[en] Several comprehensive studies of radio frequency (rf) breakdown and rf heating are reported. They are of general interest to magnetic confinement fusion, rf linac, and high power microwave source development. The major results include: (1) a ground-breaking theory of multipactor discharge on dielectric, including a successful proof-of-principle experiment that verified the newly developed scaling laws, (2) an in depth investigation of the failure mechanisms of diamond windows and ceramic windows, and of the roles of graphitization, thin films of coating and contaminants, and (3) a most comprehensive theory, to date, on the heating of particulates by an electromagnetic pulse, and on the roles of rf magnetic field heating and of rf electric field heating, including the construction of new scaling laws that govern them. The above form a valuable knowledge base for the general problem of heating phenomenology

[en] A novel experiment to investigate single-surface multipactor on a dielectric surface was developed and tested. The compact apparatus consists of a small brass microwave cavity in a high vacuum system. The cavity is ∼15 cm in length with an outer diameter of ∼10 cm. A pulsed variable frequency microwave source at ∼2.4 GHz, 2 kW peak excites the TE₁₁₁ mode with a strong electric field parallel to a dielectric plate (∼0.2 cm thickness) that is inserted at midlength of the cavity. The microwave pulses are monitored by calibrated microwave diodes. An electron probe measures electron current and provides temporal measurements of the multipactor electron current with respect to the microwave pulses. Phosphor on the dielectric surface is used to detect multipactor electrons by photoemission. The motivation of this experiment is to test recent theoretical calculations of single-surface multipactor on a dielectric

[en] Experiments have been performed demonstrating the feasibility of direct implantation of laser-ablated metal ions into a substrate. Initial experiments implanted iron ions into silicon substrates at pulsed, bias voltages up to negative 10 kV. Implantation of Fe ions into Si was confirmed by cross-sectional transmission electron microscopy and x-ray photoelectron spectroscopy. The 7.6 nm depth of damage layers below the Si surface is slightly less than predicted by code calculations for a maximum, effective ion energy of about 8 keV. The ion depth of penetration is limited by the overlying Fe film as well as the slow rise and fall of the voltage. [copyright] 2001 American Institute of Physics

[en] We use Monte Carlo simulations and analytical calculations to derive the condition for the onset of multipactor discharge on a dielectric surface at various combinations of the bias dc electric field, rf electric field, and background pressures of noble gases, such as Argon. It is found that the presence of a tangential bias dc electric field on the dielectric surface lowers the magnitude of rf electric field threshold to initiate multipactor, therefore plausibly offering robust protection against high power microwaves. The presence of low pressure gases may lead to a lower multipactor saturation level, however. The combined effects of tangential dc electric field and external gases on multipactor susceptibility are presented.

[en] The scaling laws for the initiation time of radio frequency (rf) window breakdown are constructed for three gases: Ar, Xe, and Ne. They apply to the vacuum, to the multipactor-triggered regime, and to the collisional rf plasma regime, and they are corroborated by computer simulations of these three gases over a wide range of pressures. This work elucidates the key factors that are needed for the prediction of rf window breakdown in complex gases, such as air, at various pressures

[en] The paper presents a systematic evaluation of current crowding and spreading resistance in thin film contacts, based on the exact field solution that contains very large contrasts in dimensions and resistivity. It is found that current crowding becomes more severe as the interface specific contact resistivity decreases, the resistivity ratio of the contact electrode to the thin film decreases, or the thickness of either the contact or the thin film decreases. The current transfer length $L_{\text{T}}$ from our exact field solution is compared to that of transmission line model (TLM), $L_{\text{TLM}}={{\left({\mathrm{\rho <!--\; ??\; -->}}_{\text{c}}/{\mathrm{\rho <!--\; ??\; -->}}_{\text{sh}}\right)}^1}^{/2}$, where ${\mathrm{\rho <!--\; ??\; -->}}_{\text{c}}$ is the interface specific contact resistivity, and ρ _sh is the sheet resistance of the thin film under contact. It is found that, if ${\mathrm{\rho <!--\; ??\; -->}}_{\text{c}}$ is small, $L_{\text{T}}$ is bounded by the smaller of the two dimensions—thin film thickness and contact size. As ${\mathrm{\rho <!--\; ??\; -->}}_{\text{c}}$ increases, $L_{\text{T}}$ increases, but saturates at a constant value, determined by the smaller of the two dimensions—contact size and $L_{\text{TLM}}$. The total contact resistance is decomposed into three components: the interface resistance due to ${\mathrm{\rho <!--\; ??\; -->}}_{\text{c}}$, the spreading resistance due to current crowding, and the resistance due to the contact electrode. Unambiguously identified, each component is explicitly evaluated and compared in detail. (paper)

[en] The condition for mutual, or peer-to-peer, locking of two magnetrons is derived. This condition reduces to Adler's classical phase-locking condition in the limit where one magnetron becomes the ''master'' and the other becomes the ''slave.'' The formulation is extended to the peer-to-peer locking of N magnetrons, under the assumption that the electromagnetic coupling among the N magnetrons is modeled by an N-port network.

[en] A scalable electron cyclotron resonance (ECR) plasma source was investigated for plasma cathode applications. The rectangular source utilized permanent magnets to establish the ECR condition. The microwave applicator region was windowless, making the source applicable to sputtering environment applications. The source was characterized using primarily two diagnostics: (1) a near-field and far-field Langmuir probe and (2) a downstream electron extraction electrode. Source operation and plasma properties were characterized at low pressures ranging from 0.2 to 5 mTorr and power levels up to 250 W. Evidence of grad-B drift in the plane of the source was observed. Extracted currents agreed well with predictions

[en] The current flow pattern, together with the contact resistance, is calculated analytically in a Cartesian 3-terminal thin film contact with dissimilar materials. The resistivities and the geometric dimensions in the individual contact members, as well as the terminal voltages, may assume arbitrary values. We show that the current flow patterns and the contact resistance may be conveniently decomposed into the even and odd solution. The even solution gives exclusively and totally the current flowing from the source to the gate. The odd solution gives exclusively and totally the current flowing from the source to the drain. Current crowding at the edges, and current partition in different regions are displayed. The analytic solutions are validated using a simulation code. The bounds on the variation of the contact resistance are given. This paper may be considered as the generalization of the transmission line model and the Kennedy-Murley model that were used extensively in the characterization of thin-film devices. For completeness, we include the general results for the cylindrical geometry, which are qualitatively similar to the even solution of the Cartesian geometry.

[en] The magneto-Rayleigh-Taylor instability (MRT) of a finite slab is studied analytically using the ideal MHD model. The slab may be accelerated by an arbitrary combination of magnetic pressure and fluid pressure, thus allowing an arbitrary degree of anisotropy intrinsic to the acceleration mechanism. The effect of feedthrough in the finite slab is also analyzed. The classical feedthrough solution obtained by Taylor in the limit of zero magnetic field, the single interface MRT solution of Chandrasekhar in the limit of infinite slab thickness, and Harris' stability condition on purely magnetic driven MRT, are all readily recovered in the analytic theory as limiting cases. In general, we find that MRT retains robust growth if it exists. However, feedthrough may be substantially reduced if there are magnetic fields on both sides of the slab, and if the MRT mode invokes bending of the magnetic field lines.