Effect of the space charge of emitted electrons on field electron emission

It is shown that the conventional technique of substituting the field strength at the space charge-emitter interface that is calculated with the Poisson equation into the Fowler-Nordheim formula considerably overestimates the effect of space charge on field electron emission. In this work, the space-charge-induced field attenuation as a function of the emission current density and radius of curvature of the emitter surface is derived using the model of a planar space-charge layer. It is argued that field electron emission cannot be studied in terms of the spherical diode model, since it assumes the presence of a space charge on the back (nonemitting) emitter surface, which is in fact absent. It is stated that one should consider the discrete character of the charges when investigating the space charge in field electron emission, because the mean spacing between the electrons emitted far exceeds the emission barrier width.     

北京自由电子激光器的光学速调管结构

采用KMR方程,结合即将运转的北京自由电子激光器总体实验参数,对其光学速调管结构研究.详细分析计算输入功率、电子束能散度、色散磁场、漂移空间长度及位置、以及电子束流等参数对光学速调管增益的影响.基于北京自由电子激光器的振荡器结构,提出一组对电子束能散度要求适中的实用化光学速调管参数.并对其饱和功率、功率谱以及渐变摆动器进行分析.     

Gain enhancement in two-stream free electron laser with planar wiggler and axial guide magnetic field

The theory for the two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

Side-effects of the space charge field introduced by a hollow electron beam in the electron cooler of CSRm

An electron cooler is used to improve the quality of the ion beam in a synchrotron;however it also introduces a nonlinear electromagnetic field to the accelerator,which causes tune shift,tune spread and may drive resonances leading to ion beam loss.In this paper the tune shift and the tune spread caused by the nonlinear electromagnetic field of a hollow electron beam is investigated,and the resonance driving terms of the nonlinear electromagnetic field are analysed.The differences are presented compared with a solid electron beam.Calculations are performed for ~(238)U~(32+) ion of energy 1.272 MeV stored in the main Cooler Storage Ring(CSRm) at the Institute of Modern Physics,Lanzhou.It is found that in this situation the nonlinear field caused by the hollow electron beam does not lead to serious resonances.     

One-body electron dynamics in a free electron laser

The free electron laser is analyzed by solving the one-body classical Lorentz force equation in the presence of periodic magnetic field and a plane electromagnetic wave. Phase space paths for electrons are related to those of a simple pendulum and describe laser gain, saturation, and coherent electron beam modulation.     

Betatron-synchrotron resonance in free electron laser

In terms of Bogoliubov's nonlinear theory, the first five betatron-synchrotron resonances of _s=(p q)2K, p/q=1/2, 1, 3/2, 1/3, 2/3 which may occur during laser satulation establishing process have been generally examined. Contrast to previous studies we found that the most dangerous resonance does not take place in the vicinity of _s=2k, but in that of _s=k. The width of region of _s=k is proportional to with (k _w ² /k) remittance, the passing time over the region due to the laser field being amplified is only one pass over the undulator at most and depends on the gain, and the increment of synchrotron amplitude in passing time is proportional to .In summary we conclude that the betatron-synchrotron resonances do not have any significant effect for detrapping off-axis electrons in a practical case.     

Chaos in free electron laser oscillators

The chaotic nature of a storage-ring free electron laser (FEL) is investigated. The derivation of a low embedding dimension for the dynamics allows the low-dimensionality of this complex system to be observed, whereas its unpredictability is demonstrated, in some ranges of parameters, by a positive Lyapounov exponent. The route to chaos is then explored by tuning a single control parameter, and a period-doubling cascade is evidenced, as well as intermittence.     

Study of free electron laser performance with external focusing

The influence of the focusing system on the characteristics of radiation of free electron lasers (FEL) is investigated. The results of numerical simulations for European XFEL project are presented. The versions with standard periodic focusing and with natural undulator focusing are considered. A new system of central focusing with a minimum number of quadrupole lenses is proposed.     

自由电子激光器的掠射环形谐振腔

研究一种新型自由电子激光谐振腔结构.采用双曲面-抛物面非球面镜组合的扩束系统,使振荡光束在腔内口径扩大6倍.提高了反射膜层抗激光破坏能力.本文讨论了扩束倍数、非球面参量、谐振腔长度和掠射光斑尺寸等参量对光学系统像差的影响.     

A compact free electron laser investigation

An electron beam source based on pseudospark discharge was successful in operation at the beam voltage of 200keV and beam current of 2kA. The detailed design of a compact free electron laser using an electron beam by a pseudospark discharge is described. The compact free electron laser consists of a smaller Marx generator with 6 capacitors and switches, a water capacitance of 6nF and a beam source with a high brightness of 3×10¹¹ A/(m rad)². The computer simulation shows that an output power of 101MW is expected at a frequency of 38GHz with a beam energy of 300keV, a current of 2kA and a beam emittance of 48mm mraa.     

Photo-acoustic spectroscopy of polymer with infrared free electron laser

We have been proposing a new photo acoustic spectroscopy (PAS) method with an infrared free electron laser (IR-FEL). The IR-FEL is a continuous tunable laser in the lasing wavelength in an finger-print wavelength region with high peak power. The IR-FEL resonantly induce the specific molecular vibration of the samples, resulting casue the photo acoustic pheneomena with high sensitivity. Thus, the new PAS method with the IR-FEL is high sensitive analysis method applicable to low absorbance measurement. In this study we show the feasibility of application of the MIR-FEL to the photon source of the PAS method by measuring the PAS spectrum of polymers such as a poly ethylene terephthalate (PET) film. In addition, we construct an imaging system of the FEL-PAS to make a map of the PAS signal with a high spatial resolution that is a diffraction limit of the IR-FEL.     

Numerical investigation of space charge electric field for a sheet electron beam between two conducting planes

Analytical and numerical study of the stability of sheet electron beam in periodically cusped magnetic field (PCM) is made. The beam has been considered as having diffused density profile. The conditions for beam focusing are discussed.     

Chaotic electron trajectories in a circular free electron laser

The motion of a relativistic electron is analyzed in the field configuration consisting of a circular wiggler magnetic field, an axial magnetic field, and the equilibrium self-electric and self-magnetic fields produced by the non-neutral electron ring. By generating Poincare surface-of-section maps, it is shown that when the equilibrium self-fields is strong enough, the electron motions become chaotic. Although the realistic circular wiggler magnetic field destroys the integrability of the electron motion as the equilibrium self-fields do, the role the latter plays to make the motions become chaotic is stronger than the former. In addition, the axial magnetic field can restrain the occurrence of the chaoticity.     

Gain enhancement in two-stream free electron laser with a planar wiggler and an axial guide magnetic field

The theory for a two-stream free electron laser (FEL) consisting of a relativistic electron beam transported along the axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.     

Macroscopic space charge field in disturbed quasineutral plasma

A method of calculation of the electric field intensity in a quasineutral plasma homogeneity of which is disturbed is found for the case when the problem can be formulated as one-dimensional. The general formula (19) comprising the Ohm's law, ambipolar approximation and higher approximations of the space charge electric field intensity, expressed in terms of deviationn ₊ in ion density and its derivatives, is found and the values of the errors of these approximations are derived. Numerical calculations for the sinusoidal as well as for the Gaussian form of the perturbation in the ion concentration are carried out.