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Here a comparison is shown between fast iCCD imaging and newly developed diagnostic method utilizing laser induced breakdown in a helium atmospheric pressure plasma jet. The plasma jet was powered by an 80 kHz high-voltage sine wave and propagated into the ambient air. Nd:YAG pulsed laser (4 ns pulse duration and 5 Hz repetition rate @1064 nm) was focused by a lens into the plasma jet at energy below breakdown threshold in helium. Laser and the plasma source were synchronized with the possibility to change the time delay between them. Depending on the time when the laser arrives, there is a different electron density in the laser focus at the laser pulse arrival. This affects the electron multiplication (avalanche) and the optical emission intensity of the laser induced plasma. We compared the radial profiles of the plasma jet obtained with these two methods. For the laser induced breakdown it was ±0.5 mm and for ICCD measurement it was ±1.75 mm, while the ionization wave velocities obtained with these two methods were 15 km s−1 and 20 km s−1 respectively. Electrical characteristics of the plasma jet were also presented and one can see a large hysteresis effect when the applied power to the plasma jet was reducing. We show that the laser induced breakdown spectroscopy can be used as a complementary diagnostics technique with ICCD measurements.

In this work we present results of characterization of the laser-plasma interactions. We are using atmospheric pressure plasma jet that was characterized in great detail previously [1] and the laser produced plasma [2]. Objective of this research was to investigate plasma-liquid interaction at atmospheric pressure. The plasma jet consists of a glass tube (4 mm or 1 mm inner diameter and 6 mm outer diameter) and metal powered electrode (15 mm wide) placed at 15 mm from the jet nozzle. Power supply of the plasma jet consists of a waveform generator, power amplifier and high voltage transformer and operates at 80 kHz. Deionized water is placed at 15 mm from the jet nozzle. A laser beam (Nd:YAG 1064nm, 5 ns) was focused in the middle between the jet nozzle and the target. We performed optical emission measurements for several gas mixtures (Helium-Argon, Helium- Nitrogen and pure Argon) at flow rates 2 and 4 slm. We also performed time resolved line emission measurements of the laser-jet interaction for the excited 1s3p He state (corresponding to the 388.86 nm line. Interaction of the plasma jet with water surface results in high intensity of NO and OH bands. Composition of the buffer gas has high impact on the concentration of produced radicals. Figure 1. Laser and jet plasma interaction with water surface as grounded electrode the flow rate of 4 slm: a) He/N2 (0.5%) ; b) He/Ar (0.5%) and c) Ar Acknowledgements: This research has been supported by the Ministry of Education and Science Serbia, project III41011 and ON171037, the Croatian Science Foundation project number 2753 and the COST Action TD1208 (Electrical Discharges with Liquids).

This study was aimed to investigate the influence of low-pressure RF plasma (gas, treatment time and power) and atmospheric pressure corona (number of passages and power) parameters on decolourisation of indigo dyed denim fabrics. CIEL*a*b* colourimetric system was used for determination of colour difference between untreated and differently plasma treated denim fabrics. The morphology of plasma treated fibres was assessed by SEM analysis. The results showed that decolourisation was highly affected by plasma parameters and desired "worn look" effects could be designed by adequate control of plasma processing.

In order to study the influence of low-temperature air plasma and enzymatic treatment on the dyeing properties of hemp, "cold dyeing" of hemp fabric with acid dye (C.I. acid blue 113) and direct dye (C.I direct red 81) was performed. In addition to the determination of dyeing kinetics, colour yield and colourfastness, assessment of weight loss, water retention and whiteness degree, as well as SEM analysis of differently treated samples was carried out. Low-temperature plasma treatment of hemp fabric caused an increase in the dyeing rate, final dye exhaustion and colour yield of dyed samples. The positive effect of plasma treatment was explained by plasma etching and oxidation effect on the hemp fibre surface. Enzymatic treatment led to a decrease in the dyeing rate in the case of C.I acid blue 113 and slight increase in the case of C.I. direct red 81, whereas the final exhaustion of both dyes decreased. This behaviour has been attributed to a more pronounced digestion of amorphous fibre areas. All samples showed similar and low colourfastness values, which were considered as satisfactory, taking into account that the cold dyeing procedure was carried out.

The objective of this study was to highlight the possibility of treating the cotton fabrics with fluorocarbon plasmas in order to obtain water and soil repellent material. A treatment of cotton fabrics was carried out using the low-pressure RF inductively coupled C6F6 and C6F14 plasmas. The influence of plasma parameters (power, time, flow) on fabric wettability and whiteness were considered. The fiber surface morphology changes were assessed by AFM analysis. The application C6F6 plasma insignificantly affected the wettability of cotton fabric whereas C6F14 plasma treatment led to a considerable increase in fabric hydrophobicity. Both plasmas brought about decrease in whiteness degree of cotton fabrics. http://mail.ipb.ac.rs/~marinkov/text/E4_23SPIG_cp.pdf

In this paper we present voltage-current-power characteristics of a plasma needle operating in the flow of helium at atmospheric pressure. In addition, we show some examples of how such a plasma affects plant tissues. In the characterization of the plasma needle, current and voltage waveforms were recorded by two derivative probes. These two probes are similar to the probes previously used by Puac et al for measuring transmitted power in low pressure CCP rf discharge. The instantaneous power was calculated from current and voltage waveforms and U-I characteristics of the discharge were determined. Regimes of operation with and without the grounding ring at the tip of the needle were considered. We have chosen two model systems to study the effect of the plasma needle on plant cells and tissues: sweet fern gametophyte (prothallus) and calli produced in vitro. Since the prothallus consists of a single layer of cells, the cytological effects could be easily examined. In addition, calli and prothallus are easy to manipulate and in vitro culture provides a possibility to work under constant and controlled conditions. null

Praćenje promena morfoloških svojstava površine vlakana nastalih modifikovanjem netkanog sorpcionog materijala na bazi vune kao sekundarne sirovine biopolimerom hitozanom i/ili niskotemperaturnom plazmom je od velike važnosti za sagledavanje mogućeg mehanizma sorpcije pojedinih zagađivača iz vodenog mediju- ma. U ovom radu su prikazani rezultati karakterizacije površine vlakna korišćenjem SEM, AFM i WLSI tehnika. An assessment of morphological properties after the modification of recycled wool-based non-woven sorbent with biopolymer chitosan and/or low-temperature plasma is of great importance for study on possible sorption mechanism for different contaminants from water medium. The results of fibre characterization using the SEM, AFM and WLSI techniques are presented in this paper. It was established that modification of sorbent material brought about changes of surface topography. Plasma treatment (LTP) caused the formation of pits and striations on the fibre surface, while chitosan (CHT) and plasma+chitosan (LTP+CHT) treatments resulted in masking the scales with biopolymer. These results are in accordance with surface roughness parameters arising from WLSI analysis.

Konoplja je vlakno koje nije problematično sa aspekta pripreme za bojenje i bojenja. Međutim, pošto savremeni materijali od konoplje zahtevaju modifikovanje sa ciljem poboljšanja opipa i voluminoznosti, kao i smanjenja gužvanja, neophodno je proučiti uticaj modifikovanja na ponašanje prilikom bojenja. Ovaj rad je posvećen proučavanju uticaja modifikovanja konoplje niskotemperaturnom plazmom (NTP) i/ili enzimom (ENZ) na ponašanje prilikom bojenja specifičnim bojama, sa ciljem uspostavljanja korelacije efekata dobijenih posle bojenja sa promenama na vlaknu koje su posledica modifikovanja.

Low-temperature plasma treatment causes modification of specific wool properties (felting shrinkage, wettability, dyeability, printability, pilling) as a result of interaction between active plasma particles and fibre surface. The formation of new functional groups on the fibre surface, physical sputtering and reactive plasma etching occur during the plasma treatment. The changes are confined to the wool surface, leaving the fibre bulk properties unchanged. Adequate choice of plasma treatment parameters provides options to achieve specific plasma-chemical reactions and consequently, the desired effects on the wool. This paper considers the influence of low-temperature plasma on the changes of chemical composition, morphological and electrokinetical properties of wool.

Low-temperature plasma treatment of hemp fabric causes an increase of dyeing rate, final dye exhaustion and Kubelka-Munk values of dyed samples. The positive effect of plasma treatment is more prominent in case of dyeing with C.I. Acid Blue 113 than with C.I. Direct Red 81. These changes could be explained by plasma etching and oxidation effect on the fibre surface. Untreated and plasma treated samples show similar and low colour fastness values, which were considered satisfactory taking into account that cold dyeing procedure was carried out.

Obrada niskotemperaturnom plazmom povećava brzinu iscrpljenja boje, završno iscrpljenje i intenzitet obojenja tkanine od konoplje. Poboljšanja posle obrade plazmom su izraženija kod bojenja bojom C.I. acid blue 113 nego kod C.I. direct red 81. Promena ponašanja prilikom bojenja je posledica nagrizanja i oksidacije površine vlakna konoplje plazmom. Low-temperature plasma treatment of hemp fabric causes an increase in dyeing rate, final dye exhaustion and dyeing strength of dyed samples. The positive effect of plasma treatment is more prominent in case of dyeing with C.I. acid blue 113 than with C.I. direct red 81. The observed changes in dyeing behavior could be explained by plasma etching and oxidation effect on the hemp fiber surface.

Savremena obrada tekstilnog materijala ima za cilj postizanje zahtevanog efekta uz ograničavanje modifikovanja samo na površinu vlakna. U poslednje vreme se znatna pažnja poklanja fizičkim postupcima obrade, medu kojima se niskotemperaturna plazma smatra veoma pogodnom za obradu površine vlakana. Takode, postoje i veoma efikasni hemijski postupci obrade, kao što je obrada vodonik peroksidom, biopolimerima Hi enzimima. U ovom radu su pri-kazane neke interesantne kombinacije ovih fizičkih i hemijskih metoda, kojima se modifikuje topografija površine tekstilnih vlakana i na taj način se regulišu tzv. površinska svojstva tekstilnih vlakana. Dobijena svojstva su diskutovana na bazi fizičko-hemijskih promena u površinskom sloju vlakna koje su ocenjivane preko sposobnosti kvašenja i ugla kvašenja, kao i primenom FTIR/ATR i XPS analize. SEM i AFM tehnika su korišćene za odredivanje promena u topografiji površine vlakna, kako bi se one dovele u vezu sa efikasnošću, ravnomernošću i intenzitetom obrade kod postupaka za obradu površine tekstilnih vlakana. The modern textile fibre treatments aim to obtain the required level of beneficial effect while attempting to confine the modification to the fibre surface. Recently, much attention has been focused on different physical methods of fibre surface modification, cold plasma treatment being considered as very useful. Moreover, there are efficient chemical methods available, such as peroxide, biopolymer and enzyme treatment. Some interesting combinations of these physical and chemical surface modification methods as means to modify fibre surface topography and thus controlling the surface-related properties of the fibre are presented in this paper. The properties obtained are discussed on the basis of the physico-chemical changes in the surface layer of the fibre, being assessed by wettability and contact angle measurements, as well as by FTIR-ATR and XPS analysis. The SEM and AFM technique are used to assess the changes in the fibre surface topography and to correlate these changes to the effectiveness, uniformity and severity of the textile fibre surface modification treatments.

The aim of this study was to investigate the sorption properties of recycled wool based non-woven material for heavy metal ions. To improve sorption properties wool material was treated with air low-temperature plasma (LTP) and/or biopolymer chitosan (CHT). The rate and extent of uptake of various metal cations (Pb+2, Cu+2, Zn+2) by wool, kinetics of adsorption, as well as the influence of concentration, pH and temperature on the sorption process were determined. It was found that wool even as a recycled material efficiently binds metal cations in all investigated cases. Recycled non-woven wool material is good sorbent for Pb+2 ions and it seems that it does not need any modification to improve this property. The modification of the material with LTP and/or CHT does not pass over 5 % of metal uptake improvement. Sorption properties for Cu+2 Ions improve about 10 % with LTP+CHT modification of the sorbent material, but metal salt solution still contains considerable amount of residual metal in solution (>30 %) even alter 24 hours of adsorption. The improvement in Zn+2 ions sorption is the most obvious with sorbent material modification as the LTP+CHT modified wool adsorbs 84 % more Zn+2 Ions than unmodified sorbent after 24 hours. The percentage of Zn+2 ions remaining in the solution is still considerable, but it improves from 72 % to 48 %. The further improvement in lead and copper sorption properties could be obtained by increasing pH and temperature of metal salt solution. The results indicate that the investigated non-woven recycled wool based sorbent material is potentially useful low-cost substrate for removing heavy metals from industrial effluents and other water sources.

Zbog velike zastupljenosti radiofrekvencijskih (RF) plazmi u industriji javila se potreba za definisanjem osnovnih fizičkih principa koji određuju proboj u RF električnim poljima. Uslovi, u vidu probojnog napona i pritiska, mogu se prikazati naponskom probojnom krivom, predstavljenom u V-p ravni. Oblik i položaj krive definisani su kako prirodom pozadinskog gasa tako i karakteristikama spoljašnjeg RF električnog izvora. Ova disertacija ima za cilj da nedvosmisleno definiše fizičke procese koji su odgovorni za proboj pri RF električnim poljima. Za to je korišćena Monte Karlo tehnika. Odabirom slučajnih brojeva, uz poznavanje preseka za određene procese, moguće je verno (čak se može tvrditi egzaktno) opisati kretanje roja naelektrisanih čestica između dve elektrode koje su pobuđene RF generatorom. Izgradnja modela je započeta posmatranjem kretanja elektrona u argonu pri frekvenciji od 13,56 MHz. Na primeru argona objašnjeni su osnovni mehanizmi proboja koji definišu oblik naponske probojne krive. Nadogradnja modela, kao verodostojne predstave RF proboja, uključuje efekte na površinama elektroda (refleksiju i emisiju sekundarnih elektrona), uticaj promene frekvencije i dvofrekvencijskih izvora, kao i teških čestica. Model je primenjen na različite gasove: helijum, kiseonik, sintetički vazduh i atmosfera Marsa. The wide range of radiofrequency (RF) plasma applications in industry rely on research of fundamental physical processes responsible for the RF breakdown. Conditions, such as the breakdown voltage and pressure, can be presented by breakdown voltage curves in the V-p plane. The shape and coordinates of the curve are defined by the nature of the background gas and characteristics of the applied RF electric field. The goal of this dissertation is to define physical processes responsible for the RF breakdown. For that purpose a Monte Carlo computational code has been used. If one knows cross sections for different processes by employing a random number generator, the transport of electrons between two electrodes can be determined. The development of the RF breakdown model begun by observing the motion of electrons in argon at the field frequency of 13.56 MHz. Argon was used to explain the basic mechanisms that define the shape of the breakdown voltage curve. Further upgrade of the model involved inclusion of the surface effects on electrodes (reflection and secondary electron emission), the influence of frequency and dual frequency RF power supplies, as well as the influence of heavy particles on the breakdown. The model was applied to different gases: helium, oxygen, and synthetic air, as well as the atmosphere of Mars.

Napredak uređaja za akumulaciju i skladištenje pozitrona omogućava sve preciznija merenja preseka za interakciju pozitrona sa atomima i molekulima. Nedavno kompletirani setovi sudarnih podataka za molekule koji se najčešće javljaju u pozitronskim uređajima i primenama (najpre N2, CF4 i H2O ali i drugi) omogućili su detaljne simulacije transporta pozitrona u takvim sredinama, kao i detaljan opis uređaja koji se na njima baziraju. Osnovni cilj ove disertacije jeste da na osnovu izmerenih sudarnih podataka, pomoću računarskih Monte Karlo simulacija, detaljno analizira realne uređaje i sisteme ispunjene gasom koji svoju funkciju baziraju na elementarnim procesima u kojima učestvuju pozitroni. Disertacija se fokusira na tri konkretna sistema: pozitronski trap, kompresiju snopa pozitrona rotirajućim poljem i termalizaciju pozitrona u biološki relevantnoj sredini. Otkriće i razvoj pozitronskog (Surko) trapa početkom devedesetih godina, predstavlja prekretnicu u polju fizike niskoenergijskih pozitrona i dovelo je do velikog napretka u razumevanju interakcije niskoenergijskih pozitrona sa atomima i molekulima. Trapovi su omogućili akumulaciju velikog broja pozitrona (106-108), niske energije sa energijskom raspodelom koja odgovara sobnoj temperaturi (

Zahvaljujući svojim dobrim performansama i niskoj ceni po jedinici zapremine, gasni detektori su najčešće korišćeni detektori u eksperimentalnoj fizici visokih energija. Pored fizike visokih energija, ovi detektori nalaze primene u mnogim drugim oblastima, poput dozimetrije i zaštite od zračenja, medicine, fizike kosmičkog zračenja i geofizike. Postoje brojni modeli ovih uređaja. Bez obzira da li su analitički ili numerički, stohastički ili deterministrički, svi ovi modeli koriste transportne i/ili sudarne podatke za elektrone u gasovima. Nažalost, uobičajeno je da se unutar detektorske zajednice, ovi podaci kao i tehnike za njihov proračun primenjuju nekritički. Ova praksa, kao što je diskutovano u ovoj disertaciji, veoma često vodi ka pojednostavljenim modelima detektora i neadekvatnoj metodologiji za pristup i analizu. Imajući ove činjenice u vidu, osnovni cilj ove disertacije je da na osnovama transportne teorije rojeva elektrona, ukaže na čitav spektar važnih aspekata u proračunu i implemetanciji transportnih podataka u modelovanju kao i da na konkretnim modelima detektora pokaže kako podaci i njihova implementacija utiču na izračunate signale i performanse detektora. Osim toga, u ovom radu su detaljno analizirane netipične pojave u transportu elektrona indukovane eksplicitnim efektima nekonzervativnih sudara i njihove potencijalne implikacije u modelima. Specifičnosti transporta elektrona u ukrštenom električnom i magnetskom polju, ilustrovane su na primeru detektora tipa Time Projection Chamber (TPC) koji se koriste za trodimenzionalnu rekonstrukciju putanje čestica. Kod ovih detektora magnetsko polje ima ulogu u redukciji bočne difuzije od koje direktno zavisi prostorna rezolucija dok npr. linearnost rekonstrukcije zavisi od osetljivosti brzine drifta na temperaturu i nehomogenost magnetskog polja. U ovom kontekstu potencijalne optimizacije radnih uslova, a takođe imajući u vidu i neželjene varijacije parametara tokom rada, sistematski je razmotren uticaj električnog i magnetskog polja, temperature i pritiska gasa kao i udela nečistoća u gasnoj smeši, na transportne osobine elektrona u TPC detektoru. Posebna pažnja posvećena je detektoru sa pločastim elektrodama visoke otpornosti (Resistive Plate Chamber, RPC) koji se koriste za timing i triggering u brojnim eksperimentima fizike visokih energija kao i u drugim oblastima. Rešavanjem Boltzmannove jednačine i primenom Monte Karlo tehnike, koju smo sa jedne strane koristili da proverimo rezultate dobijene Boltzmannovom jednačinom, a sa druge strane za dobijanje prostorno razloženih transportnih parametara elektrona, identifikovani su iobjašnjeni transportni fenomeni elektrona poput negativne diferencijalne provodnosti i grejanja zahvatom elektrona koji su uočeni u gasnim smešama RPC detektora koji se primenjuju na eksperimentima u CERN-u. U ovoj disertaciji, razmotreni su teorijski principi klasičnog fluidnog modela i modela zasnovanog na difuzionoj jednačini i hidrodinamičkoj aproksimaciji na osnovu kojih je razvijen numerički 1.5-dimenizionalni fluidni model RPC detektora. Ovim modelom, ispitivan je razvoj elektronske lavine i strimera pod dejstvom efekata prostornog naelektrisanja i fotojonizacije u gasu. Pokazano je da nepravilna implementacija transportnih podataka, zanemarivanjem eksplicitnih efektata nekonzervativnih sudara, može dovesti do greške od nekoliko stotina procenata u proračunu indukovanog signala. Razmatrana je i osetljivost izračunatog signala detektora na promene setova preseka za rasejanje elektrona u individualnim gasovima gasnih smeša. Konačno, u ovoj disertaciji razvijen je i mikroskopski Monte Karlo model RPC detektora koji se zasniva na praćenju pojedinačnih trajektorija elektrona i njihovih sudara sa molekulima gasa. Pomoću ovog modela, ipitivana je stohastika elektronskog lavinskog procesa. Takođe, koristeći različite setove preseka za rasejanje elektrona u individualnim gasovima gasne smeše, izračunate su vremenska rezolucija i efikasnost RPC detektora koje se dobro slažu sa eksperimentalnim vrednostima. Owing to their good performance characteristics and low price per unit volume, gaseous particle detectors remained the most commonly used detectors in high energy physics experiments. In addition to high energy physics, these detectors have also found applications in other fields such as radiation protection and dosimetry, medicine, cosmic ray physics and geophysics. A number of methods to model particle detectors have been developed. Being analytical or numerical, stochastic or deterministic, detailed knowledge of electron swarm transport properties as well as reliable cross sections for electron scattering are required as an input in modeling. The highly applied nature of the field, has inevitably driven the modeling of these systems more towards empiricism, and unfortunately often away from its roots in the fundamental transport theory of electron swarms. Thus, the main goal of this work is to bridge the gap between the fundamental transport theory of electron swarms and applications in the field of particle detectors. This goal is achieved by considering many elements of the theory which are important for accurate calculation and correct implementation of electron transport data in modeling. In addition, we provide the examples of specific detector models in which the incorrect implementation of data affects the calculated signal and detector performance characteristics. In this work, we discuss atypical manifestation of electron transport phenomena induced by the explicit effects of non-conservative collisions and potential implications arising from their inclusion in the models. The peculiarities of electron transport in crossed electric and magnetic fields are illustrated using the example of Time Projection Chamber (TPC), a detector employed for three-dimensional reconstruction of particle trajectories. In this detector, the magnetic field suppresses the transverse diffusion, which directly affects the spatial resolution. On the other hand, the reconstruction linearity depends on the sensitivity of drift velocity on the gas temperature and non-uniformity of the magnetic field. With this as one of the motivating factors, and also having in mind the unwanted variation of detector parameters with time, we systematically study the influence of the electric and magnetic fields, gas pressure and temperature, as well as the impact of impurities in the gaseous mixture, on the electron transport properties in TPC. Special attention is given to the Resistive Plate Chambers (RPCs) which are used for timing and triggering purposes in many high energy physics experiments and elsewhere. The Boltzmann equation is used for the determination of electron swarm transport properties under conditions when transport is greatly affected by nonconservative collisions. A Monte Carlo simulation technique has been used with the aim of verifying the results based on the Boltzmann equation as well as for the evaluation of spatially resolved electron transport data. This segment of data is used to explain the existence of certain kinetic phenomena, including negative differential conductivity and attachment heating, which are important for the detector behavior. Within the framework of the classical fluid model and using the diffusion equation in association with the hydrodynamic approximation, we have developed a numerical 1.5-dimension fluid model of an RPC. This model is used to study the electron avalanche and streamer development under the influence of space charge effects and photoionization. We have shown that improper use of the data, especially the lack of correct representation of the explicit effects of non-conservative collisions, can lead to errors of a several hundred percents for the calculated signals. In addition, we discuss the sensitivity of the output detector signals with respect to the sets of cross sections for electron scattering. Finally, in this thesis we present our microscopic Monte Carlo model of RPC based on the tracking of individual electron trajectories and their collisions with the gas molecules. Using this model, we study the electron avalanche fluctuations and the related processes. The detection efficiency and timing resolution are calculated using different sets of cross sections for electron scattering. We have found that our results agree very well with the measured data.

Over the past decade the use of ICCD cameras as a means for characterizing non-equilibrium plasmas has been steadily increasing. Due to their high sensitivity and high speed gateability, ICCD cameras enable time-resolved studies of the anatomy and, when adopted in conjunction with filters, monochromators, spectrometers or laser systems, time-resolved investigation of physical and chemical properties of non-equilibrium plasma discharges. This paper is meant as an introduction to ICCD technology and its use as a plasma diagnostic technique, discussing the experimental problems typically associated with its use and providing the readers with practical examples and suggestions on how to address them. In particular, the issues of ICCD camera synchronization with the voltage pulse driving the plasma discharge and of investigating small volume discharges are addressed, focusing mainly on the case of non-equilibrium atmospheric pressure plasma jets. Finally, a possible way to achieve absolute calibration of plasma discharge emission is presented and discussed. A wide range of data, mostly unpublished, is provided here to illustrate the points.

Sa sve bržim razvojem tehnologije za akumulaciju i čuvanje antimaterije raste broj primena pozitrona u nauci, industriji i svakodnevnom životu, pa je sve veća potreba za modelovanjem različitih aspekata interakcije materije i antimaterije. Modelovanje realnih situacija u kojima pozitroni nalaze primenu zahteva poznavanje dva tipa fundamentalnih podataka. Prvi tip su sudarni preseci za sve bitne sudarne procese pozitrona i atoma/molekula materije. Drugi tip, koji se oslanja na preseke, su podaci o transportu pozitrona u neutralnim gasovima. Transportne osobine su izvor informacija o grupi (ansamblu) naelektrisanih čestica koje se kreću kroz sredinu i u njih spadaju između ostalih srednja energija, brzina drifta i difuzioni tenzor. Osnovni cilj disertacije je sistematsko izučavanje transportnih parametara rojeva pozitrona u gasovima. Izučavani gasovi su odabrani imajući u vidu realne primene pozitrona. Ispitivani gasovi su Ar, H2, N2 i vodena para, a za proračun transportnih parametara korišćene su Monte Carlo simulacija i teorija za rešavanje Boltzmannove jednačine. Ove dve suštinski različite tehnike za opis transporta pozitrona u gasovima, bile su neophodne usled nepostojanja eksperimentalnih rezultate za transportne koeficijente. Dobro slaganje ove dve tehnike daje verodostojnost rezultatima prikazanim u disertaciji i reflektuje numerički integritet ove tehnike. Za modelovanje transporta roja pozitrona kroz neutralni gas potrebno je poznavanje preseka za sve procese relevantne za konkretan gas, odnosno potreban je kompletan skup preseka koji obezbeđuje balans broja čestica, impulsa i ukupne energije čestica roja. U ovoj doktorskoj disertaciji kompletirani su i preporučeni skupovi preseka za sudarne procese pozitrona u Ar, H2, N2, CF4 i H2O. U saradnji sa Centrom za proučavanje interakcija antimaterije i materije u Australiji izmereni su totalni presek za rasejanje pozitrona na molekulu vodene pare i presek za formiranje pozitronijuma. Ovi preseci su iskorišćeni kao ulazni podaci za Monte Carlo simulaciju i Boltzmannovu jednačinu, kojima su sistematski proučavani trendovi u ponašanju transportnih koeficijenata rojeva pozitrona koji se kreću pod uticajem električnih i magnetskih polja. Proučavana je osetljivost transportnih koeficijenata na proces formiranja pozitronijuma i identifikovan je veći broj kinetičkih fenomena indukovanih nekonzervativnom prirodom ovog procesa. Jedan od najdrastičnijih primera ovih fenomena je negativna diferencijalna provodnost koja se pojavljuje samo u balk komponenti brzine drifta, a ne i u odgovarajućoj flaks komponenti. Fenomen je detaljno objašnjen razmatranjem prostorno razloženih karakteristika roja pozitrona i korišćenjem teorije za prenos impulsa. Posebna pažnja posvećena je zajedničkim efektima magnetskog polja i formiranja pozitronijuma u uslovima kada ciklotronska frekvenca značajno prevazilazi kolizionu frekvencu. Utvrđeno je da magnetsko polje ukida efekat negativne diferencijalne provodnosti. Ispitivan je domen važenja aproksimacije dva člana za rešavanje Boltzmannove jednačine i pokazano je da su koeficijenti difuzije naročito osetljivi na broj članova u sferno-harmonijskoj dekompoziciji Boltzmannove jednačine. Važno mesto u disertaciji imaju testovi Tonksove teoreme primenjene na transport pozitrona u ortogonalnoj konfiguraciji električnog i magnetskog polja. Ilustrovana je neadekvatnost primene ove metode u situacijama kada je formiranje pozitronijuma izolovan i dominantan sudarni proces... Along with the fast development of technology for accumulation and storage of antimatter the number of positron applications in science, industry and everyday life is rapidly increasing and therefore there is a growing necessity for modeling of different aspects of antimatter-matter interactions. The modeling of positron-based technologies and experimental situations involving positrons requires the knowledge of two types of fundamental data. The first type is the collisional data, i.e. the cross-sections for every possible channel of interaction between the positron and the atom/molecule of matter. The second type relying on the cross-section data is the data associated with the transport of positrons in neutral gases. Transport properties are a source of information about a group or ensemble of charged particles travelling through the medium, such as their mean energy, drift velocity and diffusion tensor. The main goal of this Thesis is to systematically study transport properties of positron swarms in Ar, H2, N2 and water vapour. Gases are chosen having in mind real positron applications. A Monte Carlo simulation code has been applied and our new sets of cross-sections for positron scattering in gases are used as an input. Since there are no experimental data for positron transport in these gases, a multi-term theory for solving the Boltzmann equation has been used to validate the results obtained by a Monte Carlo simulation technique. Modeling of positron transport in neutral gas requires the knowledge of cross section set which has to be complete in the sense that it covers all important processes and therefore provides a good particle, momentum and energy balance. In this Thesis we have undertaken a programme to compile, evaluate, recommend and disseminate collision data for positrons in Ar, H2, N2, CF4 and water vapour. In collaboration with our colleagues from the Centre for Antimatter Matter Studies at the Australian National University, the total cross section for positron scattering in water vapour and cross section for positronium formation have been measured. Using these cross section sets as an input in both Monte Carlo simulation and Boltzmann equation theory, we have investigated the basic trends in behaviour of transport coefficients of positron swarms under the influence of electric and magnetic fields. The sensitivity of transport coefficients on Ps formation has been studied and a number of kinetic phenomena induced by non-conservative nature of this process have been identified. One of the most striking phenomena is negative differential conductivity (NDC) which is present in the bulk component of the drift velocity only, with no sign of it in flux component. The phenomenon is explained in details by calculating the spatially resolved characteristics of the swarm and also by using the momentum transfer theory. Special attention has been paid to the synergistic effects of magnetic fields and Ps formation on positron transport in crossed electric and magnetic fields when the cyclotron frequency is much greater then the collision frequency. When a magnetic field is applied, a new level of complexity is introduced. It is shown that the longitudinal and transverse drift velocity components behave in an entirely different manner. The bulk component of the longitudinal drift velocity is more affected than the corresponding transverse component, which unexpectedly removes NDC from the profiles of the drift speed. The domain of validity of the two-term approximation for solving the Boltzmann equation has been investigated and this study has revealed that diffusion coefficients are more sensitive on way of solving the Boltzmann's equation than the drift velocity. The important results of this Thesis are those associated with the tests of Tonks’ theorem applied to positron transport in an orthogonal configuration of electric and magnetic field. The inadequacies of this approach in situations when Ps formation is isolated and dominant process are illustrated...