Overview and Initial Results of the ETE Spherical Tokamak

EX/P4-20 Overview and Initial Results of the ETE Spherical Tokamak L.A. Berni, E. Del Bosco, J.G. Ferreira, G.O. Ludwig, R.M. Oliveira, C.S. Shibata, L.F.F.P.W. Barbosa, W.A. Vilela Instituto Nacional de Pesquisas Espaciais (INPE), Laboratório Associado de Plasma (LAP) 12201-970, São José dos Campos – SP, Brazil e-mail contact of main author: [email protected] Abstract. The ETE spherical tokamak is a small size aspect-ratio machine with major and minor radius of 30 cm and 20 cm, respectively. The vessel was made of Inconel 625 and provides good access for plasma diagnostics through 58 Conflat ports. The first plasma was obtained at the end of 2000 and presently plasma currents of about 45 kA lasting for about 4 ms with electron temperature up to 160 eV and densities of 2.2x1019 m-3 are routinely obtained. Achievement of the designed parameters for the first phase of operation is expected by the end of this year, with plasma current up to 200 kA lasting for about 15ms. This paper describes some details of the ETE project, construction and mainly the first results and analysis of basic parameters. 1. Introduction: ETE tokamak The ETE spherical tokamak (Experimento Tokamak Esférico) became operational at the end of 2000 and the main objectives of the project are plasma edge investigation, plasma heating by Alfvén waves and development of diagnostics [1]. Figure 1 presents a 3-D view of the ETE and the main parameters. The vacuum vessel was manufactured with Inconel 625, a relatively high resistivity nickel alloy. The toroidal geometry of the vessel is formed by an external tube (diameter of 1.2 m, length of 0.6m and thickness of 6.35mm) connected to an internal tube (diameter of 0.18 m, length of 1.2m and thickness of 1 mm) by two torispherical heads of thickness of 6.35 mm. A total of 58 Conflat ports (12xCF14”, 4xCF250 and 42xCF40) provide good access for plasma diagnostics. The vacuum system comprises a turbo drag (1500 l/s) and an oil-free diaphragm (4 m3/h) pumps. A base pressure of 8x10-8 Torr is achieved by conditioning the vessel with baking temperature up to 110oC. The D-shaped toroidal field coils (Imax = 100 kA) were manufactured from copper and comprise 12 turns in series that are connected by stray field compensation rings at the bottom and at the top. The solenoid (Imax = 20kA) comprises 2 layers of 130 turns each connected in series with three pairs of compensation coils. The equilibrium field coils comprise a pair of 16 turns (4x4) each (Imax = 6 kA). The maximum currents are limited by stress and heating in the coils. The power supplies of ETE are based on capacitor banks. Their energy is being continuously increased by adding more capacitor modules as well as by rising the voltage rating to its maximum to reach the first operational stage, as depicted in figure 1. The control system of the machine is based on CAMAC technology that is being developed in C language [2]. An optical link provides an isolation of 2 kV (15 kV in the near future) between the control computer and the CAMAC modules. A galvanic isolation between the CAMAC and the hazardous environments is achieved by optical and pneumatic systems. Presently the data acquisition is based on CAMAC modules and digital oscilloscopes that, in a near future, will be replaced by VME bus standard. Figure 2 presents schematically the configuration of the control and the acquisition system with the safety barrier.