ICIS2023 - 20th International Conference on Ion Sources September 17-22, 2023

Factors Influencing the Fluctuation Amplitude of the H- Ion Beam Extracted from an RF Wave Excited Ion Source Plasma

Not scheduled

20m

Victoria Conference Centre

Poster (by default) Beam Formation, Extraction, Transport, and Diagnostics Monday

Speaker

Takanori Shibata (KEK)

Description

An internal antenna type RF driven negative hydrogen (H${}^{-}$) ion source supplies beams to the J-PARC accelerator facility. The H${}^{-}$ ion beam current exhibits high stability, while it fluctuates with less than 5% amplitude of the DC current when a Faraday cup measures the current extracted from the source mounted on a test stand. Two frequencies are identified as the main oscillation components, 2 MHz and 4 MHz which are the driving RF frequency and the second harmonic, respectively. The amplitude levels of these components appear larger as parts of the beam directing specific angles passing through a slit are detected. A possible reason for observing a small amplitude oscillation in the total beam intensity is the averaged phase-shift of the local beam depending upon the position of the H${}^{-}$ ion production and the succeeding trajectory reaching the Faraday cup. To confirm if the phase-shift is the main reason for diminishing the oscillation amplitude for the total beam, the phase-shift between the 2 MHz and 4 MHz components were measured for beams passing through a 0.1 mm slit detected by a Faraday cup having a 0.1 mm entrance slit. The result indicated the phase-shift changed substantially depending upon the position, but no simple model can explain the measured spatial distribution of the phase-shift. Further attempts will be made to clarify the beam dynamics relevant to the H${}^{-}$ ion beam transport including the measurements of the beam current phase-shift with respect to the RF antenna current, and the time evolution of Balmer-$\alpha$ light emission from the source plasma.