Plasma Commissioning Scenario and Initial Tritium Inventory for Demo-CREST

Full text: This paper discusses the plasma commissioning scenario and the relationship between the initial tritium inventory and the commissioning period for a demonstration reactor concept Demo-CREST. The tritium density ratio (T-ratio) control is applied to keep the high density operation preferable for the divertor heat-handling during gradual increase of the fusion power in the commissioning phase. It is found that Demo-CREST can start from zero-fusion power operation with T-ratio 0%, in which the divertor heat-handling condition on the SOL density and the radiation power required for divertor heat load less than 10 MW/m2 is similar to that of the ITER steady state operation. The operational space for Demo-CREST was investigated by the MHD stability code ERATO and the current drive analysis code DRIVER88. The divertor heat load condition is evaluated by the two point SOL-divertor model, and the initial operation point with T-ratio 0% is confirmed by the SOL-divertor transport code SOLPS5.0. An operation route keeping high density by the T-ratio control is also proposed for the commissioning. The critical issue on this commissioning scenario is the plasma confinement. In case of smaller T-ratio than 10%, a high plasma confinement HH =1.57 similar to that of the ITER steady state operation is required. This proposed operation route has a consistency with the start-up scenario without the initial tritium loading, in which tritium production is started from the DD fusion neutron by the beam direct fusion reaction. The relationship between the initial tritium inventory and the commissioning period is evaluated for Demo-CREST. When this startup scenario without initial tritium was applied to the operation route with the T-ratio control of Demo-CREST, the commissioning period (Tcom) from T-ratio 0% to 50% results in Tcom = 360 days, under the condition of the total dead inventory 1000 g and the tritium breeding ratio (TBR) 1.05. When the commissioning period has to be shorten to Tcom = 90 days, the required initial tritium increases up to about 1000 g. Decrease of TBR results in increase of initial tritium loading. When the commissioning period has to be shorten within Tcom = 90 days, the tritium breeding during the commissioning phase is not effective to reduce the initial tritium loading even with the high TBR such as 1.10. (author)