The Child–Langmuir Law (CL), discovered a century ago, gives the maximum current that can be transported across planar diode in steady state. As quintessential example of impact space charge shielding near charged surface, it is central to studies high diodes, such as power microwave sources, vacuum microelectronics, electron and ion drivers used energy density physics experiments. CL remains touchstone fundamental sheath physics, including contemporary nanoscale quantum diodes nano gap...

This Perspective reviews the fundamental physics of space–charge interactions that are important in various media: vacuum gap, air liquids, and solids including quantum materials. It outlines critical recent developments since a previous review paper on diode [Zhang et al. Appl. Phys. Rev. 4, 011304 (2017)] with particular emphasis theoretical aspects limited current (SCLC) model: at nano-scale, time-dependent, transient behaviors; higher-dimensional models; transitions between electron...

Lumped elements are considered as very attractive structures for the realisation of MMICs with respect to considerable size-reduction. Improved models integrable lumped-element straight-line, single-loop, and spiral inductors, well interdigitated MIM capacitors, have been derived using numerical solutions inductance integral, basic microstrip theory, network analysis. The broad experimental verification shows good agreement between experiments, deviations 5-10% up 18 GHz. Besides practical...

By considering uniform emission of electrons over a finite strip width...

The emittance of high brightness electron sources, particularly field emitters and photocathodes but also thermionic is increased by surface roughness on the emitter. Such structure causes local enhancement complicates both prediction underlying emission models which such predictions depend. In present work, a method to find trajectories near regions given applied for field, photo, thermal an analytically tractable hemispherical model. dependence current density, spatial variation,...

There is, at present, no analytic solution that extends Child-Langmuir space-charge-limited emission beyond 1D. Herein, we investigate the characteristics of planar diode electron in 2D space with emphasis on transition region between beam and vacuum. Current density above predicted by is observed near edges a finite element, electrostatic ray-tracing code. The properties these increased current "wings" are examined then discussed terms their applications to cathodes which have large...

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Over the last decade, Air Force Research Laboratory, Directed Energy Directorate (AFRL/DE) has engaged in a high current density field emission cathode research program. This program explored aspects of materials as well details geometries and physics. paper summarizes results this ongoing effort to date. We review history motivation for program, which provide insight into physics issues concern...

Microwave and radio frequency (RF) sources have been a subject of intense research for nearly 100 years, with the advent High-Power (HPM) based upon relativistic electron beams emerging in 1970s. These act to transform kinetic energy an beam into radiation through interaction electrons some form external circuit. One HPM device, Cerenkov maser, consists hollow cylinder loaded dielectric material. The forms slow-wave structure which can interact. This paper considers new design approach...

Models of space-charge affected thermal-field emission from protrusions, able to incorporate the effects both surface roughness and elongated field emitter structures in beam optics codes, are desirable but difficult. The models proposed here treat meso-scale diode region separate micro-scale regions characteristic sites. consequences discrete events given for one-dimensional (sheets charge) three dimensional (rings models: former, results converge steady state conditions found by theory...

The paper describes developments in the numerical analysis of metal forming processes mainly motivated by industrial applications. It deals with a complete consideration unsteady contact developing between material and die, regeneration finite element mesh during course calculation, simulation superplastic processes. In particular, an approach relating both pressure friction force to motion relative die surface leads convenient computational procedure smooth behaviour under friction....

We present designs and simulations of a new class magnetron, the recirculating planar magnetron. This magnetron has numerous advantages as high-power microwave generator, including larger cathode anode area, fast start-up, compact extraction geometry. The following two geometries are demonstrated by electromagnetic particle-in-cell codes: 1) axial magnetic field with radial electric 2) field.

By considering the effect of Klein tunneling for low energy electrons with linear dispersion, a model has been constructed to calculate amount emitted line current density from single-layer graphene sheet, which is vertically aligned inside dc gap. It found that current-voltage scaling obtained very different traditional field emission based on Fowler-Nordheim (FN) law. Under same geometrical enhancement factor, our predicts much higher as compared FN law at voltages.

This article re-examines the Brillouin flow solutions in crossed-field diodes, with applications to magnetrons, magnetically insulated line oscillators (MILOs), and transmission lines (MITLs). The are constructed for various geometries, including planar MILOs, MITLs, cylindrical magnetrons electrons flowing azimuthal direction, MITLs MILOs axial radial direction. A common theme of this analysis is that two main external parameters used characterize flow: anode–cathode voltage (...

Enhancements in computation hardware and the development of novel software have enabled virtual prototyping several areas science engineering. In particular, authors discuss directed energy devices that generate high-power microwave pulses.

Explosive field emission cathodes have been used extensively in high power microwave tubes. These emit electrons without the use of cathode heaters. Recently, some theoretical and simulation work has performed to gain further understanding physics these cathodes. The purpose this letter is provide experimental background justification for work. general idea how explosive operate that plasma rapidly formed, which provides sea space charge limited flow. However, recent suggests edge effects,...

The fundamental Child–Langmuir limit on the maximum current density in a vacuum between two infinite parallel electrodes is one of most well known and often applied rules plasma physics. We develop simple model using capacitance, conservation energy, charge to derive space-charge-limited emission. This capacitive provides physical insight into origins (voltage)3/2/(gap distance)2 scaling classical does not require solution nonlinear differential equation normally associated with formulation....

The Buneman–Hartree condition is re-examined in a cylindrical, smooth-bore, relativistic magnetron using both the conventional, single particle model, and Brillouin flow model. These two models yield same result for only limit of planar magnetron. When b/a=1.3, where cathode radius b (>a) anode radius, difference becomes significant. b/a=4 acute, magnetic field at given voltage model exceeds four times that Such always present, whether or not. results are quantified b/a⪢1 Davidson's...

Space charge effects reduce electron emission by altering the surface barrier via two effects: increasing height (Schottky factor) and width to lowering field changing magnitude of dipole associated with density variation. A one-dimensional model using a transit time argument account for in anode-cathode (AK) gap an analytical is used approximate each factor on current density. The compared experimental data Longo [J. Appl. Phys. 94, 6966 (2003)] thermal emission. Changes contribution are...

Microwave oscillation has been measured for the first time in a 12-cavity axial-magnetic-field recirculating planar magnetron, designed to operate π mode at 1 GHz. The device operates with -300-kV pulsed cathode voltage and 0.2-T axial magnetic field, oscillates transverse currents exceeding kA when driven by an electron beam pulselength between 0.5 μs. pulses were frequencies 0.97-1 GHz achieved several hundred nanoseconds length. Mode competition was observed 5 π/6 modes.

Abstract The traveling-wave tube (TWT), also known as the amplifier (TWA) or (TWTA), is a widely used in satellite communications and radar. An electromagnetic signal inputted on one end of device amplified over distance until it extracted downstream at output. physics behind this spatial amplification an wave predicated interaction linear DC electron beam with surrounding circuit structure. Pierce, ‘father satellites,’ was first to formulate theory for beam-circuit interaction, basis which...

While the particle-in-cell (PIC) method is quite mature, verification and validation of both newly developed methods individual codes has largely focused on an idiosyncratic choice a few test cases. Many these cases involve either one- or two-dimensional simulations. This due to availability (quasi) analytic solutions historical reasons. Additionally, tests often focus investigation particular physics problems, such as particle emission collisions, do not necessarily study combined impact...

Experimental evidence shows that the electron flow in a load-limited magnetically insulated transmission line oscillator (MILO) is only partially at launch point, yet fully along downstream slow-wave structure (SWS). This results microwave pulse duration substantially less than of beam. Computer simulations suggest anode plasma formation responsible for this shortening and are able to replicate key features experimental data.

The current carried by a steady-state, finite-width beam produced space-charge-limited emission in two-dimensional parallel plate geometry is known to diverge strongly from estimates based on the classic one-dimensional Child–Langmuir problem. problem presents formidable analytic difficulties, but numerical approach this has been developed. simultaneously determines electrostatic potential and unknown density profile. Calculations show that total function of dimensionless ratio width (w)...