High performance superconducting 28 GHz ECRIS


At FAIR-GSI, a great variety of intense beams of ions from protons up to U are requested, including beams of rare isotopes. Such beams of heavy ions must be provided to the accelerator facility in routine operation with highest reliability, reproducibility, and stability. To achieve a significant increase of ion beam intensities from an electron cyclotron resonance ion source (ECRIS), an enhanced plasma density is required. According to semi-empirical scaling laws and experiments the electron density is directly related to the square of the microwave frequency. Suitable electron densities can be achieved with the use of 28 GHz microwave heating. Due to the electron cyclotron resonance condition the increased microwave frequency requires higher magnetic flux densities. For proper radial plasma confinement a stronger magnetic hexapole field with values above 2 T at the wall of the plasma chamber has to be provided.  In addition, a mirror field for axial confinement is required with two maxima in the range of 2 - 4 T.

These values can only be achieved by using superconducting magnets for the solenoid coils generating the mirror field as well as for the hexapole. An intrinsic operational advantage is given by the fact that the hexapole consists of coils instead of a permanent magnet system like in conventional ECRIS. This enables a variation and optimization of the radial confinement and allows an optimal adaptation to different working points. The production of highly charged ions facilitates the injection into a LINAC without post-acceleration. A SC-ECRIS is characterized by a high versatility, a high efficiency, good beam stability and low beam noise. Furthermore such an ion source can be operated either in high duty cycle mode or in special pulsed modes for high pulse intensities.

Intensive R&D will be mandatory to achieve the optimum operating conditions for operation at the accelerator. An improved ion extraction system adapted to the enhanced extracted ion currents shall result in efficient beam formation and transport. The complementary operation of the new SC-ECRIS and the existing ECRIS requires the design of an extended layout of the low energy beam transport (LEBT).