MURI Research at Stanford

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MURI Research at Stanford

• Oxide Cathodes
• RF Breakdown Studies
• W-band Klystrons

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Aerial photograph of SLAC - SPEAR and SSRL are
near center of picture.
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Photograph of 75 MW PPM klystron
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Simulated Vo 490 kV, Io 275 A, Po 84 MW,
? 62.7 Measured Vo 490 kV, Io 275 A, Po
78 MW, ? 60, tp 2.8 ?s
Simulation of X-band PPM klystron using 2-D MAGIC
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Cathodic Arc-Deposited
OCs
Traditional vs.
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Sketch of plasma gun
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Photograph of dual plasma gun setup with
macroparticle filters
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Graphs showing performance of plasma deposited
oxide cathodes
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Schematic of laser, deposition chamber, and beam
path
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Lambda Physik excimer laser for plasma deposition
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RF Breakdown Motivation

• Pulse shortening in HPM devices limits pulse
  energy
• SLACs 11.424 GHz klystrons require complex
  multi-gap output cavities to avoid breakdown
• Pulse compressors, mode converters, tees, and
  linac sections for NLC must support 400 MW
  pulses
• Conditioning of high power sources, waveguides
  and accelerator sections requires significant
  time

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Drawing of TM020 RF breakdown cavity
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TM020 RF breakdown cavity with removable nose
shown in foreground.
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Experimental setup to measure dark current and rf
breakdown dependence on vacuum and pulse length.
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Experimental setup to measure dark current and rf
breakdown dependence on vacuum and pulse length.
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Top Grain boundaries provide sites for
breakdown. Bottom Melting along grain
boundaries compared to total surface area.
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Dark current is approximately the same after rf
processing with background pressure ranging over
five orders of magnitude. (Pulse length is 200
ns)
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Maximum field strength before vacuum deteriorates
approximates a pulse length dependence
corresponding to the -1/3 power for unconditioned
and conditioned cavity noses.
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SEM image of processed copper surface at 678 MV/m
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Motivation for Klystrino Research
Develop High Average Power, Millimeter-Wave, RF
Sources Using Advanced Microfabrication Techniques

• Scientific/technical approaches
• LIGA fabrication of microwave circuits for
  low-cost, high-volume production
• Multiple devices on same substrate
• Outputs can be combined or phase controlled for
  beam steering
• Compact, lightweight modules can be combined for
  increased output power

LIGA substrate with Wband klystrino, 91 GHz
accelerator, and Wband sheet beam klystron
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Potential application for high average power
millimeter wave source
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Solid model of LIGA circuit, substrate, and PPM
assembly
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Aerial photograph of SPEAR and SSRL
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W-band output circuit scaled to X-band
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Section of LIGA substrate with klystrino
penultimate and output cavities
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MAGIC simulation of W-band PPM klystron output
section
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Solid model of klystrino 4-pack (4 kW average
power)