ECR ION-SOURCE USING SLOW-WAVE STRUCTURES

In this ECR ion source, the possibility of maintaining the plasma by slow wave structures (SWS), helical coil, and slotted line antennas, in the region where w(ce), w(pe) >> w(rf) (w(ce), w(pe), and w(rf) are electron cyclotron, plasma, and microwave frequencies, respectively) is exploited. The plasma parameters, plasma density, and electron temperature are maximized by coupling microwave (frequency: 2.45 GHz; power: 650 W) at two places in a magnetic mirror machine (mirror ratio R(m) congruent-to 1.45) to obtain higher beam current. Initially, the plasma is produced by coupling microwave to SWS at the mirror throat. The microwave is coupled by exciting the dominant slow wave field component of SWS, using an E-plane horn antenna. Then the plasma is brought to the region w(ce), w(pe) >> w(rf) at the mirror throat by increasing the magnetic field. Simultaneously, the ECR region is shifted from mirror throat to the center where second microwave coupling is done at the resonant region using another horn antenna. The characterization of plasma parameters are presented for both helical coil and slotted line antennas. Enhancement of plasma parameters are observed in the present scheme. Also, the SLA is found to produce better plasmas (n(e) approximately 7 x 10(12) cm-3 and T(e) approximately 12 eV) than the helical coil and hence the SLA is chosen for the ion beam characterization. The extracted ion beam current density in the present scheme is approximately 25 mA/cm2 at 2-kV extraction voltage.