Control of the Longitudinal Compression and Transverse Focus of Ultrafast Electron Beam for Detecting the Transient Evolution of Materials

Ultrafast detection is an effective method to reveal the transient evolution mechanism of materials. Compared with ultra-fast X-ray diffraction (XRD), the ultra-fast electron beam is increasingly adopted because the larger scattering cross-section is less harmful to the sample. The keV single-shot ultra-fast electron imaging system has been widely used with its compact structure and easy integration. To achieve both the single pulse imaging and the ultra-high temporal resolution, magnetic lenses are typically used for transverse focus to increase signal strength, while radio frequency (RF) cavities are generally utilized for longitudinal compression to improve temporal resolution. However, the detection signal is relatively weak due to the Coulomb force between electrons. Moreover, the effect of RF compression on the transverse focus is usually ignored. We established a particle tracking model to simulate the electron pulse propagation based on the 1-D fluid equation and the 2-D mean-field equation. Under considering the relativity effect and Coulomb force, the impact of RF compression on the transverse focus was studied by solving the fifth-order Rung–Kutta equation. The results show that the RF cavity is not only a key component of longitudinal compression but also affects the transverse focusing. While the effect of transverse focus on longitudinal duration is negligible. By adjusting the position and compression strength of the RF cavity, the beam spot radius can be reduced from 100 μm to 30 μm under the simulation conditions in this paper. When the number of single pulse electrons remains constant, the electrons density incident on the sample could be increased from 3.18×1012 m−2 to 3.54×1013 m−2, which is 11 times the original. The larger the electron density incident on the sample, the greater the signal intensity, which is more conducive to detecting the transient evolution of the material.

Electromagnetic Simulations and Measurements of the K-800 Superconducting Cyclotron RF Cavity at INFN-LNS

In this paper, a complete three-dimensional (3D) RF model of the cyclotron coaxial resonator—including the coaxial sliding shorts, the “Liner” vacuum chamber, the coupler, the trimmer, and the high RF voltage “Dee” structures—has been developed. An eigenmode analysis was used to simulate the tuning of the resonator in the operating frequency range of 15–48 MHz obtained by two movable sliding shorts and a trimmer. A driven analysis has been performed in order to compute the |S11| parameter (or impedance matching) of the cavity excited by a movable coaxial power coupler. The numerical simulations have been performed using the different peculiarities of two commercial tools, COMSOL Multiphysics and CST microwave studio. Experimental validation of the developed model is presented. The evidence of an unwanted electric field component, orthogonal to the accelerating field, was discovered and a mitigation is also proposed. The impact of the proposed modification was evaluated by using a 3D beam dynamics code under development in the framework of the Superconducting Cyclotron upgrade ongoing at INFN-LNS.

Signs of ultra-high-energy electrons emission with energy up to 105 times of beam energy are detected at downstream of the RF cavity of storage ring

In a new version of special relativity that absorbed the uncertainty principle, the Einstein-Lorentz mass formula proved to be a special case of a more universal equation. The new equation indicates that there is a “high speed but low mass” weak effect in particle motion, which will cause the generation of abnormal ultra-high energy electrons with a small probability when an electron beam passes through an accelerating electric field. The author used the method of long-times accumulation detection to test it on the BEPCII, which results show that there is indeed emission of abnormal electrons with energy up to 105 times of the beam energy at the downstream of the RF cavity of the electron storage ring. Therefor, it is suggested to use the detector with an online real-time display function, such as the “Shashlyk calorimeter”, to detect the single event of ultra-high energy electron, so to fully verify this previously unknown phenomenon and further discover new physics.

At the downstream of the RF cavity of the electron storage ring there is emission of abnormal ultra-high energy electrons with energy up to 105 times of the beam energy

After considering Heisenberg's uncertainty principle, the mass-speed relationship of special relativity i.e. the Einstein-Lorentz mass formula can be extended to a more complete equation, which predicts that abnormal ultra-high energy electrons will be generated with a small probability when the electron beam passes through an accelerating electric field. The author used the accumulating detection method of a large number of events to test at the electron storage ring of BEPCII, of which results show that under the beam energy of 2GeV there is emission of abnormal ultra-high energy electrons with the highest energy reaching 400TeV at downstream of the RF cavity. For this reason, it is recommended that particle physicists conduct more experiments to fully verify this previously unknown phenomenon and further discover new physics.