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Register a new userIncrease of amplitude of accelerating wakefield excited by sequence of short relativistic electron bunches in plasma at magnetic field use
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Earlier, the authors found a mechanism for the sequence of short relativistic electron bunches, which leads to resonant excitation of the wakefield, even if the repetition frequency of bunches differs from the plasma frequency. In this case, the synchronization of frequencies is restored due to defocusing of the bunches which get into the bad phases with respect to the plasma wave. However, in this case, the bunches are lost, which as a result of this do not participate in the excitation of the wakefield. In this paper, numerical simulation was used to study the dynamics of electron bunches and the excitation of the wakefield in a magnetized plasma by a long sequence of short bunches of relativistic electrons. When a magnetic field is used, the defocussed bunches return to the region of interaction with the field after a certain time. In this case, the electrons of the bunches, returning to the necessary phases of the field, participate in the excitation of the wakefield. Also, the use of a magnetic field leads to an increase of the frequency of the excited wave relative to the repetition frequency of bunches. The latter increases the time for maintaining the resonance and, consequently, leads to an increase of the amplitude of the excited wakefield.
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Plasma wake lens in which all short relativistic electron bunches of sequence are focused identically and uniformly is studied analytically and by numerical simulation. For two types of lenses necessary parameters of focused sequence of relativistic electron bunches are formulated. Verification of these parameters is performed by numerical simulation.
Drive particle beams in linear or weakly nonlinear regimes of the plasma wakefield accelerator quickly reach a radial equilibrium with the wakefield, which is described in detail for the first time. The equilibrium beam state and self-consistent wakefields are obtained by combining analytical relationships, numerical integration, and first-principle simulations. In the equilibrium state, the beam density is strongly peaked near the axis, the beam radius is constant along the beam, and longitudinal variation of the focusing strength is balanced by varying beam emittance. The transverse momentum distribution of beam particles depends on the observation radius and is neither separable, nor Gaussian.
We propose a new method for analytical self-consistent description of the excitation of a strongly nonlinear wakefield (a bubble) excited by an electron bunch. This method makes it possible to calculate the shape of the bubble and the distribution of the electric field in it based only on the properties of the driver, without relying on any additional parameters. The analytical results are verified by particle-in-cell simulations and show good correspondence. A complete analytical solution for cylindrical drivers and scaling laws for the properties of the bubble and other plasma accelerator parameters depending on the bunch charge and length are derived.
Dynamics of self-injected electron bunches has been numerically simulated in blowout regime at self-consistent change of electron bunch acceleration by plasma wakefield, excited by a laser pulse, to additional their acceleration by wakefield, excited by self-injected bunch. Advantages of acceleration by pulse train and bunch self-cleaning have been considered.
Plasma-based accelerators sustain accelerating gradients which are several orders greater than obtained in conventional accelerators. Focusing of electron and positron beams by wakefield, excited in plasma, in electron-positron collider is very important. The focusing mechanism in the plasma, in which all electron bunches of a sequence are focused identically, has been proposed by authors earlier. The mechanism of focusing of a sequence of relativistic positron bunches in plasma, in which all positron bunches of sequence are focused identically and uniformly, has been investigated in this paper by numerical simulation by 2.5D code LCODE. We numerically simulate the self-consistent radial dynamics of lengthy positron bunches in homogeneous plasma. In simulation we use the hydrodynamic description of plasma. In other words, the plasma is considered to be cold electron liquid, and positron bunches are aggregate of macroparticles. Positron bunches are considered to be homogeneous cylinders in the longitudinal direction. Positrons in bunches are distributed in radial direction according to Gaussian distribution. It is shown that in this case only first bunch is in the finite longitudinal electrical wakefield notequal to zero. Other bunches are in zero longitudinal electrical wakefield Ez=0. Between bunches of this sequence longitudinal electrical wakefield and radial force are not zero. The focusing radial force in regions, occupied by bunches, is constant along each bunch Fr=const. Between bunches the radial force is inhomogeneous. All positron bunches of sequence are focused identically and uniformly.
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