17,547 research outputs found
Electron dynamics and acceleration study in a magnetized plasma-filled cylindrical waveguide
No full textIn this article, EH(01) field components are evaluated in a cylindrical waveguide filled with plasma in the presence of external static magnetic field applied along the direction of the mode propagation. The electron acceleration inside the plasma-filled cylindrical waveguide is investigated numerically for a single-electron model. It is found that the electron acceleration is very sensitive to the initial phase of mode-field components, external static magnetic field, plasma density, point of injection of the electron, and microwave power density. The maximum amplitude of the EH(01) mode's field components is approximately 100 times greater than the vacuum-waveguide case for operating microwave frequency f=7.64 GHz, plasma density n(0)=1.08x10(17) m(-3), initial phase angle phi(0)=60 degrees, and microwave power similar to 14 MW in a cylindrical waveguide with a radius of 2.1 cm. An electron with 100 keV gets 27 MeV energy gain in 2.5 cm along the waveguide length in the presence of external power similar to 14 MW with a microwave frequency of 7.64 GHz. The electron trajectory is also analyzed under the effects of magnetic field when the electron is injected in the waveguide at r=R/2. (c) 2008 American Institute of Physics.open112022sciescopu
Effect of a Higher-Order-Corrected Chirped Gaussian Laser Beam on the Electron Acceleration in Vacuum
No full textFor a tightly focused laser, the beam-waist radius is of the same order as the wavelength and the lower-order-corrected Gaussian pulse description satisfies Maxwell's equations less accurately, so it, becomes necessary to include all the field components that arise from the tight focusing of the laser so as to satisfy Maxwell's equations more accurately. The effect of the seventh-order-corrected chirped Gaussian laser beam on the electron acceleration in vacuum is investigated. A numerical simulation shows that an electron maximum energy gain on the order of giga-electron volts (GeV) can be expected in the beam-waist region 45 <= k(0)w(0) <= 60, where k(0) is the laser wave number and w(0) is the laser-beam's waist size at the focal point of the beam.X11sciescopuskc
Continuity and change in Yoon Suk Yeol's positioning of South Korea as a strong, proactive, and global middle power
No full textSouth Korean President Yoon Suk Yeol has stressed marked change with his predecessor in launching the nation as a strong, proactive, and globally oriented middle power. By way of testing four core assumptions on progressives and conservatives' policy proclivities, this article evaluates these (asserted) changes in South Korea's foreign security policy. It finds a sharp change in Seoul's policy toward the North's nuclear and missile program but continuity with the Moon administration in strengthening South Korea's force structure. Fearing potential American abandonment, the Yoon administration has further sought deeper integration with American forces on the Peninsula. Yoon breaking with China is a big policy shift, as is his taking incremental steps toward the tripartite alliance with the USA and Japan that is much-dreaded by Beijing. South Korea establishing ties with European countries and NATO on the other side of the world is also significant.Peer reviewe
Shape optimization of shear fracture specimen considering plastic anisotropy
No full textIt is important to fabricate fracture specimens with minimum variation of triaxiality in order to characterize the failure behaviors experimentally. Fracture in ductile materials is usually calibrated by uniaxial tensile, shear and plane strain tests. However, it is often observed that triaxiality for shear specimen changes severely during shear fracture test. The nonlinearity of triaxiality is most critical for shear test. In this study, a simple in-plane shear specimen is optimized by minimizing the variation of stress triaxiality in the shear zone. In the optimization, the Hill48 and Yld2000-2d criteria are employed to model the anisotropic plastic deformation of an aluminum alloy of 6k21. The evolution of the stress triaxiality of the optimized shear specimen is compared with that of the initial design of the shear specimen. The comparison reveals that the stress triaxiality changes much less for the optimized shear specimen than the evolution of the stress triaxiality with the original design of the shear specimen
An Approach to Eliminate Ambiguity of Blind ML Detection for Orthogonal Space-Time Block Codes
No full textVan-Su Pham, Minh-Tuan Le, Mai Linh, S. M. Humayun Kabir, Giwan Yoo
Electron acceleration in a warm magnetized plasma-filled cylindrical waveguide
No full textThe effect of plasma-electron collision and their thermal motion is investigated on the externally injected electron in a warm magnetized plasma-filled cylindrical waveguide of cross section of 13.68 cm(2). The numerical results are presented for the external electron-energy gain and its trajectory in a nonrelativistic gamma(e)=1 and stationary v(0)=0 warm magnetized plasma-filled waveguide. Results shows that for an electron-cyclotron frequency omega(c) greater than the electron-plasma frequency omega(p), a 100 keV electron acquires a 1.74 MeV energy in a 2.5 cm distance for plasma density n(0)=1.08x10(17)/m(3), magnetic field B(0)=0.193 T, microwave frequency f=7.64 GHz, plasma-electron thermal velocity v(th)=0.2c, and plasma-electron collision frequency nu=4 GHz, which is lower than the 7 MeV electron energy in a cold magnetized plasma-waveguide case. Space-charge effects and other nonlinear effects are assumed to be negligible in this model. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.2988899]open1187sciescopu
ELECTRON ACCELERATION IN VACUUM: EFFECT OF LASER POLARIZATION IN ADDITION TO THE WIGGLER MAGNETIC FIELD
No full textIrrespective of the chirped pulse inverse free electron laser (CPIFEL) concept, a comparative study of a chirped circular-polarized (CP) laser pulse and a chirped linear-polarized (LP) laser pulse has been done numerically via electron acceleration in vacuum. We found that ultrahigh acceleration of the electron could be achieved by each chirped laser CP and LP pulse. Due to some unique property of the CP laser pulse, like a large acceleration phase channel and axial symmetry of the electromagnetic fields (EM), the acceleration gradient is expected to be higher in a chirped CP laser pulse than in a chirped LP laser pulse. A combination of periodically tapered wiggler magnetic field helps in stabilizing the transverse motion of the electron and projects one component of the laser's electric field in the direction of the electron motion, resulting in a higher energy gain. Laser parameters, like the amplitude, the initial phase of the laser and the laser frequency chirped parameter in addition to the tapered wiggler magnetic field parameters, all have strong influence on the electron energy gain. It is higher for the combination of a chirped CP laser with a circular wiggler magnetic field than for a chirped LP laser and a planar wiggler magnetic field. We show that energy gradients of several giga-electron-volts (GeV) per meter may be obtained when the parameters are adjusted in such a way to meet the IFEL resonance condition.X11sciescopuskc
ELECTRON ACCELERATION THROUGH THE EH01 WAVE MODE IN A MAGNETO COLLISIONAL PLASMA-FILLED CYLINDRICAL WAVEGUIDE
No full textA model is developed to study the effect of the electron collision frequency with background ions on EH01-mode field components, the dispersion characteristics, the trajectory and finally the electron energy gain. The hybrid EH01 mode propagating through a plasma-filled waveguide strongly influences the acceleration of electrons in the presence of an external static magnetic field. It can enhance the electron-energy gain by sustaining the electron in the accelerating phase of the EH01 mode wave. The dispersion equation is derived for the EH01 mode with the finite magnetic field, in particular, the electron- neutral collisions, taken into account. We show that due to electron collisions with the ions of the background plasma, proper choices of the parameter are essential for good operation in this region. The numerical results illustrate that the presence of the electron collision term in the dielectric tensor can reduce the electron's energy gain from 7.5 MeV to 4 MeV (in 2.5 cm along the waveguide length) in a magnetized plasma-filled waveguide.X117sciescopuskc
Measurement of the mass difference m(D-s(+))-m(D+) at CDF II
No full textWe present a measurement of the mass difference m(D-s(+))-m(D+), where both the D-s(+) and D+ are reconstructed in the phipi(+) decay channel. This measurement uses 11.6 pb(-1) of data collected by CDF II using the new displaced-track trigger. The mass difference is found to be m(D-s(+))-m(D+)=99.41+/-0.38(stat)+/-0.21(syst) MeV/c(2)
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