Modelling of dynamics and transport of carbon dust particles in tokamaks

Abstract

The transport of dust particles in tokamak fusion devices is studied using computer simulations with the dust transport code, DUSTT. Recent developments in modelling with the DUSTT code are reported. The improved model of dust dynamics in edge plasmas takes into account several additional effects, including thermionic and secondary electron emission which affects dust charging and heating, dust grain size effect on thermal radiation, and the presence of impurities in the plasma. It is shown that thermionic emission leads to enhanced dust heating by the plasma that boosts destruction of dust particles. The zone structure of tokamak plasmas is introduced for a qualitative analysis of dust survivability conditions. It is shown that a dust particle can experience net deposition in relatively cold carbon-contaminated plasma regions. Trajectories of sample dust particles in the DIII-D tokamak are simulated and analysed using the zone plasma description. Statistical averaging over an ensemble of particle trajectories is used to obtain spatial distributions of dust characteristics in the edge plasma of tokamaks. It is shown that transport of dust in tokamaks can significantly enhance penetration of carbon impurities towards the core plasma.

Modeling of dust-particle behavior for different materials in plasmas

“…It is important to note that DUSTT takes into account the reduction of thermal radiation from dust particles, the size of which is smaller than the emission wavelength, as described in Ref. 3. In addition, the DUSTT code also solves the equilibrium relation for electric current to obtain the floating potential and the charge number of the dust,…”

“…The plasma particle ͑⌫ e and ⌫ i ͒ and heat ͑P kin,i , P kin,a , P kin,e , and P pot ͒ fluxes are obtained according to the orbital motion limited ͑OML͒ theory, 50 and the summary of formulas used in DUSTT is given in Ref. 3. The secondary electron emission yield depends on the energy and angles of incident plasma electrons and ⌫ e SEE was calculated by its averaging over the velocity distribution function.…”

“…The transport of carbon dust particles in tokamak edge plasmas has been studied by Krasheninnikov et al 7 and by Pigarov et al using the numerical simulation approach. [1][2][3] In particular, these simulations demonstrated the large mobility of dust particles in various plasmas, predicted rather deep penetration of dust particles toward the core plasma in the current tokamaks, and pointed out the potential importance of dust transport for plasma performance in the next-step fusion devices. Work on validation of dust simulation codes against experiments on fusion devices has begun.…”

“…Dust also can be an important contributor to impurity contamination of the core and scrape-off-layer ͑SOL͒ plasmas in tokamak fusion devices, [1][2][3][4] which may increase radiation loss from the plasmas and affect recycling regimes in the divertor regions. Thus, novel experimental and theoretical studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] on dust composition; mechanisms of dust formation; dust thermochemical, electrical, magnetic and radiative properties; statistical distribution of dust particles over sizes, shapes, porosity, etc. ; and dust transport in fusion plasma devices have started.…”

“…Electronic mail: tanaka@ec.t.kanazawa-u.ac.jp fect the dynamics of dust particles in tokamak plasmas. While the dynamics of dust particles [1][2][3][4][5][6][7] and statistically averaged macroscopic dust profiles 2,3 in tokamak plasmas are intensively studied for carbon, the behavior of dust consisting of other fusion-related materials or of a combination of materials remains unexplored.…”