Vacuum electronics

Parker, Robert K.; Abrams, R.H.; Danly, B.G.; Levush, B.

doi:10.1109/22.989967

Cited by 155 publications

(50 citation statements)

References 40 publications

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“…[93][94][95] In general, two different types of μw sources can be distinguished: solid-state and vacuum electronic devices. Figure 10 provides an overview of high-frequency μw sources available currently.…”

Section: A Microwave Sourcesmentioning

confidence: 99%

Dynamic nuclear polarization at high magnetic fields

Maly¹,

Debelouchina²,

Bajaj³

et al. 2008

The Journal of Chemical Physics

791

847

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Dynamic nuclear polarization (DNP) is a method that permits NMR signal intensities of solids and liquids to be enhanced significantly, and is therefore potentially an important tool in structural and mechanistic studies of biologically relevant molecules. During a DNP experiment, the large polarization of an exogeneous or endogeneous unpaired electron is transferred to the nuclei of interest (I) by microwave (μw) irradiation of the sample. The maximum theoretical enhancement achievable is given by the gyromagnetic ratios (γ e /γ l ), being ∼660 for protons. In the early 1950s, the DNP phenomenon was demonstrated experimentally, and intensively investigated in the following four decades, primarily at low magnetic fields. This review focuses on recent developments in the field of DNP with a special emphasis on work done at high magnetic fields (≥5 T), the regime where contemporary NMR experiments are performed. After a brief historical survey, we present a review of the classical continuous wave (cw) DNP mechanisms-the Overhauser effect, the solid effect, the cross effect, and thermal mixing. A special section is devoted to the theory of coherent polarization transfer mechanisms, since they are potentially more efficient at high fields than classical polarization schemes. The implementation of DNP at high magnetic fields has required the development and improvement of new and existing instrumentation. Therefore, we also review some recent developments in μw and probe technology, followed by an overview of DNP applications in biological solids and liquids. Finally, we outline some possible areas for future developments.

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Section: A Microwave Sourcesmentioning

confidence: 99%

Dynamic nuclear polarization at high magnetic fields

Maly¹,

Debelouchina²,

Bajaj³

et al. 2008

The Journal of Chemical Physics

791

847

View full text Add to dashboard Cite

show abstract

“…Applications that rely on field emission will benefit, and such applications include (but are not limited to): electron beam lithography [22,23] and transmission electron microscopes [24]; spacecraft propulsion [25,26]; mm-wave Vacuum Electronic amplifiers and THz devices [27,28]; and particle accelerators and Free Electron Lasers (FEL's) [29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Space charge effects in field emission: One dimensional theory

Rokhlenko

Jensen

Lebowitz

2010

Journal of Applied Physics

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The current associated with field emission is greatly dependent on the electric field at the emitting electrode. This field is a combination of the electric field in vacuum and the space charge created by the current. The latter becomes more important as the current density increases. Here, a study is performed using a modified classical 1D ChildLangmuir description that allows for exact solutions in order to characterize the contributions due to space charge. Methods to connect the 1D approach to an array of periodic 3D structures are considered.

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“…[1,2] As the working frequency rises to upper millimeter wave range (100-300 GHz), the transverse sizes of slow-wave circuits become so small that the traditional machining technique can no longer meet the requirements of the fine machining tolerances, the adequate costs and high yield of fabrication. [1,2] The machining problem derived from the traditional manufacturing process, have caused fast rising loss in output power and bandwidth at higher frequency, prohibiting both traditional helix-TWTs and coupled cavity TWTs from upper millimeter wave frequency application. [1][2][3][4] Unfortunately, the traditional helix and coupled cavity slow-wave circuits are not compatible with microfabrication technology, due to their intrinsic shortcomings in structures.…”

Section: Introductionmentioning

confidence: 99%

“…[1,2] The machining problem derived from the traditional manufacturing process, have caused fast rising loss in output power and bandwidth at higher frequency, prohibiting both traditional helix-TWTs and coupled cavity TWTs from upper millimeter wave frequency application. [1][2][3][4] Unfortunately, the traditional helix and coupled cavity slow-wave circuits are not compatible with microfabrication technology, due to their intrinsic shortcomings in structures. [3,4] In order to overcome the structural limitations, it is very necessary to develop novel slow-wave structures and microfabrication technology for next generation TWTs on upper millimeter wave band or even higher frequency.…”

Section: Introductionmentioning

confidence: 99%

Parametric Simulation and Optimization of Cold-test Properties for a 220 GHz Broadband Folded Waveguide Traveling-wave Tube

Zheng

Chen

2009

J Infrared Milli Terahz Waves

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Characterized with full-metal structure, high output power and broad bandwidth, microfabricated folded waveguide is considered as a robust slow-wave structure for millimeter wave traveling-wave tubes. In this paper, cold-test (without considering the real electron beam) properties were studied and optimized by 3D simulation on slow-wave structure, for designing a 220 GHz folded waveguide traveling-wave tube. The parametric analysis on cold-test properties, i.e., phase velocity, beam-wave interaction impedance and cold circuit attenuation, were conducted in half-period circuit with high frequency structure simulator, assisted by analytical model and equivalent circuit model. Through detailed parametric analyses, interference between specified structural parameters is found on determining beam-wave interaction impedance. A discretized matrix optimization for interaction impedance was effectively carried out to overcome the interference. A range of structural parameters with optimized interaction impedance distributions were obtained. Based on the optimized results, a broadband folded waveguide with cold pass-band of about 80 GHz, flat phase velocity dispersion and fairly high interaction impedance was designed for a 220 GHz central frequency traveling-wave tube. A three-dB bandwidth of 20.5 GHz and a maximum gain of 21.2 dB were predicted by small signal analysis for a 28 mm-long lossy circuit.

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Vacuum electronics

Cited by 155 publications

References 40 publications

Dynamic nuclear polarization at high magnetic fields

Dynamic nuclear polarization at high magnetic fields

Space charge effects in field emission: One dimensional theory

Parametric Simulation and Optimization of Cold-test Properties for a 220 GHz Broadband Folded Waveguide Traveling-wave Tube

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