# ICFDT5 - 5th International Conference on Frontier in Diagnostic Technologies

3-5 October 2018
INFN-LNF, Italy
Europe/Rome timezone

## Electron Density Measurement of PROTO-SPHERA Plasma by Second Harmonic Interferometer

5 Oct 2018, 17:00
20m
Bruno Touschek Auditorium (INFN-LNF, Italy)

### Bruno Touschek Auditorium

#### INFN-LNF, Italy

Via E. Fermi, 40 I-00044 Frascati

### Speaker

Mr Giuseppe Galatola Teka (ENEA - FSN, Frascati (RM), Italy)

### Description

The PROTO-SPHERA (PS) [1] experiment at Frascati ENEA Research Centre produce a Spherical Torus (ST) around a Plasma Centerpost (PC). The PC is an arc discharge driven by DC voltage between two annular electrodes. This alternative and stable magnetic configuration is obtained without the internal toroidal coils and without the central ohmic transformer of a traditional tokamak. In fact, the PC, opportunely shaped by the PF Coils internal to the vessel, together with additional external poloidal field coils, forms the torus and is able to sustain its current through magnetic reconnections; moreover the torus is limited by two ordinary X-points with zero poloidal field, as in a double null divertor tokamak. After resolving many issues, the device was capable to routinely operate with a 10 kA stable longitudinal current in the PC, and 5 kA in the Torus for 0.5 seconds. In order to measure the electron density inside PS, we selected a common-path Second Harmonic Interferometer (SHI) that fits well with the expected density range and construction constraints of the chamber. The SHI [2], developed by Pisa group and installed in several plasma devices along many years is insensitive-to-vibrations device, that has allowed an easy installation on the machine, thanks to a compact modular design. In this work, we present the electron density measurements for different gases (Ar and H) in various operating conditions and its correlation with other diagnostics. In comparable plasma configurations, by using two filling gases, the maximum line-averaged electron density through the machine midplane of PS was measured as 4 $/cdot 10^{20}$ m$^{-3}$ for Argon and as 1.5 $/cdot 10^{20}$ m$^{-3}$ for Hydrogen. 1) F. Alladio, P. Micozzi et al. -“Design of the PROTO-SPHERA experiment and of its first step (MULTI-PINCH)” - Nucl. Fusion 46 (2006) S613–S624 2) F. Brandi, F.Giammanco- “Versatile second-harmonic interferometer with high temporal resolution and high sensitivity based on a continuous-wave Nd: YAG laser”- Opt.Lett., 32, 2327-2329, (2007)

### Primary author

Mr Giuseppe Galatola Teka (ENEA - FSN, Frascati (RM), Italy)

### Co-authors

Dr Danilo Giulietti (Dpt.of Physics , University of Pisa, Italy) Prof. Francesco Giammanco (Dpt.of Physics , University of Pisa, Italy) Dr Franco Alladio (ENEA-FSN) Dr Luca Boncagli (ENEA - FSN, Frascati (RM), Italy) Dr Paolo Marsili (Dpt. Physics, University of Pisa, Italy) Dr Paolo Micozzi (ENEA-FSN, Frascati (RM), Italy)

### Presentation Materials

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