Plasma core fueling by NBI and discovery of Li doping effect on beam capturing on LTX-β

The core issue impacting tokamak performance is plasma edge cooling due to recycling, which leads to peaked temperature profiles and anomalous thermal conduction. This requires excessive heating power, exacerbating plasma surface interactions (PSI) and making the plasma regime unpredictable and prone to disruptions. The current practical approach involves reducing plasma performance by lowering plasma current and enhancing the toroidal field, as seen in two recent JET DT-campaigns. The resulting Q_DT=1/3 << 1 on JET essentially invalidates the high recycling regime and projects a reduced plasma current of 10-11 MA in ITER by q-scaling.

The alternative is the low recycling regime, which utilizes plasma edge pumping by lithium and core fueling by an energetic neutral beam injection (NBI). Contrary to common beliefs, lithium is the only material that tokamak plasma should face, as it eliminates PSI and ensures predictable plasma behavior. Lithium prevents tritium accumulation in the vessel from burning plasma and allows Real Time Tritium Recovery. The He ash pumping is feasible, it is not detailed here. LTX-β has demonstrated the viability of NBI core fueling in low recycling regimes. With only 4% Li3+ doping in LTX-β plasma (confirmed by ADAS-based modeling), a 50% capture of 20 keV NBI particle flux has been achieved, which can be replicated in other tokamaks. The similar effect in a burning plasma, naturally doped with 10% He++, would reduce NBI charge exchange losses to an acceptable level of less than 25%.