Abstract
The performance of the electron cyclotron resonance ion source (ECRIS) increases proportionally to the microwave frequency squared. This behavior encourages the use of higher microwave frequencies. However, a higher frequency would require a stronger magnetic field for the efficient operation of ECRIS. A rather complicated magnetic field configuration results from the combination of solenoids for the axial confinement and a multipolar radial field usually provided by permanent magnets. These fields produce the so-called B-minimum structure which is required for a stable and efficient operation of ECRIS. The highest multipole field achieved so far in an ECR ion source by using permanent magnets is about 1.3 T. This makes the efficient operation at a microwave frequency of about 18 GHz possible. We introduce here a new approach to further increase the magnetic multipole field provided by permanent magnets. According to our two-dimensional (2D) simulations, a remarkable improvement in the radial magnetic field of the multipole can be achieved. The idea was tested using a simple construction in the plasma chamber of the JYFL 6.4 GHz ECRIS. The multipole field increased from 0.37 to 0.5 T while the solenoids for the axial magnetic field were excited. This result is consistent with our 2D simulations. Based on our simulations and the simple test with the JYFL 6.4 GHz ECRIS, we believe that a multipole field value of 2 T is feasible in ECRIS while still using permanent magnets.
Published Version
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