Divertor pumping and other reactor application issues for H-mode

We summarize results from DIII-D in regard to issues for reactor application of H-mode. Recently, DIII-D has begun to operate a cryopump (D ₂ pumping speed =31,000 l/s at a pressure of 2 mTorr). Initial results are very favorable for density control in H-mode. The plasma density could be reduced by 50%. Energy confinement is unchanged so the temperature rises in proportion to the density drop. Ability to access these less collisional plasmas in H-mode is favorable to current drive application. With the all-graphite wall, impurity accumulation has been eliminated. The exceedingly good confinement of VH-mode offers the possibility of retaining good confinement while radiating copious power from the plasma edge using injected noble gas impurities.