Multicharged Si and Fe ions are produced from solid materials in a 2.45 GHz electron cyclotron resonance (ECR) ion source. The ECR plasma is confined in a magnetic mirror field superimposed on an octupole magnetic field. Ar gas is normally chosen for working gas at pressures of 10−4 to 10−3 Pa. Si and Fe ions are produced by sputtering and evaporating solid materials, which are safe and easy to handle. The Fe (or Si) target is mounted at the tip of an insulated holder and inserted into the plasma. The negative dc bias voltages are applied to the target and multicharged Fe (or Si) ions are produced. Fe filament is evaporated in the ECR plasma by direct ohmic heating, and multicharged Fe ions are produced. Multicharged ions up to Fe6+ are produced by using both methods of sputtering and evaporating and Si4+ by using the sputtering method. The maximum ratio of the Fe and Si ion currents to total Ar ion current are about 15% and 13% obtained by the sputtering method, respectively. The maximum current densities of Fe+ and Fe4+ are 1.1×10−1 and 4.1×10−4 mA/cm2 obtained by the sputtering method, respectively.
The two-frequency heating technique was studied to increase the beam intensities of highly charged ions provided by the high-voltage extraction configuration (HEC) ion source at the National Institute of Radiological Sciences (NIRS). The observed dependences on microwave power and frequency suggested that this technique improved plasma stability but it required precise frequency tuning and more microwave power than was available before 2013. Recently, a new, high-power (1200 W) wide band-width (17.1-18.5 GHz) travelling-wave-tube amplifier (TWTA) was installed. After some single tests with klystron and TWT amplifiers the simultaneous injection of the two microwaves has been successfully realized. The dependence of highly charged ions (HCI) currents on the superposed microwave power was studied by changing only the output power of one of the two amplifiers, alternatively. While operating the klystron on its fixed 18.0 GHz, the frequency of the TWTA was swept within its full limits (17.1-18.5 GHz), and the effect of this frequency on the HCI-production rate was examined under several operation conditions. As an overall result, new beam records of highly charged argon, krypton, and xenon beams were obtained at the NIRS-HEC ion source by this high-power two-frequency operation mode.
Production of multicharged ions is experimentally studied on an electron cyclotron resonance (ECR) source. The ECR zone for a microwave frequency of 2.45 GHz is formed at the bottom of a mirror trap. The x-ray spectra are measured by Si-pin diode detector in the various operating conditions. Available energy range of the x-ray measurement is several keV approximately several tens keV. Measurements are carried out at either line of sight including the ECR zone along the geometrical axis or at off-ECR zone from the side wall. The temperatures determined at both positions are about 2–3 keV from the observed spectrum with assuming nonrelativistic maxwellian plasma. The intensities of Ar Kα and bremsstrahlung radiation correlate to pressure and microwave power dependence of multicharged-ion production. But the dependence of the temperature is not clear. Therefore the multicharged-ion production largely depends on an abundance of high energy electrons rather than the change of the temperature of them in this energy region; and it is suggested that the emission profiles of the x-ray radiation peaks at the center of the mirror at the low pressure.
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