The Field Theory of Collective Cherenkov Radiation Associated with Electron Beams

Classical Cherenkov radiation is a celebrated physics phenomenon of electromagnetic (EM) radiation stimulated by an electric charge moving with constant velocity in a three dimensional dielectric medium. Cherenkov radiation has a wide spectrum and a particular distribution in space similar to the Mach cone created by a supersonic source. It is also characterized by the energy transfer from the charge's kinetic energy to the EM radiation. In the case of an electron beam passing through the middle of a an EM waveguide, the radiation is manifested as collective Cherenkov radiation. In this case the electron beam can be viewed as a one-dimensional non-neutral plasma whereas the waveguide can be viewed as a slow wave structure (SWS). This collective radiation occurs in particular in traveling wave tubes (TWTs), and it features the energy transfer from the electron beam to the EM radiation in the waveguide. Based on a Lagrangian field theory, we develop a convincing argument that the collective Cherenkov effect in TWTs is, in fact, a convective instability, that is, amplification. We also derive, for the first time, expressions identifying low- and high-frequency cutoffs for amplification in TWT

Toward “smart tubes” using iterative learning control

In the paper, we present our progress toward designing a “smart” high-peak power microwave (HPM) tube. We use iterative learning control (ILC) methodologies in order to control a repetitively pulsed high-power backward-wave oscillator (BWO). The learning-control algorithm is used to drive the error between the actual output and its desired value to zero. The desired output may be a given power level, a given frequency, or a combination of both. The learning-control methodology is then verified in simulation. This methodology is applicable to a wide variety of HPM sources

Communicating with microwave-propelled sails

We describe a communication channel for a microwave-propelled sail, a novel concept for a deep-space scientific probe. We suggest techniques to recover the great loss introduced by the large distances, and we have conducted various simulations to understand the effects on the performance of the system. Possible disruption in the channel by high-energy solar flares, which increase the error in the estimation of the received signal, is accounted for. We developed the simulation for a full communication system on an additive white Gaussian noise (AWGN) channel, including the random-time solar-flare disturbance. We show that turbo codes can be exploited that perform very well at low SNRs and have high coding gain

Studies of relativistic backward-wave oscillator operation in the cross-excitation regime

We first reported the operation of a relativistic backward-wave oscillator (BWO) in the so-called cross-excitation regime in 1998. This instability, whose general properties were predicted earlier through numerical studies, resulted from the use of a particularly shallow rippled-wall waveguide [slow wave structure (SWS)] that was installed in an experiment to diagnose pulse shortening in a long-pulse electron beam-driven high-power microwave (HPM) source. This SWS was necessary to accommodate laser interferometry measurements along the SWS during the course of microwave generation. Since those early experiments, we have studied this regime in greater detail using two different SWS lengths. We have invoked time-frequency analysis, the smoothed-pseudo Wigner-Ville distribution in particular, to interpret the heterodyned signals of the radiated power measurements. These recent results are consistent with earlier theoretical predictions for the onset and voltage scaling for this instability. This paper presents data for a relativistic BWO operating in the single-frequency regime for two axial modes, operating in the cross-excitation regime, and discusses the interpretation of the data, as well as the methodology used for its analysis. Although operation in the cross-excitation regime is typically avoided due to its poorer efficiency, it may prove useful for future HPM effects studies

A neural-network model of the input/output characteristics of a high-power backward wave oscillator

This paper discusses an approach to model the input/output characteristics of the Sinus-6 electron beam accelerator-driven backward wave oscillator. Since the Sinus-6 is extremely fast to warrant the inclusion of dynamical effects, and since the sampling interval in the experiment is not fixed, a static continuous neural network model is used to fit the experimental data. Simulation results show that such a simple nonlinear model is sufficient to accurately describe the input/output behavior of the Sinus-6-driven backward wave oscillator (BWO) and that the fitted output waveforms are basically noiseless. This model will be used to control the BWO in order to maximize the radiated power and the efficiency. This paper is also intended to introduce high-power microwave researchers to control concepts that may enhance the outputs of a wide spectrum of sources

Responsive Algorithms for Defending Recon gurable Networks

We present algorithms to self-heal reconfigurable networks when they are under attack. These algorithms reconfigure the network during attack to protect two critical invariants. First, they insure that the network remains connected. Second, they insure that no node increases its degree by more than O(log n). We show both theoretically and empirically that our algorithms can successfully maintain these invariants even for large networks under massive attack by a computationally unbounded adversary

Time-domain detection of superluminal group velocity for single microwave pulses

Single microwave pulses centered at 9.68 GHz with 100-MHz ͑full width at half maximum͒ bandwidth are used to evanescently tunnel through a one-dimensional photonic crystal. In a direct time-domain measurement, it is observed that the peak of the tunneling wave packets arrives (440Ϯ20) ps earlier than the companion free space ͑air͒ wave packets. Despite this superluminal behavior, Einstein causality is not violated since the earliest parts of the signal, also known as the Sommerfeld forerunner, remain exactly luminal. The frequency of oscillations and the functional form of the Sommerfeld forerunner for any causal medium are derived

A Switched Oscillator as an Antenna for High Power THz Generation

This paper presents an approach to high power THz generation that uses a Switched Oscillator (SwO) as a photoconductively-switched antenna. A simplified model is used to demonstrate the SwO as an effective THz radiator. Numerical simulations are used to optimize various parameters of interest with the primary objective of maximizing the radiated energy and minimizing losses. The radiation Q and resonant frequency are obtained as function of each parameter

Study of Pulsed RF Signal Extraction and Irradiation from a Capacitive Nonlinear Transmission Line

Research on Nonlinear Transmission Lines (NLTLs) has long been carried out to produce oscillating pulses. The radiofrequency (RF) pulses generated by the NLTLs can be radiated by antennas connected to the output of the lines. Possible applications of NLTLs as an RF generator include aerospace radars, telecommunications, battlefield communication disruption, and medical devices. There have been relatively few articles that presented experimental results regarding the extraction and the radiation of the RF signal from NLTLs. This article reports the excellent results obtained with a low voltage lumped capacitive NLTL in which oscillations of the order of 230 MHz were produced and radiated using Double-Ridged Guide (DRG) antennas. The RF signal was extracted using a decoupling circuit based on a Chebyshev high-pass filter. The NLTL was evaluated through time domain and frequency domain analyses of the pulsed RF signal measured on a resistive load connected to the output of the line, as well as on transmitting and receiving by antennas. The LT-SPICE model of the line was implemented and the comparison of simulation and experimental results presented a good agreement

Towards Stable Interstellar Flight: Levitation of a Laser-Propelled Sailcraft

Exploring and traveling to distant stars has long fascinated humanity but has been limited due to the vast distances. The Breakthrough Starshot Program aims at eliminating this limitation by traveling to Alpha Centauri, which is 4.37 light-years away. Thus, it is only possible if a vehicle travels at a substantial fraction of the speed of light. The Breakthrough Starshot Program initiatives to develop a proof-of-concept that is accelerating a sail to relativistic speeds using a laser beam aimed at the sail. At this high speed, while a stable beam riding is one of the crucial concerns of this concept, the dynamic stability analysis of a sail is hardly present in the previous literature. Furthermore, it is important to investigate the dynamic stability in the experiment before driving the sail to relativistic speeds. As a proof of concept, we study the dynamic stability of the sail levitated at a certain height by a laser beam. The sail's dynamics are modeled as a rigid body whose shape is parameterized by a sweep function. We estimate the region of attraction (ROA) for dynamic stability analysis using Lyapunov theory and Sum-of-square (SOS) programming. The ROA confirms how much a levitated sail can tolerate the transverse and angular perturbations. We also conclude on some of the important parameters of the sail that affects the dynamic stability. Simulation results validate our theoretical analysis.Comment: A computational error have been found. It will be resubmitted when it will be fixe