27pA03
高βリップルトカマクにおけるα粒子のエネルギー損失に関する研究
Research for alpha particle losses in a high beta rippled tokamak
文野 通尚1、中村 祐司1、鈴木 康浩2、篠原 孝司3、松永 剛3、谷 啓二4
M.Bunno1, Y.Nakamura1, Y.Suzuki2, K.Shinohara3, G.Matsunaga3 and K.Tani4
京大エネ科1、NIFS2、JAEA3、日本アドバンストテクノロジー(株)4
Kyoto University1, NIFS2, JAEA3, NAT4
In a tokamak plasma, the confinement ofenergetic ions depends on the magnetic fieldstructure. If plasma pressure is finite, diamagnetic
current jdia and Pfirsch-Schlüter current jPS flow in aplasma to keep the magnetohydrodynamic (MHD)
equilibrium. These equilibrium currents generate
the poloidal and toroidal magnetic field and alter
the field structure. Moreover, if we consider thenon-axisymmetry of field structure such as toroidal
field (TF) ripples, non-axisymmetric component of
the equilibrium current jripple can alter TF ripples
themselves. When plasma beta becomes high, thischange of field structure due to equilibrium currents(i.e., jPS, jdia and jripple) might affect the confinementof energetic ions. It is well known that Shafranov
shift, which is caused by jPS, changes the birth
profile of alpha particles and affects these losses.
Therefore, we focus on how jPS and jripple affect theconfinement of alpha particles in a high beta
plasma.
For this purpose, alpha particle orbits
should be followed for the different magnetic fieldstructures with and without the field component due
to equilibrium current. We artificially created threecases of the field structure by solving MHD
equilibrium equation. In Case.(i), the fieldcomponent due to whole equilibrium currents (i.e.,jPS, jdia and jripple) are included. Since the effect ofjripple is taken into account, it is exactly thethree-dimensional (3D) MHD equilibrium fieldstructure and the most accurate one. In Case.(ii),the field component due to jripple is artificiallysubtracted from 3D MHD equilibrium field (i.e.,Case.(i)). Since jPS and jdia can be calculated bysolving two-dimensional (2D) MHD equilibrium
equation, it can save the computation time if theeffect of jripple can be ignored. In Case.(iii), the fieldcomponent due to jdia is artificially subtracted fromCase.(ii). In terms of equilibrium current, the fieldstructure of each case can be categorized as below.
Case.(i): jPS, jdia and jripple
Case.(ii): jPS and jdia
Case.(iii) : jPS
Since the field structures of all three cases include

TF ripples generated by the toroidal field coils(TFCs), they have the non-axisymmetric fieldcomponent.
In this research, the structural design of areactor is referred to the ITER reactor which has 18TFCs. Keeping the plasma pressure profile, thesafety-factor profile and the shape of plasmaboundary, the MHD equilibrium is solved using theVMEC code with changing plasma beta. With thefield structures of Case.(i), Case.(ii) and Case.(iii),alpha particle orbits are followed using theF3D-OFMC code. If the particles reach the firstwall before the kinetic energy is reduced by thethermal energy due to the Coulomb collision, they
are assumed to become lose.
Figure 1 shows the volume averaged beta
value <β> dependence on loss power fraction forfusion alpha particles. The loss power fraction isdefined by the ratio of the total kinetic energy of allloss particles and the total initial energy of allparticles. In a relatively low beta plasma (<β>~2%),
the equilibrium currents (jdia and jripple) negligibly
affected the confinement of alpha particles. While
in a high beta plasma (<β>=6%), jdia significantly
increased alpha particle losses. In a high beta
plasma, jripple also increased these losses, but they
are not so effective when it is compared to jdia.

Fig.1 The blue, green and red x-marks respectively showloss power fraction for Case.(i), Case.(ii) andCase.(iii). Points of each color show the averagevalue and the error bars show the standard
deviation of loss power fraction