Two-frequency heating technique at the 18 GHz electron cyclotron resonance ion source of the National Institute of Radiological Sciences

Abstract

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.

X-ray pinhole camera setups used in the Atomki ECR Laboratory for plasma diagnostics

“…7 Formerly, the TrapCAD was successfully used for the interpretation of the fluctuation of the highly charged ions one of the injected rf frequency. 10 The code is based on the one electron approach neglecting the particle-particle interactions. Circularly polarized plane wave is assumed to be propagating along the chamber axis.…”

Concept design of new compact electron cyclotron resonance ion source with permanent magnets for multi-ion radiotherapy

“…The KLY was used daring output power of 0 to 1200 W (blue dot). Two-frequency heating method [8,9,10] was used from 1300 to 2000 W (red dot). Dotted line shows requirement values.…”

Recent developments of ion sources for life-science studies at the Heavy Ion Medical Accelerator in Chiba (invited)

“…Between 1998 and 2013 numerous experiments were carried out at NIRS; in each experiment a positive effect of the second microwave was demonstrated. 21 The mechanism is still not completely clear. Our basic observation is that when the primary microwave power increases, the plasma shows instability.…”

“…Some recent observations of the additional frequency dependence suggested that an electron orbit effect might play some role. 21 One approach to verify or to reject this assumption is a computer simulation. Calculations by the TrapCAD code have continued.…”