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21 Jul 2003

Volume 83, Issue 3, pp. 407-587

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Appl. Phys. Lett. 83, 575 (2003); http://dx.doi.org/10.1063/1.1594830 (3 pages)

P. Yu, M. Mustata, J. J. Turek, P. M. W. French, M. R. Melloch, and D. D. Nolte
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Experimental and computational estimate of bipolar flow parameters in an explosive field emission cathode

D. Shiffler, K. L. Cartwright, Kim Lawrence, M. Ruebush, M. LaCour, K. Golby, and D. Zagar

Appl. Phys. Lett. 83, 428 (2003); http://dx.doi.org/10.1063/1.1589164 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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Explosive field emission cathodes constitute an important class of cathodes for high power microwave tubes. These cathodes have the advantages of being light weight and the capability of operating cold. In the past, this class of cathodes suffered from large amounts of outgassing, nonuniform emission, and very high emittance. These effects tended to dominate the diode performance, masking effects due to the anode. However, a type of carbon cathode has enabled the role of the anode in the diode to be better determined. In this letter, we compare experimental results with simulated diode performance, allowing an estimate of the bounds on the secondary emission coefficient from the anode surface as well as the amount of neutral gas liberated from this surface. In general, secondary electrons and neutral atoms lead to plasma formation in high power microwave devices, which in turn deleteriously affect the tube performance. Hence, an estimate of such quantities for use in particle-in-cell codes can prove pivotal for accurate modeling of experimental devices. © 2003 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Ion characteristics of laser-produced plasma using a pair of collinear femtosecond laser pulses

Z. Zhang, P. A. Van Rompay, and P. P. Pronko

Appl. Phys. Lett. 83, 431 (2003); http://dx.doi.org/10.1063/1.1592616 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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Femtosecond laser-pulse absorption is studied in silicon ablation plasmas by means of a pair of identical 1016 W/cm2 collinear pulses separated on a picosecond time scale. The second laser-pulse modifies ionic characteristics of the preformed plasma, such as ion yield, ion energy, and average charge state. Resonance absorption is demonstrated to be the dominant mechanism by comparing results of s and p polarization. It is shown that maximum effects occur when a well defined critical density surface of the initial plasma forms together with an optimum density gradient scale length of kL = 1.5. The optimal enhancement of ion yield, which occurs at 5 ps delay, is a factor of 2 greater than that produced by a single pulse with twice the energy of each individual double pulse. Applications are identified in regard to cluster beam formation and plasma isotope enrichment in ultrafast ablation plumes. © 2003 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
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