PROPOSED FIRST BEAMLINES FOR CANDLE

A conceptual pre-injector design for the KEK-ERL test accelerator

Carbon nanotube (CNT)-based cold cathodes are promising sources of field emission electrons for advanced electron devices, particularly for ultra-high-resolution imaging systems, due to their high brightness and low energy spread. While the electron field emission properties of single-tip CNT cathodes have been intensively studied in the last few decades, a systematic study of the influencing factors on the electron beam properties of CNT cold cathodes and the resolution of the secondary electron images has been overlooked in this field. Here, we have systematically investigated the effect of the structural properties of a CNT cold cathode on the electron beam properties and resolution of secondary electron microscope (SEM) images. The aspect ratio (geometric factor) and the diameter of the tip of a vertically standing CNT cold cathode significantly affect the electron beam properties, including the beam size and brightness, and consequently determine the resolution of the secondary electron images obtained by SEM systems equipped with a CNT cold cathode module. Theoretical simulation elucidated the dependence of the structural features of CNT cold cathodes and electron beam properties on the contribution of edge-emitted electrons to the total field emission current. Investigating the correlations between the structural properties of CNT cold cathodes, the properties of the emitted electron beams, and the resolution of the secondary electron images captured by SEM equipped with CNT cold cathode modules is highly important and informative as a basic model.

We propose an efficient scheme to produce ultrahigh-brightness tens of MeV electron beams by designing a density-tailored plasma to induce a wakefield in the weakly nonlinear regime with a moderate laser energy of 120 mJ. In this scheme, the second bucket of the wakefield can have a much lower phase velocity at the steep plasma density down-ramp than the first bucket and can be exploited to implement longitudinal electron injection at a lower laser intensity, leading to the generation of bright electron beams with ultralow emittance together with low energy spread. Three-dimensional particle-in-cell simulations are carried out and demonstrate that high-quality electron beams with a peak energy of 50 MeV, ultralow emittance of ∼28 nm rad, energy spread of 1%, charge of 4.4 pC, and short duration less than 5 fs can be obtained within a 1-mm-long tailored plasma density, resulting in an ultrahigh six-dimensional brightness B6D,n of ∼2 × 1017 A/m2/0.1%. By changing the density parameters, tunable bright electron beams with peak energies ranging from 5 to 70 MeV, a small emittance of ≤0.1 mm mrad, and a low energy spread at a few-percent level can be obtained. These bright MeV-class electron beams have a variety of potential applications, for example, as ultrafast electron probes for diffraction and imaging, in laboratory astrophysics, in coherent radiation source generation, and as injectors for GeV particle accelerators.

Signals of high-energy bremsstrahlung in the TRISTAN accumulation ring was observed with lead-glass counters, accompanied by a sudden decrease in the electron beam lifetime which occurred due to microparticle trapping in the electron beam. The observation showed a trapped microparticle made a periodic oscillation; the period was 1 s. The observation coincides with the result based on our newly developed theory for vertical oscillation of a trapped microparticle. Furthermore, the calculated variation in the beam lifetime also coincides with the actual variation in the beam lifetime. >

The effects of the phase variation, the evolution of the electron beam, the evolution of the radiation intensity, and the higher-order modes due to waveguides on a free-electron laser (FEL) oscillator have been analyzed by using two electron beams of different energies based on the proposed FEL facility which is to be operated in the far-infrared and infrared regions. The three-dimensional (3D) effects on a FEL oscillator due to waveguides and higher-order modes were studied using an extended 3D FEL code with two electron beams that we have developed. The effects of the variation on the amplitude of radiation on the electron beam's emittance and energy spreads were also calculated in the case of waveguide for multi-particle and multi-pass numbers by using a new 3D code. The phase variation, the variation in the beam envelope, the evolution of the amplitude, and power were calculated for the fundamental mode. The results were compared with those of the higher-order modes of the wiggler for various TE and TM modes for determining the FEL's performance which is required for high-quality electron beams.

Transverse coherence properties of X-ray beams in third-generation synchrotron radiation sources

Active harmonic EU cavity: Commissioning and operation with beam

Extended interaction oscillator (EIO) operated in the terahertz range puts greater demand on current density and brightness of electron beam. The pseudospark (PS)-sourced electron beam is a good candidate to drive such high frequency EIOs as it has a very high combined beam current density and brightness. This paper presents the numerical studies of oscillation startup time in a G-band EIO based on a pseudospark-sourced electron beam. It was found that the G-band EIO circuit's oscillation startup time and efficiency are relative to the gap length of it with the same period. The authors also present the latest results that demonstrate the successful design and optimization of G-band EIO driven by a 402 mA (500 A/cm2) PS-sourced electron beam. A peak power over 1.27 kW at 184 GHz was achieved using an electron beam, which can be generated by PS discharge.

This thesis describes the experimental and theoretical basics of free electron laser science, serving as an excellent introduction for newcomers to this young field. Beyond that, it addresses electron-beam lifetimes in third-generation synchrotron light sources, in particular with a view to optimizing them in the forthcoming ESRF upgrade. The lifetime of the electron beam in a storage ring is a measure of how fast electrons are being lost, and is thus an essential parameter determining the required injection frequency, which in turn affects beam stability and power consumption. The main limitation on the beam lifetime in these synchrotron light sources is the Touschek effect, i.e. the single scattering between two electrons in a bunch. In this thesis a model able to predict the Touschek lifetime is presented. The model is successfully tested against measurements and used to study the influence of other parameters such as current and size of vacuum chamber. Not least, it enables the settings of sextupole magnets to be optimized.

Bounds on the brightness and quality of fermion beams are derived from Pauli's exclusion principle and the finite density of quantum eigenstates for free fermions. These bounds are applied to electron-beam sources to derive limitations on the quality ( gamma J/ Delta gamma /sub z/) of the electron beams they generate. In the absence of electromagnetic fields, the quality of a relativistic electron beam of current density J and kinetic energy ( gamma -1)mc/sup 2/ cannot exceed (J gamma pi ec)/sup 1/2/ lambda /sub c//sup -3/2/, where lambda /sub c/ is the Compton wavelength. The normalized brightness cannot exceed 2 Delta gamma ecc lambda /sub c//sup -3/, where Delta gamma mc/sup 2/ is the electron energy spread, and will be 1/ pi times the beam quality for a beam of maximal quality. It is concluded that the qualities of electron beams produced by existing linear accelerators for free-electron lasers could be increased by six to eight orders of magnitude before reaching the quality limit. >

Cherenkov interaction and post-acceleration experiments of high brightness electron beams from a pseudospark discharge

A new technique for the growth of III–V compounds by molecular-beam epitaxy has been developed which uses electron beam heating for evaporating the group III liquid metals. The growth chamber is vertical and incorporates three large capacity 40 cc hearths for Ga, Al, and In. The metal beam fluxes are measured and feedback controlled using a chopped ion gauge signal detection scheme. The beam signal is input to a Eurotherm 820 digital controller which regulates the e-beam power supply and the control system is interfaced with an AT&T 3B2 computer. The dynamic response of the group III metal beam fluxes is very fast and well-controlled. The beam fluxes can be changed by two orders of magnitude in <10 s without oscillation. The beam flux can be precisely tailored through the digital controller over a very wide range. This enables the growth of variable band gap III–V alloys with almost arbitrary composition. In addition, the system geometry provides excellent uniformity over large diameter wafers. This technique appears very attractive for production of III–V epilayers.

The sensitivity of nonlinear harmonic generation to electron beam quality in free electron lasers

3D simulations on output power fluctuation in a short bunch rf-linac FEL

Linear colliders offer unique opportunity to study γγ,γe interactions. Using the laser backscattering method one can obtain γγ and γe colliding beams with the energy and luminosity comparable to that in e+e− collisions or even higher (due to absence of some beam collision effects). In order to reach ultimate parameters of photon colliders the “geometric” luminosity of initial electron beams should be higher than that in e+e− collisions. In this report requirements to beam emittances at photon colliders are analyzed and a novel method of obtaining electron beams with small transverse emittances is considered: the electron beam is cooled during a head-on collision with the focused powerful laser pulse. With reasonable laser parameters (laser flash energy about 10 J) one can decrease the transverse normalized emittances by a factor of 10 per one stage. A limit on the final (after few stages) transverse emittance of the electron beam is much lower than that given by other known methods.