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An experiment is performed on a large plasma device operated by the Basic Plasma Science Facility at the University of California, Los Angeles, in which an electrically floating structure is placed near the end of the 18-m magnetized plasma column. The structure consists of a flat carbon plate that acts as a mask for a smaller, ring-shaped LaB6 emissive surface whose temperature can be externally controlled. This configuration has been previously used to study electron heat transport and pressure-driven avalanches [B. Van Compernolle and G. J. Morales, Phys. Plasmas 24, 112302 (2017)] by biasing the LaB6 ring-cathode with respect to a distant anode in a cold afterglow plasma. In contrast, the present study is performed during the active portion of the steady-state discharge in which the nominal plasma parameters are determined by the injection of an electron beam from a BaO cathode at the opposite end. It is found that, even without an applied bias on the LaB6 cathode, the self-consistent potential and current profiles are modified near the end plate as the LaB6 temperature is increased, resulting in density increases on the field lines in contact with the ring-cathode. In the absence of enhanced ionization, at the largest cathode temperatures, the ambient density can be doubled. A theoretical model is presented that provides a quantitative explanation for the experimental observations.An experiment is performed on a large plasma device operated by the Basic Plasma Science Facility at the University of California, Los Angeles, in which an electrically floating structure is placed near the end of the 18-m magnetized plasma column. The structure consists of a flat carbon plate that acts as a mask for a smaller, ring-shaped LaB6 emissive surface whose temperature can be externally controlled. This configuration has been previously used to study electron heat transport and pressure-driven avalanches [B. Van Compernolle and G. J. Morales, Phys. Plasmas 24, 112302 (2017)] by biasing the LaB6 ring-cathode with respect to a distant anode in a cold afterglow plasma. In contrast, the present study is performed during the active portion of the steady-state discharge in which the nominal plasma parameters are determined by the injection of an electron beam from a BaO cathode at the opposite end. It is found that, even without an applied bias on the LaB6 cathode, the self-consistent potential and cu...

Results are presented from basic heat transport experiments and gyrokinetic simulations of multiple magnetized electron temperature filaments in close proximity. This arrangement samples cross-field transport from nonlinear drift-Alfven waves and large scale convective cells. Experiments are performed in the Large Plasma Device (LAPD) at UCLA. A biased LaB6 cathode injects low energy electrons (below ionization energy) along a strong magnetic field into a pre-existing large and cold plasma forming an electron temperature filament embedded in a colder plasma, and far from the machine walls. A car bon masking plate with several holes (each 1cm diameter, 1.5 cm apart) is used to create 3 electron temperature filaments. By covering two holes in the mask drift-Alfven and thermal waves from a single filament have been characterized and compared to previous studies with a different electron beam source1. The observed eigenmode structures also compares favor ably with recent 3D gyrokinetic simulations2. The 3-filament case exhibits a complex wave pattern and enhanced cross-field transport. Detailed mode analysis and comparison with non linear simulations is reported.

A broad experimental survey is made of the properties of spontaneously generated magnetic fluctuations in a large linear device in which the plasma density has different cross-field gradient scales. It includes steep gradients at the plasma–wall edge as well as at an interior plasma–plasma interface, thus phenomena of interest to magnetic fusion research as well as to space plasma physics is illustrated. Fluctuations in uniformly magnetized columns and plasmas with an axial gradient in the confining magnetic field are studied. Some of the highlights include the identification of a universal spectrum for drift-Alfven turbulence and the role of partial reflections in shaping the spectra.

The results are presented for a basic heat transport experiment involving an off-axis heat source in which avalanche events occur. The configuration consists of a long, hollow, cylindrical region of elevated electron temperature embedded in a colder plasma, and far from the device walls [Van Compernolle et al. Phys. Rev. E 91, 031102(R) (2015)]. The avalanche events are identified as sudden rearrangements of the pressure profile following the growth of fluctuations from ambient noise. The intermittent collapses of the plasma pressure profile are associated with unstable drift-Alfven waves and exhibit both radial and poloidal dynamics. After each collapse, the plasma enters a quiescent phase in which the pressure profile slowly recovers and steepens until a threshold is exceeded, and the process repeats. The use of reference probes as time markers allows for the visualization of the 2D spatio-temporal evolution of the avalanche events. Avalanches are observed only for a limited combination of heating power...

A systematic study is made of the spontaneous growth of fluctuations in temperature, density, and magnetic field in a narrow (on the order of the electron skin depth) field-aligned temperature filament embedded in a large magnetized plasma. Two broad classes of fluctuation (“low” and “high” frequency modes) have been identified and studied in detail. A high-frequency drift-Alfven mode grows at frequencies about one tenth the ion gyrofrequency in the region of the filament where the temperature gradient is large. The measured radial profiles of the density and magnetic field fluctuations associated with this mode agree well with theoretical predictions. The high-frequency mode has been observed to exhibit several interesting nonlinear features, including steepening wave form, progression in azimuthal mode number, coupling to the low frequency mode with subsequent sideband generation, and eventually a transition to broad band turbulence. The nature of the low-frequency mode which has frequencies about one f...

This experiment illustrates the spatiotemporal pattern of the fluctuations that spontaneously develop in a magnetized temperature filament whose transverse scale is comparable to the electron skin depth. A high-frequency mode exhibits a striking spiral structure and is identified as a drift-Alfv\'en eigenmode. A low-frequency mode is found to be localized near the center of the filament. It is documented that the fluctuations significantly increase the transport of heat beyond the prediction of classical theory based on Coulomb collisions.

A systematic laboratory study of controlled density and temperature filaments having transverse scale length comparable to the electron skin-depth has been performed in the large plasma device (LAPD) at UCLA. It is found that large amplitude shear Alfven waves develop spontaneously and are localized within the filaments. As the plasma conditions change (e.g., lowering the plasma beta parameter or increasing the heating power) the highly coherent eigenmodes develop into broad band Alfvenic turbulence. A kinetic description that includes the effect of coulomb collisions has been developed to understand the linear properties of the modes. Excellent agreement with the measured eigenfunctions is found for the density filaments in the higher beta regime in which the modes remain strongly coherent. The similarity between the broad band fluctuation spectra generated in a variety of plasma configurations suggest the possibility of a universal process involving filamentary structures and spontaneously generated Alfvenic turbulence.

In this analytical and computer simulation study we explore the dynamics of a narrow electron stream embedded in a magnetized plasma. The transverse dimension of the stream is envisioned to be on the order of the electron skin depth, as is appropriate to several problems of current interest (e.g., auroral beams, reconnection). Within the layer the drift velocity exceeds the thermal velocity, and thus the Buneman instability is excited. The method of matched asymptotic expansions is used to describe the linear stage of the instability for a nonuniform drift profile. It predicts a lowering of the growth rate and a rapid decrease in wave amplitude at the spatial location where the beam mode resonance is encountered. A particle-in-cell (PIC) simulation is used to verify the predictions of the analysis and to illustrate the important nonlinear behavior. It is found that the rapid flash of the Buneman instability excites a lower-hybrid wave, causes strong perpendicular ion acceleration, and results in a region ...

The transport of heat deposited by a small low-voltage electron beam in a strongly magnetized plasma is studied for a time interval in excess of two thousand ion-gyro periods. Electron temperatures are observed to evolve along and across the magnetic field at the classically predicted rates up to times approaching one thousand gyro periods. At later times the onset of low-frequency fluctuations (below one-tenth the ion gyrofrequency) coincides with departures from classical behavior.

We have investigated an effect that is inherent to weakly stable plasmas: an enhanced large-velocity interaction. This behavior is not unique to two dimensions, but is quite similar to the higher-order terms in a three-dimensional dominant approximation expansion, as shown in the studies of Ware2 and of Tidman and Eviatar.3 The increased level of fluctuations generated by fast electrons is quite similar in both two and three dimensions. However, because both the emission and absorption of fluctuations by fast electrons is retained by the two-dimensional Fokker-Planck theory to lowest order (no dominant approximation is needed), these electrons interact at a significantly higher level than predicted by an extrapolation based on the usual three-dimensional dominant calculation. Small-angle collisions do not dominate in two dimensions, and the soft core of the logarithmic potential implies that any enhanced fluctuations affect the transport significantly. In three dimensions, a substantial tail would be necessary before a corresponding effect is observed.4,5 These results are essential to a complete understanding of two-dimensional particle simulations, especially those of weakly stable plasmas.

Magnetic field-aligned structures in current, density, and temperature are common features of the auroral ionospheric plasma. These structures both generate and transform low frequency waves in the plasma. The results of laboratory studies of two processes involving magnetic field-aligned density depletions (striations) that play a role in auroral plasma dynamics are presented. The first process involves the spontaneous generation of density and magnetic fluctuations at the striation edge. The nature of the fluctuations depends upon the electron plasma beta. At high beta (greater than the electron to ion mass ratio, m/M) the drift Alfven wave is excited. At lower beta the density and magnetic field fluctuations separate and the shear Alfven wave dominates. This process creates an environment conducive to electron acceleration along the magnetic field when the striation size is on the order of the electron skin depth because the shear Alfven wave then has a substantial field-aligned electric field. The sec...

Density and magnetic fluctuations arising spontaneously in a narrow field-aligned density striation in a magnetized discharge He plasma are found to exhibit a radial eigenmode structure. The nature of the fluctuations depends upon the electron plasma beta, βe. For βe greater than the electron to ion mass ratio (βe>m/M) the frequency spectrum exhibits sharply peaked eigenfrequencies with the density and magnetic fluctuations strongly coupled so that the growing mode is identified as the drift-Alfven wave. For βe less than the mass ratio (βe

The high‐frequency electromagnetic field generated by a density‐modulated, helical electron beam propagating in a magnetized plasma is calculated. The magnetic fluctuations are found to exhibit spatially localized (evanescent) resonances at harmonics of the electron‐cyclotron frequency, whose width is determined by the pitch angle of the beam, and whose existence is a consequence of the helical geometry. In addition, electrostatic modes are radiated near the hybrid frequencies, and electromagnetic modes are radiated above the upper‐hybrid frequency. The predicted frequency spectrum and mode structure in configuration space are in good agreement with experimental observations of discrete emission lines at the electron‐cyclotron harmonics [Phys. Fluids B 5, 3789 (1993)].

A theoretical and numerical modeling study is made of a novel heating configuration recently implemented in the Large Plasma Device at the University of California, Los Angeles. The injection of an electron beam from a masked LaB6 cathode into a magnetized plasma results in a hollow, cylindrical filament of elevated temperature. The hot cylindrical ring has an axial extent that is about one-thousand times larger than its thickness, and the peak temperature can be ten times larger than that of the surrounding plasma. The simultaneous positive and negative radial pressure gradients provide an ideal platform for the investigation of transport phenomena of contemporary interest, including avalanches [Van Compernolle et al., Phys. Rev. E 91, 031102 (2015)] and nonlocal transport. The present study delineates both the parameter regimes achievable by classical transport and the linear stability of the self-consistent profiles, including temperature and density gradients. An avalanche model is developed based on the self-consistent evolution of drift-wave eigenfunctions in nonlinearly modified profiles of electron temperature and plasma density.

The drift-cyclotron loss-cone mode was first studied in mirror machines. In such devices, particles with small pitch angles are not confined, creating a hole in the velocity distribution function that is a source of free energy and leads to micro-instabilities in the cyclotron-range of frequencies. In the edge region of tokamak devices operating under H-mode conditions, ion loss also occurs. In this case, gradient drift carries ions moving opposite to the plasma current preferentially into the divertor, creating a one-sided loss cone. A simple analysis shows that for the quiescent H-mode plasmas in DIII-D the critical gradient for instability is exceeded within 2 cm of the separatrix, and the maximum growth rate at the separatrix is 3 × 107 s−1.

[1] In a magnetized plasma with two ion species, shear Alfven waves (or guided electromagnetic ion cyclotron waves) have zero parallel group velocity and experience a cut-off near the ion-ion hybrid frequency. Since the ion-ion hybrid frequency is proportional to the magnetic field, it is possible, in principle, for a magnetic well configuration to behave as an Alfven wave resonator in a two-ion plasma. This study demonstrates such a resonator in a controlled laboratory experiment using a H+-He+ mixture. The resonator response is investigated by launching monochromatic waves and sharp tone-bursts from a magnetic loop antenna. The observed frequency spectra are found to agree with predictions of a theoretical model of trapped eigenmodes.

An electromagnetic, 3D gyrokinetic particle code is used to study the relaxation of a magnetized electron temperature filament embedded in a large, uniform plasma of lower temperature. The study provides insight into the role played by unstable drift-Alfven waves observed in a basic electron heat transport experiment [D. C. Pace et al., Phys. Plasmas 15, 122304 (2008)] in which anomalous cross-field transport has been documented. The simulation exhibits the early growth of temperature-gradient-driven, drift-Alfven fluctuations that closely match the eigenmodes predicted by linear theory. At the onset of saturation, the unstable fluctuations display a spiral spatial pattern, similar to that observed in the laboratory, which causes the rearrangement of the temperature profile. After saturation of the linear instability, the system exhibits a markedly different behavior depending on the inclusion in the computation of modes without variation along the magnetic field, i.e., kz = 0. In their absence, the initi...

Analysis of the time series obtained with the Doppler backscattering system (Hillsheim et al 2009 Rev. Sci. Instrum. 80 0835070) in the DIII-D tokamak (Luxon 2005 Fusion Sci. Technol. 48 828) shows that intermediate wave number plasma density fluctuations in low confinement (L-mode) tokamak plasmas are chaotic. The supporting evidence is based on the shape of the power spectrum; the location of the signal in the complexity-entropy plane (C-H plane) (Rosso et al 2007 Phys. Rev. Lett. 99 154102); and the population of the corresponding Bandt–Pompe (Bandt and Pompe 2002 Phys. Rev. Lett. 88 174102) probability distributions.

A particle-in-cell code is used to investigate the evolution of a density plume moving through a background plasma with supersonic speed directed along the confinement magnetic field. For scale lengths representative of laboratory and auroral phenomena, the major nonlinear effects identified by the present simulations are the formation of a bipolar current system from the ballistic electrons, the appearance of transient potential layers, and the carving of deep density cavities. A 3D magnetic topology is generated by the self-consistent ballistic and diamagnetic currents that accompany highly localized potential layers.

An investigation is made of a shear Alfven wave resonator for burning plasma conditions expected in the ITER device. For small perpendicular scale-lengths the shear mode, which propagates predominantly along the magnetic field direction, experiences a parallel reflection where the wave frequency matches the local ion-ion hybrid frequency. In a tokamak device operating with a deuterium–tritium fuel, this effect can form a natural resonator because of the variation in local field strength along a field line. The relevant kinetic dispersion relation is examined to determine the relative importance of Landau and cyclotron damping over the possible resonator parameter space. A WKB model based on the kinetic dispersion relation is used to determine the eigenfrequencies and the quality factors of modes trapped in the resonator. The lowest frequency found has a value slightly larger than the ion-ion hybrid frequency at the outboard side of a given flux surface. The possibility that the resonator modes can be driven unstable by energetic alpha particles is considered. It is found that within a bandwidth of roughly 600 kHz above the ion-ion hybrid frequency on the outboard side of the flux surface, the shear modes can experience significant spatial amplification. An assessment is made of the form of an approximate global eigenmode that possesses the features of a resonator. It is identified that magnetic field shear combined with large ion temperature can cause coupling to an ion-Bernstein wave, which can limit the instability.

A radial fractional transport model [Kullberg et al., Phys. Rev. E 87, 052115 (2013)], that correctly incorporates the geometric effects of the domain near the origin and removes the singular behavior at the outer boundary, is compared to results of off-axis heating experiments performed in the Rijnhuizen Tokamak Project (RTP), ASDEX Upgrade, JET, and DIII-D tokamak devices. This comparative study provides an initial assessment of the presence of fractional transport phenomena in magnetic confinement experiments. It is found that the nonlocal radial model is robust in describing the steady-state temperature profiles from RTP, but for the propagation of heat waves in ASDEX Upgrade, JET, and DIII-D the model is not clearly superior to predictions based on Fick's law. However, this comparative study does indicate that the order of the fractional derivative, α, is likely a function of radial position in the devices surveyed.

Ray tracing calculations are performed for shear Alfven waves in two-ion species plasmas in which the magnetic field varies with position. Three different magnetic topologies of contemporary interest are explored: a linear magnetic mirror, a pure toroidal field, and a tokamak field. The wave frequency is chosen to lie in the upper propagation band, so that reflection at the ion-ion hybrid frequency can occur for waves originally propagating along the magnetic field direction. Calculations are performed for a magnetic well configuration used in recent experiments [S. T. Vincena et al., Geophys. Res. Lett. 38, L11101 (2011) and S. T. Vincena et al., Phys. Plasmas 20, 012111 (2013)] in the Large Plasma Device (LAPD) related to the ion-ion hybrid resonator. It is found that radial spreading cannot explain the relatively low values of the resonator quality factor (Q) measured in those experiments, even when finite ion temperature is considered. This identifies that a damping mechanism is present that is at least an order of magnitude larger than dissipation due to radial energy loss. Calculations are also performed for a magnetic field with pure toroidal geometry, without a poloidal field, as in experiments being planned for the Enormous Toroidal Plasma Device. In this case, the effects of field-line curvature cause radial reflections. A poloidal field is included to explore a tokamak geometry with plasma parameters expected in ITER. When ion temperature is ignored, it is found that the ion-ion hybrid resonator can exist and trap waves for multiples bounces. The effects of finite ion temperature combine with field line curvature to cause the reflection point to move towards the tritium cyclotron frequency when electron temperature is negligible. However, for ITER parameters, it is shown that the electrons must be treated in the adiabatic limit to properly describe resonator phenomena.

A theoretical and experimental investigation is made of a wave resonator based on the concept of wave reflection along the confinement magnetic field at a spatial location where the wave frequency matches the local value of the ion-ion hybrid frequency. Such a situation can be realized by shear Alfven waves in a magnetized plasma with two ion species because this mode has zero parallel group velocity and experiences a cut-off at the ion-ion hybrid frequency. Since the ion-ion hybrid frequency is proportional to the magnetic field, it is expected that a magnetic well configuration in a two-ion plasma can result in an Alfven wave resonator. Such a concept has been proposed in various space plasma studies and could have relevance to mirror and tokamak fusion devices. This study demonstrates such a resonator in a controlled laboratory experiment using a H+-He+ mixture. The resonator response is investigated by launching monochromatic waves and impulses from a magnetic loop antenna. The observed frequency spectra are found to agree with predictions of a theoretical model of trapped eigenmodes.

A calculation is presented of the radiation pattern of shear Alfven waves generated by a burst of charged particles in a charge-neutral plasma with two-ions of differing charge-to-mass ratios. The wake pattern is obtained for the inertial and kinetic regimes of wave propagation. Due to the presence of two ion-species, the Alfven waves propagate within two different frequency bands separated by a gap. One band is restricted to frequencies below the cyclotron frequency of the heavier species and the other to frequencies between the ion-ion hybrid frequency and the cyclotron frequency of the lighter species. The radiation pattern in the lower frequency band is found to exhibit essentially the same properties reported in a previous study [Van Compernolle et al., Phys. Plasmas 15, 082101 (2008)] of a single species plasma. However, the upper frequency band differs from the lower one in that it always allows for the Cherenkov radiation condition to be met. The methodology is extended to examine the Alfvenic wake of point-charges in the inertial and adiabatic regimes. The adiabatic regime is illustrated for conditions applicable to fusion-born alpha particles in ITER.

An experimental investigation of the low-frequency density fluctuations in the plasma edge region of the TJ-K stellarator [N. Krause et al., Rev. Sci. Inst. 73, 3474 (2002)] finds that the ensemble- averaged frequency spectra exhibit a near exponential frequency dependence whose origin can be traced to individual pulses having a Lorentzian temporal shape. Similar features have been previously observed [D. C. Pace et al., Phys. Plasmas 15, 122304 (2008)] in a linear magnetized device under conditions in which cross-field pressure gradients are present. The reported observation of such features within the turbulent environment of a toroidal confinement device provides support for the conjecture that the underlying processes are a general feature of pressure gradients. Also presented is the magnetic field strength dependence of the pulse widths and the waiting time distribution between pulses.

The results of a theoretical modeling study and experimental investigation of the propagation properties of shear Alfven waves of small transverse scale in a plasma with two ion species are reported. In the two ion plasma, depending on the mass of the heavier species, ion kinetic effects can become prominent, and significant parallel electric fields result in electron acceleration. The theory predicts the appearance of frequency propagation gaps at the ion-ion hybrid frequency and between harmonics of the lower cyclotron frequency. Within these frequency bands spatial structures arise that mix the cone-propagation characteristics of Alfven waves with radially expanding ion Bernstein modes. The experiments, performed at the Basic Plasma Science Facility (BaPSF) at UCLA, consist of the spatial mapping of shear waves launched by a loop antenna. Although a variety of two ion-species combinations were explored, only results from a helium-neon mix are reported. A clear signature of a shear wave propagation gap, as well as propagation between multiple harmonics, is found for this gas combination. The evanescence of shear waves beyond the reflection point at the ion-ion hybrid frequency in the presence of an axial magnetic field gradient is also documented.

Nonresonant fast ions (${\mathit{E}}_{\mathit{i}}$/${\mathit{T}}_{\mathit{i}}$\ensuremath{\sim}100) with large ratios of perpendicular-to-parallel energy (${\mathit{E}}_{\mathrm{\ensuremath{\perp}}}$/${\mathit{E}}_{\mathrm{\ensuremath{\parallel}}}$\ensuremath{\sim}100) have been observed in rf-produced, electron-cyclotron-resonance-heating-produced and low-density Ohmic plasmas in the Continuous Current Tokamak device by means of a scannable fast neutral spectrometer. Superthermal ions (${\mathit{E}}_{\mathit{i}}$/${\mathit{T}}_{\mathit{i}}$\ensuremath{\sim}20) are also observed in high-harmonic ion cyclotron-heated tokamak discharges (\ensuremath{\omega}/${\mathrm{\ensuremath{\Omega}}}_{\mathit{i}}$\ensuremath{\sim}20), but appear to be isotropic, possibly due to pitch-angle scattering. These measurements strongly suggest the existence of a universal mechanism of perpendicular ion acceleration.

A simplified numerical study is made of the structures that are formed in a magnetized temperature filament due to oscillatory convection from large amplitude drift waves. This study is motivated by a recent experiment [D. C. Pace, M. Shi, J. E. Maggs et al., Phys. Plasmas 15, 122304 (2008)] in which Lorentzian-shaped temporal pulses are observed. These pulses produce a broadband, exponential frequency power spectrum. The model consists of an electron heat transport equation in which plasma convection arising from pressure-gradient driven drift-waves is included. It is found that above a critical wave amplitude, spatially complex structures are formed, which give rise to temporal pulses having positive and negative polarities at different radial positions. The temporal shape of the pulses can be fit by a Lorentzian function. The associated spatial structures exhibit temporally oscillatory heat plumes (positive polarity) and cold channels (negative polarity). The idealized effect of a static flow on these structures is explored. Depending on the flow direction (relative to the azimuthal propagation of the drift waves), the temporal Lorentzian pulses can be suppressed.

Two different experiments involving pressure gradients across the confinement magnetic field in a large plasma column are found to exhibit a broadband turbulence that displays an exponential frequency spectrum for frequencies below the ion cyclotron frequency. The exponential feature has been traced to the presence of solitary pulses having a Lorentzian temporal signature. These pulses arise from nonlinear interactions of drift-Alfven waves driven by the pressure gradients. In both experiments the width of the pulses is narrowly distributed resulting in exponential spectra with a single characteristic time scale. The temporal width of the pulses is measured to be a fraction of a period of the drift-Alfven waves. The experiments are performed in the Large Plasma Device (LAPD-U) [W. Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] operated by the Basic Plasma Science Facility at the University of California, Los Angeles. One experiment involves a controlled, pure electron temperature gradient associated...

An exploratory investigation, both computational and experimental, is made of the diagnostic possibilities of a fast wave-based method for measuring the ion density and temperature profiles of tokamak plasmas. The concept consists of simultaneously launching several discrete frequencies and detecting their amplitude and phase at various toroidal locations. This study focuses on an array of frequencies that match the second harmonic of the ion gyrofrequency at various radial locations in the plasma profile. The method is explored with simple, wave-propagation codes for parameters corresponding to the Electric Tokamak (ET) [R. J. Taylor, et al., Nucl. Fusion 42, 46 (2002)] and ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)]. An experimental investigation of the concept has been performed in a large tokamak (ET) in which six frequencies are launched and detected at four toroidal locations. Positive results obtained indicate that the concept and other variants deserve to be pursued in greater depth, using more sophisticated codes.

A particle-in-cell (PIC) code has been developed that is capable of describing the propagation of compressional and shear Alfven waves excited from a boundary. The code is used to elucidate the properties of Alfven wave cones radiated from sources having transverse scale comparable to the electron skin depth. Good agreement between theoretical predictions and simulation results is found over a wide range of frequencies. An investigation has been undertaken of the effect of hot ions on the Alfven wave cones. The PIC simulations demonstrate that as the ion temperature is increased there is a reversal in the cone angle. The reversal implies that there is a cross-field focusing of the shear Alfven waves. This is a feature which is presently being considered in studies of field-line resonances in the earth’s magnetic field. The PIC results also illustrate the damping of shear modes due to the Doppler-shifted cyclotron resonance with hot ions.

A frequency selective Alfven wave resonator results from the application of a locally nonuniform magnetic field to a plasma source region between the cathode and anode in a large laboratory device. When a threshold in the plasma discharge current is exceeded, selective amplification produces a highly coherent (δω∕ω

The enhancement of the ponderomotive potential near gyroresonance is investigated both experimentally and theoretically. Because of nonadiabaticity near gyroresonance the potential is finite and depends on the transit time of the particle through the rf field structure.

The effect of the ponderomotive force in the interaction of a capacitor rf field with a nonuniform plasma is investigated.

Ion cyclotron resonance heating (ICRH) and its intrinsic effect on confinement in tokamaks is investigated. The stochastic nature of ICRH in the absence of collisions is examined through finite-mapping equations. The threshold RF amplitude for the transition from superadiabatic to stochastic behaviour is found to be exceeded in present-day experiments. The effect of heating on confinement is evaluated by studying the drift orbit changes due to heating with collisions included through a Monte-Carlo method. The results indicate that transport induced by the ion cyclotron range of frequencies (ICRF) could be significant at the higher RF power levels planned for the next generation of experiments.

Thomson radar returns from the ionosphere subjected to a step-function excitation of electromagnetic waves show the immediate rise of electrostatic waves near the resonant height ${\ensuremath{\omega}}_{p}\ensuremath{\simeq}{\ensuremath{\omega}}_{0}$. The observed secular temporal variation $E\ensuremath{\propto}t$ agrees with a theory based on direct conversion of electromagnetic waves to electrostatic waves by preexisting density inhomogeneities. The rise time is at least an order of magnitude smaller than previously reported. The frequency spectrum shows this conversion is characterized by frequencies at the pump frequency ${\ensuremath{\omega}}_{0}$.

We have derived analytic expressions, in terms of Airy functions, for the fields and for the reflection and mode conversion coefficients of Langmuir and electromagnetic waves in an inhomogeneous, unmagnetized plasma. Our results, which are valid in the limit of nonrelativistic electron temperature, T/mc2≪1, agree with earlier numerical calculations.

A sharp transport barrier, accompanied by a bifurcated poloidal rotation and a radial electric field, is formed at the plasma edge by driving a radial current across the outer magnetic surfaces of a tokamak. A decrease in particle transport is observed for negative radial E fields. When the radial current is turned off, the E field and the rotation damp on a time scale comparable with the ion-ion collision time.

Single-component plasmas are found to exhibit a reversal in the roles of cyclotron and upper hybrid resonances familiar in neutral plasmas. There is a global resonance at the cyclotron frequency $\ensuremath{\omega}=\ensuremath{\Omega}\ensuremath{\equiv}\frac{\mathrm{qB}}{\mathrm{mc}}$ and a local field cancellation at layers where $\ensuremath{\omega}={\ensuremath{\Omega}}_{1}={({\ensuremath{\Omega}}^{2}\ensuremath{-}{\ensuremath{\omega}}_{p}^{2})}^{\frac{1}{2}}$, ${\ensuremath{\omega}}_{p}$ being the local plasma frequency. Thermal effects limit the amplitude of the global resonance and produce energy absorption at the $\ensuremath{\omega}={\ensuremath{\Omega}}_{1}$ layers.

An ICRF full‐wave equation is used to investigate the process of inverse mode conversion of a short‐wavelength ion Bernstein wave (IBW) into a long‐wavelength fast magnetosonic wave. Appropriate boundary conditions are presented to set‐up the numerical analysis. For conditions corresponding to fundamental minority heating in tokamaks (minority concentration above 2% and k∥

A kinetic theory of electrostatic cyclotron waves in a single component plasma slab of density n0(x) immersed in a uniform magnetic field B0z is presented. The space charge electric field E0(x)x in such a plasma modifies the single particle gyrofrequency from Ω=qB0/mc to Ω1(x)=[Ω2−ω2p(x)]1/2 in the limit rc/L ≪1 (where rc is the orbit size and L−1=d ln E0/dx), causing the upper hybrid frequency to have the value (Ω21+ω2p)1/2 =Ω. Finite Larmor radius effects introduce a velocity dependence into the single particle gyrofrequency Ω1, leading to energy transfer to the particles located at the resonant layers where ω−kyvE(x) =Ω1(x) [vE(x)y being the E×B drift velocity]. This energy transfer mechanism is operative even when kz =0. Another nonzero Larmor radius effect is the appearance of thermal modes that are the analogs of Bernstein modes of neutral plasmas. When driven by an external capacitor plate antenna, these modes exhibit behavior similar to Tonks–Dattner resonances.