Corrugated waveguide and directional coupler for CW 250-GHz gyrotron DNP experiments

A 250-GHz corrugated transmission line with a directional coupler for forward and backward power monitoring has been constructed and tested for use with a 25-W continuous-wave gyrotron for dynamic nuclear polarization (DNP) experiments. The main corrugated line (22-mm internal diameter, 2.4-m long)...

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Bibliographic Details
Published in:IEEE transactions on microwave theory and techniques 2005-06, Vol.53 (6), p.1863-1869
Main Authors: Woskov, P.P., Bajaj, V.S., Hornstein, M.K., Temkin, R.J., Griffin, R.G.
Format: Article
Language:English
Subjects:
Applied sciences
Beams (radiation)
Circuit properties
Corrugated waveguides
Directional couplers
Electric, optical and optoelectronic circuits
Electronics
Exact sciences and technology
Gyrotrons
Insertion loss
Microwave circuits, microwave integrated circuits, microwave transmission lines, submillimeter wave circuits
millimeter-wave directional couplers
millimeter-wave waveguides
Monitoring
Nuclear power generation
Optical coupling
Polarization
Power transmission lines
Probes
Propagation losses
Testing
transmission-line measurements
Waveguides
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Summary:A 250-GHz corrugated transmission line with a directional coupler for forward and backward power monitoring has been constructed and tested for use with a 25-W continuous-wave gyrotron for dynamic nuclear polarization (DNP) experiments. The main corrugated line (22-mm internal diameter, 2.4-m long) connects the gyrotron output to the DNP probe input. The directional coupler, inserted approximately midway, is a four-port crossed waveguide beamsplitter design. Two beamsplitters, a quartz plate and ten-wire array, were tested with output coupling of 2.5% (-16dB) at 250.6 GHz and 1.6% (-18dB), respectively. A pair of mirrors in the DNP probe transferred the gyrotron beam from the 22-mm waveguide to an 8-mm helically corrugated waveguide for transmission through the final 0.58-m distance inside the NMR magnet to the sample. The transmission-line components were all cold tested with a 248/spl plusmn/4-GHz radiometer. A total insertion loss of 0.8 dB was achieved for HE/sub 11/-mode propagation from the gyrotron to the sample with only 1% insertion loss for the 22-mm-diameter waveguide. A clean Gaussian gyrotron beam at the waveguide output and reliable forward power monitoring were achieved for many hours of continuous operation.
ISSN:0018-9480
1557-9670
DOI:10.1109/TMTT.2005.848097