The AWAKE experiment at CERN aims to drive strong plasma wakefields with a self-modulated proton drive bunch, and to use these wakefields for electron acceleration. During the self-modulation process, protons are defocused by the transverse plasma wakefields and form a halo around the focused bunch core. The two-screen setup integrated in AWAKE measures the transverse, time-integrated proton bunch distribution downstream the \unit[10]{m} long plasma to detect defocused protons. By measuring the maximum radii of the defocused protons we attempt calculate properties of the self-modulation. In this article, we develop a routine to identify the maximum radius of the defocused protons, based on a standard contour method. We compare the maximum radius to the logarithmic lineouts of the image to show that the radius identifies the edge of the signal.

AWAKE develops a new plasma wakefield accelerator using the CERN SPS proton bunch as a driver. The proton bunch propagates through a 10 m long rubidium plasma, induced by an ionizing laser pulse. The co-propagation of the laser pulse with the proton bunch seeds the self modulation instability of the proton bunch that transforms the bunch to a train with hundreds of bunchlets which drive the wakefields. Therefore the plasma radius must exceed the proton bunch radius. Schlieren imaging is proposed to determine the plasma radius on both ends of the vapor source. We use Schlieren imaging to estimate the radius of a column of excited rubidium atoms. A tunable, narrow bandwidth laser is split into a beam for the excitation of the rubidium vapor and for the visualization using Schlieren imaging. With a laser wavelength very close to the D2 transition line of rubidium (780 nm), it is possible to excite a column of rubidium atoms in a small vapor source, to record a Schlieren signal of the excitation column and to estimate its radius. We describe the method and show the results of the measurement.

We present the set-up and test-measurements of a waveguide-integrated heterodyne diagnostic for coherent transition radiation (CTR) in the AWAKE experiment. The goal of the proof-of-principle experiment AWAKE is to accelerate a witness electron bunch in the plasma wakefield of a long proton bunch that is transformed by Seeded Self-Modulation (SSM) into a train of proton micro-bunches. The CTR pulse of the self-modulated proton bunch is expected to have a frequency in the range of 90-300 GHz and a duration of 300-700 ps. The diagnostic set-up, which is designed to precisely measure the frequency and shape of this CTR-pulse, consists of two waveguide-integrated receivers that are able to measure simultaneously. They cover a significant fraction of the available plasma frequencies: the bandwidth 90-140 GHz as well as the bandwidth 255-270 GHz or 170-260 GHz in an earlier or a latter version of the set-up, respectively. The two mixers convert the CTR into a signal in the range of 5-20 GHz that is measured on a fast oscilloscope, with a high spectral resolution of 1-3 GHz dominated by the pulse length. In this contribution, we will describe the measurement principle, the experimental set-up and a benchmarking of the diagnostic in AWAKE.

The proton driven plasma wake field acceleration experiment AWAKE at CERN will start at the end of this year. In 2017 an S-band electron injector producing bunches of a few ps in length will be added to probe the wake fields stimulated by a driving proton beam. In the future this electron injector will have to be upgraded to obtain electron bunches with a length of 100-200 fs in order to demonstrate injection into a single bucket of the plasma wave and therefore sustainable acceleration with low energy spread. Target bunch parameters for the study are a bunch charge of 100 pC, 100 fs bunch length, an emittance smaller than 10 mm mrad and a beam energy > 50 MeV. The status of a study to achieve these parameters using X-band accelerator hardware and velocity bunching will be presented.

AWAKE is a proton driven plasma wakefield acceleration experiment at CERN which uses the protons from the SPS. It aims to study the self modulation instability of a proton bunch and the acceleration of an externally injected electron beam in the plasma wakefields, during the so called Phase II until the technical stop of LHC and its injector chain (LS2) in 2019. The external electron beam of 0.1 to 1nC charge per bunch will be generated using an S-band photo injector with a high QE semiconducting cathode. A booster linac was designed to allow variable electron energy for the plasma experiments from 16 to 20 MeV. For an RF gun and booster system, emittance control can be highlighted as a challenging transmission task. Once the beam emittance is compensated at the gun exit and the beam is delivered to the booster with an optimum beam envelope, fringing fields and imperfections in the linac become critical for preserving the injection emittance. This paper summarises the rf design studies in order to preserve the initial beam emittance at the entrance of the linac and alternative mitigation schemes in case of emittance growth.

The AWAKE experiment requires an automated online rubidium (Rb) plasma density and gradient diagnostic for densities between 1 and 10$\cdot$10$^{14}$ cm$^{-3}$. A linear density gradient along the plasma source at the percent level may be useful to improve the electron acceleration process. Because of full laser ionization of Rb vapor to Rb$^{+}$ within a radius of 1 mm, the plasma density equals the vapor density. We measure the Rb vapor densities at both ends of the source, with high precision using, white light interferometry. At either source end, broadband laser light passes a remotely controlled Mach-Zehnder interferometer built out of single mode fibers. The resulting interference signal, influenced by dispersion in the vicinity of the Rb D1 and D2 transitions, is dispersed in wavelength by a spectrograph. Fully automated Fourier-based signal conditioning and a fit algorithm yield the density with an uncertainty between the measurements at both ends of 0.11 to 0.46 $\%$ over the entire density range. These densities used to operate the plasma source are displayed live in the control room.

Safety is likely the most critical concern in many process industries, yet there is a general uncertainty on the proper engineering to reduce the risks and ensure the safety of persons or material at the same time as providing the process control system. Some of the reasons for this misperception are unclear requirements, lack of functional safety engineering knowledge or incorrect protection functionalities attributed to the BPCS (Basic Process Control System). Occasionally the control engineers are not aware of the hazards inherent to an industrial process and this causes an incorrect design of the overall controls. This paper illustrates the engineering of the SIS (Safety Instrumented System) and the BPCS of the plasma vapour controls of the AWAKE R&D; project, the first proton-driven plasma wakefield acceleration experiment in the world. The controls design and implementation refers to the IEC61511/ISA84 standard, including technological choices, design, operation and maintenance. Finally, the publication reveals the usual difficulties appearing in these kind of industrial installations and the actions to be taken to ensure the proper functional safety system design.

In plasma wakefield accelerators (e.g. AWAKE) the proton bunch self-modulation is seeded by the ionization front of a high-power laser pulse ionizing a vapour and by the resulting steep edge of the driving bunch profile inside the created plasma. In this paper, we present calculations in 2D linear theory for a concept of a different self-modulation seeding mechanism based on electron injection. The whole proton bunch propagates through a preformed plasma and the effective beam current is modulated by the external injection of a short electron bunch at the centre of the proton beam. The resulting sharp edge in the effective beam current in the trailing part of the proton bunch is driving large wakefields that can lead to a growth of the seeded self-modulation (SSM). Furthermore, we discuss the feasibility for applications in AWAKE Run 2.

We investigate numerically the detection of the self-modulation instability in a virtual detector located downstream from the plasma in the context of AWAKE. We show that the density structures, appearing in the temporally resolving virtual detector, map the transverse beam phase space distribution at the plasma exit. As a result, the proton bunch radius that appears to grow along the bunch in the detector results from the divergence increase along the bunch, related with the spatial growth of the self-modulated wakefields. In addition, asymmetric bunch structures in the detector are a result of asymmetries of the bunch divergence, and do not necessarily reflect asymmetric beam density distributions in the plasma.

In this thesis I observe experimentally and study in simulations the seeded selfmodulation of a relativistic proton bunch in AWAKE, the Advanced Proton Driven Plasma Wakefield Acceleration Experiment. The 400 GeV/c proton bunch from the CERN SPS with a rms length of 12 cm propagates in a 10m long plasma with a density adjustable between 2-10x10^14 electrons/cm3. The seeded self-modulation process results in focusing and defocusing of the protons, thereby forming a bunch train that resonantly drives wakefields to large amplitudes. I use the two-screen measurement setup, to observe the result of the proton bunch self-modulation and to learn about its physics (i.e. growth of the process). The idea is to obtain images of protons that were defocused by the transverse wakefields, 2 and 10m downstream the end of the plasma. From these images I determine the maximum transverse momentum of the defocused protons as well as infer their point of origin along the plasma. I use simulations to guide the understanding of the experimental results. At a plasma density of 7.7x10^14 electrons/cm3, the maximum defocused protons exit the wakefields with a transverse momentum of (390+-25) MeV/c, 4m after the plasma entrance. This measured transverse momentum is larger than that from the bunch emittance (sigma_pr =20MeV/c) plus that from the initial seed wakefield (15MV/m) integrated over the plasma interaction length. This therefore proves for the first time that the wakefields grow along the plasma and that the proton bunch strongly evolves in its transverse dimension, as a result of the seeded self-modulation process.

The Advanced Wakefield Experiment (AWAKE), to be constructed at CERN, will be the first experiment to demonstrate proton-driven plasma wakefield acceleration. The 400 GeV proton beam from the CERN SPS will excite a wakefield in a plasma cell several meters in length. To probe the plasma wakefield, electrons of 10-20 MeV will be injected into the wakefield following the head of the proton beam. Simulations indicate that electrons will be accelerated to GeV energies by the plasma wakefield. The AWAKE spectrometer is intended to measure both the peak energy and energy spread of these accelerated electrons. Under certain conditions it is also possible to use the spectrometer to measure the transverse beam emittance. The expected resolution of these measurements is investigated for various beam distributions, taking into account an optimised vacuum chamber and scintillator screen design and results of beam and optical tests.