Trapped electrons in the quantum degenerate regime

A full strength Coulomb interaction between trapped electrons can be felt only in absence of a neutralizing background. In order to study quantum degenerate electrons without such a background, an external trap is needed to compensate for the strong electronic repulsion. As a basic model for such a system, we study a trapped electron pair in a harmonic trap with an explicit inclusion of its Coulomb interaction. We find the eigenenergy of the ground state, confirming earlier work in the context of harmonium. We extend this to a complete set of properly scaled energies for any value of the trapping strength, including the excited states. The problem is solved either numerically or by making harmonic approximations to the potential. As function of the trapping strength a crossover can be made from the strongly to the weakly-coupled regime, and we show that in both regimes perturbative methods based on a pair-wise electron description would be effective for a many-particle trapped electron system, which resembles a Wigner crystal in the ground state of the strongly coupled limit.Comment: 6 pages, 3 figure

High-brightness, compact soft x-ray source based on Cherenkov radiation

Cherenkov radiation in the soft x-ray region is generated in narrowband regions at inner-shell absorption edges. Mainly low-Z elements are suitable Cherenkov sources, which emit in a photon energy range from 30 eV to 1 keV and require moderate electron energies up to 25 MeV. Generally, in the soft x-ray region materials are highly absorbing and therefore the Cherenkov radiation theory is discussed for absorbing media. A detailed description includes transition radiation that is generated at the interface when the relativistic electron exits the material. We show that the transition radiation yield equation, when it is adopted for an absorbing medium, includes Cherenkov radiation. Based on this approach it is shown that the spectral intensity of Cherenkov radiation in the soft x-ray region is large compared to transition radiation for moderate electron energies. First measurements of soft x-ray Cherenkov radiation in the water-window spectral region, generated in titanium and vanadium foils, are discussed in detail. The measured spectral and angular distribution of the radiation, and the measured total yield (≈ 10 -4 photon per electron) are in agreement with theoretical predictions based on the refractive index data. We show that the brightness that can be achieved using a small electron accelerator is sufficient for practical x-ray microscopy in the water window.</p

Taking snapshots of atomic motion using electrons

55 years after Richard Feynman’s famous Caltech lecture ‘There is plenty of room at the bottom’ [1], heralding the age of nano science and technology, many of the possibilities he envisaged have come true: Using electron microscopy it is nowadays possible to resolve and even identify individual atoms; STM and AFM not only provide us with similar spatial resolution on surfaces, but also allow dragging individual atoms around in a controlled way; X-ray diffraction has revealed the complicated structures of thousands of proteins, giving invaluable insight into the machinery of life

Cool beams for ultrafast electron imaging

By near threshold photoionization of a laser-cooled and trapped atomic gas we create dense, picosecond electron bunches at electron temperatures three orders of magnitude lower than in conventional field and photoemission sources. The superior coherence properties of this ultracold source will enable single-shot electron diffraction of macromolecules and ultrafast nanodiffraction. Recently we have recorded the first diffraction patterns of graphite using the ultracold source. To control and manipulate highly coherent, ultrashort pulsed beams we are developing compact 3 GHz microwave cavities as versatile time-dependent electron optical elements. We have demonstrated bunch compression – longitudinal focusing – to below 100 fs using a 3 GHz microwave cavity in TM010 mode. Alternatively, a cavity in TM010 mode may be used to lower the energy spread of an electron bunch by longitudinal defocusing. We use microwave cavities in TM110 mode for measuring bunch lengths, but also to chop the continuous beam of an electron microscope into a high repetition rate train of femtosecond single-electron pulses while conserving emittance

Single-shot Femtosecond Electron Diffraction

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Met koude elektronen atomen zien bewegen

In december 2007 was dr.ir Jom Luiten een van de gelukkige prijswinnaars van een Vici-subsidie. I-hf kreeg deze prijs voor een onderzoeksvoorstel waarmee hij atomen in actie wilde zien. Ondertussen zljn we een jaar verder en is er dus meer te vertellen over hoe het met het onderzoeksproject staat

RF bunch compression for single-shot femtosecond electron diffraction

No abstrac

Ultracold and ultrafast electron source

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