Making 1 MW cw HF practical

Transcription

1 Making 1 MW cw HF practical 4 to 10 MHz antenna ESA Electrically Small Antenna to interface with UMD 50 Ohm IOT rf source. - Factor of 5 to 10 smaller than dipole - Frequency tunability demonstrated High Power Vacuum Tube High cw power handling 10 MHz beam modulation IOT tube PCSS Photoconductive Semiconductor Switching Achieved 700 kv/cm switching field Demonstrated repetition rates of up to 65 MHz at 20 kv switching amplitude Direct rf drive approach Challenges Optimize tradeoff between antenna efficiency/size/tunablity Improve PCSS photonic efficiency 3 kv, 10 MHz driver for grid Direct Drive Concept PCSS die for size comparison 1

2 HF Power Generation Options Option 1: Conventional vacuum tube technology Leverage vacuum tube technology Option 2: Semiconductor switching, Class D topology kv Photoconductive Solid State Switches - 20 kv R on << R Load 2

3 Limits of MOSFET switching N-Channel MOSFET Cross Section Parasitic BJT: - Needs to remain off under all conditions - Latchup due to high dv/dt - Observed with 1,200 V SiC MOSFETS in Type D topology - External power needs to be removed to turn off latchup. dv/dt limitation: 120 V/ns excellent value for MOSFET demonstrated with PCSS: 20,000 V/ns 3

4 The RF Power Source Power levels to impact ionosphere physics: Ranging from 65 to 85 dbw (virtual antenna to CME detection) To match max HAARP output ( ~ 95 dbw) Translated to absolute power levels on ground: Array of the order of tens of antennas HF Power: ~ 100 kw to MW for single unit Tunable: 3 to 10 MHz HAARP currently at ~ 10 (20) kw per unit too low to significantly reduce footprint 4

5 Drive Considerations traditional RF generator (IOT tube) coaxial cable Load/antenna 50 Ohms typically 377 Ohm Antenna has two jobs: Match coaxial cable impedance and radiate efficiently direct drive RF generator (PCSS) Load/antenna 377 Ohm Effective antenna input impedance more freely selectable Tuning elements distribute in antenna. 5

6 Switch limitation 50 kv switch On-State Resistance is limited 0.1 Ohms a realistically achievable value Higher load resistance would be beneficial (classical approach fixed at 50 Ohms) 6

7 Hard Antenna Limits Electric breakdown at antenna feed (of the order of 2.5 cm wide) (may be mitigated by dielectric insulation at feed) Electric breakdown in antenna gap (of the order of 6 cm wide) (may not be mitigated with dielectric sheets) Peak fields: Dielectric too lossy at MW power levels E feed = 6 kv/cm E gap E gap = 12 kv/cm Assuming homogeneous fields at 1 MW power cw E feed 7

8 Breakdown at HF freq. If air gap, ions will not clear gap in a half cycle (no choice for gap has to be air isolated) ωt 0 - E = E 0 cos(ωt) + E 0 π/6 - π/2 0 5π/ ½ /2 E ½ /2 E 0 π + 7π/ E ½ /2 E 0 At 10 MHz, the ions will remain in gap at sub-mm gaps already (atmosphere, 10 kv/cm) Space charge enhanced breakdown is likely 8

9 Breakdown at HF frequecnies 1 cm gap in air Expected breakdown field: ~ 22 kv/cm (homogeneous gap) Field in gap at 1 MW: 12 kv/cm (macro field) Antenna high field design will be crucial in final implementation (Corners and sharply protruding shapes need to be avoided) Heavy Rain could pose a problem (albeit no field stressed insulators in gap) 9

10 Two Barge Array m 67.5 m 10 MHz Dipole 5 MHz Dipole HAARP Element 95 dbw Power required: 16.1 MW array 0.67 MW per element 120 x 32.2m Compare HAARP: 33 acres, equivalent to 365 m x 365 m (factor 17 reduced footprint area) COLLABORATIVE RESEARCH ON NOVEL HIGH POWER SOURCES FOR AND PHYSICS OF IONOSPHERIC MODIFICATION 10

11 HAARP dipole vs. ESA Single HAARP antenna limited to ~ (2x) 10 kw power - Primarily limited due to electric breakdown in matching network ESA antenna roughly limited to ~ 1 MW power - Matching network moved into large scale antenna - Approx. factor 10 larger physical size of matching enables factor 100 higher power ESA antenna highly resonant - Requires active adjustment of parameters for even small frequency changes (~ 10 khz) ESA antenna may be driven by - Conventional (IOT) - Direct drive sinusoidal - Direct drive, square switcher HAARP radiation efficiency: ~ 55 to 75 % ESA system efficiency: ~ 90% (demonstrated at 500 W) 11

12 The Light Source Bulk PCSS: Photonic to (current) RF converter Commercially available UV lasers - MHz repetition rate - Peak optical power 6.5 kw - Up to 60 W average (3% wall plug efficiency) 1 m x 0.4 m foot print 19 rack mount power supply Pulsed UV LEDs: - MHz repetition rate - Peak optical power 4 W - ~ 10 % efficiency Pulsed Excimer arc lamp: - Peak optical power 320 W - Limited efficiency, < 1 % Microdischarge: - > 100 khz rep rate demonstrated - Peak optical power 10.5 W - Limited efficiency, ~ 1.5 % For high power HF generation: Laser at high cost, but most practical 12

13 Overall Electrically Small Antenna, ESA, is practical - 1 MW cw power - Mechanically tunable - 50 Ohm input setting - Direct drive setting Bulk PCSS - Unsurpassed performance (on/off switch), 50 kv, several 100 A - Photonic converter, pay optical power penalty for repetitive applications - Future: PIN PCSS with potentially 2 orders of magnitude higher efficiency IOT tube - Leverage proven technology - Grid drive challenging to get high efficiency ( PIN PCSS) 13

14 2015 Journals 1. D. Mauch, W. Sullivan III, A. Bullick, A. Neuber, J. Dickens, High Power Lateral Silicon Carbide Photoconductive Semiconductor Switches and Investigation of Degradation Mechanisms, IEEE Trans. Plasma Sci. 43, , R. Tiskumara, R. P. Joshi, D. Mauch, J. C. Dickens, and A. A. Neuber, Analysis of high field effects on the steady-state current-voltage response of semiinsulating 4H-SiC for photoconductive switch applications, J. Appl. Phys. 118, (2015) 3. D. Mauch, C. Hettler, W. W. Sullivan, A. A. Neuber, and J, Dickens, Evaluation of a Pulsed Ultraviolet Light-Emitting Diode for Triggering Photoconductive Semiconductor Switches, IEEE Trans. Plasma Sci. 43, (2015) 4. J. Stephens, A. Fierro, D. Trienekens, J. Dickens, and A. Neuber, Optimizing drive parameters of a nanosecond, repetitively pulsed microdischarge high power nm source, Plasma Sources Science and Technology 24, (6pp) (2015). Conference proceedings 1. V. Meyers, D. Mauch, J. Mankowski, J. Dickens, and A. Neuber, Characterization of the optical properties of GaN: Fe for high voltage photoconductive switch applications. Proceedings of the IEEE Pulsed Power Conference (PPC), 2015 IEEE, pp D. Mauch, J. Shaver, V. Meyers, D. Thomas, J. Mankowski, J. Dickens, and A. Neuber, Optimization of the Optical Triggering of SiC Photoconductive Semiconductor Switches, Presented at the IEEE Pulsed Power Conference (PPC), 2015 IEEE. 3. D. Thomas, D. Mauch, J. Dickens, A. Neuber, Characterization of intra-bandgap defect states through leakage current analysis for optimization of 4H-SiC photoconductive switches, Proceedings of the IEEE Pulsed Power Conference (PPC), 2015 IEEE, pp J. Shaver, D. Mauch, R. Joshi, J. Mankowski, J. Dickens, A. Neuber, A 2D finite difference simulation to investigate the high voltage blocking characteristics of 4H-SiC photoconductive semiconductor switches, Proceedings of the IEEE Pulsed Power Conference (PPC), 2015 IEEE, pp B. Esser, S. Beeson, J. Makowski, J. Dickens, and A. Neuber, Tunable Electrically Small Antenna at 45 to 100 MHz, Proceedings of the IEEE Pulsed Power Conference (PPC), 2015 IEEE, pp J. Stephens, D. Mauch, S. Feathers, J. Mankowski, J. Dickens, and A. Neuber, Nanosecond, Pulsed Microdischarge UV and VUV Sources, Presented at the 2015 IEEE International Conference Plasma Science (ICOPS), in Belek, Antalya, Turkey 14

15 The Researchers at TTU Daniel Mauch, PCSS PhD student Vincent Meyers, PCSS MS student Shannon Feathers, PCSS triggering, MS student Ben Esser, ESA MS student alumni Kenan Blackerby, MS student, ESA BD Brock Woodrum Undergrad, Driver Dsgn. Nicholas Wilson Undergrad, Trigger 15