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Western Consortium on the NanoPhysics of Electron Dynamics near Surfaces in High Power Microwave Devices and Systems
Ryan UmstattdNaval Postgraduate School
Presented at the MURI 2004 Kick-Offat the Baltimore ICOPS, 28 June 2004
Western Consortium Team Members
•UC Davis: N.C. Luhmann, Jr., J. P. Heritage, C.W. Domier, K.Liu
•Stanford: G. Caryotakis, L. Laurent, G. Scheitrum
•Naval Postgraduate School: R. Umstattd
•Collaborators: G. S. Park: SNU P. Li: BVERI
M. Gundersen: USC
Some program highlights…
• Thermionic cathodes
-Oxide
-Scandate*
• Field emitter arrays
• Explosive emission cathodes & guns
• RF breakdown experiments & simulations
*70 A/cm2 demonstrated with 5 μs pulses at a 500 Hz repetition rate at 1000 ˚C—200 A/cm2 appears achievable for HPM applications.
Thermionics• Plasma deposition of cathodes
– Performed at Stanford facility in collaboration w/ BVERI colleagues
– Vast improvements in system since original use for oxide cathode deposition
• Focus: Long life cathodes for conventional microwave tubes and high current density “clean” cathodes for HPM sources
• Goal: Cathodes with work functions in the target range of 1.4-1.6 eV
Field Emitters
• Si tips– UCD
• CNT emitters– UCD/LLNL
• Photo-gated arrays– UCD
• Active control– NPS/USC
Explosive Emitters
• Carbon microfiber in Pierce gun– Long pulse testing commercial
applications– Short pulse testing compact pulsed power
• Hollow cathodes• High Brightness• High Energy
BLT
molybdenum cathode
anode
3 mm
4 cm
e-beam
RF Breakdown Experiments
• TM020 cavity with removable noses
• Examine materials and processing
• Copper surface before (left) and after (right) Gas Cluster Ion Beam (GCIB) Processing (collaboration with Epion)
• Comparison between measured experimental data (left) and 3D PIC simulations (right) using a 4x4 mm emitting spot, an electron current of 7 kA, and a copper ion current of 30 A*.
• Macroscopic versus microscopic models
RF Breakdown Simulations
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* V. Dolgashev and S. Tantawi