Davis Millimeter-Wave Research Center

Microwave/Millimeter Wave Technology

Plasma Diagnostics

 

 

RESEARCH  ACTIVITIES

Plasma diagnostics

 

µ-wave vacuum electronics

 

µ-wave solid state technology

 

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Director:
Prof. N.C. Luhmann, Jr.

 

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Ghausi Hall, Room 1104

 

 

The high power microwave source laboratory comprises 2000 square feet with 0.5 MW ac service and a chilled water recirculation system, thereby permitting high average power experiments. The laboratory houses a superconducting magnet solenoid which is utilized for the development of high power 94 GHz harmonic gyrotrons and gyro-TWTs (see Fig. 1). More recently, the group has had a large effort to develop sheet beam klystrons (SBKs) including a quasi-optical W-Band pulsed 50 kW WSBK and a 10 kW cw version. Figure 2 shows the pulsed tube on test where it delivered 56 kW with 53 dB gain which is a record for a slow wave source at this frequency. Other efforts are aimed at extending the SBK technology to the THz region where 1-50 W sources are predicted.

 

 

     

 

Fig 1. W-Band gyro-TWT cathode test facility showing the superconducting magnet (left) and frequency synthesizer-based driver (right).

 

 

    

 

Fig 2. W-Band quasi-optical WSBK under test.

 

 

 

 

Also shown in Fig. 2 is a photograph of the multiple rapid cathode life test facility employed to test these and other thermionic cathodes. This laboratory also houses an electroplating facility (see Fig. 3) for use with the high power microwave circuits under development at UC Davis, a 3-D computerized imaging microscope and a 180-270 GHz scalar network analyzer (see Fig. 3).

 

 

    

 

Fig 3. Electroplating facility (left), and a WR-4.3 scalar network analyzer system for characterization measurements over a frequency range of 170 to 260 GHz (right).

 

 

 

 

 

 

Below, various other equipment and facilities within Ghausi Hall 1104 are pictured.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
In addition, under the DARPA HiFIVE program, a 100 W 220 GHz sheet beam TWT (SBTWT) is being developed with a bandwidth in excess of 40 GHz (see below).
 
 
                     

 

 

 

 

UC Davis has an active program in developing high current scandate dispenser cathodes for use in high power microwave and THz sources. We adapted and developed the sol-gel technique to produce the Sc2O3-added tungsten powders with spherical shape and uniform controllable particle size ranging from nanometers to micrometers. By judicious control over sintering conditions, these powders were densified into nanostructured and microstructured Sc2O3-added tungsten matrices with uniform tungsten grains and homogenous pore distribution.  The cathodes machined and tested in both diodes with the pulse mode (high current density, > 100 A/cm2) and in Cathode Life Test Vehicles (CLTV) with a Pierce gun configuration under CW mode  (40 A/cm2 CW more than 2500 hours life time) revealed very high current density.

Fabrication of scandate dispenser cathodes for high current density and long lifetime includes:

 

1.     Cold press /isostatic press to make cathode pellets

     

 

2.     Cathode pellets sintered under hydrogen atmosphere or Vacuum, up to 2000oC

 

3.     Small lathe for cathode machining and cleaning, and also Nano CNC for maching cathodes with smooth surface, sharp edges, and high tolerances.

   

 

4.     Cathode testing including:

a.     Multiple rapid thermionic cathode life testing facilities with a closely-spaced diode configuration

    

 

b.     Modified Cube in an actual gun configuration

 

c.      Cathode life testing vehicles (CLTV) with a pierce gun construction both pulse and CW Testing

 

d.     Pulse Modulator  and 30 kV modulator ( ~ 200 nsec to full cw )

    

 

 

 

 

 

 

 

 
 
 
 
 
 
              
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