Guoxing Xia

Proton-driven plasma wakefield acceleration: a path to the future of high-energy particle physics

New acceleration technology is mandatory for the future elucidation of fundamental particles and their interactions. A promising approach is to exploit the properties of plasmas. Past research has focused on creating large-amplitude plasma waves by injecting an intense laser pulse or an electron bunch into the plasma. However, the maximum energy gain of electrons accelerated in a single plasma stage is limited by the energy of the driver. Proton bunches are the most promising drivers of wakefields to accelerate electrons to the TeV energy scale in a single stage. An experimental program at CERN—the AWAKE experiment—has been launched to study in detail the important physical processes and to demonstrate the power of proton-driven plasma wakefield acceleration. Here we review the physical principles and some experimental considerations for a future proton-driven plasma wakefield accelerator.

AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN

The Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE) aims at studying plasma wakefield generation and electron acceleration driven by proton bunches. It is a proof-of-principle R&D experiment at CERN and the world׳s first proton driven plasma wakefield acceleration experiment. The AWAKE experiment will be installed in the former CNGS facility and uses the 400 GeV/c proton beam bunches from the SPS. The first experiments will focus on the self-modulation instability of the long (rms ~12 cm) proton bunch in the plasma. These experiments are planned for the end of 2016. Later, in 2017/2018, low energy (~15 MeV) electrons will be externally injected into the sample wakefields and be accelerated beyond 1 GeV. The main goals of the experiment will be summarized. A summary of the AWAKE design and construction status will be presented.

A proposed demonstration of an experiment of proton-driven plasma wakefield acceleration based on CERN SPS

The proton bunch-driven plasma wakefield acceleration (PWFA) has been proposed as an approach to accelerate an electron beam to the TeV energy regime in a single plasma section. An experimental program has been recently proposed to demonstrate the capability of proton-driven PWFA by using existing proton beams from the European Organization for Nuclear Research (CERN) accelerator complex. At present, a spare Super Proton Synchrotron (SPS) tunnel, having a length of 600 m, could be used for this purpose. The layout of the experiment is introduced. Particle-in-cell simulation results based on realistic SPS beam parameters are presented. Simulations show that working in a self-modulation regime, the wakefield driven by an SPS beam can accelerate an externally injected ~10 MeV electrons to ~2 GeV in a 10-m plasma, with a plasma density of 7 × 10 14 cm −3 .

Plasma wakefield excitation with a 24 GeV proton beam

Proton driven plasma wakefield acceleration has recently been proposed as a means of generating high energy electron beams. In this paper, different options for a demonstration experiment with the CERN PS beam are considered. We review a possible magnetic compression of the PS bunches and resulting electric fields in the plasma. Results are then presented for self-modulation of the proton bunch for different plasma densities and lengths. It is found that the latter option offers interesting possibilities for a first experiment.

Numerically optimized structures for dielectric asymmetric dual-grating laser accelerators

Optical scale dielectric structures are promising candidates to realize future compact, low cost particle accelerators, since they can sustain high acceleration gradients in the range of GeV/m. Here, we present numerical simulation results for a dielectric asymmetric dual-grating accelerator. It was found that the asymmetric dual-grating structures can efficiently modify the laser field to synchronize it with relativistic electrons, therefore increasing the average acceleration gradient by ∼10% in comparison to symmetric structures. The optimum pillar height which was determined by simulation agrees well with that estimated analytically. The effect of the initial kinetic energy of injected electrons on the acceleration gradient is also discussed. Finally, the required laser parameters were calculated analytically and a suitable laser is proposed as energy source.

Update of Proton Driven Plasma Wakefield Acceleration

In this paper, the update of proton driven plasma wakefield acceleration (PDPWA) is given. After a brief introduction to the scheme of PDPWA, a future demonstration experiment is discussed. The particle‐in‐cell simulation results based on the realistic proton beams from the CERN Super Proton Synchrotron (SPS) are presented, followed by a simulation study of proton bunch compression.

Beam quality study for a grating-based dielectric laser-driven accelerator

Dielectric laser-driven accelerators (DLAs) based on grating structures are considered to be one of the most promising technologies to reduce the size and cost of future particle accelerators. They offer high accelerating gradients of up to several GV/m in combination with mature lithographic techniques for structure fabrication. This paper numerically investigates the beam quality for acceleration of electrons in a realistic dual-grating DLA. In our simulations, we use beam parameters of the future Compact Linear Accelerator for Research and Applications facility to load an electron bunch into an optimized 100-period dual-grating structure where it interacts with a realistic laser pulse. The emittance, energy spread, and loaded accelerating gradient for modulated electrons are then analyzed in detail. Results from simulations show that an accelerating gradient of up to 1.13 ± 0.15 GV/m with an extremely small emittance growth, 3.6%, can be expected.

Collider design issues based on proton-driven plasma wakefield acceleration

Abstract Recent simulations have shown that a high-energy proton bunch can excite strong plasma wakefields and accelerate a bunch of electrons to the energy frontier in a single stage of acceleration. It therefore paves the way towards a compact future collider design using the proton beams from existing high-energy proton machines, e.g. Tevatron or the LHC. This paper addresses some key issues in designing a compact electron–positron linear collider and an electron–proton collider based on the existing CERN accelerator infrastructure.

Dual-gratings with a Bragg reflector for dielectric laser-driven accelerators

The acceleration of a beam of electrons has been observed in a dielectric laser-driven accelerator with a gradient of 300 MV/m. It opens the way to building a particle accelerator “on a chip” much more cheaply than a conventional one. This paper investigates numerically an efficient dielectric laser-driven accelerating structure, based on dual-gratings with a Bragg reflector. The design of the structure boosts the accelerating field in the channel, thereby increasing the accelerating gradient by more than 70% compared to bare dual-gratings, from analytical calculations. This is supported by two-dimensional (2D) particle-in-cell simulations, where a 50 MeV electron bunch is loaded into an optimized 100-period structure to interact with a 100 fs pulsed laser having a peak field of 2 GV/m. It demonstrates a loaded accelerating gradient of 1.48 ± 0.10 GV/m, which is (85 ± 26)% higher than that of bare dual-gratings. In addition, studies of the diffraction effect show that the optimized structure should be fab...

High quality electron beam generation in a proton-driven hollow plasma wakefield accelerator

Simulations of proton-driven plasma wakefield accelerators have demonstrated substantially higher accelerating gradients compared to conventional accelerators and the viability of accelerating electrons to the energy frontier in a single plasma stage. However, due to the strong intrinsic transverse fields varying both radially and in time, the beam quality is still far from suitable for practical application in future colliders. Here we propose an efficient proton-driven accelerating regime in a hollow channel. In this regime, the electron witness bunch is positioned in the region with a strong accelerating field, free from plasma electrons and ions. We show that the witness electron beam carrying the charge of about 10% of 1 TeV proton driver charge can be accelerated to 0.6 TeV with preserved normalized emittance in a single channel of 700 m. This high quality and high charge beam may pave the way for the development of future plasma-based energy frontier colliders.