Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization

Torrezan, Antonio C.; Shapiro, Michael A.; Sirigiri, J.R.; Temkin, Richard J.; Griffin, Robert G.

doi:10.1109/ted.2011.2148721

Cited by 160 publications

(29 citation statements)

References 21 publications

(27 reference statements)

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“…The corrugated waveguide is designed for transferring the microwave power from a 330-GHz tunable gyrotron [12] to a 500-MHz DNP-NMR spectrometer. A VNA (Agilent E8363B with millimeter wave extender V03VNA2-T/R) was used to measure the amplitude and phase profiles over a 10 cm × 10 cm scanned cross section of the measurement plane.…”

Section: Experimental Setup and Measurementsmentioning

confidence: 99%

Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns

Jawla

Nanni

Shapiro

et al. 2012

IEEE Trans. Plasma Sci.

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This work focuses on the accuracy of the mode content measurements in an overmoded corrugated waveguide using measured radiated field patterns. Experimental results were obtained at 250 GHz using a vector network analyzer with over 70 dB of dynamic range. The intensity and phase profiles of the fields radiated from the end of the 19 mm diameter helically tapped brass waveguide were measured on planes at 7, 10, and 13 cm from the waveguide end. The measured fields were back propagated to the waveguide aperture to provide three independent estimates of the field at the waveguide exit aperture. Projecting that field onto the modes of the guide determined the waveguide mode content. The three independent mode content estimates were found to agree with one another to an accuracy of better than ±0.3%. These direct determinations of the mode content were compared with indirect measurements using the experimentally measured amplitude in three planes, with the phase determined by a phase retrieval algorithm. The phase retrieval technique using the planes at 7, 10, and 13 cm yielded a mode content estimate in excellent agreement, within 0.3%, of the direct measurements. Phase retrieval results using planes at 10, 20, and 30 cm were less accurate due to truncation of the measurement in the transverse plane. The reported measurements benefited greatly from a precise mechanical alignment of the scanner with respect to the waveguide axis. These results will help to understand the accuracy of mode content measurements made directly in cold test and indirectly in hot test using the phase retrieval technique.

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Section: Experimental Setup and Measurementsmentioning

confidence: 99%

Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns

Jawla

Nanni

Shapiro

et al. 2012

IEEE Trans. Plasma Sci.

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“…This technique for achieving continuous tuning has also been implemented in a 330 GHz second harmonic oscillator [60]. A continuous tuning range of 1.2 GHz was observed experimentally via a combination of magnetic, voltage and thermal tuning.…”

Section: Gyrotrons For Dnp Nmrmentioning

confidence: 99%

“…The theoretical start currents for the first six axial modes TE −4,3, q , where q = 1, 2, 3, 4, 5, 6, are shown as dash-dotted lines and they were computed using linear theory. (Adapted from [60]).…”

Section: Figmentioning

confidence: 99%

THz Dynamic Nuclear Polarization NMR

Nanni

Barnes

Griffin

et al. 2011

IEEE Trans. Terahertz Sci. Technol.

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160

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Dynamic nuclear polarization (DNP) increases the sensitivity of nuclear magnetic resonance (NMR) spectroscopy by using high frequency microwaves to transfer the polarization of the electrons to the nuclear spins. The enhancement in NMR sensitivity can amount to a factor of well above 100, enabling faster data acquisition and greatly improved NMR measurements. With the increasing magnetic fields (up to 23 T) used in NMR research, the required frequency for DNP falls into the THz band (140–600 GHz). Gyrotrons have been developed to meet the demanding specifications for DNP NMR, including power levels of tens of watts; frequency stability of a few megahertz; and power stability of 1% over runs that last for several days to weeks. Continuous gyrotron frequency tuning of over 1 GHz has also been demonstrated. The complete DNP NMR system must include a low loss transmission line; an optimized antenna; and a holder for efficient coupling of the THz radiation to the sample. This paper describes the DNP NMR process and illustrates the THz systems needed for this demanding spectroscopic application. THz DNP NMR is a rapidly developing, exciting area of THz science and technology.

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“…As an example of the existing interest in this problem, let us mention a recent paper [14] devoted to definition of the effective cavity length. In recent years, the interest in this problem was also motivated by the development of gyrotrons for spectroscopic applications [15][16][17]. In such gyrotrons, the frequency can be continuously tunable by varying the external magnetic field leading to simultaneous variation of the axial profile of the cavity field.…”

mentioning

confidence: 99%

“…In such gyrotrons, the frequency can be continuously tunable by varying the external magnetic field leading to simultaneous variation of the axial profile of the cavity field. As a rule, increasing the external magnetic field causes transition from the mode with one axial variation to the mode with two variations and so on (see, e.g., [16]). …”

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Field Formation in the Interaction Space of Gyrotrons

Nusinovich

Dumbrājs

2015

J Infrared Milli Terahz Waves

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For gyrotron applications in plasma installations, one of the most important factors is the gyrotron efficiency. To maximize the interaction efficiency, it is necessary not only to optimize such operating parameters as the magnetic field, beam voltage, and current but also the axial profile of the electromagnetic (EM) field in the interaction space. The present paper describes a study of the effect of the profile of an irregular waveguide serving as a resonator on the axial structure of the EM field. Specific attention is paid to the profile of the uptaper connecting the regular part of a resonator to the output waveguide. Conditions of applicability of the nonuniform string equation, which is widely used in gyrotron designs for finding the axial structure of the EM field, are discussed. Also discussed are the occurrence of reflections from a smooth uptaper and the analogy between the nonuniform string equation and the stationary Schrodinger equation.

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Operation of a Continuously Frequency-Tunable Second-Harmonic CW 330-GHz Gyrotron for Dynamic Nuclear Polarization

Cited by 160 publications

References 21 publications

Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns

Mode Content Determination of Terahertz Corrugated Waveguides Using Experimentally Measured Radiated Field Patterns

THz Dynamic Nuclear Polarization NMR

Field Formation in the Interaction Space of Gyrotrons

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