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The stability of plasma-based accelerators against transverse misalignments and asymmetries of the drive beam is crucial for their applicability. Without stabilizing mechanisms, even small initial offsets of the drive beam centroid can couple coherently to the plasma wake, grow, and ultimately lead to emittance degradation or beam loss for a trailing witness beam. In this work, we demonstrate the intrinsic stability of a beam propagating in a plasma column. This result is relevant in the context of plasma-based positron acceleration, where a wakefield suitable for the transport and acceleration of a positron witness beam is generated in a plasma column by means of an electron drive beam. The stable propagation of the drive beam is a necessary condition for the experimental implementation of this scheme. The differences and similarities of stabilizing mechanisms in a plasma column compared to a homogeneous plasma are identified via theory and particle-in-cell simulations. Experimental tolerances are given, demonstrating the experimental feasibility of the scheme. [ABSTRACT FROM AUTHOR]

Beam diagnostics is important to guarantee good quality of beam in a particle accelerator. Both the electron and positron run in the tunnel in some modern electron–positron colliders such as circular electron–positron collider (CEPC) to be built and Beijing Electron–Positron Collider II (BEPC II). To measure the electron and positron beams, picking-up these two different bunches in real time is a notable concern. As the time interval between adjacent electron and positron bunches is quite small, for example, 6 ns in CEPC, high-speed switch electronics is required. This paper presents the prototype design of a high-speed radio frequency (RF) electronics that can pick up nanosecond positron–electron beam bunches with a switching time of fewer than 6 ns. Fast separation of electron and positron is achieved based on RF switches and precise delay adjustment of the controlling signals (∼10 ps). Initial tests have been conducted in the laboratory to evaluate the performance of electronics; the results indicate that this circuit can successfully pick up the bunch signal within a time interval of 6 ns, which makes it possible to further measure the electron and positron beams simultaneously. [ABSTRACT FROM AUTHOR]

Plasma wakefield acceleration in the blowout regime is particularly promising for high-energy acceleration of electron beams because of its potential to simultaneously provide large acceleration gradients and high energy transfer efficiency while maintaining excellent beam quality. However, no equivalent regime for positron acceleration in plasma wakes has been discovered to date. We show that after a short propagation distance, an asymmetric electron beam drives a stable wakefield in a hollow plasma channel that can be both accelerating and focusing for a positron beam. A high charge positron bunch placed at a suitable distance behind the drive bunch can beam-load or flatten the longitudinal wakefield and enhance the transverse focusing force, leading to high efficiency and narrow energy spread acceleration of the positrons. Three-dimensional quasistatic particle-in-cell simulations show that an over 30% energy extraction efficiency from the wake to the positrons and a 1% level energy spread can be simultaneously obtained. Further optimization is feasible. [ABSTRACT FROM AUTHOR]