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Related Concept Videos

Double Resonance Techniques: Overview01:12

Double Resonance Techniques: Overview

Double resonance techniques in Nuclear Magnetic Resonance (NMR) spectroscopy involve the simultaneous application of two different frequencies or radiofrequency pulses to manipulate and observe two distinct nuclear spins. One important application of double resonance is spin decoupling, which selectively suppresses coupling with one type of nucleus while observing the NMR signal from another nucleus, simplifying the spectrum and enhancing resolution.
Spin decoupling is usually achieved by...
Tandem Mass Spectrometry01:21

Tandem Mass Spectrometry

Tandem mass spectrometry is a technique that uses multiple mass analyzers in series to obtain a higher selectivity and reduce chemical noise during analyte detection. Instruments with multiple analyzers separated by an interaction cell enable secondary fragmentation and selected study of the fragment ions.Secondary fragmentations occur in the interaction cell and can be induced by various factors. Fragmentation induced by collision with inert gases, such as N2, Ar, He, etc., is called...
¹H NMR Signal Multiplicity: Splitting Patterns01:13

¹H NMR Signal Multiplicity: Splitting Patterns

When protons A and X are coupled, their nuclear spin energy levels are slightly modified. This is because the energy required to excite proton A to a spin state parallel to proton X is slightly different from the energy required for it to become anti-parallel to spin X. Consequently, there are two possible excitation frequencies for A (A1 and A2), depending on the spin state of X, and vice versa. The mutual nature of coupling implies that the difference between frequencies A1 and A2, indicated...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
What is a Mode?01:07

What is a Mode?

The mode is one of the commonly used measures of a central tendency. It is defined as the most frequent value in a data set.
There can be more than one mode in a data set if multiple values have the same highest frequency. For instance, suppose that the Statistics exam scores of 20 students are: 50; 53; 59; 59; 63; 63; 72; 72; 72; 72; 72; 76; 78; 81; 83; 84; 84; 84; 90; 93. Here, the mode is 72, as it occurs most frequently, five times.
A data set with two modes is called bimodal. For example,...
Mass Analyzers: Common Types01:19

Mass Analyzers: Common Types

The quadrupole mass analyzer consists of four cylindrical metal rods arranged in a diamond carrying a DC voltage and a radio-frequency AC voltage. The motion of ions through the quadrupole depends on the field strength, causing only ions of a certain m/z to resonate successfully and strike the detector at a given field strength. Though the transmission rate for these analyzers is high, the exact elemental composition of the sample is not determined because of low resolution; however, they are...

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Transmission of Multiple Signals through an Optical Fiber Using Wavefront Shaping
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Ping-pong modes: a new form of multipactor.

R A Kishek1

  • 1Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA.

Physical Review Letters
|March 10, 2012
PubMed
Summary

A new resonant multipactor discharge model combines one- and two-surface impacts. This method enhances the electric field boundary and band overlap, validated by simulations.

Area of Science:

  • Plasma physics
  • Vacuum electronics
  • Charged particle dynamics

Background:

  • Multipactor discharge is a significant phenomenon in vacuum electronic devices.
  • It is driven by secondary electron emission and can lead to device failure.
  • Understanding and controlling multipactor is crucial for high-power RF systems.

Purpose of the Study:

  • To propose and analyze a novel resonant multipactor discharge mode.
  • To investigate the conditions for this resonant mode, involving one- and two-surface impacts.
  • To determine the impact of this mode on the multipacting region boundaries and higher-order bands.

Main Methods:

  • Theoretical analysis of a resonant multipactor mode.
  • Derivation of conditions based on transit time and secondary electron yields.

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  • Validation using 3D particle-in-cell code simulations.

    • Main Results:

    • A novel resonant multipactor mode is proposed, combining single- and double-surface impacts.
    • This mode requires an odd number of RF half-periods for transit and a secondary yield product greater than unity.
    • For low frequency-diameter products, this mode significantly increases the upper electric field boundary and causes overlap of higher-order multipacting bands.
    • Results show excellent agreement with 3D particle-in-cell simulations.

    Conclusions:

    • The proposed resonant multipactor mode offers a new perspective on discharge dynamics.
    • This understanding can help in mitigating or controlling multipactor in vacuum electronic devices.
    • The findings have practical implications for the design and operation of high-frequency, high-power systems.