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

Batsch, Fabian; Muggli, Patric; Martyanov, Mikhail; Gschwendtner, Edda; Caldwell, Allen; Moody, Joshua; Oez, Erdem

doi:10.1016/j.nima.2018.02.067

Article
Report number	arXiv:1802.04604
Title	Interferometer-based high-accuracy white light measurement of neutral rubidium density and gradient at AWAKE
Author(s)	Batsch, Fabian (CERN ; Munich, Max Planck Inst. ; Munich, Tech. U.) ; Martyanov, Mikhail (Munich, Max Planck Inst.) ; Oez, Erdem (Munich, Max Planck Inst.) ; Moody, Joshua (Munich, Max Planck Inst.) ; Gschwendtner, Edda (CERN) ; Caldwell, Allen (Munich, Max Planck Inst.) ; Muggli, Patric (CERN ; Munich, Max Planck Inst.)
Publication	2018-02-24
Imprint	2018-02-13
Number of pages	5
Note	5 pages, 8 figures, EAAC2017 conference proceeding
In:	Nucl. Instrum. Methods Phys. Res., A 909 (2018) 359-363
In:	3rd European Advanced Accelerator Concepts Workshop, La Biodola, Isola d'Elba, Italy, 24 - 30 Sep 2017, pp.359-363
DOI	10.1016/j.nima.2018.02.067
Subject category	physics.ins-det ; Detectors and Experimental Techniques ; physics.plasm-ph ; Other Fields of Physics
Accelerator/Facility, Experiment	CERN SPS ; 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.
Copyright/License	publication: © 2018 The Authors (License: CC-BY-4.0)

$(a) Plot of Rb vapor density vs. time (UTC) during a gradient scan. The downstream density (blue) is increases and then lowered again while the density upstream (red) is kept constant. \ (b) The resulting density gradient over 10 m along the vapor source vs. time (UTC). Positive gradients indicate that the density is higher downstream.$

$(a) Interference pattern without Rb in the Rb vapor source. The oscillation shows nearly constant period. \ (b) Interference pattern with $n_{Rb}=1.365\cdot10^{14}$ cm$^{-3}$ in the source. Around the transition lines (D1 at 795 nm and D2 at 780 nm), the period changes in a density-dependent way. The red lines represent the offset of the oscillation (see later).$ Show more plots

Corresponding record in: Inspire

Back to search

Record created 2018-02-14, last modified 2023-09-29

Similar records

Fulltext:

PDF

Fulltext from Publisher:

PDF

Add to personal basket
Export as BibTeX, MARC, MARCXML, DC, EndNote, NLM, RefWorks

CERN Document Server

Access articles, reports and multimedia content in HEP

Main menu

CERN Accelerating science