The influence of the space charge fields on the dynamics of the particles of the bunch, which is moved in a bending magnet is calculated. It is shown, that such influence of the Coulomb force on the energy of the particles of a modulated beam causes in the decreasing of the bunch energy spread during the compression due to energy deviation along the compressed bunch, i.e. bunch cooling. The necessary conditions of the maximal cooling are found. The attainable ordering of the bunch is investigated.
Temporally-modulated electron beams have a wide array of applications ranging from the generation of coherently-enhanced electromagnetic radiation to the resonant excitation of electromagnetic wakefields in advanced-accelerator concepts. Likewise producing low-energy ultrashort microbunches could be useful for ultra-fast electron diffraction and new accelerator-based light-source concepts. In this Letter we propose and experimentally demonstrate a passive microbunching technique capable of forming a picosecond bunch train at $\sim 6$~MeV. The method relies on the excitation of electromagnetic …
High-brightness electron bunches, such as those generated and accelerated in free-electron lasers (FELs), can develop small-scale structure in the longitudinal phase space. This causes variations in the slice energy spread and current profile of the bunch which then undergo amplification, in an effect known as the microbunching instability. By imposing energy spread modulations on the bunch in the low-energy section of an accelerator, using an undulator and a modulated laser pulse in the centre of a dispersive chicane, it is possible tomanipulate the bunch longitudinal phase space. This allows…
We investigate numerically the detection of the self-modulation instability in a virtual detector located downstream from the plasma in the context of AWAKE. We show that the density structures, appearing in the temporally resolving virtual detector, map the transverse beam phase space distribution at the plasma exit. As a result, the proton bunch radius that appears to grow along the bunch in the detector results from the divergence increase along the bunch, related with the spatial growth of the self-modulated wakefields. In addition, asymmetric bunch structures in the detector are a result …
Simulation of longitudinal dynamics of laser-cooled and RF-bunched C$^{3+}$ ion beams at heavy ion storage ring CSRe
类锂重离子束的激光冷却正在实验冷却储存环（CSRe）上进行。最近，在CSRe进行了一项预备实验，以测试使用脉冲激光系统对相对论性$^{12}$ C $^{3+}$离子束进行激光冷却的重要先决条件。不幸的是，离子和脉冲激光之间的相互作用不能被检测到。为了研究激光冷却过程并为后续的激光冷却实验寻找最佳的冷却参数，采用多粒子跟踪方法模拟了CSRe中激光冷却离子束的详细纵向动力学过程.通过改变射频聚束器频率和连续波激光波长，对$^{12}$ C $^{3+}$离子束进行了激光冷却模拟。模拟结果表明，仅用一台连续激光器和射频聚束器就可以实现大动量扩散离子束的激光冷却，满足了激光冷却实验的要求。得到了射频聚束器频率或激光频率扫描的最佳参数。此外，估计的加热效应的激光冷却在CSRe。对纵向调制激光冷却离子束的肖特基噪声谱进行了数值模拟，充分解释和预测了实验结果。高灵敏度的谐振肖特基拾波器的肖特基谱和本文开发的模拟方法相结合，将有助于研究在CSRe即将进行的激光冷却实验中的RF聚束和超冷离子束的纵向动力学。
Seeded Self-modulation (SSM) has been demonstrated to transform a long proton bunch into many equidistant micro-bunches (e.g., the AWAKE case), which then resonantly excite strong wakefields. However, the wakefields in a uniform plasma suffer from a quick amplitude drop after reaching the peak. This is caused by a significant decrease of the wake phase velocity during self-modulation. A large number of protons slip out of focusing and decelerating regions and get lost, and thus cannot contribute to the wakefield growth. Previously suggested solutions incorporate a sharp or a linear plasma long…
Temporally-shaped electron bunches at ultrafast time scales are foreseen to support an array of applications including the development of small-footprint accelerator-based coherent light sources or as probes for, e.g., ultrafast electron-diffraction. We demonstrate a method where a transversely-segmented electron bunch produced via photoemission from a transversely-patterned laser distribution is transformed into an electron bunch with modulated temporal distribution. In essence, the presented transformation enables the mapping of the transverse laser distribution on a photocathode surface to …
A new method able to transport charged particle beams along curved paths is presented. It is based on curved capillary-discharge waveguides in which the induced azimuthal magnetic field is used both to focus the beam and keep it close to the capillary axis. We show that such a solution is highly tunable, it allows to develop compact structures providing large deflecting angles and, unlike conventional solutions based on bending magnets, preserves the beam longitudinal phase space. The latter feature, in particular, is very promising when dealing with ultra-short bunches for which non-trivial m…
We consider a semi-infinite open-ended cylindrical waveguide with uniform dielectric filling placed into collinear infinite vacuum waveguide with larger radius. Electromagnetic field produced by a point charge or Gaussian bunch moving along structure's axis from the dielectric waveguide into the vacuum one is investigated. We utilize the modified residue-calculus technique and obtain rigorous analytical solution of the problem by determining coefficients of mode excitation in each subarea of the structure. Numerical simulations in CST Particle Studio are also performed and an excellent agreeme…
Terahertz-based longitudinal phase space diagnostics of laser wakefield accelerated electron beams
Tsinghua University（清华大学）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；Beijing Academy of Quantum Information Sciences（北京量子信息科学研究院）
Of all nuclear physics experiments none are more fundamental than ``elastic'' $p,p$ and, secondarily, $p,d$ or $d,d$ scattering. Recognizing that these particles are themselves composite, ``elastic'' scattering may be accompanied by temporary internal rearrangement with undetectably small energy loss. % This paper argues that correct calculation of the spin dependence of $p,p$ elastic scattering must account for a previously-neglected relativistic effect of ``$G$'', the anomalous magnetic dipole moment (MDM) of the scattering particles and proceeds to describe storage ring $p,p$ scattering con…
