MEASUREMENT OF GASEOUS IMPURITIES IN JT-60U

Using quadrupole mass analyzers, measurements were made of gaseous impurity pressures at the inner and outer divertor regions and at the mid-plane during neutral beam heated discharges in JT-60U. The hydrocarbon partial pressures in both divertor regions increase with the deuterium pressure, as a common function of deuterium pressure, (i.e., P-CD4 = 3 X 10(-2) P-D2(0.7) for CD4), irrespective of different discharge conditions of neutral beam heating power, direction of ion grad-B drift and gas puffing. On the other hand, the pressures of CO and CO2 are rather insensitive to the deuterium pressure. The sum of the gaseous impurity partial pressures is dominated by CO and CO2 in the low recycling discharges, and by hydrocarbons in the high recycling discharges. The total gaseous impurity pressure, as a fraction of the deuterium pressure, is on the order of 50% and 1-10% in the respective recycling regimes.