We have demonstrated generation and transport of a patterned electron beam from a Diamond Field-Emitter Array (DFEA) cathode in a radio frequency (rf) gun. DFEAs are arrays of micrometer-scale pyramids with nanometer-scale tips. They can be fabricated with base widths ranging from 3 μm to 25 μm and pitches as small as 5 μm. They have an inherent 1:0.7 base to height ratio. DFEAs operate as field-emitter cathodes and potentially produce intrinsically shaped electron beams, which are of interest for a number of accelerator applications. We report on the results of a recent experiment in which a beam, consisting of several beamlets, was produced from a DFEA cathode in an rf gun and transported 2.54 m along a beam line. A macrobunch charge of 60 pC was measured at a cathode field gradient of 15.1 MV/m.
Many applications, such as compact accelerators and electron microscopy, demand high brightness electron beams with small source size and ultralow emittance. Diamond emitters manufactured with semiconductor processes can be employed in such compact beam sources. The micrometer-scale pyramid structure of the emitter allows enhancement of the external field compared to that at the substrate, leading to electron emission with small beam size. We investigate the dependence of the field enhancement on the shape of the emitter and the resulting emission characteristics. The beam formation and dynamics are simulated with the LSP [D. Welch, D. Rose, R. Clark, T. Genoni, and T. Hughes, Comput. Phys. Commun. 164, 183 (2004)] particle-in-cell code to obtain the macroscopic observables. To account for the semiconductor charge transport in the bulk material and the tunneling through the surface, a first-principle semiclassical Monte Carlo emission model is developed and applied to the diamond pyramid. Using this Monte Carlo emission model and the result from the geometric field enhancement calculation, we construct a simple model to qualitatively explain the measured emission characteristics. A comparison between our model and experiments indicates that the beam current is mostly emitted at the apex of the emitter.
We present a contactless method of detecting small changes in the surface temperature of metallic samples over a short time period. The thermometry method incorporates a contactless heater and simplifies sample preparation requirements for calorimetric measurements. We demonstrate that we can measure small temperature shifts (250μK) in 5ms at midrange temperatures (155K). This method does not serve as a conventional thermometer but as an in situ thermometer useful for narrow temperature ranges, such as the region of a phase transition (often exploited in bolometers). The manganite material Nd0.5Sr0.5MnO3 was chosen as a test material for our experiments because it is a well characterized material where resistivity and magnetization [Kuwakara et al., Science 270, 961 (1995)] and thermal conductivity [Kim et al., American Physical Society March Meeting, W24.009 (2004)] have been previously measured and the material undergoes a metal-insulator transition.
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