Development of a compact permanent magnet helicon plasma source for ion beam bioengineering

Abstract

A compact helicon plasma source was developed as a millimeter-sized ion source for ion beam bioengineering. By employing a stacked arrangement of annular-shaped permanent magnets, a uniform axial magnetic flux density up to 2.8 kG was obtained. A cost effective 118 MHz RF generator was built for adjusting forward output power from 0 to 40 W. The load impedance and matching network were then analyzed. A single loop antenna and circuit matching elements were placed on a compact printed circuit board for 50 Ω impedance matching. A plasma density up to 1.1 × 10(12) cm(-3) in the 10 mm diameter tube under the magnetic flux density was achieved with 35 W applied RF power.

Battery-powered pulsed high density inductively coupled plasma source for pre-ionization in laboratory astrophysics experiments

“…31 Although a number of other authors have labeled their small radius (R < 2 cm) RF discharges as helicon sources, 10,11,[32][33][34] the presence of propagating waves was not directly verified in any of these experiments. Only Shinohara et al 33 found compelling evidence for helicon mode operation by identifying two separate mode transitions from a CCP mode to an ICP mode and then to a helicon mode.…”

“…Only Shinohara et al 33 found compelling evidence for helicon mode operation by identifying two separate mode transitions from a CCP mode to an ICP mode and then to a helicon mode. Given that there are a number of practical uses for small RF plasma sources, 11,32,34 we expect that additional dedicated experiments designed to explore the scaling of helicon source operation with tube radius would yield interesting, useful results.…”

“…In contrast, a rough scaling of density with field strength has been observed in many helicon experiments 28,29 due to the linear proportionality between n e and B 0 in Eq. (11), with transitions between different axial or radial modes leading to jumps in the n e vs. B relation.…”

“…Driving each MOSFET at somewhat less than 50% duty cycle is generally necessary for stable operation. The circuit for the 1Q output, which consists of the right side of U3 (pins [8][9][10][11][12][13][14] and the attached components, is included in the diagram in Fig. 6.…”

“…a) Electronic mail: vernon.chaplin@gmail.com Low pressure RF plasmas, which include capacitively coupled plasmas (CCPs), inductively coupled plasmas (ICPs), and wave-heated plasmas (WHPs) such as helicons, are widely used in industrial materials processing, 9 as well as in other fields such as electric propulsion 10 and bioengineering. 11 They have been used for pre-ionization in at least one spheromak experiment similar to the Caltech experiments 12 and also to assist startup in some tokamaks. 13 In our experiment, 2-3 kW of RF power was delivered to the plasma through an external antenna by a customized pulsed 13.56 MHz RF amplifier.…”