Improved chopping of a lithium beam for plasma edge diagnostic at ASDEX Upgrade

M. Willensdorfer, E. Wolfrum, R. Fischer, J. Schweinzer, M. Sertoli, B. Sieglin, G. Veres, F. Aumayr

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Abstract

The lithium beam diagnostic at ASDEX Upgrade routinely delivers electron density profiles in the plasma edge by lithium beam impact excitation spectroscopy. An accurate background subtraction requires a periodically chopped lithium beam. A new, improved chopping system was developed and installed. It involves a voltage modulation for the extractor electrode and the beam deflection plates. The modulation of the extractor electrode reduces the unused portion of lithium ions and improves the stability of the beam with respect to its position. Furthermore, the data indicate an extended emitter lifetime. The extractor chopping was also found to be insensitive to sparks. The deflection chopping experiments demonstrated beam chopping in the kilohertz range. The significantly higher modulation frequency of the deflection chopping improves background subtraction of fast transient events. It allows a more accurate density measurements in the scrape off layer during impurity injections and edge localized modes.

Original languageEnglish
Article number023501
JournalReview of Scientific Instruments
Volume83
Issue number2
DOIs
Publication statusPublished - Feb 2012

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ASJC Scopus subject areas

  • Instrumentation

Cite this

Willensdorfer, M., Wolfrum, E., Fischer, R., Schweinzer, J., Sertoli, M., Sieglin, B., Veres, G., & Aumayr, F. (2012). Improved chopping of a lithium beam for plasma edge diagnostic at ASDEX Upgrade. Review of Scientific Instruments, 83(2), [023501]. https://doi.org/10.1063/1.3682003