Equilibrium properties and main design parameters of a long pulsed spherical torus
Nicolai, A. (Corresponding author)
Publikationen vor 2000; PRE-2000; Retrocat
Jülich Forschungszentrum Jülich, Zentralbibliothek, Verlag 1999
58 p.
Report
Book
Addenda
Berichte des Forschungszentrums Jülich 3727
OpenAccess
OpenAccess
Please use the identifier: http://hdl.handle.net/2128/23137 in citations.


At tight aspect ratios tokamak plasmas possess features not present at large aspect ratios, such as natural elongation, triangularity, a natural divertor configuration and a considerable bootstrap effect. However, the pulse duration in ST's (Spherical Tori) seems to be considerably smaller than in conventional takamaks due to the much smaller flux swing of the primary solenoid in ST's. To explore the requirements for a tight aspect ratio device with Jong pulse durations, a 95% bootstrap driven device (I$_{p} \approx$ 2.5 MA) is considered operating at a $\beta$ = 18%. Here $\beta$ is defined as the ratio of the volume averaged pressure to the volume averaged energy density of the (total) magnetic field. (The quantity $\beta_{vac}$ = 45% which is the ratio of the volume averaged pressure to the volume averaged energy density of the toroidal vacuum field, is considerably larger. The seed current is assumed to be driven by neutral injection which partly provides the plasma heating as well. Ignoring the plasma initialization and the ramp up phase in a first step, the flat - top state is analyzed by means of the TORUS- II code. In this code a combination of a 'semifree' boundary equilibrium code with a consistent description of the bootstrap current is used. The calculations are based an the aforementioned plasma current, the aspect ratio A = 1.2, the centerpost current I$_{cp}$ = 3.0 MA and the mean proton density <n$_{p}$> = 5.9 10$^{13}$ cm$^{-3}$. Some typical results are: 1. At the mean plasma temperatures < T$_{e}$ > = < T$_{i}$ > $\approx$ 1500 eV the prescribed bootstrap fraction f$_{boot}$ =95% is reached for the minor half axis a = 1.30 m. 2. Without the action of the shaping coils the natural elongation is only $\kappa_{nat}$ = 1.6. The triangularity is then $\delta$ = 0.6, and the Shafranov - shift is d$_{SH}$ = 0.35 m. To achieve an elongation $\epsilon$ = 2.0, the current I$_{div}$, =0.3 MA in the divertor coils is needed. 3. Due to the poloidal $\beta_{p} \approx$ 1 a magnetic well is generated at the outboard side. Here the geodesic curvature of the field lins becomes small and a partly omnigeneous plasma state is reached.