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

Original Timeline

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

Conclusion

• Lots of exciting efforts ahead of us!– Look forward to working with you all…

• Upcoming cathode conferences:– International Vacuum Nanoelectronics

Conference (IVNC) @ MIT, July 11-16– International Vacuum Electron Sources

Conference (IVESC) in Beijing, Sept 6-10