Accumulation Process of Negative Ions in a Hollow-Type Magnetized Plasma

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1) A magnetized plasma from CF_4 gas is generated by the electron cyclotron resonance discharge and a follow-type magnetized plasma is produced by use of a disk-type obstacle at the downstream region of the plasma. Inside the hollow-type plasma, fluorine positive and negative ions are accumulated, generating an ion-ion plasma. By means of a probe measurement, the ratio of negative ion density to electron density becomes more than 20. This phenomenon can be explained by a difference of radial diffusion speeds of electrons and negative ions. As the radial direction diffusion speed is decided by the collision frequency with neutral particles and a step length (a Lamor radius), the negative ions have much larger diffusion speed than that of electrons. As a result, positive and negative ions are preferably diffused into the vacuum region inside the hollow plasma. On the other hand, along the line of magnetic field, electron and ions freely move. At the end plates, high energy electrons tend … More s to flow into the plates beyond a barrier of sheath potential. Otherwise, the negative ions are reflected by the sheath barrier potential and well confined between the end plates. By this process, negative ions are effectively accumulated inside the hollow plasma2) By means of a multi-hole type obstacle, a multi-string plasma is produced at the down-flow region of the magnetized plasma from CF_4 gas. In this case, negative ions accumulate around the string plasmas. Here, many string plasmas are generated with same interval and large volume negative-ion accumulation can be produced. As a results, the large area negative ion source with cross-section of 30 cm^2 has been successfully generated. By use of a magnetic filter a negative ion-beam can be extracted from this plasma source and can be used for the large-area negative ion processing and the neutral beam processing.3) By means of a UV-range pulsed laser, amount of negative ions inside the follow plasma is measured and it is compared with the probe data. Less