Density limits in TEXTOR-94 auxiliary heated discharges

In a tokamak plasma the maximum achievable density is limited. A too high d ensity will result in a violent end of a discharge. Two types of density li mit disruption can be distinguished: (a) impure and moderately heated disch arges, if the radiative power exceeds the input power, (b) clean, auxiliary heated discharges, where the Greenwald limit is encountered. It has been f ound that in TEXTOR-SI these two density limits differ by the radiative ins tability in the plasma boundary, which preceeds the disruption. A symmetric radiative mantle and a detachment are observed prior to the first type, wh ile the Greenwald limit has a MARFE precursor. Control of the impurity cont ent, edge and recycling properties prevents the growth of the MARFE and mak es it possible to exceed the Greenwald limit in TEXTOR-94 by more than a fa ctor of 2. High densities have been obtained by means of normal gas feed. M aximum central densities of n(e)(0) = 1.3 x 10(20) m(-3) have been obtained . The maximum achievable density scales with the input power and plasma cur rent. Non-disruptive discharges, with a stationary (t > 25 tau(E)) density a factor of 1.93 above the Greenwald limit have been produced in L mode. Th e radiative losses and impurity concentration have been maintained at a rel atively low level during the entire high density phase.