Plasma-emitter electron accelerators

This paper considers the physical processes associated with the extraction of electrons from the gas discharge plasma in plasma emitters where the emission boundary is stabilized with a fine grid. The ways of improving the uniformity of the emission current density distribution are discussed. Accelerators designed on the basis of plasma emitters are capable of producing pulsed beams of current 10–10³ A, current density 0.1–1.0 A/cm², pulse duration 10⁻⁷–10⁻³ s, and cross-sectional area up to 10⁴ cm². Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 92–96, April, 2000.     

Optics of broadband infrared diagnostics for accelerators

This review is devoted to an analysis of the properties and potentiality of optical synchrotron diagnostics, which is now a flexible means to study bunches (beams) of charged particles during their acceleration (storage) and interaction. The review briefly describes the history and main optical features of the devices used in experimental investigations of synchrotron radiation, beginning with the studies at the Lebedev Physical Institute. More elaborately considered is the infrared synchrotron method of diagnostics, which was developed at the Joint Institute for Nuclear Research and is based on optical methods developed at the Lebedev Physical Institute and Moscow State University. The main attention of the practical experiments is focused on designing, creating, and using special (broadband and long-focus) infrared optics, including mirrors, lenses, and heat-resistant windows. The merits and advantages of infrared diagnostics in comparison with optical diagnostics are shown in real examples.     

Nondestructive diagnostics of charged particle beams in accelerators

The basic techniques for nondestructive diagnostics and detection of losses of charged particle beams used in accelerator engineering are reviewed. The data provided may help choose the systems for diagnostics and detection of losses of beams and give a qualitative picture of the operation principles of such devices. Quantitative characteristics that define the limits of applicability of each diagnostic technique are outlined.     

Polarized beams for electron accelerators

NEA-GaAs based photocathodes allow the production of spin-polarized electron beams for fundamental research. We demonstrate how semiconductor properties influence salient parameters such as polarization and beam brightness. We present techniques that provide remedies for the extreme sensitivity to environmental factors. These are discussed for the specific installation that has provided spin-polarized beam at the MAMI facility during the last decade.     

Coherent X-ray radiation from a relativistic electron in a combined medium

A theory of coherent X-ray radiation from a relativistic electron crossing a combined medium that consists of amorphous and crystal plates is constructed within the dynamic diffraction theory. The field reflection asymmetry relative to the target surface determined by the angle between the atomic planes and the target surface is taken into account in the theory. The expressions describing the spectral-angular densities of parametric X-ray and diffracted transition radiations in this medium are derived and investigated.     

Coherent thermal radiation

The radiation emitted by a heated body is generally quoted as a typical example of incoherent radiation, in distinction to laser radiation. One is nearly isotropic, the other highly directional; one is spectrally broad, the other quasi-monochromatic. It may come as a surprise that the thermal radiation of a large number of substances is coherent, both in space and time, when it is observed at a distance from the body that is shorter than the wavelength. This behaviour can be understood within an electromagnetic approach to thermal emission. Several recent experiments have confirmed these unexpected properties.     

X radiation sources based on accelerators

Light sources based on accelerators aim at producing very high brilliance coherent radiation, tuneable from the infrared to X-ray range, with picosecond or femtosecond light pulses.The first synchrotron light sources were built around storage rings in which a large number of relativistic electrons produce “synchrotron radiation” when their trajectory is subjected to a magnetic field, either in bending magnets or in specific insertion devices (undulators), made of an alternating series of magnets, allowing the number of curvatures to be increased and the radiation to be reinforced.These “synchrotron radiation” storage rings are now used worldwide (there are more than thirty), and they simultaneously distribute their radiation to several tens of users around the storage ring.The most effective installations in term of brilliance are the so-called 3rd generation synchrotron radiation light sources. The radiation produced presents pulse durations of the order of a few tens of ps, at a high rate (of the order of MHz); it is tuneable over a large range, depending on the magnetic field and the electron beam energy and its polarisation is adjustable (in the VUV-soft-X range). Generally, a very precise spectral selection is made by the users with a monochromator.The single pass linear accelerators can produce very short electron bunches (). The beam of very high electronic density is sent into successive undulator modules, reinforcing the radiation's longitudinal coherence, produced according to a Free Electron Laser (FEL) scheme by the interaction between the electron bunch and a light wave. The very high peak brilliance justifies their designation as 4th generation sources. The number of users is smaller because an electron pulse produces a radiation burst towards only one beamline. Energy Recovery Linacs (ERL) let the beam pass several times in the accelerator structures either to recover the energy or to accelerate the electrons during several turns, and thus provide subpicosecond beams for a greater number of users.A state-of-the-art of X sources using conventional (and not laser plasma based) accelerators is given here, underlying the performance already reached or forecast and the essential challenges. To cite this article: M.-E. Couprie, J.-M. Filhol, C. R. Physique 9 (2008).     

Coherent exciton-surface-plasmon-polariton interaction in hybrid metal-semiconductor nanostructures

We report measurements of a coherent coupling between surface plasmon polaritons (SPP) and quantum well excitons in a hybrid metal-semiconductor nanostructure. The hybrid structure is designed to optimize the radiative exciton-SPP interaction which is probed by low-temperature, angle-resolved, far-field reflectivity spectroscopy. As a result of the coupling, a significant shift of approximately 7 meV and an increase in broadening by approximately 4 meV of the quantum well exciton resonance are observed. The experiments are corroborated by a phenomenological coupled-oscillator model predicting coupling strengths as large as 50 meV in structures with optimized detunings between the coupled exciton and SPP resonances. Such a strong interaction can, e.g., be used to enhance the luminescence yield of semiconductor quantum structures or to amplify SPP waves.     

Numerical analysis of space charge effects in electron bunches at laser-driven plasma accelerators

Laser-driven Plasma Accelerators (LPA) have successfully generated high energy, high charge electron bunches which can reach many kA peak current, over short distances. Space charge issues, even in transport lines as simple as a drift section, have to be carefully taken into account since they can degrade the beam quality, preventing any further application of such electron beams. We analyse the space charge effects within an electron bunch with numerical simulations in order to assess their effect on the beam. We use LPA beam parameters published in previous experimental studies. These studies can give an indication of the working point where space charge can dominate the beam dynamics and has to be taken into account in the application of such beams.     

Coherent X-ray radiation generated by a relativistic electron in an artificial periodic structure

A theory of coherent X-ray radiation from a relativistic electron crossing an artificial periodic layered structure in the Laue scattering geometry is constructed. The expressions describing the spectral-angular radiation parameters are obtained. It is shown that the radiation yield in such a medium may substantially exceed the radiation yield in a crystal under analogous conditions.     

大气压等离子体炬电子密度的光谱诊断

利用空心针-板放电装置产生了大气压等离子体炬,采用光谱法测量了其内部及表面的电子密度. 向空心针中通入氩气,在大气环境中产生了长度为1cm的等离子体炬.实验分别测量了Hα谱线和ArⅠ(696.54nm)谱线,通过反卷积方法分离出其相应的Stark展宽,并由此计算了电子密度.结果发现,采用Hα谱线和ArⅠ(696.54nm)谱线Stark展宽计算得到的等离子体的电子密度分别为1.0×10¹⁵cm^－3和3.78×10^{15关键词： 等离子体炬 电子密度 气体温度 Stark展宽}     

Neutrino beams at accelerators

Prospects for neutrino oscillation experiments with neutrino factories based on muon decay and conventional superbeams are discussed with a special emphasis on the neutrino beam properties.     

Nanometer-precision contour-measurement technique for the diagnostics of multilayer nanostructures

A new technique of contour measurements with nanometer precision for the diagnostics of multilayer structures and other samples applied in optical and silicon technologies, and metal processing is proposed. This paper describes the development of two main technical solutions to achieve and verify nanometer resolution of the contour measuring instrument—single-crystal-silicon guide and test plates. The use of a crystal as a linear guide gives the possibility to achieve long-term stability of its bearing surface within a few nanometers. A test sample of a multilayer structure is developed and its parameters are controlled by means of transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). The results of measuring test samples with a step height of 100 and 200 nm by means of the contour measurement technique are presented.     

Formation of wide-aperture electron beams in electron accelerators with explosive emission cathodes

The problems concerning the formation of electron beams of microsecond duration, electron energy 500–600 keV, and current density up to 20–30 A/cm² with a rectangular cross section of area 0.1–1 m² in high-current electron accelerators with explosive emission cathodes are considered. The designs of vacuum diodes capable of producing such beams to be used in high-power lasers and for ionization of gas in large volumes are presented. Institute of High-Current Electronics, Siberian Division of the Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 87–91, April, 2000.     

Intense source of slow positrons from pulsed electron accelerators

A pulsed LINAC is used for pair production in a tantalum target of 2.5 radiation lengths in an energy range from 80 to 260 MeV. Several well-annealed tungsten vanes are placed immediately behind the target and thermalize a small fraction of the fast positrons. The slow positrons are extracted from the target region and magnetically guided over a distance of 17 m to the detector at the end of an S-shaped solenoid. Two Nal detectors with well-known detection efficiency are used to register the 511 keV annihilation-rays. To reduce pile-up effects 50 mm of Pb were placed in front of the detectors. At an average electron current of 1 A we could detect about 10⁷ slow positrons per second. The positron yield is proportional to the electron current, and shows an increase with the electron energy for our target. The positron energy distribution has a FWHM of 1.8 eV.     

Coherent tunable far infrared radiation

Tunable, cw, far infrared (FIR) radiation has been generated by nonlinear mixing of radiation from two CO₂ lasers in a metal-insulator-metal, (MIM) diode. The FIR difference-frequency power was radiated from the MIM diode antenna to a calibrated indium antimonide bolometer. Two-tenths of a microwatt of FIR power was generated by 250 mW from each of the CO₂ lasers. Using the combination of lines from a waveguide CO₂ laser, with its larger tuning range, with lines from CO₂, N₂O, and CO₂ isotope lasers promises complete coverage of the entire far infrared band from 100 to 5000 GHz (3–200 cm^–1) with stepwise-tunable cw radiation.Contribution of the National Bureau of Standards, not subject to copyright