On phenomena in ionized gases
Download 9.74 Mb. Pdf ko'rish
|
- Bu sahifa navigatsiya:
- Studies of laser-induced plasma in argon using emission spectroscopy and laser Thomson scattering: thermodynamic equilibrium and
- 2. LTE in the argon plasma
- 3. TS for the electron parameters measurements
- Electric field measurements in DBD plasma jet using intensity ratio of helium lines
- Figure 1
- W-band Extended Interaction Oscillator based on a pseudospark-sourced electron beam
- Effect of Plasma Activated Medium on human Head Neck cancerous Tumor Spheroids.
- PTR-TOF analyzis of glow discharge products in Titan related atmosphere
|
3. References. [1] C. Charles and R. Boswell, Phys. Plasmas 11 (2004) 1706. [2] H. Byhring et al., Phys. Plasmas 15 (2008) 102113. [3] N. Gulbrandsen et al., Phys. Plasmas 22 (2015) 033505. Topic number 8 Ratio 357
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
357
T. Pięta UP 1 P , M. Sankhe 2 2
U K. Dzierzega 1 , S. Pellerin P 2 P , M. Wartel 2 , W. Zawadzki 1 , and B. Pokrzywka 3
P P
P
P
3 Mt Suhora Observatory, Pedagogical University of Cracow, 30-084 Kraków, Poland
Scattering of electromagnetic waves by free electron of a plasma, named the Thomson scattering is a powerful and largely used method to measure important plasma parameter – the electron temperature T e and density n e . Thomson scattering has played an important role in the studies of nuclear fusion plasmas where it is still the most reliable method for measurements of the electron temperature. However, using high power probe laser beam to generate a scattered signal by free electrons can lead to plasma heating via inverse Bremsstrahlung and thus can modify the plasma parameters. In this work, we have studied the effect of the probe beam laser energy on T e and n
e in
argon plasma and the existence of the local thermodynamic equilibrium (LTE).
The plasma was created with frequency doubled Nd:YAG laser, at 532 nm pulses of 4.5 ns duration and a repetition rate of 10 Hz, by focussing the laser beam in a chamber filled with 1 bar argon. For the Thomson scattering (TS), another Nd:YAG laser at 532 nm, named “the probe laser”, with similar duration as the plasma generating one and energy from 1 mJ to 15 mJ, was used. The probe laser beam is directed perpendicularly to the plasma generating one and the emission from laser induced plasma and the scattered light were observed at 90° and imaged onto an entrance slit of a spectrograph (Acton SP- 2750i). The radiation scattered from free charges is mainly due to electrons because their mass is much lower than the mass of ions resulting in their much higher acceleration in an electric field of the laser and consequently large dipole radiation. Applied to laser- induced plasma, TS allows to directly determine parameters of the plasma electrons e.g. T e and n
e
without any assumption about plasma
thermodynamic equilibrium. 2. LTE in the argon plasma Laser-induced plasma (LIP) is usually described statistically assuming the local thermodynamic equilibrium (LTE). At this approach, velocities of plasma components, populations of their energy levels and chemical composition of plasma are described by the Maxwellian velocity distribution function, the Boltzmann distribution function and the Saha-Eggert equation, respectively. Each of these functions is dependent on the distinctive temperature: kinetic, excitation and ionic - which are equal under LTE conditions. Unfortunately, it is very common that the LTE plasma is assumed a priori, without any experimental verification. Even if such validation takes place, usually only optical emission methods are applied. The main goal of this work was to investigate the equilibrium state of laser-induced plasma in argon at different stages of its evolution using optical emission spectroscopy (OES) and laser Thomson scattering (LTS) technique 1 . Spatially resolved electron temperature and electron density were directly derived from TS spectra while excitation temperature was calculated from the spectra of argon atoms and ions employing the Boltzmann plot method. Our preliminary results show huge discrepancy between intensity ratios of ionic to atomic argon lines computed with measured electron density and temperature and assuming plasma in LTE, and those directly obtained from emission spectra. It implies either incorrect data processing or some principal problems with thermodynamic state in such kind of plasma.
3. TS for the electron parameters measurements Using high power probe laser beam to generate a scattered signal by free electrons can lead to plasma heating via inverse Bremsstrahlung and modify the plasma parameters Our first results show that in general the electron density seems not to be disturbed or modified by the probe laser. It is not the case for the electron temperature: Te could be considerably increased by the probe laser beam.
1 K. Dzierżęga, A. Mendys, B. Pokrzywka, What can we learn about laser-induced plasmas from Thomson scattering experiments, Spectrochim. Acta Part B 98 (2014), 76 358
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Electric field measurements in DBD plasma jet using intensity ratio of helium lines
M. M. Kuraica P 1 P , U G. B. Sretenović 1 P , V. V. Kovačević P 1 P , I. B. Krstić P 1 , B. M. Obradović 1 , N. Cvetenović 1, 2
and R. Brandenburg 3 P
P 1 P
P
P
3 Leibniz Institute for Plasma Science and Technology (INP Greifswald), Greifswald, Germany
In this paper a method is proposed and tested for electric field measurements in the streamer head of DBD helium plasma jet. The method uses intensity ratio of two helium singlet lines: He I 2 1 P-
1 D at 667.8 nm and He I 2 1 P-3
1 S at 728.1 nm. The method is based on our earlier work in helium dielectric barrier discharge (DBD). Collisional-radiative model for the involved atomic levels is utilized to obtain the functional dependence of the line ratio on the local electric filed strength. The obtained values of the electric field are compared with the results obtained by Stark polarization spectroscopy.
One of the most promising and patient friendly plasma devices for biomedical applications is non- thermal atmospheric pressure plasma jet. It can be found in various constructions and under various operation conditions. Non-thermal atmospheric pressure plasma jet requires noble gas as working media and AC or pulsed high voltage supply. It is a source of guided ionization waves, typically one ionization wave – streamer per one voltage half cycle. If discharge gets in contact with target, streamer becomes only one part of the entire discharge which transforms to transient glow discharge. The electric field strength is one the most important parameters of streamer discharges and the knowledge of the electric field in the streamer head can give information about other parameters, such as electron density and production of different active chemical species. The well-established Stark polarization spectroscopy method suffers from a low intensity of used helium lines, thus the new les demanding method would be of great interest [1,2]. Here we present preliminary results of the electric field measurements in the streamer head of DBD helium plasma jet using the intensity ratio of two helium singlet lines: He I 2 1 P-3
1 D at 667.8 nm and He I 2 1
1 S at 728.1 nm [3]. 2. Experiment Investigated DBD plasma jet consisted of quartz capillary of the inner diameter of 1 mm and outer diameter of 2 mm, with two metallic electrodes wrapped around it. The amplitude of applied sinusoidal voltage was 2.5 kV and the frequency was 10 kHz. Five millimetres downstream the exit tube copper grounded electrode was placed. High resolution spectrometer equipped with iCCD camera was used for all measurements. 3. Results Figure 1 presents comparison of the results obtained by two methods. The preliminary results are promising and further studies should be preceded. -1 0
2 3 4 5 6 7 8 9 0 5 10 15 20 25 30 U = 5.0 kV pp E [kV /cm] z [mm]
Line ratio Stark polarization spectroscopy Glass tube Gro
u n d e d pl at e el ec tr od e G rou nd ed r
ing el
ec tr od e Effluent
Figure 1: Comparison of the electric field strength inside the capillary of the plasma jet and in the effluent obtained by two independent methods.
[1] M. M. Kuraica and N. Konjević Appl. Phys. Lett. 70 (1997) 1521–3 [2] G. B. Sretenović, I. B. Krstić, V. V. Kovačević, B. M. Obradović and M. M. Kuraica J. Phys. D. Appl. Phys. 47 (2014)102001 [3] S. S. Ivković, G. B. Sretenović,
B. M. Obradović, N. Cvetanović and M. M. Kuraica J. Phys. D. Appl. Phys. 47 (2014) 55204
6
XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
W-band Extended Interaction Oscillator based on a pseudospark-sourced electron beam
A.W. Cross 1 , H. Yin
1 , L. Zhang 1 , W. He
1 , Y. Yin
2 , J. Zhao 3 and A.D.R. Phelps 1
P 1 P
2 University of Electronic Science and Technology of China, Chengdu, 610054, China 3 P
The pseudospark discharge is a low-pressure gas discharge, capable of generating extremely high currents within short rise times by means of a hollow cathode structure. A high-quality, sub- millimetre diameter electron beam was generated during the discharge process which possesses a high current density and brightness. A pseudospark (PS) sourced electron beam did not require the use of an external guide magnetic field as the beam is self-focused by ion channel focusing. The PS electron beam was used to drive a W-band (75-110 GHz) Extended Interaction Oscillator (EIO). The EIO combines the merit of a short interaction length and is best suited to be driven by a small diameter, high current density electron beam. The pseudospark discharge is therefore an ideal cathode for an EIO. Experimental results presented will show that with a 35 kV discharge voltage, the EIO successfully produced W -band radiation pulses with 200 W peak power and 20 ns duration, agreeing well with the 3D Particle-in-Cell (PIC) simulations using MAGIC.
A pseudospark (PS) is an axially symmetric, self- sustained, transient, low pressure (typically 50–500 mTorr) gas discharge in a hollow cathode/planar anode configuration, which operates on the low pressure side of the hollow cathode analog to the Paschen curve [1]. The production of higher current- density electron beams, compared to thermionic cathodes, from a pseudospark discharge has been convincingly demonstrated [2]. The current density of a pseudospark-sourced electron beam can achieve ~1kA/cm
2 [3], which enables a wide range of applications in generating millimetre and terahertz radiation. 2. Experimental results A four-gap pseudospark discharge chamber was used which can hold-off a discharge voltage of up to 40 kV, was connected to a W-band EIO, fig 1.
pseudospark-sourced electron beam and the schematic drawing of the experiment .
The discharge voltage was swept from 38 kV to 25kV to achieve the maximum output power. The peak power of the radiation was measured to be 200W. The output frequency was measured to be ~94GHz.
The pseudospark-sourced electron beam which is focused by the positive ion channel generated from the pseudospark discharge process was successfully used to drive a W-band EIO circuit to generate coherent radiation. The background unmagnetized plasma can be considered as a dielectric media with a dielectric constant of ε r =1-ωpe
2 /ω 2 . As the operating frequency is far away from the plasma frequency the plasma would have negligible effect on the output power of the EIO. As the current density of the pseudospark-soured electron is much higher than a thermionic electron beam, it is an excellent electron beam source to drive a pulsed EIO circuit operating at higher frequencies with reasonable high radiation power.
[1] K. Frank and J. Christiansen, IEEE Trans. Plasma Sci., 17, 748 (1989). [2] H. Yin, A. W. Cross, at al Phys. Plasmas 16, 063105 (2009). [3]
Applied Physics Letters, 107, 913, 133501, 2015. 8 360 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
Effect of Plasma Activated Medium on human Head & Neck cancerous Tumor Spheroids.
J.Chauvin 1,2
P , U F.Judée 1 P , N.Merbahi P 1 P , P.Vicendo P 2
P
P
P
P
This work investigates the effect of Plasma Activated Medium (PAM) on human head and neck cancerous cells using FaDu multicellular tumour spheroids (MCTS). Results indicate that PAM induces cell detachment as soon as the first day post PAM treatment and in a PAM time-dependant manner. The presence of hydrogen peroxide in PAM has been shown to be responsible for this cell detachment. However, a rapid regrowth of the multicellular tumour spheroids size is observed after PAM treatment probably due to a defense mechanism exhibited by FaDu cells. To counteract this effect, successive treatment were done and growth inhibition obtained.
Chemotherapy and radiotherapy have a low rate of success against Head and Neck Cancer due to a high level of resistance [1]. For over a decade, cold atmospheric plasma has been studied in the biomedical field. It high reactivity allow the creation of RONS [2] that are cytotoxic on various cancer cell lines [3-4] and may induce cell death via apoptosis [4]. Recently, we reported that PAM induced cell death mainly by the involvement of hydrogen peroxide [3]. This work studies the effect of PAM on FaDu MultiCellular Tumor Spheroids (MCTS) and the involvement of hydrogen peroxide in PAM treatment.
The first effect observed is a volume loss at day one post-treatment associated with
a cell
detachment. This effect may be attributed to H 2 O 2 . The second effect is a rapid re-growth the following days attributed to the auto-organization of MCTS and FaDu defence mechanism (Fig. 1).
treatment for several exposure times. This increase of spheroids growth may be attributed both to loss of MCTS auto-organization and to FaDu defense mechanisms induced by an external attack. After 4 successive treatments (Fig. 2), FaDu MCTS were successfully disrupted. However, after each treatment the previously exhibited effects: cell detachment and proliferation were observed until the forth one.
Fig 2. Successive treatment of FaDu spheroids 3. References
[1] Mutschelknaus L, Peters C, Winkler K, Yentrapalli R, Heider T, Atkinson MJ, Exosomes Derived from Squamous Head and Neck Cancer Promote Cell Survival after Ionizing Radiation, PLoS ONE, 2016 11[3]: e0152213 [2]
Cambridge University Press, 2008, 1017 p [3]
Judée, F.; Fongia, C.; Ducommun, B.; Yousfi, M.; Lobjois, V.; Merbahi, N. Short and Long Time Effects of Low Temperature Plasma Activated Media on 3D Multicellular Tumor Spheroids, Sci Reports, 2016, 6, 21421.
[4]
Utsumi, F.; Kajiyama, H.; Nakamura, K.; Tanaka, H.; Hori, M.; Kikkawa, F. Selective Cytotoxicity of Indirect Nonequilibrium Atmospheric Pressure Plasma against Ovarian Clear-Cell Carcinoma, Springerplus,
17
361 XXXIII ICPIG, July 9-14, 2017, Estoril/Lisbon, Portugal
PTR-TOF analyzis of glow discharge products in Titan related atmosphere
S. Chudjak P , F. Krcma P , V. Mazankova Faculty of Chemistry, Brno University of Technology, Brno, Czech Republic
The glow discharge at atmospheric pressure was generated in the nitrogen-methane (1 to 5 %) gaseous mixtures related to the Titan’s atmosphere. The discharge itself was monitored by optical emission spectrometry that confirmed presence of active nitrogen species and various radicals formed from methane. Besides them, the CN spectral bands were observed. Intensities of all light emitting species were studied in the dependence on applied power and composition of nitrogen- methane mixture. The stable discharge products were analysed by proton transfer time of flight mass spectrometry of the exhausting gas. Presence of huge number of amino and cyano compounds was confirmed as well as aliphatic and some aromatic hydrocarbons. Their relative concentrations were determined under the same conditions as optical emission spectra were collected.
The laboratory studies of chemical processes initiated by electrical discharges in extra-terrestrial planetary atmosphere’s gaseous mixtures started to be important during last years because of observing many exoplanets and search of potential exo-biology or even exo-life. The most studied exo-atmosphere is Titan’s one because it was proposed that current Titan’s atmosphere is similar \as Earth atmosphere before life formation. Download 9.74 Mb. Do'stlaringiz bilan baham: 
|