Demonstration of a positron beam-driven hollow channel plasma wakefield accelerator

Abstract

Plasma wakefield accelerators have been used to accelerate electron and positron particle beams with gradients that are orders of magnitude larger than those achieved in conventional accelerators. In addition to being accelerated by the plasma wakefield, the beam particles also experience strong transverse forces that may disrupt the beam quality. Hollow plasma channels have been proposed as a technique for generating accelerating fields without transverse forces. Here we demonstrate a method for creating an extended hollow plasma channel and measure the wakefields created by an ultrarelativistic positron beam as it propagates through the channel. The plasma channel is created by directing a high-intensity laser pulse with a spatially modulated profile into lithium vapour, which results in an annular region of ionization. A peak decelerating field of 230 MeV m−1 is inferred from changes in the beam energy spectrum, in good agreement with theory and particle-in-cell simulations.

Multi-proton bunch driven hollow plasma wakefield acceleration in the nonlinear regime

“…Assuming the micro-bunching techniques will be developed in the frame of AWAKE project, the hollow channels would open the path to emittance-preserving accelerating structures for future high-energy physics facilities. The least developed part of the concept is the production of long hollow channels, which is far from maturity 50 . However, the channel could be sectionalized into multiple plasma cells with almost no decrease of the longitudinal fields, provided that the gap between cells is shorter than the betatron period of driver particles 69 .…”

“…Last but not least, the blowout regime is asymmetric with respect to the witness charge, and the accelerating bucket for positrons is extremely narrow 49 . Hollow channels are free from these drawbacks, and this stimulates theoretical studies even though experimental implementation of such channels is still in its infancy 50 .…”

Roadmap to the Future

“…Hollow or nearly hollow channel plasmas have been proposed as a candidate regime for positron acceleration. Some recent experiments have demonstrated hollow channels free of plasma on axis [18]. Future experiments will require an even greater degree of control, and plasma source development must proceed hand in hand with every experimental program.…”

Summary report of working group 4: Beam-driven acceleration

“…A new regime of acceleration of positrons in a self-loaded PWFA was discovered [2]. The positron PWFA program at FACET allowed demonstration, for the first time, of acceleration in linear and quasi-nonlinear regimes, and acceleration in a hollow plasma channel [1]. Also, the Trojan Horse experiment was able to capture and accelerate laser-ionized electrons through Plasma Wakefield Acceleration, as part of emittance preservation studies.…”

“…His group has demonstrated, for the first time, the acceleration of a positron witness bunch in a hollow plasma channel. This work builds upon previous experimental efforts [1] that demonstrated the formation of extended plasma channels by ionization of a gas using intense laser pulses with a transverse high-order Bessel profile. Using a high-resolution imaging spectrometer, they measured an average energy loss of 11 MeV from the drive beam in a 25-cm-long channel.…”