Masters Degrees (Physics)

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1-D particle-in-cell simulations of plasmas with kappa velocity distributions.
(2013) Abdul, Reginald Francis.; Mace, Richard Lester.
The main aim of this project was the development of a particle-in-cell (PIC) plasma simulation code. While particle-in-cell simulations are not new, they have largely focused on using an initial Maxwellian particle loading. The new feature the code implemented for this project is the use of kappa distributions as an initial loading. This specialises the code for the investigation of waves and instabilities in space plasmas having kappa-type velocity distributions. The kappa distribution has been found to provide a better fit to space plasma particle velocity distributions than the Maxwellian in a wide variety of situations. In particular, it possesses a power law tail which is a frequent feature of charged particle velocity distributions in space plasmas. Traditionally, the treatment of such out-of-equilibrium velocity distributions has been via a summation over several Maxwellians with different temperatures and average number densities. Instead, the approach used in this work is guided by recent advances in non-extensive statistical mechanics, which provide a rigorous underpinning for the existence of kappa distributions. As case studies, the simulation code was used to investigate the ion-acoustic instability as well as electrostatic Bernstein waves in both Maxwellian and kappa plasmas. Results were compared to kinetic theory and the differences in the Maxwellian and kappa plasma behaviours are discussed. To analyse the instabilities various diagnostics were used, including Fourier analysis of the wave fields to determine the dispersion relation, and particle binning to determine the particle velocity distributions. Both the Maxwellian and kappa particle loading algorithms were found to agree well with the theoretical velocity distributions and the dispersion relations were found to agree with kinetic theory for both kappa and Maxwellian plasmas. The code was developed in the C programming language using an incremental approach that enabled careful testing after each new level of sophistication was added. A version of the code was parallelised using Message Passing Interface (MPI) to take advantage of the distributed supercomputing environment provided by the CHPC.
57 Fe Mössbauer studies of 57 Mn* implanted III-V semiconductors InP and InAs.
(2011) Dlamini, Wendy Bonakele.; Naidoo, D.; Bharuth-Ram, Krishanlal.
III-V compound semiconductors such as Gallium Arsenide, Indium Phosphide as well as Indium Arsenide have recently demonstrated the capability of applications in high speed semiconductor devices compared to those made from Silicon. As a result, III-V compound semiconductors have drawn attention of material researchers, in particular in understanding the effects that may occur during manufacturing of these devices. Optical and electrical properties of a device may alter when a foreign atom is introduced during the manufacturing of the device. However, the foreign atom may also lead to the formation of lattice disorder (defects). A convenient way of introducing impurity atoms into a substrate and tailoring their functionality for particular applications is by ion implantation. Mössbauer spectroscopy is a useful technique usually utilized for understanding site location of the impurity atoms in a lattice and the formation of defect complexes. The focus of this dissertation is the study of lattice location of ion implanted ⁵⁷Mn/⁵⁷Fe ions in the III-V semiconductors InP, n-type InAs and p type InAs, and the annealing of implantation induced lattice damage in these samples. ⁵⁷Fe Mössbauer spectroscopy studies have been conducted on III-V semiconductors InP, n-type InAs and p-type InAs with the 57Fe Mössbauer state being populated following the implantation of radioactive ⁵⁷Mn⁺ ions which has the advantage that extremely low fluence implantations are sufficient to give data with good statistics. The ⁵⁷Mn⁺ ions were accelerated to 60 keV at the ISOLDE/CERN facility and implanted with fluences of up to 2x10¹² ions/cm² into single crystal samples which were held at 300 –700 K in an implantation chamber. βdecay of the Mn⁺ imparts an average recoil energy of 40 keV to the daughter ⁵⁷*Fe which are then re-distributed onto interstitial and/or substitutional sites, or trapped in defect complexes and damage sites. The Mössbauer spectra were collected with a light-weight parallel plate avalanche counter, with ⁵⁷Fe enriched stainless steel electrodes, mounted on a conventional drive unit outside the implantation chamber. The spectra were analyzed with the Mössbauer fitting code VINDA which allowed for simultaneous fits of the set of spectra for each sample collected at different temperatures. Acceptable fits to the Mössbauer spectra of the InP, n-type InAs and p-type InAs samples required three components: an asymmetric doublet attributed to Fe atoms in implantation induced damaged environments, a single line assigned to Fe on substitutional In sites, and a weak symmetric doublet assigned to impurity-vacancy complexes. In InP there is already an appreciable substitutional Fe (Feѕ) fraction on implantation at room temperature; while in the InAs samples FeS only becomes significant above 400 K. In all samples, the asymmetric doublet dominates the spectra below 400 K. Implantation damage, however, anneals quite rapidly and at high temperatures (above 400 K), the single line due to Feѕ dominates the spectra while the Fe-defect complex dissociates at 500 K. The implantation induced damage is observed to anneal fast in the arsenide samples compared to the phosphide sample. The slow annealing of the damage in InP was supported by the higher Debye temperature (290 K) extracted from the temperature dependence of the site population for the damage site in InP compared with InAs (194 K and 200 K for n-type and p-type, respectively). Variations in the isomer shift and quadrupole splitting for the damage site in InP at high temperatures (above 400 K) suggest structural changes in the neighborhood of the ⁵⁷Fe probe. Furthermore, the isomer shifts of the spectral components were consistent with near trivalent state and fully trivalent state i.e., Fe³⁺ with d⁵ electron configuration for Fe ions in the damage site and at the substitutional (In) site, respectively. The impurity Fe atoms associated with vacancies are identified to be in the Fe²⁺ state with a d⁶ electron configuration.
Analysing transient effects in the ionosphere using narrowband VLF data.
(2009) Bremner, Sherry.; Collier, Andrew Blaine.
Very Low Frequency (VLF) radio waves propagate within the Earth-ionosphere waveguide with very little attenuation. Modifications of the waveguide geometry affect the propagation conditions, and hence, the amplitude and phase of VLF signals. Changes in the ionosphere, such as the presence of the D-region during the day, or the precipitation of energetic particles, are the main causes of this modification. Using narrowband receivers monitoring remote VLF transmitters, the amplitude and phase of these signals are recorded. A multivariate data analysis technique, Principal Component Analysis (PCA), is applied to the data in order to determine parameters such as seasonal and diurnal changes which affect the variation of these signals. Data was then analysed for effects from extragalactic gamma ray bursts, terrestrial gamma ray flashes and solar flares. Only X-rays from solar flares were shown to have an appreciable affect on ionospheric propagation.
Applications of Lie symmetry analysis to the quantum Brownian motion model.
(2008) Naicker, Viroshan.
Lie symmetry group methods provide a useful tool for the analysis of differential equations in a variety of areas in physics and applied mathematics. The nature of symmetry is that it provides information on properties which remain invariant under transformation. In differential equations this invariance provides a route toward complete integrations, reductions, linearisations and analytical solutions which can evade standard techniques of analysis. In this thesis we study two problems in quantum mechanics from a symmetry perspective: We consider for pedagogical purposes the linear time dependent Schrodinger equation in a potential and provide a symmetry analysis of the resulting equations. Thereafter, as an original contribution, we study the group theoretic properties of the density matrix equation for the quantum Brownian motion of a free particle interacting with a bath of harmonic oscillators. We provide a number of canonical reductions of the system to equations of reduced dimensionality as well as several complete integrations.
Assessment of the efficiency of solar radiation concentrating system.
(2009) Artur, Célia Domingas.; Pillay, Sadhasivan Rangan.; Løvseth, J.
A Solar Radiation Concentrating System for generation of high temperature heat for a solar oven was developed and evaluated at the University of KwaZulu-Natal, Westville Campus, Durban - South Africa. The system concentrates direct solar radiation on a small area receiver which absorbs the radiation and converts it into thermal energy that may be stored and used for several applications where food preparation and water pasteurization is the priority. The concentrator, area 2.2 m², is a half satellite communication dish covered with trapezoidal acrylic mirror tiles. The receiver/absorber is a spiral coil of blackened stainless steel pipe. Oil is circulated as heat transfer fluid. To determine the optimal dimension and position of the receiver, two experimental methods were used: (1) The tiles were scanned using a vertical, self adjusting laser beam to get a distribution of reflected radiation across the focal volume. (2) A thin, blackened stainless steel plate was placed at appropriate distances in the focal volume, and temperature distribution scanned using a temperature gun. The latter method proved to be the more useful. Results of the analysis of system performance showed that the system has the capability to produce high temperatures for domestic purposes. The efficiency of the system is about 35 %.
The association between VLF and ELF chorus emissions and electron precipitation.
(2009) Musumpuka, Remmy.; Hughes, Arthur R. W.; Collier, Andrew Blaine.
This is an investigation into the association between ionospheric absorption caused by electron precipitation and ELF:3 Hz-3 kHz and VLF:3 kHz-30 kHz, chorus. Ionospheric absorption was measured using the chain of riometers in Finland and related to chorus events recorded simultaneously at SANAE (L=4.2), Antarctica. The displacement in longitude of the Finnish riometers from SANAE’s conjugate point made it impossible to establish a clear relationship between chorus and riometer absorption. The diurnal variation of chorus has been established for the years 2002, 2004 and 2005 and it is shown that chorus can occur at any Local Time(LT) but has a well defined maximum probability of occurring between 0800 LT to 0900 LT. To study the occurrence of chorus automatically we have developed an Index of ELF/VLF activity which enables us to identify chorus and distinguish it from other emissions such as hiss and whistlers. This index of VLF Activity was established by computing the standard deviation of the VLF signal amplitude and it has been observed that the index is larger for the chorus signature as opposed to the hiss which is low and does not vary widely due to the hiss’ steady signal. This index is called ASD index of “VLF Activity”.
Avoidance of trappings in continual collapse of spherical stars.
(2019) Govender, Terricia.; Goswami, Rituparno.
In this dissertation we study the physical process of a spherically symmetric perfect uid experiencing a continuous gravitational collapse in concurrence with continuous radiating energy in an outward spacetime. Trapped surfaces are avoided and the nal fate of the collapse is a at spacetime. In addition, the collapsing matter conforms to the weak and dominant energy conditions at all epochs. Our investigation clearly unveils the purpose of the equation of state and reveals the bounds on the thermodynamic potentials the equation of state admits for such a model. We a rm that these models are generic without any of the issues and paradoxes attached to horizons and singularities, because the system of Einstein eld equations accepts such a theoretical account for an open set of initial data and the equation of state function in their respective functional spaces. High resolution radio telescopes of today, should ideally detect the existence of these compact bodies in the sky.
Beam generated instabilities in space plasma.
(1999) Misthry, Surversperi Suryakumari.; Bharuthram, Ramesh.
Electrostatic instabilities associated with a model applicable to the auroral acceleration region consisting of an ion beam, precipitating electrons and stationary background electrons are theoretically investigated. The kinetic dispersion relation is solved numerically without approximations. It is shown that two low-frequency plasma instabilities are present and these may generate the low-frequency electric field fluctuations (LEFs) that have been observed in the acceleration region. A parameter variation study is carried out in order to reveal the features of the instabilities. The model is adapted to suit two possible regions of study: (1) drifting cool ions and (2) drifting cool ions and counter-streaming hot electrons. The slow ion-acoustic instability which dominates at low ion beam drift velocities is studied by varying plasma parameters such as the propagation angle, ky/k, the wavenumber, k, the cold background electron density, nco, the hot electron temperature and the cool ion beam temperature. The second mode, the modified two-stream instability, which dominates at larger ion beam drift velocities and at oblique angles of propagation is investigated in a similar manner. To complete the study of these two instabilities, the effect of drifting hot electrons is examined briefly through a similar parameter variation study.
Binary and ternary molecules blend bulk heterojunction organic solar cell.
(2015) Mkhwanazi, Emmanuel Khulekani.; Mola, Genene Tessema.
Bulk heterojunction organic solar cells were prepared and characterized in terms of electrical and optical properties of the photosensitive medium. Two cases of organic solar cells were developed in this investigation with active layers composed of P3HT:PCBM molecules blend and P3HT:PTB7:PCBM ternary molecules blend, at stoichiometric ratio 1:1 and 2:1:1, respectively. The ternary molecules blend active layer attracted the attention of the re- searchers because of the possibility of broadening the absorption band. The performance of the devices was investigated and found better device per- formance in binary molecules blend while low charge mobility was observed in the ternary molecules blend active layer. The highest power conversion efficiency (n) obtained were 1.6 % for P3HT:PCBM blend and 0.56 % for P3HT:PTB7:PCBM active layer. The result indicated that the charge trans- fer mechanisms in the ternary molecules blend were not favorable on the extraction and transportation of charges to the electrodes. The morpholo- gies of the films and charge transfer properties in the two media are discussed based on SEM images and electrical measurements.
Biochemical-physical mechanisms of light-tissue interactions.
(2021) Buthelezi, Musawenkosi Doctor.; Chetty, Naven.; Adeleye, Oluwabamise.
Optical tissue phantom samples simulating the optical properties of the human prostates and brain tissues were fabricated. The experimental set-up was designed to be cost-effective but reliable, allowing for convenience in its usage and replication, making it ideal for biomedical optical measurements. Gel agar was the base material, and aluminum oxide (Al 2 O3 ) with black ink was employed as the scatter and absorber, respectively. The latter were mixed in various amounts into the gel agar to simulate the desired phantom tissues. Argon red laser and He-Ne green laser light, with wavelengths of 630 nm and 532 nm were incident on varying thicknesses of the phantom samples. The transmitted and incident light powers were measured to determine the scattering and absorption coefficients, from which the attenuation coefficients, penetration depth, and optical albedo were estimated. The optical penetration depths were found to be 0.30 for brain and 0.15 for prostate tissue phantoms. The fabricated tissues successfully mimicked the brain and prostate tissues, with µ a = 0.69 cm−1and µ a = 0.24 cm−1 absorption coefficients as well as 𝜇𝜇𝑠𝑠 = 1.73 cm−1 and µ s = 5.48 cm−1 scattering coefficients at 532 nm and 630 nm wavelengths, respectively. The optical albedo for brain phantom was found to be a = 0.71 and a = 0.96 for prostate phantom tissue. The results verify the reliability of the experimental technique and suitability of the fabricated tissues for use in biomedical, going forward, thus allowing for future work without the need for experimentally complex and expensive setups.
Bulk heterojunction organic solar cell.
(2014) Dlamini, Wiseman Mpilo.; Mola, Genene Tessema.
The low material costs and the ease fabrication procedures of organic solar cells has earned them too much interest from scientists all over the world. Much of the e orts were given to the improvement of the power conversion e ciency ( ) and the durability of the organic solar cells. Organic solar cells with the structure ITO/PEDOT:PSS/P3HT:PCBM/LiF/Al were fabricated under ambient laboratory conditions and J-V characteristics were studied. The active layers were composed of P3HT:PCBM blend. Power conversion e ciencies close to 2% and ll-factor as high as 60% were obtained. Stoichiometric ratio of the polymers P3HT:PCBM at 1:0.8 was observed to give the best performing samples. The samples were thermally annealed to enhance the optical properties of the devices by recovering the ordering or crystallization in P3HT and PCBM.
Characterisation and quantum application of plasmonic waveguides.
(2016) Francis, Jason Tarunesh.; Tame, Mark Simon.
Plasmonics o ers sub-di raction confinement of light, which a ords enhanced coupling to emitter systems (e.g. quantum dots). This feature makes possible a range of on-chip quantum photonic components - most notably single-photon sources and switches. This potential use of plasmonics, along with the nonlinearity provided by emitter systems, opens up quantum plasmonics as a viable route to realising quantum information processing. In this setting, the excitation of single surface plasmon polaritons (SPPs) on waveguides via single photons and the confirmation of single-photon states upon output is an important goal. In the work reported here, plasmonic waveguides were experimentally probed with single photons. A measurement of the secondorder quantum coherence function yielded a value of g(2)(0) = 0:160 0:002. A value less than 0.5 is indicative of single-excitation states. Furthermore, to confirm successful SPP excitation, the transverse-magnetic mode restriction and exponential decay of SPPs were verified. Having firmly established the ability to probe plasmonic waveguides in the classical and quantum regimes, quantum random number generation was implemented using a plasmonic beam splitter. The random bit sequences produced passed the NIST Statisitical Test Suite once post-processed to correct for a slightly asymmetric beamsplitter.
Characterisation of polarisation-entangled photon source for quantum key distribution.
(2016) Fadol, Samah S. Abu Ali.; Ismail, Yaseera.; Petruccione, Francesco.
Entanglement in real physical systems has been of great interest due to its importance in quantum mechanics. It has applications related to quantum information science speci cally quantum cryptography since it eliminates the possibility of photon number splitting attack during the key distribution process (Quantum Key Distribution). This thesis deals with creation, detection and characterisation of the correlated polarised photon pairs, which were emitted from a nonlinear BBO crystal via Spontaneous Parametric Down Conversion (SPDC) process. The procedure that leads to the construction of a polarisation-based entangled system is discussed by considering some of the measurement techniques, which can be applied to study fundamental quantum mechanics and its applications in quantum communication. This thesis consists of a set of experiments to validate the entanglement of single photon pairs. The rst experiment realised by generating of polarised based entangled photon pairs. The quantum correlation between the entangled photon pairs have been tested by measuring the visibility of the system and by verifying the maximal violation of CHSH (Clauser, Horne, Shimony and Holt) inequality. In the second experiment, the delity of the system has been measured by carrying out the state tomography to reconstruct the two-photon density matrix and consider the interference e ect of two photons. This helps to study the preservation of the quantum state during the propagation.
Characterization and improvement of a direct solar radiation detector.
(2004) Macome, Marcelino Adriano.; McPherson, Michael.
A low-cost Direct Solar Radiation Detector (DSRD) was developed in house in the Department of Physics at the University of KwaZulu-Natal (Westville). A main use of this instrument is to gather solar energy data that are to be used in the design of systems that concentrate and convert solar energy into thermal energy (concentrating solar thermal energy systems). These data are compiled into a database from which the efficiency and potential use of many solar systems can be based. It was required that the detector was fully characterized with respect to spectral range, polar (angular) response and environmental stability. Based on this analysis it was also required to investigate possible ways of improving the detector. An Eppley Normal Incidence Pyrheliometer (NIP) mounted on an Eppley Sun Tracker (ST) was used as a reference instrument. The ST is a power driven tracker with an axis parallel to the Earth's axis of rotation. The NIP and DSRD were mounted together on the tracker in order to correlate their responses and also to calibrate the DSRD. The results indicate that the modified DSRD works better in that it follows the reference instrument. The correlation between the NIP data and the DSRD data is better with the value of correlation factor close to unity and the root mean square error value close to zero. This means that the modifications carried out on the detector have improved the low cost in-house detector and hence the quality of data collected.
Chemical pollution arising from heavy inorganic industries in Richards Bay - an assessment.
(2004) Dyson, Catherine.; Low, Murray R.
The industrial port of Richards Bay on the eastern seaboard of KwaZulu-Natal, South Africa has undergone rapid growth over the last 25 years. This industrial growth has inevitably led to an increase in the anthropogenic pollutant inputs in the area. However, the degree of this contamination has not previously been assessed not been accompanied by an awareness of its environmental impacts. This project serves to assess the current environmental situation of the area and provide background levels against which the environmental impacts of further growth in the area can be assessed. The main pollution point sources in the area were identified as a pulp and paper plant, a sulfuric acid/fertiliser plant and aluminium smelters. The chemical and physical processes involved within these industries were identified and discussed in detail. The common inorganic pollutants emitted by these industries were identifies as trace metals, sulfur dioxide, NOx gases and fluoride. It was these pollutants that therefore became the focus of this study. Reservoirs within Richards Bay that may become sinks for contamination were identified and water, sediment and soil samples were taken from these reservoirs. The samples were analysed for trace metal contamination, pH, alkalinity and fluoride levels. Analysis of the acidity and alkalinity of water, sediment and soils samples demonstrated that there is presently no long-term acidification of the environment in Richards Bay. The only samples that showed increased acidity were the soils taken from the roadside sites immediately outside the industries. This lack of overall acidification indicates that, at present, there are no detrimental effects of acidic emissions on the hydrosphere and geosphere. Only cursory investigations were conducted into the fluoride levels found in water samples. None of the samples analysed demonstrated detectable amounts of fluoride present. Comprehensive trace metal analyses were performed on the water, sediment and soil samples through the use of ICP-AES. Levels obtained were compared with levels from samples taken from relatively uncontaminated background sites. Trace metal analysis indicated contamination of the freshwater reservoirs when compared with the background, while the soils and saltwater reservoirs remain largely uncontaminated. However, the contaminated areas did not show levels greater than quality guideline concentrations. Further studies should be conducted with regards to the trace metal contamination of the biosphere and the bioavailability of the contaminants already present in the waters, sediments and soils. More detailed investigations should also be conducted into the levels of atmospheric pollutants and fluoride levels in all reservoirs.
Computational studies of percolation : determination of the cluster number scaling function for lattices in 2 dimensions.
(2010-09-30) Nduwayo, Léonard.
The main aim of this work is to study percolation theory on regular two dimensional
Constant-temperature dynamics in the Wigner representation of quantum mechanics.
(2011) Megnidio-Tchoukouegno, Mireille Merlise.; Sergi, Alessandro.
This dissertation deals with theory and algorithms for computer simulations of classical and quantum systems in the canonical ensemble. First, the approach of Nos e-Hoover and its generalization, known as the Nos e- Hoover chain dynamics, are introduced. Such methods are used in classical molecular dynamics simulations to control the temperature of particle systems through a coupling to a few additional fictitious variables, mimicking an in nite thermal reservoir. In order to introduce the extension of the Nos e-Hoover method to quantum systems, the features of the Wigner representation of quantum mechanics are reviewed. Finally, a recent approach [A. Sergi and F. Petruccione, J. Phys. A 41 355304 (2008)], which extends the Nos e-Hoover and Nos e-Hoover chain equations in quantum phase space, is described. Such a method is applied to a single harmonic mode, and the conditions for quantum-to-classical transitions as a function of the thermodynamical temperature are studied by means of numerical simulations. It is shown that, in the case of strong coupling, the open system dynamics simulated by Nos e-Hoover chain equations leads to quantum-classical transition of the Wigner function of the harmonic mode. Agreement between the numerical and analytical results is also found. The algorithms and results illustrated are of interest to the numerical simulation of the quantum dissipative dynamics of more general systems.
Construction and analysis of the receiver for a solar thermal cooker system.
(2013) Govender, Paulene.; Matthews, Alan Peter.; Løvseth, J.
One of the key components in a solar thermal cooker system is the receiver since the performance of the receiver greatly affects the entire system. Absorption of the maximum amount of reflected radiation is crucial for ensuring the system is operating at high efficiency. A small-scale solar thermal cooker was constructed and tested. The main focus was the design, construction and analysis of a receiver for the solar cooker. The receiver was constructed from mild steel and contains water as the heat transfer fluid. The receiver consists of two half shells fixed to either end of a short cylinder to form an elongated boiling chamber for the water as it is heated by concentrated solar radiation. One of the half shells is exposed to the concentrated solar radiation and is coated with a high-temperature resistant black paint. The size of the receiver was determined by the method of ray-tracing. The maximum temperature the water attained within the receiver during solar heating was 136 C. The highest receiver efficiency was 66%. It was shown that there has been effective heat transfer within the system.
Corrosive sulphur in transformers.
(2013) Naicker, Sharlene-Asia.; Moodley, Mervlyn.
Failures in power transformers, in the majority of cases, have been linked to the formation of copper sulphide (Cu₂S) and corrosive sulphur. Cu₂S is conductive and affects the dielectric properties of the insulation system in the transformer. The formation of Cu₂S and corrosive sulphur in transformers is of worldwide concern to power utility companies, like Eskom, and large industrial manufacturing plants that maintain their own transformers. This research deals with determining and understanding the formation mechanism of Cu₂S as well as investigating factors that influence the acceleration of the corrosive sulphur formation. Data from oil test results was obtained from an experimental set-up belonging to eThekwini Electricity. The set-up consists of two 100 kVA transformers, one containing corrosive oil and the other containing clean oil. While varying the load and temperature of the transformer, oil samples were taken at various intervals and tested for corrosive sulphur by monitoring the concentration of dibenzyl disulphide (DBDS) and the dielectric strength of the oil. This data was used to investigate the reaction rates, activation energies and various thermodynamic parameters of the corrosive sulphur and Cu₂S, and to establish the factors affecting their formation. At high temperatures, the DBDS concentration was found to reach equilibrium. The activation energy for the DBDS reacting with copper and further formation of DBDS was found to be 47.4 KJmol⁻¹ and 35.2 KJmol⁻¹ respectively. This research also determined that a significant amount of the initial concentration of DBDS was needed in order to react with copper. This experimental study also showed that DBDS and Cu₂S reactions do not play a major part in influencing the physical properties of the transformer and transformer oil. Surface physics concepts were employed to discuss the interaction dynamics of Cu₂S on copper surfaces. The main focus of the surface physics investigation compared the results from this experiment with results from other surface physics investigations in published literature.
The crossfield current-driven ion acoustic instability in a two-ion plasma.
(1987) Govender, Jagathesan.; Bharuthram, Ramesh.
The behaviour of the crossfield current-driven ion acoustic instability in a plasma containing two ion species is theoretically examined. In our model the electrons are assumed to be hot and the ions cold, i.e. Tₑ »Tᵢ (~ 0), where both ion species are given the same temperature. The length and time scales are such that the electrons are magnetized and the ions unmagnetized. The linearised Vlasov equation is used to set up a dispersion relation for electrostatic waves for Maxwellian equilibrium velocity distributions of the electrons and ions. For the ion acoustic wave, a study is made of the dependence of the critical electron drift velocity (Vͨₒ) required to excite an instability on several parameters. The parameters include light ion fraction, heavy to light ion mass ratio, magnetic field strength and the propagation angle. In general the maximum value of Vͨₒ is found to be smaller than that for an unmagnetized plasma. Approximate analytic solutions of the dispersion relation are used to make comparisons with solutions from the full dispersion relation. The effect of drifts due to inhomogeneities in external magnetic field, perpendicular electron temperature and electron density on the growth rate of the ion acoustic instability are investigated in the ion rest frame. Finally, in a reference frame in which the electrons are stationary, both ion species are given external drifts. The effects of the ion drift velocities (both equal and unequal), electron to ion temperature ratio, light ion fraction, and heavy to light ion mass ratio on the growth rate of the ion acoustic instability are then studied.

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