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SUMMARY:Measurement of Azimuthal Bremsstrahlung Photon Emission from a 28-
 GHz ECR Ion Source Using NaI(Tl) Detectors
DTSTART;VALUE=DATE-TIME:20260519T102000Z
DTEND;VALUE=DATE-TIME:20260519T104000Z
DTSTAMP;VALUE=DATE-TIME:20260624T105733Z
UID:indico-contribution-3822@indico.tlabs.ac.za
DESCRIPTION:Speakers: Mwingereza John Kumwenda (University of Dar es Salaa
 m)\nThe emission of high-energy bremsstrahlung photons beyond the expected
  critical energy during electron cyclotron resonance (ECR) heating has att
 racted significant attention\, and its underlying mechanism remains not fu
 lly understood. In this study\, we measured the azimuthal angular distribu
 tion of bremsstrahlung photons produced in a 28 GHz ECR ion source at the 
 Busan Center of the Korea Basic Science Institute (KBSI). Three round-type
  NaI(Tl) scintillation detectors were used to simultaneously measure brems
 strahlung photons emitted radially from the plasma chamber. An additional 
 NaI(Tl) detector was positioned downstream of the ECR ion source to monito
 r the overall photon intensity. The ion source was operated at an RF power
  of 1 kW to extract an 16O ion beam\, with dominant charge states of O³
 ⁺ and O⁴⁺. Bremsstrahlung photon energy spectra were recorded at nin
 e azimuthal angles on the extraction side of the ion source. To evaluate p
 ossible systematic uncertainties arising from differences among the three 
 detectors\, measurements were repeated by alternating the detector positio
 ns. Geant4 Monte Carlo simulations were performed to account for geometric
 al acceptance and energy-dependent detection efficiency caused by non-unif
 ormities in the material budget. The true bremsstrahlung spectra were then
  reconstructed using an inverse-matrix unfolding method. The extracted end
 -point energies of the bremsstrahlung spectra were (2.040 ± 0.045) MeV at
  150°\, (1.650 ± 0.040) MeV at 330°\, and (1.610 ± 0.040) MeV at 330°
  for detectors D1\, D2\, and D3\, respectively. These values exceed the ma
 ximum electron kinetic energy of approximately 1.330 MeV expected from sta
 ndard ECRIS operating parameters. The higher end-point energy observed nea
 r 150° appears to correlate with the structural configuration of the ion 
 source and the the shape of the ECR plasma. However\, the secondary maximu
 m near 330°\, located roughly 180° opposite to 150∘ which is among the
  maximum angles\, cannot be explained solely by the shape of the ECR plasm
 a. We interpret these observations as evidence of unconfined high-energy e
 lectrons reaching the chamber wall and producing bremsstrahlung radiation.
  These escaping electrons likely arise from imperfect magnetic confinement
  within the ECR plasma. The results provide new insight into the mechanism
 s of high-energy bremsstrahlung production in ECR ion sources and suggest 
 that improved magnetic confinement design could reduce electron losses and
  associated high-energy photon emission.\n\nhttps://indico.tlabs.ac.za/eve
 nt/139/contributions/3822/
LOCATION:NRF-iThemba LABS\, Old Faure Road\, Cape Town Auditorium
URL:https://indico.tlabs.ac.za/event/139/contributions/3822/
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