Relaxation of Coulomb States in semiconductors probed by FEL radiation

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Successful user operation of a superconducting radio-frequency photoelectron gun with Mg cathodes

At the electron linac for beams with high brilliance and low emittance (ELBE) center for high-power radiation sources, the second version of a superconducting radio-frequency (SRF) photoinjector has been put into operation and has been routinely applied for user operation at the ELBE electron accelerator. SRF guns are suitable for generating a continuous wave electron beam with high average currents and high beam brightness. The SRF gun at ELBE has the goal to generate short electron pulses with bunch charges of 200–300 pC at typical repetition rates of 100 kHz for the production of superradiant, coherent terahertz radiation. The SRF gun includes a 3.5-cell, 1.3-GHz niobium cavity and a superconducting solenoid. A support system with liquid nitrogen (LN2) cooling allows the operation of normal-conducting, high quantum efficiency photocathodes. We present the design and performance of the SRF gun as well as beam measurement results of the operation with Mg photocathodes at an acceleration gradient of 8  MV/m (4 MeV kinetic energy). In the last section, we discuss the SRF gun application for production of coherent terahertz radiation at the ELBE facility

Thz Solar Telescope For Detection Flare Synchrotron Radiation

Recent solar flare observations have shown the existence of a spectral component exhibiting fluxes increasing with frequency in the sub-THz spectrum simultaneously with the well known spectral component peaking at microwaves bringing challenging constraints for interpretation. This double spectral feature cannot be well explained by existing models. One possibility is to associate the high frequency emissions to incoherent synchrotron radiation (ISR) produced by flare accelerated beams of high energy electrons with intensity peaking at THz frequencies. Certain wave-particle instabilities may set in the electron beam, giving rise to bunching of the electrons which could radiate powerful broadband coherent synchrotron radiation (CSR) in the microwave spectrum peaking at wavelengths comparable to the size of the bunching. Although this CSR process has been observed in laboratory accelerators, only now has its association to solar flare physics been explored. Simulations have shown that the mechanism may be extremely efficient and highly localized in solar flares. To demonstrate the high energy ISR emission in flares it is necessary to measure the complete continuum spectra at higher THz frequencies, outside the terrestrial atmosphere. A THz telescope has been developed with a 75 mm primary reflector with rough surface to diffuse part of the incoming visible and near IR radiation. Golay cell detectors are preceded by low-pass membranes and band-pass metal mesh resonant filters tuned at 3 and 7 THz. © 2011 IEEE.Shimabukuro, F.I., The observation of 3.3-mm bursts and their correlation with soft X-ray bursts (1970) Solar Phys., 15, pp. 424-432Akabane, K., A flare-associated thermal burst in the mm-wave region (1973) Solar Phys., 33, pp. 431-437Zirin, H., Tanaka, K., The flares of August 1972 (1973) Solar Phys., 32, pp. 173-207Kaufmann, P., Raulin, J.-P., Gimenez, D.C.C.G., Levato, H., Gary, D.E., Costa, J.E.R., Marun, A., Correia, E., A new solar burst spectral component emitting only in the terahertz range (2004) Astrophysical Journal, 603 (2 II), pp. L121-L124. , DOI 10.1086/383186Kaufmann, P., Sub-terahertz, Microwaves and High Energy Emissions during the 6 December 2006 Flare, at 18:40 UT (2009) Solar Phys., 255, pp. 131-142Silva, A.V.R., Evidence that Synchrotron Emission from Nonthermal Electrons Produces the Increasing Submillimeter Spectral Component in Solar Flares (2007) Solar Phys., 245, pp. 311-326Trottet, G., Radio Submillimeter and ã-Ray Observations of the 2003 October 28 Solar Flare (2008) Astrophys. J., 577, pp. 509-514Sakai, J.I., Simulating the emission of electromagnetic waves in the terahertz range by relativistic electron beams (2006) Astron.Astrophys., 457, p. 313Sakai, J.I., Nagasugi, Y., Emission of electromagnetic waves by proton beams in solar plasmas (2007) Astron.Astrophys., 474, pp. L33Kaufmann, P., A Synchrotron/Inverse Compton Interpretation of a Solar Burst Producing Fast Pulses at 3mm Wavelength and Hard X-Rays (1986) Astron.Astrophys., 157, pp. 11-18Fleishman, G.F., Kontar, E.P., Sub-THz radiation mechanisms in solar flares (2010) Astrophys. J., 709, pp. L127-L132Williams, G.P., FAR-IR/THz radiation from the Jefferson Laboratory, energy recovered linac, free electron laser (2002) Rev. Sci. Instrum., 73, pp. 1461-1463Kaufmann, P., Raulin, J.-P., Can microbunch instability on solar flare accelerated electron beams account for bright broadband coherent synchrotron microwaves? (2006) Phys.Plasmas, 13, p. 070701Klopf, J.M., Kaufmann, P., Raulin, J.-P., Examination of broadband coherent synchrotron radiation to describe THz and sub-THz solar flare spectral emissions (2010) Bulletin American Astronomical Society, 42, p. 905Kaufmann, P., Selective Spectral Detection of Continuum Terahertz Radiation Proc. SPIE 7741, San Diego, CA, 28 June-2 July, 2010, , paper 7741-77Melo, A.M., Metal mesh resonant filters for terahertz frequencies (2008) Applied Optics, 47, pp. 6064-6069Fernandes, L.O.T., Photometry of THz Radiation Using Golay Cell Detector, , this XXX URSI GAKaufmann, P., Search for Continuum Solar Flare Radiation in the Terahertz Range Proc. of IRMMWTHz 2010 Conference, Rome, Italy, 5-10 September, 2010Shih, A., The Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS) (2008) American Geophysical Union, Fall Meeting, , abstract SM11B-160

Relaxation of Coulomb States in Semiconductors Probed by FEL Radiation

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Chemical Shift and Exchange Interaction Energy of the 1s States of Magnesium Donors in Silicon. The Possibility of Stimulated Emission

Spectroscopy of valley-orbit split-off states in silicon doped by magnesium. Calculation of Relaxation rates of donor states

Emotions as a dynamical system: the interplay between the meta-control and communication function of emotions

International audienceClassical models of emotions consider either the communicational aspect of emotions (for instance the emotions conveyed by the facial expressions) or the second order control necessary for survival purpose when the autonomy of the system is an issue. Here, we show the interdependence of communication and meta-control aspects of emotion. We propose the idea that emotions must be understood as a dynamical system linking two controllers: one devoted to social interactions (i.e. communication aspects) and another one devoted to the interactions within the physical world (i.e metacontrol of a more classical controller). Illustrations will be provided from applications involving navigation among di erent goal places according to di erent internal drives or object grasping and avoidance