Abstract
In this paper, wakefields driven by a relativistic electron beam in a cold homogeneous plasma are studied using 2D fluid simulation techniques. It has been shown that in the limit when the transverse size of a rigid beam is greater than the longitudinal extension, the wake wave acquires a purely electrostatic form, and the simulation results show a good agreement with the 1D results given by Bera et al. [Phys. Plasmas 22, 073109 (2015)]. In the other limit when the transverse dimensions are equal to or smaller than the longitudinal extension, the wake waves are electromagnetic in nature, and 2D effects play a crucial role. Furthermore, a linear theoretical analysis of 2D wakefields for a rigid bi-parabolic beam has also been carried out and compared with the simulations. It has also been shown that the transformer ratio, which is a key parameter that measures the efficiency in the process of acceleration, becomes higher for a 2D system (i.e., for a beam having a smaller transverse extension compared to the longitudinal length) than the 1D system (i.e., for a beam having a larger transverse extension compared to the longitudinal length). Furthermore, including the self-consistent evolution of the driver beam in the simulation, we have seen that the beam propagating inside the plasma undergoes transverse pinching, which occurs much earlier than the longitudinal modification. Due to the presence of transverse dimensions in the system, the 1D rigidity limit given by Tsiklauri [Phys. Plasmas 25, 032114 (2018)] gets modified. We have also demonstrated the modified rigidity limit for the driver beam in a 2D beam–plasma system.
Highlights
During the past two decades of research, the plasma wakefield acceleration (PWFA) scheme has unarguably made amazing progress because of its applications, which widely range from medical to industry to high energy physics.1–4 The scheme uses extremely large electric fields associated with plasma waves to accelerate charge particles
In the simulation, when the transverse dimensions of a rigid bi-Gaussian beam are greater than their longitudinal extension, we have observed that the wake wave excited by the beam acquires a pure electrostatic form
We have used rigid beam approximation for the first set of simulations to illustrate the effect of finite transverse beam size on excitation
Summary
Scitation.org/journal/adv to boost the energy of the existing linacs. Success of this scheme has been demonstrated in a number of experiments by accelerating electrons up to GeV energies. We report a detailed study of the relativistic electron beam driven wakefield in a cold plasma using 2D fluid simulation techniques. Including the self-consistent evolution of the driver beam in the simulations [fluid as well as particle-in-cell (PIC)], we have studied the rigidity of the driver beam. PIC simulations are mainly used to support and validate the fluid results Using both these simulation techniques, it has been shown that the relativistic driver beam propagating through a cold homogeneous plasma undergoes transverse pinching that gives rise to the beam density along the beam direction. Due to pinching in the transverse direction, we have shown that the rigidity limit in terms of beam velocity (vrb = 0.9999c) given by Tsiklauri for 1D cases gets modified.
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