Erratum to: The catalytic effect of Al-KIT-5 and KIT-5-SO3H on the conversion of fructose to 5-hydroxymethylfurfural

Research on Chemical Intermediates -     

Scaling of accelerating gradients and dephasing effects in channel-guided laser wakefield accelerators

Future wakefield accelerator (LWFA) experiments are expected to operate in the short pulse resonant regime and employ some form of laser guiding, such as a preformed plasma channel. Performance of an LWFA may be characterized by the maximum axial electric field E_m, the dephasing length L_d, and the corresponding dephasing limited energy gain W_d. Dephasing is characterized by the normalized phase slippage rate Δβ_p, of the wakefield relative to a particle moving at the velocity of light. This paper presents analytical models for all of these quantities and compares them with results from simulations of channel-guided LWFAs. The simulations generally confirm the scaling predicted by the analytical models, agreeing within a few percent in most cases. The results show that with the proper choice of laser and channel parameters, the pulse will propagate at a nearly constant spot size r_M over many Rayleigh lengths and generate large accelerating electric fields. The spot size correction to the slippage rate is shown to be important in the LWFA regime, whereas Δβ_p, is essentially independent of laser intensity. An example is presented of a 25-TW, 100-fs laser pulse that produces a dephasing limited energy gain in excess of 1 GeV     

Analysis of the deflection system for a magnetic-field-immersedmagnicon amplifier

A linear analysis of the electron-beam deflection system in a magnicon amplifier is presented. The system consists of identical cavities, one driven and the remainder passive, separated by a drift space and immersed in an axial magnetic field. The cavities contain a rotating TM₁₁₀ mode. The length of each cavity is πν _z/ω, and that of the drift space is πν_z/ω_c, where ω is the RF frequency, ω_c is the relativistic gyrofrequency in the guide field, and ν_z is the mean axial velocity of the beam electrons. The linearized electron orbits are obtained for arbitrary initial axial velocity, radial coordinate, and magnetic field. The small-signal gain and the phase shift are determined. The special case where ω_c/ω=2 has unique features and is discussed in detail. For the NRL magnicon design, a power gain of 10 dB per passive cavity is feasible. Results from numerical modeling of a magnicon with two passive cavities are presented. Operation of the output cavity at the fundamental and higher harmonics of the input drive frequency is briefly discussed     

Theory of a rotating-mode coaxial infrared grating laser

Analysis is presented for a novel interaction that makes possible a compact infrared grating laser configuration. The laser utilizes an annular axis encircling beam that is confined by an axial magnetic field and passes along a grating blazed axially on the center conductor of a coaxial resonator. A smooth cylindrical outer conductor completes the Fabry-Perot resonator to provide the necessary feedback for sustained oscillation. Linear analysis leads to an eigenvalue equation for cavity resonance frequencies, start-oscillation currents, and a gain-bandwidth relationship. The latter permits estimation of an upper bound on the ideal-beam power extraction efficiency. The nonlinear studies make use of analytical and numerical methods to gain a detailed understanding of electron motion in the presence of both axially focusing and radio frequency fields, and to determine the nonlinear efficiency. There is significant degradation of the interaction efficiency when the beam has finite annular thickness. Efficiency enhancement by means of a down-tapered axial field is demonstrated. A point design for lasing at ~160 μm in the far-infrared, utilizing a 100-kV beam with a pitch angle of 55° is presented. The start-oscillation current is a sensitive function of the resonator quality factor (or finesse); for a well-designed resonator, it is on the order of tens of Amperes     

Study of gain in C-band deflection cavities for afrequency-doubling magnicon amplifier

An experimental study of the gain between two half-wavelength, 5.7-GHz TM₁₁₀ mode pillbox cavities, separated by a quarter-wavelength drift space, and powered by a 170-A, 500-keV electron beam immersed in an 8.1-kG magnetic field is reported. These cavities constitute the first section of a planned multicavity deflection system, whose purpose is to spin up an electron beam to high transverse momentum (α≡υ⊥/υ_z⩾1) for injection into the output cavity of a frequency-doubling magnicon amplifier. A gain of ~15 dB was observed in the preferred circular polarization, at a frequency shift of approximately -0.18%, in the opposite circular polarization, at a frequency shift of approximately +0.06%. These results are in good agreement with theory