SIESTA: A high current ion source for erosion and retention studies

Area of Science:

• Nuclear Fusion Engineering
• Materials Science
• Plasma Physics

Background:

• Fusion devices require robust wall materials capable of withstanding extreme conditions.
• Understanding erosion and retention mechanisms is critical for fusion reactor longevity.
• High-current ion sources are essential tools for simulating plasma-wall interactions.

Purpose of the Study:

• To develop and characterize a high-current ion source for sputtering and thermal desorption spectrometry (TDS) analysis.
• To optimize ion beam parameters for erosion and retention studies relevant to fusion device wall materials.
• To investigate the performance of a DuoPIGatron ion source with advanced beam manipulation optics.

Main Methods:

• Utilized a DuoPIGatron ion source with variable acceleration potential (500 V - 10 kV).
• Employed a mass-filtering dipole magnet and a quadrupole doublet lens for beam focusing.
• Conducted experiments in a high-vacuum target chamber (10⁻⁸ mbar base pressure) with in situ capabilities including target heating (up to 1300 K) and a magnetic suspension balance.
• Measured ion flux density and beam emittance for D₃⁺ ions.
• Performed ex situ sputter yield measurements on gold samples.

Main Results:

• Achieved maximum ion current at the target by mapping ion source operating parameters.
• Quadrupole doublet lens increased ion flux to the target by up to a factor of 4.
• Quantified neutral particle population in the beam at 0.8%.
• Attained low ion impact energies (200 eV/D) with D₃⁺ current of 100 μA, yielding a flux density of 3.7 × 10¹⁹ m⁻² s⁻¹.
• Reached maximum D₃⁺ flux density of 6 × 10¹⁹ m⁻² s⁻¹ at 2 keV/D impact energy.
• Experimental sputter yields for gold showed good agreement with simulations and literature data.

Conclusions:

• The developed high-current ion source is effective for simulating plasma-wall interactions in fusion devices.
• Optimized beam focusing and energy control enable precise studies of erosion and retention.
• The system provides valuable data for the selection and development of fusion reactor wall materials.