KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
Focusing of both electron and positron bunches in an electron-positron collider is necessary. The focusing mechanism in the plasma, in which all electron bunches are focused identically, has been proposed earlier*. This mechanism is considered for positron bunches by using simulation with LCODE**. Three types of lenses with different trains of cosine profile positron bunches are considered depending on the bunch length, the distance between bunches, and their charge. It has been shown that all positron bunches are focused identically at special parameters of the first positron bunch, wherein the middle of bunches are focused weaker than their fronts.
* V. I. Maslov et al. PAST. 3(2012) 159.
** K. V. Lotov, Phys. Plas. 5 (1998) 785.
KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
PIC simulation by means of 2.5D UMKA code * of the wakefield excitation by a sequence of three Gaussian laser pulses in plasma was carried out. The dependence of excited wakefield intensity on power and width of laser pulses was investigated. It was shown the coherent addition of wakefield, excited by each laser pulse of the sequence, for linear case, while for the nonlinear case the coherency was destroyed. The profiled sequence of laser pulses was also considered. The possibility to obtain the same total wakefield excited by the profiled sequence of laser pulses with decreasing intensity, as for the uniform sequence was studied.
* G. I. Dudnikova et al. Comp. Techn. 10 (2005) 37.
KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
Recently the proposal to use X-ray Exawatt pulse for particle acceleration in a crystal has been declared *. Short X-ray high-power pulse excites wakefield in electron plasma of metallic density which can be used for high gradient acceleration of charged particles. This wakefield is suited for laser wakefield acceleration. In this paper there are simulated with PIC code UMKA: excitation of the large wakefield amplitude up to several TV/m in electron plasma of metallic density by a powerful X-ray laser pulse; laser-plasma wakefield acceleration of self-injected electron bunch in such setup; combined acceleration by plasma wakefield driven by a laser pulse (LPWA) and by self-injected electron bunch (PWFA).
* T.Tajima. Eur. Phys. J. Special Topics 223 (2014) 1037.
KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
Earlier, high-gradient accelerating electrons of a relativistic beam was demonstrated. However, due to dynamic processes in the plasma, there are problems in maintaining the small size and small energy spread of the accelerated electron bunch while maintaining sufficient values of the accelerating wakefields. Also, the question arises about the values of the limiting bunch dimensions at which the accelerating process is stable. To form a stable accelerated electron bunch, a method is usually used that involves the formation of the same accelerating fields at the location of the bunch. The same fields (plateau due to beam loading (see *, **)) in the region of the accelerated bunch allow all its parts to move as a whole, and ensure the preservation of the spatial distribution of electrons over time, which, in fact, means an accelerated beam of good quality. In this report, the problem of electron bunch accelerating by a short or long electron driver-bunch is considered.
* Romeo S., Ferrario M., Rossi A.R. Phys. Rev. Accel. Beams. 23 (2020) 071301.
** Maslov V.I. et al. Problems of Atomic Science and Technology. 6 (2020) 47.
KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
The quality of the electron or positron beam, accelerated in plasma accelerators, is still insufficient for applications. Accurate control over the properties of the electron or positron beam is a key issue for wakefield plasma accelerators. The effect of the presence of a witness-beam (the effect of the spatial charge distribution of the witness beam) (see [*, **]) to compensate the energy spread of the positron beam in plasma wakefield accelerators has been studied. This paper presents the results of a numerical simulation on the optimization of the parameters of the driver-bunch and witness-bunch for the formation of a self-consistent longitudinal distribution of the accelerating plateau-type field, which leads to the same values of the wakefield for the whole bunch of accelerated particles and minimizing bunch degradation during acceleration by means of an ion-driver-bunch with external injection into the plasma wake accelerator. The dependence of the longitudinal distribution of the accelerating wakefield on the density and shape of the accelerated bunch in the blowout regime was investigated. Plateau formation and energy spread compensation were observed.
* Romeo S., Ferrario M., Rossi A.R. Phys. Rev. Accel. Beams. 23 (2020) 071301.
** Katsouleas T. et al. Particle Accelerators. 22 (1987) 81.
KhNU, Kharkov, Ukraine
NSC/KIPT, Kharkov, Ukraine
The efficiency of electron acceleration by a wakefield, excited in a plasma by an electron bunch, is determined by the transformer ratio (see *, **). The transformer ratio is the ratio of energy acquired by the witness to energy lost by the driver. The transformer ratio can be increased by shaping driver-bunch. In this work, using a non-linear version of the 2d3v code lcode (see ***), numerical simulation of excitation of a wakefield in a plasma in blowout regime by a shaped relativistic electron bunch was performed. There is also the problem of maintaining the small dimension and small energy spread of the accelerated electron bunch while maintaining sufficient values of the accelerating gradient and the transformer ratio. Also, the question arises about the values of the limiting dimension of the witness-bunch at which the acceleration process is stable. Numerical simulation solves the problem of electron bunch acceleration of the best quality with simultaneous maximization of the transformer ratio and maximization of the witness bunch length, at which the accelerating gradient and the focusing force are constant.
*Maslov V.I. et al. Problems of Atomic Science and Technology. 4 (2012) 128.
**Baturin S.S., Zholents A. Phys. Rev. ST Accel. Beams. 20 (2017) 061302.
***Lotov K.V. Phys. Plasmas. 5 (1998) 785.