Commissioning of the electron injector for the AWAKE experiment

The advanced wakefield experiment (AWAKE) at CERN is the first proton beam-driven plasma wakefield acceleration experiment. The main goal of AWAKE RUN 1 was to demonstrate seeded self-modulation (SSM) of the proton beam and electron witness beam acceleration in the plasma wakefield. For the AWAKE experiment, a 10-meter-long Rubidium-vapor cell together with a high-power laser for ionization was used to generate the plasma. The plasma wakefield is driven by a 400 GeV/c proton beam extracted from the super proton synchrotron (SPS), which undergoes a seeded self-modulation process in the plasma. The electron witness beam used to probe the wakefields is generated from an S-band RF photo-cathode gun and then accelerated by a booster structure up to energies between 16 and 20 MeV. The first run of the AWAKE experiment revealed that the maximum energy gain after the plasma cell is 2 GeV, and the SSM mechanism of the proton beam was verified. In this paper, we will present the details of the AWAKE electron injector. A comparison of the measured electron beam parameters, such as beam size, energy, and normalized emittance, with the simulation results was performed.

[1]  P. Muggli,et al.  Generation and delivery of an ultraviolet laser beam for the RF-photoinjector of the AWAKE electron beam , 2019 .

[2]  John Schmerge,et al.  The Quantum Efficiency and Thermal Emittance of Metal Photocathodes , 2009 .

[3]  B. Goddard,et al.  External Electron Injection for the AWAKE Experiment , 2018, 2018 IEEE Advanced Accelerator Concepts Workshop (AAC).

[4]  V. Verzilov,et al.  The electron accelerators for the AWAKE experiment at CERN—Baseline and Future Developments , 2018, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.

[5]  J. R. Henderson,et al.  Experimental Observation of Plasma Wakefield Growth Driven by the Seeded Self-Modulation of a Proton Bunch. , 2018, Physical review letters.

[6]  Z. Sheng,et al.  Path to AWAKE: Evolution of the concept , 2015, 1511.09032.

[7]  E. Chevallay,et al.  Production of long bunch trains with 4.5 μ C total charge using a photoinjector , 2012 .

[8]  J. R. Henderson,et al.  Experimental Observation of Proton Bunch Modulation in a Plasma at Varying Plasma Densities. , 2018, Physical review letters.

[9]  P. Muggli.  The AWAKE Proton-driven Plasma Wakefield Experiment at CERN , 2015 .

[10]  Allen Caldwell,et al.  AWAKE Design Report: A Proton-Driven Plasma Wakefield Acceleration Experiment at CERN , 2013 .

[11]  O. R. Jones,et al.  Status of the proton and electron transfer lines for the AWAKE Experiment at CERN , 2016 .

[12]  John M. Dawson,et al.  Nonlinear Electron Oscillations in a Cold Plasma , 1959 .

[13]  E. Gschwendtner.  AWAKE, A Particle-driven Plasma Wakefield Acceleration Experiment , 2017, 1705.10573.

[14]  W. Mori,et al.  Limits of linear plasma wakefield theory for electron or positron beams , 2005 .

[15]  G. Xia,et al.  A numerical approach to designing a versatile pepper-pot mask for emittance measurement , 2019, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.

[16]  P. Muggli,et al.  Seeding of the self-modulation in a long proton bunch by charge cancellation with a short electron bunch , 2018, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.

[17]  K. Lotov.  Physics of beam self-modulation in plasma wakefield accelerators , 2015, 1503.05104.

[18]  J. Vieira,et al.  AWAKE readiness for the study of the seeded self-modulation of a 400 GeV proton bunch , 2017, 1708.01087.

[19]  L. Soby,et al.  Acceleration of electrons in the plasma wakefield of a proton bunch , 2018, Nature.