Microwave gyrotron

Gyrotrons produce high-power microwaves up to megawatt range... 

Gyrotrons -PCTFE m [FLUORINE COMPOUNDS, ORGANIC - POLYCHLOROTRIFLUOROETHYLENE] (Vol 11) - [MICROWAVE TECHNOLGY] (Vol 16) - [MICROWAVETECHNOLGY] (Voll6)... 

Another report to mention is that of Toda et al., where they place an NMR coil directly above the microwave cavity of an X-band ESR system and shuttle the sample between the center of the microwave cavity and the NMR coil.30 They observed -19-fold enhancement with toluene and the BDPA radical at 0.40 T. Since their research program is focused on developing gyrotrons for high-field DNP, they did not further pursue X-band DNP experiments. 

Microwaves can be produced by four types of macroscopic cavity resonators that use the ballistic motion of electrons across a cavity opening the klystron, the magnetron, the traveling-wave tube (TWT), and the gyrotron. They can also be generated by field-effect transistors at low frequencies, by Gunn42 diodes, and by IMP ATT diodes. 

Bajaj VS, Farrar CT, Homstein MK et al (2003) Dynamic nuclear polarization at 9 T using a novel 250 GHz gyrotron microwave source. J Magn Reson 160 85-90... 

At microwave frequencies in the range 72-145 GHz, the critical parameters for high-power transmission are the dielectric characteristics of the window material the dielectric loss factor tan 5 and the permittivity e[. (or the refractive index n = because they affect power absorption and reflection [42]. The dielectric loss factor tan 8 in low loss samples is usually measured as the decrease in the Q factor of a resonant cavity [43]. Low dielectric loss materials find application as the output windows of high-power microwave tubes. A specific case is that of windows for Gyrotron tubes operating in the 70-170 GHz frequency region with output powers in excess of 1 MW, as will be discussed later. 

A gyrotron-based system operating at a frequency of 24 GHz with microwave power up to 6 kW has been used to develop YAG transparent ceramics through reactive sintering from oxide precursors [153], TEOS with contents of 0.3 and 0.5 wt% was used to provide Si02 as sintering aid. 

Gyrotrons are capable of producing high microwave power on the order of 100 kW at microwave... 

If the electron gun is moved to the side of the waveguide and the microwave power is extracted from the wave-guide opening in proximity to the electron gun, as shown in Fig. 6.29, then it is termed a gyrotron... 

Here the situation changed strongly with the availability of gyrotrons as a reliable high-frequency microwave sources with high output power (see review by Felch et which has triggered a fascinating new develop-... 

Significant progress in DNP arises from improved instmmentation, mainly from high power microwave sources that have become available in recent years. These developments were much influenced by Griffin s pioneering work using gyrotron... 

Prisner and coworkers started to use Fremy s salt as a radical, which exhibits a narrow EPR linewidth of less than 0.1 mT at 260 GHz [ 124] and yields much higher enhancements (—10 compared to -6) for N-TEMPOL [122]. The gyrotron microwave source exhibited a striking improvement over that previously reported for the 45 mW source, yielding an enhancement value of -29 on water protons using Fremy s salt, compared to —10 previously reported for the 45 mW source (Fig. 12). 

Fig. 12 Water H NMR spectra reported by Prisner and coworkers, conducted at 9.2 T (260 Hz, 400 MHz) acquired with (dots) and without microwave pumping (solid line) on 40 mM aqueous Fremy s salt solutions using (a) a high power gyrotron, and (b) a low power solid-state microwave source. (Reproduced from [123] by permission of the PCCP Owner Societies)...

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