Deuterium retention characteristics in Li film by coating and during flowing liquid Li limiter operation in experimental advanced superconducting tokamak

Abstract

Lithium (Li) is a promising low-Z material for particle recycling and impurity control to improve plasma performance in fusion devices. In the experimental advanced superconducting tokamak (EAST), Li coating has become a routine method for wall conditioning, and a flowing liquid Li (FLiLi) limiter has been successfully tested several times. Deuterium retention characteristics in the Li film coated on the international thermonuclear experimental reactor-like tungsten divertor and FLiLi during plasma discharges, which is important for the utilization of Li in future fusion devices, were investigated in EAST. It is found that the absorption of the fuel particles by Li coatings decreases gradually, and recycling gradually increases over a series of discharges. The maximum net amount of deuterium retained reached ∼0.8 g, corresponding to 12% deuterium in the Li. This corresponds to a whole day’s worth of shots with a total of 87 plasma discharges and a total of ∼640s plasma time after 11.75 g Li was deposited. Compared to the Li coating, it is shown that FLiLi continuously traps fuel particles and achieves a higher deuterium retention ratio over both the short- and long-term, leading to lower recycling. Meanwhile, it is also observed that the fuel particle retention ratio increases when FLiLi is closer to the plasma. This result is likely due to higher plasma heating power and limiter temperature, which cause an increased Li efflux from FLiLi due to a higher limiter temperature, which then redeposits on the other plasma-facing surfaces and increases fuel particle absorption. It is estimated that ⩾80% of the retained D particles are captured by the continual renewal of the Li redeposition film during the FLiLi operation. This investigation would also be useful for D/T retention in future fusion devices if Li is used as a plasma-facing component.

Advances in the long-pulse steady-state high beta H-mode scenario with active controls of divertor heat and particle fluxes in EAST

“…In EAST, Li coating was used as a routine wall conditioning method. However, the absorption of the fuel particles by Li coatings decreases gradually, and recycling gradually increases over series of discharges [34]. The maximum net amount of deuterium retained reached ~0.8 g, corresponding to 12% Gas balance analysis confirmed a progressive increase in the fuel retention: the retention ratio, defined as the fraction of the fuel retained on the walls divided by the total injected fuel, increased from -0.8 to 0.55 with repeated FLiLi insertion.…”

“…In EAST, Li coating was used as a routine wall conditioning method. However, the absorption of the fuel particles by Li coatings decreases gradually, and recycling gradually increases over series of discharges [34]. The maximum net amount of deuterium retained reached ∼0.8 g, corresponding to 12% deuterium in the Li.…”

Deuterium recycling and wall retention characteristics during boron powder injection in EAST

“…This relationship can be expressed by equation (1): Here, Q retention is the amount of retained D particles in wall, Q , puffing Q , pumping Q vessel and Q plasma are the amount of injected D particles, pumped D particles, neutral D particles in the vacuum vessel, and deuterium ions in plasma, respectively. The equations used in the calculations were taken from a previous study [15]. Deuterium (D) particles are introduced into the plasma discharge vessel through normal gas puffing, supersonic molecule beam injection (SMBI), and neutral beam injection (NBI).…”

“…The retention ratio (%) represents the retention fraction, while the retention rate (D atoms/s) is the derivative of the retention amount with respect to time, reflecting the real-time rate at which D particles are retained. The detailed gas balance calculation process, as well as the calibrated pumping speeds of all pumping systems, were described in reference [15], and the measurement error in the gas balance was estimated to be approximately 8%.…”

“…The essential plasma parameters for these three shots were similar. Here, D particle recovery amount is defined as the number of particles released from the retained particles during plasma operation and after plasma discharge [15]. Puffing particles increased before 7.4 s, indicating an increased gas injection rate, as shown in figure 4(a).…”