Beugung von Elektronenwellen an magnetischen Strukturen

Boersch, H.; Hamisch, H.; Wohlleben, D.; Grohmann, Kleanthes Κ.

doi:10.1007/bf01377649

Cited by 44 publications

(13 citation statements)

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“…The stable operating point of a resulting saturated SEEA would therefore occur at the second crossover energy. 2 However, positive charging may also be possible, as the secondary yield is expected to increase dramatically for grazingincidence impacts, as would be the case here 13 .…”

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confidence: 78%

“…While there remains debate regarding the mechanism for surface flashover, 1 secondary electron emission avalanche (SEEA) has emerged as the dominant theory. In this model, 2,3 electrons are field-emitted from the cathode triple junction formed by the intersection of the vacuum, the electrode, and the insulator, where field enhancement may occur 4 . These electrons strike the insulator surface and produce secondary electrons, which also strike the surface to produce additional secondaries and form the avalanche.…”

mentioning

confidence: 99%

“…This deflection is usually assumed to be a result of positive charging of the insulator surface. 2,5 Displacement current may play a similar role in altering the electron trajectories when the rate of change of voltage is sufficiently high, allowing flashover initiation in the absence of a pre-existing surface charge. For a solid cylindrical insulator between parallel plate electrodes, the displacement current during the leading edge of an applied voltage pulse will generate a magnetic field parallel to the insulator surface, which will cause electrons emitted from the surface or the triple junction to be deflected towards the surface (Fig.…”

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confidence: 99%

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Displacement current and surface flashover

Harris

Caporaso

Blackfield

et al. 2007

Applied Physics Letters

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High-voltage vacuum insulator failure is generally due to surface flashover rather than insulator bulk breakdown. Vacuum surface flashover is widely believed to be initiated by a secondary electron emission avalanche along the vacuum-insulator interface. This process requires a physical mechanism to cause secondary electrons emitted from the insulator surface to return to that surface. Here, it is shown that when an insulator is subjected to a fast high-voltage pulse, the magnetic field due to displacement current through the insulator can provide this mechanism. This indicates the importance of the voltage pulse shape, especially the rise time, in the flashover initiation process.

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Displacement current and surface flashover

Harris

Caporaso

Blackfield

et al. 2007

Applied Physics Letters

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“…Subsequent application of the Huygens' principle allows the diffraction amplitude a t a n arbitrary distance from the object to be represented by the Kirchoff diffraction integral [4].…”

Section: Some Generaz Remarks On the Relation With Geometrical Opticsmentioning

confidence: 99%

Mainly on the Fresnel Mode in Lorentz Microscopy

Guigay

Wade

1968

Physica Status Solidi (b)

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We consider the problem of the determination of magnetic Structures by transmission electron microscopy. A stationary phaee approximation to the Kirchoff diffraction integral yields a criterion for the validity of geometrical optics in calculating image intensity distributions a t any diffraction plane. Our criterion is particularly useful for the Fresnel diffraction case since the usual criterion Ap, > h c/e [l] is strictly valid only for the Fraunhofer diffraction condition.Nous considbrons le problhme de la dbtermination de structures magnbtiques en microscopie blectronique par transmission. En effectuant une approximation de phase stationneire de l'int6grale de Kirchoff, nous obtenons un crithre de validitb de l'optique gbombtrique en ce qui concerne le calcul des distributions d'intensitb sur un plan d'observation quelconque. Ce critRre est particulierement utile lorsqu'on se trouve dam les conditions de diffraction de Fresnel, puisque le crithre usuel Ap, > h c/e [l] n'est strictement valable que dans les conditions de diffraction de Fraunhofer. l) This is the flux quantum (8 x 10-7 G om2) in the Gaussian system, with I Planck's constant, c the velocity of light, e the electron charge. 52 physica 2@/2

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“…The limiting factor in the design of high voltage vacuum insulators is generally vacuum surface flashover, rather than the bulk strength of the insulating material 8 . The most widely accepted theory of surface flashover holds that an avalanche of secondary electrons occurs along the insulator surface, desorbing gas through which the breakdown occurs [8][9][10][11] . The gradients envisioned for DWAs, and especially the 100 MV/m gradient envisioned for proton radiotherapy, are well beyond the capabilities of conventional, straight-walled vacuum insulator materials.…”

Section: Introductionmentioning

confidence: 99%

Vacuum insulator development for the dielectric wall accelerator

Harris

Blackfield

Caporaso

et al. 2008

Journal of Applied Physics

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At Lawrence Livermore National Laboratory, we are developing a new type of accelerator, known as a Dielectric Wall Accelerator, in which compact pulse forming lines directly apply an accelerating field to the beam through an insulating vacuum boundary. The electrical strength of this insulator may define the maximum gradient achievable in these machines. To increase the system gradient, we are using "High Gradient Insulators" composed of alternating layers of dielectric and metal for the vacuum insulator. In this paper, we present our recent results from experiment and simulation, including the first test of a High Gradient Insulator in a functioning Dielectric Wall Accelerator cell. a) Electronic mail: harris89@llnl.gov 2

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Beugung von Elektronenwellen an magnetischen Strukturen

Cited by 44 publications

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Displacement current and surface flashover

Displacement current and surface flashover

Mainly on the Fresnel Mode in Lorentz Microscopy

Vacuum insulator development for the dielectric wall accelerator

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