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Description
Third-generation electron cyclotron resonance (ECR) ion sources utilize superconducting magnets to achieve the enhanced plasma confinement necessary to produce intense, highly-charged ion beams. While the classical model predicts that plasma density, and thus, beam current, scales with the square of the heating frequency, two-frequency RF heating may alter this relationship. Additionally, higher RF power and frequencies generate a greater population of energetic electrons, which drive bremsstrahlung emission and impose a significant thermal load on the 4 K liquid helium cryostat. We investigate two-frequency RF heating (18 GHz and 28 GHz) in the 3rd-generation VENUS ECR ion source to determine whether an optimal power ratio exists to maximize beam intensity and favorably shift the charge state distribution to higher charge states. By analyzing non-invasive axial bremsstrahlung emission, we ascribe spectral temperatures to the hot electron population under varying power levels and ratios. The work presented here confirms previous measurements while exploring the deviation from single-frequency density scaling and x-ray emission properties. These findings will advance our fundamental understanding of multi-frequency heating on plasma behavior and inform RF tuning strategies for the upcoming fourth-generation MARS-D ECR ion source.
| Classification | MC3: Fundamental processes and plasma studies |
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