DocumentCode :
845845
Title :
Corrugated waveguide and directional coupler for CW 250-GHz gyrotron DNP experiments
Author :
Woskov, Paul P. ; Bajaj, Vikram S. ; Hornstein, Melissa K. ; Temkin, Richard J. ; Griffin, Robert G.
Author_Institution :
Plasma Sci. & Fusion Center, Massachusetts Inst. of Technol., Cambridge, MA, USA
Volume :
53
Issue :
6
fYear :
2005
fDate :
6/1/2005 12:00:00 AM
Firstpage :
1863
Lastpage :
1869
Abstract :
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±4-GHz radiometer. A total insertion loss of 0.8 dB was achieved for HE11-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.
Keywords :
dynamic nuclear polarisation; gyrotrons; millimetre wave directional couplers; 25 W; 250 GHz; 250.6 GHz; Gaussian gyrotron beam; backward power monitoring; continuous-wave gyrotron; corrugated transmission line; corrugated waveguide; crossed waveguide beamsplitter design; dynamic nuclear polarization; forward power monitoring; insertion loss; millimeter-wave directional couplers; millimeter-wave waveguides; quartz plate; transmission-line measurements; Directional couplers; Gyrotrons; Insertion loss; Monitoring; Optical coupling; Polarization; Power transmission lines; Probes; Propagation losses; Testing; Corrugated waveguides; millimeter-wave directional couplers; millimeter-wave waveguides; transmission-line measurements;
fLanguage :
English
Journal_Title :
Microwave Theory and Techniques, IEEE Transactions on
Publisher :
ieee
ISSN :
0018-9480
Type :
jour
DOI :
10.1109/TMTT.2005.848097
Filename :
1440689
Link To Document :
بازگشت