Plasma Wall Interaction in Diva

Heat flux to the material surfaces in a tokamak

“…This paper describes an experimental study on the thermal interaction between plasma and walls in the divertor tokamak, DIVA [1][2][3][4][5]. The other interactions relevant to the release of the metal impurity, such as ion sputtering and arcing, are discussed in Ref.…”

“…It is well known that a sheath potential built up in front of an electrically insulated conducting plate plays an important role as a thermal barrier. The heat flux q (Wcm~2) towards an electrically insulated conducting plate in a plasma is written as follows [7]: Q = 7 Is T e (1) where I s (A cm 2 ) is the ion saturation current density, T e (eV) is the electron temperature and y is called a heat transmission rate; 7 = 7.8 for hydrogen plasma of T e = Ti, where Ti is the proton temperature.…”

Pulsed methane injection experiment on DIVA

“…DIVA is a tokamak with an axisymmetric divertor. A detailed description of the device and recent experimental results are given in Refs [3][4][5]. In the present experiment, the experimental conditions of the basic plasma into which methane gas is injected are as follows: toroidal field: 10 kG, peak plasma current: 14 kA, and ratio of divertor hoop current ID to plasma current Ip: 1.2.…”

“…In the present discharge of IDAP = 1-2, the separatrix magnetic surface is located at about 1 cm from the shell surface, and the particle flux guided to the burial chamber is about 10% of the total particle flux which diffuses from the main plasma. A large portion of the total proton loss flux consists in direct recycling at the gold-plated shell surface [4]. With these facts, in the present paper, we assume that the presence of the scrape-off layer which guides charged particles to the burial chamber can be neglected.…”

“…This is due to the fact that the inert gold surface eliminates the light-impurity contamination of the plasma. Although, in the methane injection experiment, the intrinsic carbon contamination grows to 3% of the electron density in the central region, a sizeable fraction of Z e ff is accounted for by metallic impurities since resistivity and radiation losses, which are measured by a pyroelectric detector, are not changed when the amount of light impurity is reduced to half of its value by flashing titanium on about half of the divertor chamber [4].…”