[en] A Pierce-type mode analysis is presented for a planar electron beam in a rippled planar waveguide. This analysis describes the gain of a traveling-wave tube consisting of that geometry. The dispersion relation is given by the determinant of a matrix based on the coupling of different free-space modes through the boundary conditions. For the case of high-frequency, low-power amplifiers, the dispersion relation reduces to a simple cubic expression for the Compton regime, leading to three roots analogous to the Pierce solution of a standard traveling-wave tube. The analysis shows that this type of traveling-wave tube is capable of very high gain at extremely high frequencies

[en] This paper will review some of the recent developments in the area of high-brightness electron beams. Most of the paper will be devoted to emittance compensation concepts relating to high-brightness beam production in photoinjectors. Recent interpretation of emittance compensation and the residual emittance after compensation in terms of wave breaking has provided valuable insights into the process. Wave breaking also appears to have an influence on emittance growth and halo production in transport lines, which we will briefly discuss. There has been advances in understanding the emittance growth of bunches in circular motion, particularly related to the cancellation of longitudinal and transverse energy-independent forces. Finally, some non-intercepting bunch length and emittance diagnostic approaches will be reviewed

[en] A mode analysis is presented for the case of a planar electron beam in a ridged waveguide slow-wave structure. By matching boundary conditions between a Fourier expansion of the mode between the ridges with a space-harmonic expansion of the mode in the region below the ridges, a dispersion relation for a traveling-wave interaction is found. The dispersion relation is numerically solved for both the case with and without beam. For the nominal geometry, gains as high as 30 dB/cm at 300 GHz are found for a 15 A, 155 keV beam

[en] A small-signal gain analysis of the planar dielectric Cherenkov maser is presented. The analysis results in a Pierce gain solution, with three traveling-wave modes. The analysis shows that the dielectric Cherenkov maser has a remarkable broadband tuning ability near cutoff, while maintaining reasonable gain rates. Numerical simulations verifying the small-signal gain results are presented, using a particle-in-cell code adapted specifically for planar traveling-wave tubes. An instantaneous bandwidth is numerically shown to be very large, and saturated efficiency for a nominal high-power design is shown to be in the range of standard untapered traveling-wave tubes

[en] Modeling a 3-dimensional (3-D) elliptical beam with a 212-D particle-in-cell (PIC) code requires a reduction in the beam parameters. The 212-D PIC code can only model the center slice of the sheet beam, but that can still provide useful information about the beam transport and distribution evolution, even if the beam is emittance dominated. The reduction of beam parameters and resulting interpretation of the simulation is straightforward, but not trivial. In this paper, we describe the beam parameter reduction and emittance issues related to the initial beam distribution. As a numerical example, we use the case of a sheet beam designed for use with a planar traveling-wave amplifier for high power generator for RF ranging from 95 to 300GHz [Carlsten et al., IEEE Trans. Plasma Sci. 33 (2005) 85]. These numerical techniques also apply to modeling high-energy elliptical bunches in RF accelerators

[en] We will quickly go through the history of the non-linear transmission lines (NLTLs). We will describe how they work, how they are modeled and how they are designed. Note that the field of high power, NLTL microwave sources is still under development, so this is just a snap shot of their current state. Topics discussed are: (1) Introduction to solitons and the KdV equation; (2) The lumped element non-linear transmission line; (3) Solution of the KdV equation; (4) Non-linear transmission lines at microwave frequencies; (5) Numerical methods for NLTL analysis; (6) Unipolar versus bipolar input; (7) High power NLTL pioneers; (8) Resistive versus reactive load; (9) Non-lineaer dielectrics; and (10) Effect of losses.

[en] Here we present the first analysis of a new device called the bi-resonant klynac, which is a combined klystron and linac. In a bi-resonant klynac, all RF cells, except for the cell that acts as the input for the klystron section, belong to a single resonant circuit. This resonant coupling configuration leads to increased operational stability and can tolerate significant temperature variations. In this paper, a basic analysis of this device is presented, including discussions of how it operates and of the advantages of resonantly coupling the RF generation directly to the linac. We additionally describe the approach used to numerically model the klynac and we include detailed simulations of a 50-kV, 10-A klynac that produces a 1-MeV, 0.1-A output beam. This type of device may be especially useful for situations where an electron beam is needed at low cost.

[en] We describe a conceptual proposal to combine the Dielectric Wakefield Accelerator (DWA) with the Emittance Exchanger (EEX) to demonstrate a high-brightness DWA with a gradient of above 100 MV/m and less than 0.1% induced energy spread in the accelerated beam. We currently evaluate the DWA concept as a performance upgrade for the future LANL signature facility MaRIE with the goal of significantly reducing the electron beam energy spread. The preconceptual design for MaRIE is underway at LANL, with the design of the electron linear accelerator being one of the main research goals. Although generally the baseline design needs to be conservative and rely on existing technology, any future upgrade would immediately call for looking into the advanced accelerator concepts capable of boosting the electron beam energy up by a few GeV in a very short distance without degrading the beam's quality. Scoping studies have identified large induced energy spreads as the major cause of beam quality degradation in high-gradient advanced accelerators for free-electron lasers. We describe simulations demonstrating that trapezoidal bunch shapes can be used in a DWA to greatly reduce the induced beam energy spread, and, in doing so, also preserve the beam brightness at levels never previously achieved. This concept has the potential to advance DWA technology to a level that would make it suitable for the upgrades of the proposed Los Alamos MaRIE signature facility.

[en] A novel approach to producing short-wavelength radiation is proposed, where two offset electron beams of slightly different energies are merged within a dipole magnet and interact. With proper modulation of the two beams, the two-stream instability can be exploited to efficiently generate narrow-band millimeter-wave radiation. This type of source dispenses with the problematic structure required in other generation mechanisms and eliminates complex machining, delicate alignment, expensive parts, and catastrophic failures. Preliminary simulations have shown promise for a 100-GHz design, which is also scalable to 1 THz. This concept requires only low-voltage, low-current electron beams and could lead to a device capable of generating up to 100 W at 1 THz, while remaining simple and compact.

[en] Currently ongoing at Los Alamos National Laboratory is a program to develop high-power, planar 100-300 GHz traveling-wave tubes. An enabling technology for this effort is a sheet electron beam source and much of our effort has been geared toward understanding sheet beam generation and transport. Toward this end we have developed a robust, high resolution optical diagnostic for measuring the transverse density profiles of our electron beams. The diagnostic consists of a thin metal foil followed by an YAG:Ce or YAP:Ce scintillator crystal, both mounted on a vacuum actuator that allows us to position the foil/scintillator combination at arbitrary positions along the beam's longitudinal axis. The electron beam strikes the metal foil and is stopped, generating Bremsstrahlung x rays that are imaged by the scintillator crystal. This image is then captured by an optical system using a high-speed, intensified gated camera. Using this diagnostic, we have measured beam profiles with resolutions as low as 0.05 mm from a 0.51 μP electron gun operated between 20 and 120 kV