Interferometer-based high-accuracy white light measurement of neutral rubidium density and gradient at AWAKE

Abstract

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.

arXiv comment5 pages, 8 figures, EAAC2017 conference proceeding

References in corpus (6)

• Self-modulation instability of a long proton bunch in plasmas
• AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN
• Path to AWAKE: Evolution of the concept
• AWAKE readiness for the study of the seeded self-modulation of a 400\,GeV proton bunch
• A Rubidium Vapor Source for a Plasma Source for AWAKE
• Numerical Studies of Electron Acceleration Behind Self-Modulating Proton Beam in Plasma with a Density Gradient

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• Controlled Growth of the Self-Modulation of a Relativistic Proton Bunch in Plasma
• Proton Bunch Self-Modulation in Plasma with Density Gradient
• Experimental Study of Wakefields Driven by a Self-Modulating Proton Bunch in Plasma
• Generation of 10-m-lengthscale plasma columns by resonant and off-resonant laser pulses
• Experimental study of extended timescale dynamics of a plasma wakefield driven by a self-modulated proton bunch
• Long range propagation of ultrafast, ionizing laser pulses in a resonant nonlinear medium
• Simulation and Experimental Study of Proton Bunch Self-Modulation in Plasma with Linear Density Gradients