  This work presents a tunable varactor with tunability in the range of 100s of
MHz and a capacitance delta of about 36 pF by employing a perpendicular
magnetic field to a capacitively-coupled (CCP) RF plasma cell. A comprehensive
high-frequency circuit model for the fabricated varactor is proposed and
verified experimentally for a plasma electron number density of
$2.95\times10^{17}m^{-3}$ which has a tunability of 146 MHz with a magnetic
flux density ranging from 0 to 246 milliTesla. Under a pressure of 64
milliTorrs, the Argon ccp was found to have a variable capacitance ranging from
4 pF to 41.72 pF.
