Feasibility study on high current density ion sources using a compact high density plasma source

Abstract

Feasibility of a high current density ion source is studied through the simulation of ion extraction system and the basic experiments of a high density plasma source. Numerical simulation of extraction system is performed by using a free boundary ion source code of IGUN？. The possibility of a high current density ion source is confirmed at relatively low extraction electric field, and the required plasma density for this kind of ion source is estimated to be high. For example, a proton ion source of 414mA/㎠ current density with 50kV extraction voltage needs the plasma density of up to $8.9 \times 10^{11}#/cm^3$. To get the high-density plasma satisfying high plasma density requirement, a compact microwave plasma source using permanent magnets is developed by imposing axially much higher B-field than that of electron cyclotron resonance, which may limit to the plasma density due to the existence of density cut-off. The plasma can be initiated in this plasma source when the microwave energy is delivered via the coaxial feedthrough by applying sufficient Helium gas puffing of 200mTorr. The maximum microwave absorption is observed near 15mTorr and the plasma density is above $10^{12}#/cm^3$ in such region. The compact microwave plasma source shows the possibility as a high density plasma source for high-current density ion sources at relatively low extraction voltage.