Tungsten Contamination by Neutral Beam Shine-through in the JET ILW
The JET ILW experiment will have W divertor and Be main chamber walls. However, the W coated neutral beam shine-through protection tiles are in the main chamber. Therefore, shine-through of the 120kV injected neutral beams will cause some W sputtering, which can contaminate the JET plasma. EDGE2D based calculations are presented which indicate that 0.1MW of W radiation might occur in the absence of impurity pinches. The 16 JET NB sources can each produce 2.1MW of deuterium NBI power. The fractional power of the JET neutral beams is 0.515, 0.382, and 0.103 for the full, 1/2, and 1/3 energy components. The total 120 kV power passing through the plasma and hitting the wall is up to 1.7MW deceasing with plasma density. This calculation ignores charge exchange with Be which will further reduce the shine-through. Since the operation with the maximum beam voltage will cause the most shinethrough and the most W sputtering, we perform these calculations at 125kV, and do not further consider the 1/3 energy component. The fraction of the total power which reaches the vessel wall opposite the injector deceases with plasma density. Since each PINI follows a different path through the plasma, then each PINI will experience a different shine-through at any single plasma condition. For the plasma equilibrium considered in this calculation (Pulse No: 78647) the values of the full energy shine-through as a function of plasma line average density are plotted in figure 1. Apparently, most of the shine-through power is caused by the two most normal PINIs which have the shortest paths though the plasma. For the plasma used in this calculation, the full energy power striking the vessel protection plates is about 1.7MW and the half energy power is 0.5MW.