Coherent interaction of ion and electron beams in systems with electron cooling

A hydrodynamic approximation is used to study the behavior of dipole modes of the transverse oscillations of an ion beam in a storage ring with an electron cooling section. It is shown that in addition to the finite interaction time of the beams, instability may be caused by a specific interaction effect between the ion and electron beams in the magnetic field which leads to redistribution of energy between the various modes of the ion beam oscillations. In this case, the condition that the determinant of the transfer matrix for the cooling section does not exceed unity no longer guarantees the stability of the transverse coherent oscillations of the ion beam and all the eigenvalues of the complete matrix of the ion motion including the storage ring must be analyzed. Calculations of the stability of ion beam dipole oscillations are presented for the parameters of CELSIUS.     

Transverse cooling of electron beams

The possibility of cyclotron maser cooling of the transverse motion of electrons in a beam with the oblate velocity distribution characteristic of the setups with electron cooling has been analyzed.     

Towards cooling of high-intensity ion beams

Buffer gas beam coolers may become excellent beam preparation devices for high-resolution mass separation. The small beam emittance provided makes efficient isobar resolution a realistic goal. In order to fulfill the needs of future facilities providing high-intensity beams of rare isotopes, it is desirable to increase the beam intensity limit of such devices from typically several tens of nanoamperes to microamperes. This requires the usage of high-voltage radiofrequencies in a low-pressure gas environment. A buffer gas beam cooler, dedicated to this purpose, is under development at the NSCL. The study of voltage breakdowns under such conditions and the design of an electrode system minimizing them is mandatory.      

离子通道电子束回旋脉塞的等离子体波效应

研究了离子通道回旋电子束脉塞（ICECM）中的等离子体波非线性效应。利用流体理论与自洽非线性理论方法对ICECM中等离子体波效应的微观机理进行了分析。研究发现,等离子体波加强了电子束的纵向群聚,束-波互作用的能量交换效率及系统增益得到明显提高。数值模拟计算表明,对于中等等离子体密度、1.5kA电流和1MV加速电压的电子束,系统能够获得的脉冲功率和频率分别为200MW和280GHz的毫米波束。     

离子通道电子束回旋脉塞的等离子体波效应

 研究了离子通道回旋电子束脉塞（ICECM）中的等离子体波非线性效应。利用流体理论与自洽非线性理论方法对ICECM中等离子体波效应的微观机理进行了分析。研究发现，等离子体波加强了电子束的纵向群聚，束-波互作用的能量交换效率及系统增益得到明显提高。数值模拟计算表明，对于中等等离子体密度、1.5kA电流和1MV加速电压的电子束，系统能够获得的脉冲功率和频率分别为200MW和280GHz的毫米波束。     

Tapered laser cooling of stored coasting ion beams

We propose a scheme for tapered laser cooling of coasting ion beams in storage rings. Tapered cooling has recently been shown to be crucial for attaining crystalline ion beams. The scheme proposed here, based on a relative displacement of a co- and a counterpropagating Gaussian laser beam, gives a radial variation in the equilibrium velocities to which particles are cooled. The variation is approximately linear in a relatively large range transverse to the laser beams. Expressions for the spatially dependent equilibrium velocities and the range of the tapered cooling forces are derived. We discuss the dependence on laser beam parameters as well as the limitations of this cooling scheme.     

Cyclotron autoresonance maser with high Doppler frequency up-conversion

An LIA-unit with explosive emission injector was used as a basis for CARM with high Doppler frequency up-conversion when the wave frequency is 7 to 9 times the cyclotron frequency of electrons. Using a high-selectivity Bragg resonator as an electrodynamic system of CARM we investigated two regimes having essentially different properties: the dispersion characteristics of the electron beam and the wave either intersected or were tangential to one another. In the first case, the radiation power amounted to 50 MW at the wavelength of 4.4 mm with efficiency 8%. The efficiency significantly smaller than the design value was evidently caused by a high level of parasitic superluminiscence of the beam. In the second regime of operation at 6 mm, the radiation power was 30 MW with a low level of parasitic superluminiscence and efficiency 10% which was close to the calculated value.     

Cyclotron resonance maser as a solar flare trigger

We propose a new mechanism of solar flaring, which is based on explosive phenomena in magnetic traps in the presence of a two-component plasma composed of fast electrons with anisotropic velocity distribution and a dense cold background plasma with high ionization. It is assumed that such a plasma is generated in a coronal magnetic trap in a preflare stage. This system, which is essentially a cyclotron resonance maser, becomes unstable under certain conditions and gives rise to an explosive cyclotron instability, which develops at first in a very small local area and is accompanied by intense heating of the background plasma and release of fast electrons at the trap ends. The energy of fast particles is collected from the entire volume of the magnetic trap and is localized in the form of heat in the explosion area from which thermal and shock waves are propagated. The model makes it possible to explain the main solar flare effects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 6, pp. 699–712, June, 1996.     

Processing of vacuum microelectronic devices by focused ion and electron beams

Localized physical and chemical reactions induced by focused ion and electron beams, i.e. dual beams, have been used to fabricate field emitters (FEs) and their arrays, field-emitter arrays (FEAs), without masking and annealing processes. Issues arising from beam processing such as beam-induced damage and contamination were eliminated to provide FEAs with low leakage current. Quick prototyping and repairing processes of FEs and FEAs using dual-beam processing have been demonstrated. Nb- or Au-gated Pt FEAs have been fabricated using dual beams. The fabricated FEAs showed a turn-on voltage of 40 V for field emission with a typical emission current of about 1 μA/tip. Received: 21 August 2002 / Accepted: 21 August 2002 / Published online: 12 February 2003 RID="*" ID="*"Corresponding author. Fax: +81-6/6850-6662, E-mail: takai@rcem.osaka-u.ac.jp     

Dynamics of laser beams in inhomogeneous electron positron ion plasmas

Nonlinear interaction of laser and electron–positron–ion plasmas is investigated by invoking the variational principle and numerical simulation, in terms of a nonlinear Schr o¨dinger equation with inhomogeneities effect. It is shown that the plasma inhomogeneity has great influence on the laser beam dynamics. The laser beam can be self-trapped, focused, or defocused depending on the inhomogeneity character. The linearly decreasing axial plasma density makes the laser beam defocus, while the linearly increasing axial plasma density results in self-trapping of the beam. The self-focusing of the trapped beam is found in a high-density region. For the Gaussian types of density distribution, the beam field submits nonlinearly oscillating regime. The results provide an efficient way to manipulate the dynamics of laser beam propagating in plasma.     

单电子回旋辐射

由来自美国和德国的科学家组成的合作组正在进行一项称作Project8 的实验,探测做轨道转动的单个电子发出的辐射频率。这一频率,从而电子的能量,可以非常精确地测量。如果能够进一步提高能量分辨率,Project 8 实验可能成为一种新的测量中微子质量的方法。实验装置的核心是一个小的低压气室,放置在1 T 的磁铁内。气室中含有少量的氪-83 气体,当其原子核发生β衰变时产生电子。这些电子在磁场作用下沿圆形轨道运动,同时发射出频率大约为25 GHz的回旋辐射,可以用灵敏的微波放大器探测。在探测到的辐射功率随时间和频率变化的关系图中,向斜上方排列的辐射条纹是单个电子发出的辐射(见附图)。理论上已知,做圆周运动的电子会连续地发出辐射,导致电子逐渐损失能量,转动速率随着时间线性增加。所探测到的辐射条纹具有理论预言的线性关系。据此,研究人员将这些条纹与单个电子联系起来(图中频率的跃增对应于电子与气室中剩余的原子或分子的碰撞)。通过测量与第一个条纹相关的频率,能够确定氪-83 核发射的电子能量,精度达到30 eV。     

三维电子回旋脉塞的数值模拟研究

为了打破二维模拟回旋脉塞的一些局限性,研究了电子回旋受激辐射的基本原理,使用唯象的描述方法,以统计物理学为基础,在电子回旋中心坐标系中完成了三维Yee网格模型中对电子注平衡态物理模型的数值建模,并结合PIC方法和FDTD算法进行电子回旋脉塞的数值模拟.为了减少计算时间,在模拟中加入了MPI并行算法,加速比能提高到2.7以上.最后以一个94 GHz的回旋振荡管为例,对它的整体结构进行了模拟,并通过对频谱,功率,工作模式等方面验证了模拟的正确性. 关键词： 电子回旋脉塞 Yee网格模型 PIC方法 FDTD算法     

A long-pulse millimeter-wave free electron maser

An experimental free electron maser (FEM) facility is described which operates in the millimeter-wave regime. The experiment demonstrates that high gain and beam extraction efficiency can be obtained with low-current but high-quality electron beams. In the oscillator configuration, microwave powers of 110 kW were achieved with a 300-kV, 4-A beam, corresponding to a beam extraction efficiency of 9.2%. At low beam currents, with the system operating in the linear regime, the FEM gain curve was measured. The experiment uses a Pierce-type gun with a calculated beam emittance of 10.7-mm mrad at 300 kV and 4 A. The wiggler is of the iron permanent magnet hybrid design. The experiment is intended as a first step towards the development of continuous-wave (CW) devices that use beam energy recovery to make use of low-current, high-voltage power supplies     

Analysis of the electron cyclotron maser instability

A single nonlinear equation which describes the temporal evolution of the field amplitude of the electron cyclotron maser instability is derived self-consistently. The results deduced from this nonlinear equation are found to agree well with those of particle simulation.