Showing papers by "T.D. Rognlien published in 1992"

IX. Boundary Physics

Abstract: In this chapter, we focus on the physics basis for the expected operating conditions at the BPX di-vertor and inner wall limiter. The essential features of the BPX device have been fully described in previous chapters. The main reasons for choosing the divertor configuration are the desire to obtain H-mode operation with high confinement and to obtain \" high-recycling \" operation in which a high-density, low-temperature plasma is formed in front of the target plates so as to minimize sputtering and impurity transport back to the core plasma. It is planned for BPX to operate primarily in the double-null (DN) configuration to maximize the contact area for heat removal. However, upper and lower single-null (SN) operation is also possible to minimize the H-mode power threshold. Inner-wall limiter configurations can also be obtained to provide a further option for increasing the power handling capabilities of the device. In terms of the plasma conditions in the scrape off layer (SOL), BPX represents a significant ex-trapolation from present machines because of its high power and relatively compact size. It also op erates at more than twice the toroidal field of any other operating divertor tokamak. Table 9.1 gives a comparison between BPX and other tokamaks in terms of expected heat flux across the separatrix and at the divertor targets. the actual contact area at the divertor targets.) With 17 MW of ion cyclotron resonance frequency (ICRF) + ohmic heating (OH) power, BPX could produce 420 MW of fusion power at Q = 25. Then Plea = 0.2 x Q + PICH = 100 MW should be deposited in the plasma and must be lost by radiation to the walls and conduction to the divertor plates. The peak divertor heat flux at the end of the Q = 25 burn phase (~20 MW/m2 exclusive of toroidal peaking factors) is expected to be higher than values in most present tolcamaks1-3: 2130 MW/m2 in JET, 115 MW/m2 in JT*O and DIII-D. At Q = 5 with Pfw = 100 MW and P loss = 40 MW, the peak divertor heat flux will be down to about 12 MW/m2. Active sweeping of the X-points will be used to reduce the temperature rise to manageable levels for inertially cooled divertor targets. The predicted operating conditions at the diver-1256 tor are derived primarily from numerical simulations using the B2 code,4 similar to the approach of the NET, INTOR, and …

Simulation of Tokamak Divertor Plasmas including Cross-Field Drifts

Abstract: The effects of plasma currents and cross-field drifts on single null tokamak divertor operation are simulated using a fully implicit 2-D fluid code. Equations solved are those for particle continuity, parallel momentum, electron energy, ion energy, electrostatic potential, and neutral gas diffusion. The core and scrape-off layer regions are separated by a magnetic separatrix, both of which are included in the simulation. The core plasma is poloidally periodic, and the inner and outer private flux regions are properly connected. The code utilizes a fully implicit method-of-lines scheme to advance the variables in time with a Krylov technique or a direct Newton iteration with a numerical Jacobian. Results are presented on the effects of currents and cross-field drifts for DIII-D single-null parameters.