Abstract
An advanced tokamak is characterized by increased confinement, stability and steady state operation. The increased confinement and stability are obtained through modifications to the shape and profiles of the plasma and through stability feedback control. These modifications have to be self-consistent. The increased confinement makes it possible to make smaller and thereby lower cost reactors for the same power output as compared to conventional tokamaks. Four potential modes for advanced tokamaks are currently being studied on DIII-D: radiative improved mode, high internal inductance ℓi mode, negative central shear (NCS) mode, and quiescent double barrier (QDB) mode.High-density plasma are important for reactors and recent experiments in DIII–D have shown that it is possible to operate substantially above the Greenwald limit. Control of the internal transport barriers that are responsible for the increased confinement have been improved in counter injected neutral beam plasmas. One of the limiting instabilities for the performance of high bootstrap fraction negative central shear plasmas is the resistive wall mode. These modes have to a certain degree been suppressed in DIII–D by using the six-section correction coil. With a newly installed upper inner divertor in DIII–D it has been possible to obtain improved density and impurity control. An upgrade of the electron cyclotron system is being done on DIII–D. Three 1 MW gyrotrons are being added. This system has been used to completely suppress the neoclassical tearing mode by applying electron cyclotron current drive at definite positions and in very localized areas. Finally, the implication of the recent findings for fusion reactors will be discussed.
Published Version
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