Auto-find”
transitions
• Extract appropriate molecular
info from Exomol and HITRAN
databases
• Use literature values to get other
spectroscopic constants not
included in these databases
• Generate molecular spectra with
PGOPHER
https://www.nist.gov/
Tennyson et al., J. Mol. Spec., 2016, 327, 73-94.
Rothman et al. Journal of Quantitative Spectroscopy & Radiative Transfer, 2013, 130, 4
http://www.spectralfit.com/
PGOPHER, a Program for Simulating Rotational Structure, C. M. Western, University of Bristol, http://pgopher.chm.bris.ac.uk
Example Spectra: Whole Plasmoid
Tungsten electrode, 7 kV
Example Spectra: Height Resolved
Hβ
O I (5P→5S)
0 cm
(cathode level)
+10 cm
OH
Example Spectra: Height Resolved
O I (5P→5S)
Hβ
+20 cm
OH
O I (5P→5S)
Hβ
+40 cm
Electrode Composition
Molecular Fitting
#
Trot OH [K]
0
No emission
1
4540 ± 490
2
3680 ± 360
3
3700 ± 350
4
3670 ± 350
5
3790 ± 370
Temperature Fitting
#
Trot [K] 0407-18
Trot [K] 0407-19
Trot [K] 0407-20
0
No emission
No emission
No emission
1
No emission
7680 ± 900
5910 ±740
2
5820 ± 730
5730 ± 720
5570 ± 700
3
5130 ± 650
5270 ± 670
4870 ± 620
4
4630 ± 590
4110 ± 520
4070 ± 500
5
4040 ± 510
No emission
No emission
Blackbody Fitting
This is not exactly a blackbody curve,
however, a Planck function can be fit to the
spectra
Possible mechanisms of continuum emission:
• Triatomics
• Thermal radiation
• Bremsstrahlung radiation
Summary
• First time-resolved measurements of OH rotational
temperature in ball plasmoids
• High temperature early in discharge, decreases over
time
• First continuum fits of ball plasmoid emission
spectra
• Possible radiation processes:
• Triatomic emission
• Bremsstrahlung radiation
• Thermal radiation
Future Directions
X-Band horn antennas
Plasmoid
Amplifier
Function
Generator
Frequency
Multipliers
Amplifiers
Splitter
(difference)
“Magic”
Tee
(sum)
Coax cable
Phase
Shifter
•
•
•
•
Attenuator
Amplifier
X-band interferometer operating at ~9.2 GHz
Measure phase shift and attenuation of beam induced by plasmoid
Calculate electron “column density” as a function of time
Deduce primary electron recombination mechanism?
Acknowledgements
• McCall Research Group
• Amber N. Rose
• Prof. Nick Glumac – instrumentation and emission spectroscopy
• Prof. J. Gary Eden – microwave interferometry