Texas Tech Effort Overview

Transcription

1 Collaborative Research on Novel High Power Sources for and Physics of Ionospheric Modification Texas Tech Effort Overview Outline: Overview, Texas Tech Research MURI Personnel Summarized MURI Efforts 1

2 CENTER FOR PULSED POWER AND POWER ELECTRONICS 6 Faculty Members (Associate and Full Professors) 4 Senior Research Associates 1 Senior Planner 1 Accountant/Purchasing Agent 4 Technicians 23 Graduate Students 20 Undergraduate Students All personnel, except for a visiting scholar, are U.S. citizens 2

3 Texas Tech University 150 Undergraduate Programs 100 MS Degree Programs 50 Ph.D. Programs New 25,462 Undergraduate Students Mexico 6,175 Graduate and Law Students 4,224 Graduate and Undergraduate Students in Engineering 687 Graduate (167) and Undergraduate (520) Students in ECE AR Louisiana The Center for Pulsed Power and Power Electronics is interdisciplinary and has students and faculty from ECE, Physics, and ME. 3

4 Lab floor area: On campus: 1400 m 2 including 2 high bay areas with overhead cranes Off campus: 1000 m 2 for sensitive research and development Personnel: 6 faculty members 4 full time technicians, 2 secretaries, 25 graduate students, 12 undergraduates, visiting scientists. Facilities Modern CNC machine shop Space simulation chamber Megavolt class pulsed power machines Competitive Funding ~ $4 Million / year 4

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6 Space Simulation Chamber Plasma Thruster Arc Jet in Operation 6

7 Research Topics at TTU Photoconductive solid state switching (SiC and GaN) Nonlinear Transmission lines High Power Microwave source development High rep rate rf sources HPM wave synthesis Dense metal plasmas, equation of state SiC switch testing/analysis Compact switching power supplies Square Pulse Marx Generators Surface breakdown/cathode phenomena High Power Microwave breakdown Vacuum UV Spectroscopy in atmospheric gases Explosively driven HPM and pulsed power systems EM interaction with electronic systems Linear Transformer Drivers Beam Steerable Pulsed Ring down Array Shaped charge/bullet defeat Low Jitter (1 ns) repetitive (>100 pps) spark gap switch Sequentially switched railgun Large (MW) generator synchronization Time dependent modeling of pulsed ring down antennas Blasting cap electrical analysis Explosive Switching and Ferroelectric Generators Current Recent Past

8 Explosive Driven Directed Energy Test Bed at TTU Field Tested 2009/2011 at Redstone Arsenal ~ 100 MW microwave output 8

9 . Compact MILO Design Choke cells 4 cell resonator Extractor vane Output window Waveguide Insulator Electron collector Explosive emission cathode Cathode base Critical for compact sealed device: Optimal geometry Compact vacuum interface Efficient robust explosive emission cathode Very low out gassing 9

10 Low Temperature Metal Plasmas Copper Goal Use high current exploding wires, and MHD simulation to benchmark and progress existing models (transport and EOS) in extreme environments 100+ kk temperatures possible 0.01 g/cm 3 solid density Demonstrated Performance Using EWs and MHD, sub-ev metalnonmetal region studied * Semi-empirical conductivity model developed Consistent with EW experiments Consistent with other models and exp. data ** * J. Stephens, A. Neuber, Phys. Rev. E 86, (2012). ** A.W. DeSilva, J.D. Katsouros, Phys. Rev. E (1998). 10

11 Electret HPM Windows Objective Use charged electret to alter the initial conditions of microwave surface flashover Electret provides small DC field which can alter ion cluster density Demonstrated Performance Average flashover time increase by 60+ ns * Over 4x higher radiated energy with a negatively charged electret * 3/13/2014 * J. Stephens, A. Neuber et al., Phys. Plasmas 19, (2012). 11

12 VACUUM UV EMISSION IN ATMOSPHERIC BREAKDOWN VUV vacuum spectrograph(s) VUV Photomultiplier ( nm) Gated ICCD (nanosecond shutter time, nm) Current, di/dt, gap voltage (optically isolated) diagnostics with nanosecond resolution Species verification from spectral simulation, using temperature dependent software developed at TTU Planned detection schemes down to 70 nm Emissions between nm are due to atomic oxygen and nitrogen Most intense VUV emission occurs during the nanoseconds before voltage collapse, while peak VIS emission occurs after Streamers are propagating during the time that VUV is emitted Rogers, Neuber et al. IEEE Trans. on Plasma Sci. 38, pp ,

13 Non intrusive VUV diagnostics n e ~ 3 x cm -3 at anode ~ 0.5 % N 2 dissociation percentage Experimental and simulated spectrum of atomic nitrogen emission between 130 and 150 nm. 3/13/2014 Laity, Fierro, Dickens, Neuber, Frank, APL 102, (2013) A Fierro, G Laity and A Neuber, J. Phys. D: Appl. Phys. 45 (2012) (11pp) 13

14 Microdischarge UV/VUV Source Goals Develop a powerful UV/VUV source Applications High rep-rate, low jitter, triggered gas switches PCSS switching Fundamental Photo-plasma studies Sterilization 0 ns 10 ns 20 ns 30 ns 40 ns 50 ns 60 ns 70 ns 80 ns 90 ns Demonstrated Performance 3.4 W Avg, 40 W peak VUV yield at Lyman-α (121.5 nm) Typically reported ~tens of mw +MHz rep-rated emission cm -3 electron densities when fired on a nitric oxide target gas * Stephens, Dickens, Neuber, et al. Appl. Phys. Lett. 104, (2014). 14

15 Nonlinear Transmission Line Pulse Burst freq. 2 GHz ~ 1 MW radiated NLTL output waveforms demonstrating 65 MHz burst-mode operation. 15

16 Radial PCSS Photoconductive Solid State Switch 20 kv 65 MHz burst mode switching into a 52 Ω load 16

17 MURI Personnel at TTU Andreas Neuber John Mankowski James Dickens Daniel Mauch, PhD EE student David Thomas, MS EE student Paul Gatewood, MS EE student Joel Perez, technician Lee Waldrep, machinist

18 Ionosphere Heating Sources PCSS Direct Drive Concept Background Switch geometry Material parameters and modification Electron irradiation Annealing Laser enhanced diffusion Triggering Wavelengths Other switch design parameters Project Objectives Development of a compact, high voltage (10-25 kv) photoconductive switch capable of ~ 5 10 MHz operation at ~1-2 MW Demonstrated Performance Blocking of DC electric fields up to 700 kv/cm Maximum switched current of 1kA at 30 kv Switched 250 A at 20 kv at a burst repetition frequency of 65 MHz 18

19 Ionosphere Heating Sources PCSS Challenges Device Efficiency Recombination at defect sites Mid-gap defect sites Surface Recombination Contact resistance Device Lifetime Space charge effects Current density at SiC/metal interface Device Lifetime Vary current density, record any changes in switch properties (V-I curve) Simulation (Silvaco Atlas) Joule heating Space charge effects Hole mobility Transient trapping effects AFM / SEM analysis of failed devices Sub-contact doping effects Characterization of Defect States Thermally stimulated current spectroscopy (TSC) Extraction of trap parameters from experimental IV curves and simulation fitting Sub-bandgap IR illumination at cryogenic temperatures 19

20 Electrically Small Antennas Design Goals Electrically small a few meters in size High power Megawatt output Instantaneous bandwidth a few percent Tuning adjust resonant frequency with structural modification Project Objective Design and simulate an electrically small antenna for the 2 10 MHz range capable of high power applications, 50 Ohms and ~377 Ohms impedance. Approach Simulate and optimize the design in HFSS for the operational frequency range Build and test a scaled version of the design for operation at higher freq., possibly around 100 MHz Current Issues Tradeoff between size and bandwidth Resonant structure High field on surface of dielectric Limits input power Losses in the dielectric Increase bandwidth, decrease efficiency Future Evaluate magnetic materials (ferrites) 20