A Model on AC Contact Resistance Antoulinakis, F.; Lau, Y. Y.
2018 IEEE International Conference on Plasma Science (ICOPS),
2018-June-24
Conference Proceeding
Electrical contact is an important issue to high power microwave sources, pulsed power systems, field emitters, thin film devices and integrated circuits, and interconnects, etc. Contact resistance, ...and the enhanced ohmic heating that results, have been treated mostly under steady state (DC) condition. In this paper, we consider the AC contact resistance for a simple geometry1, namely, that of two semi-infinite cylindrical conductors of different radii joint at z = 0. The conductivity of the two cylinders may assume different values. In the DC case, this model was solved exactly by Zhang and Lau 1. We have constructed an exact solution under AC condition, and we have shown that in the limit of zero frequency, our AC solution reduces to the DC solution. New features that accompany AC condition, such as the resistive skin effect, inductive, and capacitive effects, as well as radiation losses will be explored.
The Michigan Accelerator for Inductive Z-pinch Experiments (MAIZE) is a single-stage, 1-MA linear transformer driver at the University of Michigan. The MAIZE facility has been the site of various ...experimental studies, including wire array Z-pinches for X-ray source development and cylindrical foil loads for implosion stability analysis. In order to better understand and investigate these and other experiments, a 4-frame extreme ultraviolet camera was implemented, the optical stability of a 12-frame laser shadowgraphy system was improved, B-dot probes were upgraded, and a Rogowski coil was constructed. New conical load hardware was also developed to reduce the inductance of the transmission line and thus improve the current delivered to the loads.
Solenoid Siberian snakes have successfully maintained polarization in particle rings below 1 GeV, but never in multi-GeV rings, because the spin rotation by a solenoid is inversely proportional to ...the beam momentum. High energy rings, such as Brookhaven’s 255 GeV Relativistic Heavy Ion Collider (RHIC), use only odd multiples of pairs of transverse B-field Siberian snakes directly opposite each other. When it became impractical to use a pair of Siberian Snakes in Fermilab’s 120GeV/c Main Injector, we searched for a new type of single Siberian snake that could overcome all depolarizing resonances in the 8.9–120GeV/c range. We found that a snake made of one 4-twist helix and 2 dipoles could maintain the polarization. This snake design could solve the long-standing problem of significant polarization loss during acceleration of polarized protons from a few GeV to tens of GeV, such as in the AGS, before injecting them into multi-hundred GeV rings, such as RHIC.
The threshold for the onset of backward wave oscillation (BWO) in a traveling-wave tube (TWT) was formulated by Johnson 1. In this paper, we extend Johnson's model to include random variations of ...circuit phase velocity along the tube axis. We find that Johnson's BWO threshold is minimally affected by these random variations. We next ignore these random variations, but include finite reflections at the two ends of a TWT and study their effects on Johnson's threshold. The latter theory is developed and being compared with results from an experimental helix test circuit. We will explore a 4-wave treatment 2 for BWO, and its connection with the Briggs-Bers criterion 3 for the existence of absolute instability.
We provide a close examination of the beam mode and its interaction with the circuit mode in the immediate vicinity of the lower band edge in a traveling wave tube. We model the circuit mode as a ...hyperbola in the (w, k) plane in the immediate vicinity of the lower band edge, where w is the frequency and k is the wavenumber. We find that an absolute instability may arise, according to the Briggs-Bers criterion 1, if the beam current is sufficiently high, even if the beam mode intersects with the circuit mode at a point in the (w, k) plane with a positive group velocity. This threshold condition is deduced analytically and confirmed by numerical calculations. When the threshold current is exceeded, the Green's function 1, at a fixed position, exponentiates in time as t to the 1/3 power initially, but as (wi*t) at later time, where wi is the imaginary part of the unstable polepinch root of w according to the Briggs-Bers criterion 1. This finding differs from some previous works 2, 3on absolute instabilities at the lower band edge, and points to the vulnerability to absolute instabilities at both the upper and lower band edges of a TWT.
Joule heating limits the operation of most current carrying components and devices, especially in nanoscale circuits such as carbon nanofiber based field emitters, graphene electronics, and ...nanolasers 1. For many materials of interest it is important to consider the temperature dependence of the thermal and electrical conductivities when calculating the effects of Joule heating. We examine the effects of linear temperature dependence of the electrical and thermal conductivities on the heating of a one-dimensional conductor by solving the coupled non-linear steady state electrical and thermal conduction equations. We find that there are conditions under which no steady state solution exists. In the special case in which the temperature dependence of the electrical conductivity may be neglected, we have obtained explicit expressions for these conditions. The maximum temperature and its location within the conductor are examined for various boundary conditions. We note that the absence of a steady state solution may indicate the possibility of thermal runaway 2.
Solenoid Siberian snakes have successfully maintained polarization in particle rings below 1 GeV, but never in multi-GeV rings because the Lorentz contraction of a solenoid's integral B dl would ...require impractically long high-field solenoids. High energy rings, such as Brookhaven's 255 GeV Relativistic Heavy Ion Collider (RHIC), use only odd multiples of pairs of transverse B-field Siberian snakes directly opposite each other. When it became impractical to use a pair of Siberian Snakes in Fermilab's 120 GeV Main Injector, we searched for a new type of single Siberian snake, which should overcome all depolarizing resonances in the 8.9 - 120 GeV range. We found that one snake made of one 4-twist helix and 2 short dipoles could maintain the polarization. This snake design might also be used at other rings, such as Japan's 30 GeV J-PARC, the 12 - 24 GeV NICA proton-deuteron collider at JINR-Dubna, and perhaps RHIC's injector, the 25 GeV AGS.
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