Applicability of Laser-Induced Desorption Quadruple Mass Spectrometry (LID-QMS) for the Determination of Local Deuterium Retention

Abstract

Laser-induced desorption quadruple mass spectrometry (LID-QMS) is under development in the target exchange and analysis chamber of MAGNUM-PSI. Research to the applicability of LID-QMS as a diagnostic to determine local deuterium inventories is conducted. It is concluded that LID-QMS can only be used without calibration with thermal desorption spectroscopy (TDS) for the analysis of standard tungsten samples without created damage when the fluence achieved with Pilot-PSI is known and ≤ 3 ∙ 1026𝑚−2. Assumptions about the trap energy and trap density in tungsten are necessary for the desorption area determination. These assumptions are validated with TMAP7 simulations for samples and exposures used in this work. Uncertainties arising from assumptions on the trapping depth are included in the error analysis. When using different exposure conditions it is necessary to cross calibrate against TDS to re-validate assumption made. No influence of LID-QMS on TDS profiles is observed. Inconsistencies observed are indicated to be due to irregularities in surface modifications probably arising from irregularities during plasma exposures. This statement is supported by optical microscopy pictures. A trend of increasing deuterium retention for increasing bias voltage is observed. Desorption from high energy traps with LID-QMS seems to be impossible. This is shown by comparing two damaged targets with known trap properties: for both the sample analyzed with LID-QMS and TDS and the sample only analyzed with TDS the high energy traps are completely filled when fitting TDS profiles with TMAP7.