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We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported in [1]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement.

Plasma wakefield acceleration is a promising technology to reduce the size of particle accelerators. The use of high energy protons to drive wakefields in plasma has been demonstrated during Run 1 of the AWAKE programme at CERN. Protons of energy 400 GeV drove wakefields that accelerated electrons to 2 GeV in under 10 m of plasma. The AWAKE collaboration is now embarking on Run 2 with the main aims to demonstrate stable accelerating gradients of 0.5–1 GV/m, preserve emittance of the electron bunches during acceleration and develop plasma sources scalable to 100s of metres and beyond. By the end of Run 2, the AWAKE scheme should be able to provide electron beams for particle physics experiments and several possible experiments have already been evaluated. This article summarises the programme of AWAKE Run 2 and how it will be achieved as well as the possible application of the AWAKE scheme to novel particle physics experiments.

A: One of the main characteristics of the Goubau line is that it supports a low-loss, nonradiated surface wave guided by a dielectric-coated metal wire. The dominant mode of the surface wave along the Goubau line is a TM 01 mode, which resembles the pattern of the electromagnetic fields induced in the metallic beam pipe when the charged particle beam passes through it. Therefore, the Goubau line can be used for the preliminary bench test and performance optimization of the beam diagnostic instruments without requiring charged particle beams from the accelerators. In this paper, we discuss the basic properties of the Goubau line for testing beam diagnostic instruments and present the initial test results for button-type beam position monitors (BPMs). The experimental results are consistent with the theoretical estimations, which indicates that Goubau line allows effective testing of beam diagnostic equipment. K: Beam-line instrumentation (beam position and profile monitors; beam-intensity monitors; bunch length monitors); Instrumentation for particle accelerators and storage rings -high energy (linear accelerators, synchrotrons); Instrumentation for particle accelerators and storage rings -low energy (linear accelerators, cyclotrons, electrostatic accelerators)

In the Trojan Horse injection process for plasma-based particle accelerators, we have investigated how the longitudinal phase space of the witness bunch would be governed by the parameters of the ionization laser and background plasma in the limit of quasistatic wakefield approximation. The tunneling ionization rate distribution by the laser pulse is introduced to describe the ionization time interval and initial distribution of the witness electrons. The quasilinear (or equivalently quasistatic) regime of the charged particle beam-driven wakefield is considered to make the phase of the wake potential constant in time in the driver beam frame. In the simulations, it is shown that the ionization laser phase on the quasistatic wake potential determines the longitudinal space-charge field of the witness bunch. We also find that the relative energy spread of the witness bunch can be estimated by the sum of three effects: The ionization time interval, wakefield slope, and space-charge fields of the witness bunch. Analytical expressions for the characteristic distance from the ionization to trapping positions, rms length, and relative energy spread of the witness bunch are obtained approximately and compared with the particle-in-cell simulations.Published under license by AIP Publishing. https://doi. Phys. Plasmas 13, 056709 (2006). FIG. 6. The average energy and energy spread of the witness bunch for k p n i ¼ -3.3. (blue dashed line) The asymptotic behavior of the relative energy spread. (blue solid curve) The analytical expression (10) for the relative energy spread. (blue circles) The PIC simulation result of the relative energy spread. (red circles) The PIC simulation result of the average energy. Physics of Plasmas ARTICLEscitation.org/journal/php