Speaker: Bill Capecchi, University of Wisconsin-Madison
Abstract: Neutral beam injection (NBI) can fulfill a crucial role in sustaining, fueling, and heating low recycling plasmas in the Lithium Tokamak Experiment-β (LTX-β). Initial results and modeling showed limited heating and low coupling of the beam due to a strong dependence on variations in beam and plasma parameters throughout a discharge, and were only successful at a modest beam energy of 13 keV, well below the maximum beam energy of 20 keV. Modeling of these discharges suggested heating above that observed, indicating the need for improved determination of the injected beam power and profile shape. A 2D tungsten wire calorimeter has been designed and installed at the outlet of the neutral beam neutralizer which will give shot specific beam profile data and allow improved constraints on future beam modeling. A neutral particle analyzer (NPA) from UW-Madison is being installed to provide direct measurement of the confined fast ion population energy distribution. LTX-β is completing a vented maintenance phase during which the neutral beam was realigned to a more optimal injection geometry. Previous modeling has predicted peak beam coupling occurs at a tangency radius around 35 cm; the actual shift from 19 to 33 cm (limited by scrape-off on the injection port) is predicted to improve beam coupling by 30% at a beam energy of 13 keV. Improvements to coupling increase with beam energy; at the max beam energy of 20 keV the coupled fraction is expected to double. The status and plans for the upcoming run campaign will be discussed.