Laserski inducirana lavinasta ionizacija u atmosferskom plazmenom mlazu helija

master's thesis

• Title (english): Laser-induced avalanche ionisation in a helium atmospheric pressure plasma jet
• Author: Aleksandar Opančar
• Mentor: Slobodan Milošević (mentor)
• Mentor: Željko Skoko (komentor)
• Committee member: Željko Skoko (predsjednik povjerenstva)
• Committee member: Slobodan Milošević (član povjerenstva)
• Committee member: Hrvoje Buljan (član povjerenstva)
• Committee member: Dalibor Paar (član povjerenstva)
• Committee member: Ivan Kupčić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2020-09-18, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Ovaj rad bavi se razvijanjem jedne eksperimentalne metode za mjerenje koncentracije elektrona u atmosferskom plazmenom mlazu helija. Metoda se zasniva na postizanju laserskog sloma unutar plazmenog mlaza fokusiranjem nanosekundnog infracrvenog laserskog pulsa. Laserski puls poveća koncentraciju elektrona s vrijednosti u mlazu n_0, koju želimo saznati, na vrijednost nf koju je lakše izmjeriti standardnim metodama. Ideja metode je iz koncentracije nf izračunati koncentraciju n_0. Za tu potrebu razvijen je model evolucije laserske plazme koji omogućuje povezivanje koncentracija n_0 i n_f preko energije laserskog pulsa. Korištenjem ove metode dobivena je vremenska ovisnost koncentracije elektrona u jednoj točki atmosferskog plazmenog mlaza helija. Dobivene vrijednosti dobro se uklapaju u vrijednosti iz literature. Korištenjem step motora automatizirano je pomicanje leće koja fokusira laserski puls u plazmeni mlaz. Sposobnost preciznog automatiziranog pomicanja fokusa otvara mogućnosti prostorno ovisnog mjerenja koncentracija u cijelom mlazu. U ovom je radu dobiven kvalitativni izgled koncentracije elektrona duž radijalne osi plazmenog mlaza. Pronađen je karakteristični donut oblik u primarnom izboju, ali ne i u sekundarnom izboju.

Abstract (english)

This paper deals with the development of an experimental method for measuring the electron density in a helium atmospheric pressure plasma jet (APPJ). The method is based on achieving a laser induced breakdown within the plasma jet by focusing a nanosecond infrared laser pulse. The laser pulse increases the electron density from the value in the jet n_0, which we want to find out, to the value n_f , which is easier to measure by standard methods. The idea of the method is to calculate the electron density n_0 from the electron density n_f. For this purpose, a model of laser plasma evolution that enables the connection of the electron densities n_0 and n_f via the laser pulse energy has been developed. Using this method, the time dependence of the electron density at one point of the helium APPJ was obtained. The values obtained fit well with the values from the literature. Using a stepper motor, the movement of the lens that focuses the laser pulse into the plasma jet is automated. The ability of precise automated focal spot translation opens up the possibility of spatially resolved measurement of electron density throughout the jet. In this paper, a qualitative electron density profile along the radial axis of the plasma jet is obtained. A characteristic donut shape was found in the primary discharge, but not in the secondary discharge.

• Keywords: laserski inducirani slom; atmosferski plazmeni mlaz; dijagnostika plazme; helij
• Keywords (english): laser induced breakdown; atmospheric pressure plasma jet; plasma diagnostics; helium
• Language: croatian
• URN:NBN: urn:nbn:hr:217:578511
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2021-01-08 13:32:36