Acceleration of a trailing positron bunch in a plasma wakefield accelerator

Abstract

High gradients of energy gain and high energy efficiency are necessary parameters for compact, cost-efficient and high-energy particle colliders. Plasma Wakefield Accelerators (PWFA) offer both, making them attractive candidates for next-generation colliders. In these devices, a charge-density plasma wave is excited by an ultra-relativistic bunch of charged particles (the drive bunch). The energy in the wave can be extracted by a second bunch (the trailing bunch), as this bunch propagates in the wake of the drive bunch. While a trailing electron bunch was accelerated in a plasma with more than a gigaelectronvolt of energy gain, accelerating a trailing positron bunch in a plasma is much more challenging as the plasma response can be asymmetric for positrons and electrons. We report the demonstration of the energy gain by a distinct trailing positron bunch in a plasma wakefield accelerator, spanning nonlinear to quasi-linear regimes, and unveil the beam loading process underlying the accelerator energy efficiency. A positron bunch is used to drive the plasma wake in the experiment, though the quasi-linear wake structure could as easily be formed by an electron bunch or a laser driver. The results thus mark the first acceleration of a distinct positron bunch in plasma-based particle accelerators.

Laser-driven high-quality positron sources as possible injectors for plasma-based accelerators

“…For instance, a short longitudinal size is highly desirable for injection in additional wakefield acceleration stages. The extremely small positron-accelerating region, of a few microns, in plasma wakefield accelerators have led to alternative schemes being investigated, such as self-loaded PWFA 11,22 . In SL-PWFA, the front of a long, high-charge positron beam drives a wakefield, which accelerates the positrons contained in the back of the bunch, in a positron-accelerating region larger than in the regular electron-driven wakefield.…”

FACET-II facility for advanced accelerator experimental tests

“…A positron bunch was used to drive the plasma wake in the experiment, though the quasilinear wake structure could as easily be formed by an electron bunch or a laser driver. The results marked the first acceleration of a distinct positron bunch in plasma-based particle accelerators [13]. Hollow channel plasma wakefield acceleration is a proposed method to provide high-acceleration gradients for electrons and positrons alike: a key to future lepton colliders.…”

Measuring the magnetic axis alignment during solenoids working

“…In the last decades, resistive and superconductive axially-symmetric magnets have been investigated and employed at an increasing rate in several and heterogeneous research fields 1 – 3 . As an example, in particle accelerators, magnetic elements such as solenoids are applied in low-energy beam transport sections 4 , 5 , and in modern radio-frequency (RF) linear accelerators (linacs) 6 , for emittance compensation, transverse focusing, and electron cooling. Examples of resistive solenoids employed as focusing lenses in RF linacs are Linac3 7 and Linac4 8 at CERN.…”