DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Air Force Research Laboratory Integrity  Service  Excellence S. L. Heidger, B. W. Hoff, D. M. French, W. W. Tang, D. A. Shiffler Directed Energy Directorate Air Force Research Laboratory Plasma and Electro-Energetic Physics Program Review NLTL Modulated Carbon Fiber Cathode

2 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Abstract Gated field emission cathodes can provide short electron pulses without the requirement of laser systems or cathode heating required by photoemission or thermionic cathodes. The large electric field requirement for field emission to take place can be achieved by using a high aspect ratio cathode with a large field enhancement factor which reduces the voltage requirement for emission. In this paper, a cathode gate driver based on the output pulse train from a nonlinear transmission line (NLTL) is experimentally demonstrated. The application of the pulse train to a tufted carbon fiber field emission cathode generates short electron pulses. The pulses are approximately 2 ns in duration with emission currents of several mA, and the train contains up to 6 pulses at a frequency of 100 MHz. Particle-In-Cell (PIC) simulation is used to predict the characteristic of the current pulse train generated from a single carbon fiber field emission cathode using the same technique.

3 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Overview Concept NLTL design and testing NLTL Modulated Cathode Experiment ICEPIC simulation results

4 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Concept

5 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Concept (cont.) Modulated Electron Beam

6 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution NLTL Design Printed circuit board design Capacitors: reverse-biased Schottky diodes (CREE PN C2D05120A) Inductors: board traces (~120 nH per L-C section)

7 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Spice Modeling f = 37 MHz f = 105 MHz f = 114 MHz f = 202 MHz

8 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Low Voltage NLTL Testing

9 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution NLTL Cathode Modulator Experimental Setup Carbon Fiber Cathode

10 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Experimental Results Observed electron pulses had a duration of approximately 2ns with currents of a few milliamps, at a frequency of 100 MHz. Evidence for plasma formation was observed toward the end of the current pulse train.

11 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Single Fiber Simulations Single fiber emitter simulations performed in ICEPIC Fowler-Nordheim emission algorithm (field emission)

12 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Simulation Results Single Fiber Cathode Simulation ResultsTuft Cathode Experimental Results

13 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Conclusions Experimental demonstration of gating of a tufted carbon fiber cathode using direct application of voltage from a NLTL Observed electron pulses had a duration of approximately 2ns with currents of a few milliamps, at a frequency of 100 MHz ICEPIC simulations using a single fiber cathode agree qualitatively with tuft cathode experimental results.

14 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Acknowledgements This work was funded by the Air Force Research Laboratory, by the Air Force Office of Scientific Research under AFOSR LRIR 12RD02COR, and by the Department of Defense High Performance Computer Modernization Program under subproject AFKED01314C4O.

15 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Publications D. M. French, B. W. Hoff, W. Tang, S. Heidger, J. Allen-Flowers, “Nonlinear transmission line based electron beam driver”, Rev. Sci. Instrum. 83, (2012).

16 DISTRIBUTION STATEMENT A – Unclassified, Unlimited Distribution Questions?