In this paper the integrated modelling for the steady-state regime of a fusion neutron source DEMO-FNS (R/a=3.2m/1m, B=5T, Ip=4-5MA)  is complemented by the helium balance in the divertor and core plasma. The model describes the power and particle balances consistently in the divertor and core plasmas according to approach  and finds the condition to fulfill the global requirements on: neutron source value Sneut >1019/s, maximal peaking heat load is limited by qpk <10MW/m2, keeping up-down symmetry and avoidance of deep detachment, μ<1, condition for plasma current overdrive Ipl ≤ IBS+ICD , when the plasma current Ipl is generated by the noninductive methods from neutral beam ICD and from the bootstrap current IBS and on a source by pellets Spel>fT/(1-fT)SNB, that control the tritium fraction fT =nT/(nT+nD) in a core, where SNB is the D source from neutral beam, Spel is the pellet source of D and T.
The energy and particle balances in the core plasma are modelled with transport equations in the ASTRA code  using ITER IPB(y, 2)  with prescribed H-factor, ratio of main ions and helium confinement times to the energy confinement time τp/τE, τНе/τE , tritium fraction, fT, electron averaged density <ne> (maintained by the pellet source Spel) and density at the pedestal (see Table 1). Model for the pedestal poloidal beta and the pedestal width is taken from [5,6].
The state of divertor plasma is determined by the values of the incoming heat flux PSOL, the neutral pressure in divertor volume pn, the concentration of the neon impurity CNe and the pumping speed Cpump to pump out the helium ash produced by the fusion reaction (see Table 2). Results of SOLPS4.3  series runs are approximated by analytical dependencies (scalings) in order to install the boundary conditions and heat and particle fluxes through the separatrix into the core plasma.
Self-consistent modeling of central and divertor plasma for DEMO-FNS  allows to determine the acceptable window of the divertor parameters pn and CNe where the global requirements are fulfilled (see Figure). It should be noted that in comparison to the modelling without helium balance  the acceptable parameter window become significantly constricted. The neutron yield is weakly reduced but remained to be at the reasonable level Sneut= 1.1·1019/s. As one of the neutron reduction factor is the decrease of the tritium fraction in the core plasma in order to fulfill the requirement to tritium fraction control with pellet source (see Table 3). The up-down symmetry requirement (μ<1 red line in Figure) become a strong factor in the divertor neutral pressure pn limit. We need to make an accurate investigation of a single X-point configuration as it can be more efficient to mitigate the power load to divertor plates.
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Table 1 Set of core plasma parameters
τp/τE, τНе/τE 4
Ipl, MA 4.5
<ne> 1019/m3 7
Table 2 Set of divertor plasma parameters
PSOL, MW 37.5
pn, Pa 2
Cpump, m3/s 20
qpk, MW/m2 9.7
Table 3 Result global values
Sneut 1019/с 1.1
IBS, MA 1.7
ICD, MA 2.8
PDT МW 31
PDT_pp /PDT_bp 1.8
|Affiliation||National Research Center "Kurchatov Institute"|
|Country or International Organization||Russia|