Magnetic Sheath Character Of Edge Plasma In Fusion Device

The magnetic sheath structure of edge plasma in fusion device is investigated by using fluid dynamics method. Ion thermal pressure and ion magnetization are considered and the effects of the intensity of magnetic field, magnetic field direction, different plasma density and ion temperature on the character of plasma sheath are researched. And the suspended potential of the wall and the Bohm criterion of plasma magnetized sheath under the ion temperature effect are also deduced.Take H ion and its isotope as an example, we do research on the character of plasma sheath under many parameters. We get that the absolute of wall potential increase when the magnetic field tilt angle increase, and sheath thickness decrease first and then increase. As angle increasing, the density of net charge and ion appear vibration for the ion gyromotion under the strong magnetic field.; When the intensity of magnetic field increases, the sheath thickness decreases.; When ion temperature is higher,the sheath thickness is lower; When the plasma density is higher, the sheath thickness is lower.The result is the same with the character of plasma sheath without magnetization. In lower plasma density, the density of ion and net charge appear peak value at the boundary of plasma sheath; When ion mass is higher, the absolute value of wall potential is higher, and the sheath thickness is higher.Because the temperature of edge plasma in fusion device is more than ten to one hundred electron volt, the interaction between high energy electrons or ions and wall may creates secondary electrons, and the effects of secondary electrons to the character of plasma sheath are also researched. Secondary electrons emission makes that the absolute value of wall potential and sheath thickness decrease. The coefficient of secondary electrons is higher, and the absolute value of wall potential and sheath thickness are lower. On the considering of secondary electrons emission, through researching the effects of the intensity of magnetic field, magnetic field direction, different plasma density and ion temperature on the character of plasma sheath, we find that the results are the same with the condition of no secondary electrons emission.Based on the research of secondary electrons density distribution in the sheath, we find that ion mass is higher and the density distribution of secondary electrons is lower. It's because that ion mass is higher, absolute of wall potential higher, the velocity and energy of electrons at the wall lower, and the secondary electrons produced by the interaction of electrons and wall are less.; Ion temperature is higher, and the density of secondary electrons is higher. It's because that ion temperature is higher, absolute of wall potential lower, the velocity and energy of electrons at the wall higher, and the secondary electrons produced by the interaction of electrons and wall are more.