Eur. Phys. J. Appl. Phys. (2017) 77: 30802 DOI: 10.1051/epjap/2017160479 THE EUROPEAN PHYSICAL JOURNAL APPLIED PHYSICS Regular Article Methods for spectroscopic measurement of electric field in atmospheric pressure helium discharges ⋆ Bratislav M. Obradovi´ c 1, a , Nikola Cvetanovi´ c 2 , Sasa S. Ivkovi´ c 1 , Goran B. Sretenovi´ c 1 , Vesna V. Kovaˇ cevi´ c 1 , I.B. Krsti´ c 1 , and Milorad M. Kuraica 1 1 Faculty of Physics, University of Belgrade, PO Box 368, 11001 Belgrade, Serbia 2 Faculty of Transport and Traffic Engineering, University of Belgrade, Vojvode Stepe 305, 11000 Belgrade, Serbia Received: 16 December 2016 / Received in final form: 5 February 2017 / Accepted: 7 February 2017 c  EDP Sciences 2017 Abstract. A short overview of the emission spectroscopy methods for measuring the macroscopic electric field in high pressure discharges with helium is given. The occurrence of macroscopic electric field is a con- sequence of the space charge buildup. It is a common feature of discharge sheaths, streamer heads and double layers. The spectroscopic methods are based on polarization-dependent Stark splitting and shifting of atomic lines in the presence of a relatively strong electric field. For high pressure discharges Stark shifting of helium lines and their forbidden counterparts is used. The advantage of Stark methods is their ab initio basis which makes them independent on other plasma parameters. A different method for field measure- ment, based on the helium line ratio, can be applied in cases where the Stark method cannot be used. 1 Introduction The occurrence of macroscopic, collective electric field is common in the laboratory plasma. It is a consequence of separation of the charged particles that leads to the space charge buildup and, in turn, to a directed macroscopic electric field governed by the Poisson equation. The region of significant macroscopic field occurs commonly in the so called sheath regions, the boundary layers where plasma is in contact with the confining chamber or the electrodes. It is also present in the so called double layers and similar occurrences of directed collective field found both in the laboratory and astrophysical plasmas, for instance in the atmospheres of outer planets. The formation of streamer heads is another example of a high field region. In all these cases, the electric field distribution in space and time, often determines the energy and flux of the charged par- ticles, thereby determining the ionization rates and other characteristics of the bulk plasma. A number of experimental methods based on emis- sion spectroscopy have been developed for measuring the macroscopic field in plasma sheaths, see for instance [1–3]. Methods are commonly based on Stark splitting and shift- ing of atomic lines in the presence of a relatively strong electric field. Compared to laser techniques [4–7], emis- sion spectroscopy can only be used for higher values of a e-mail: obrat@ff.bg.ac.rs ⋆ Contribution to the topical issue “The 15th International Symposium on High Pressure Low Temperature Plasma Chemistry (HAKONE XV)”, edited by Nicolas Gherardi andTom´aˇ s Hoder the electric field and provides somewhat reduced spatial resolution but requires a simpler apparatus and offers ease of use, especially where higher line intensities are avail- able. On the other hand, the laser spectroscopy techniques are based on high lying Rydberg states which overlap at atmospheric pressure due to pressure broadening. The emission spectroscopy methods are mainly concen- trated on the use of helium and hydrogen lines and were applied to various types of discharges at lower [1–3] and higher pressure [8–10]. The advantage of these methods is their ab initio basis, hence they can be used for mea- suring the electric field spatiotemporal distributions in diverse plasmas, independently of other plasma parame- ters and fulfillment of special conditions. Due to the Stark effect, hydrogen and helium lines are split into components with each component shifted in the field. For measuring the electric field from the line profile, numerical fitting procedure can be established [11]. The use of the Stark effect of hydrogen lines for field measurements was so far unsuccessful for atmospheric pressure barrier discharges due to delayed excitation. Additionally, a method which is not based on the Stark effect is recommended for certain cases in helium and results obtained by it are presented. 2 The fitting model and experimental conditions The model function for fitting of lines influenced by the Stark effect, is formed by assigning a line profile f to each 30802-p1