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• In the absence of ion temperature measurements, a technique often adopted in tokamak plasmas is to estimate the ion temperature by reverse engineering of the total neutron yield, assuming Maxwellian distributions for the ions. • When ICRH external heating is applied, the ion distributions are no longer Maxwellian. • An improvement of the procedure is proposed to account for Non-Maxwellian ion distributions in order to get a better estimate of the ion temperature. Accurate measurements of the ion and electron temperatures in tokamaks are essential for understanding the heating and transport properties of the plasma. While electron temperature measurements are readily available in most devices (e.g. with electron cyclotron emission or Thomson scattering diagnostics), ion temperature estimates usually require more sophisticated procedures such as charge-exchange recombination spectroscopy [ 1 ] or crystal spectroscopy [ 2 ]. In the absence of such dedicated ion temperature measurements, a technique often adopted in tokamak plasmas is to estimate the ion temperature by reverse engineering of the total neutron yield, assuming Maxwellian distributions for the ions. In the absence of external ion heating, this procedure is satisfactory since it mainly depends on the nuclear reaction cross sections and the bulk ion density, usually inferred from a combination of the electron density and the plasma dilution measurements. On the other hand, when Ion-Cyclotron Resonance Heating (ICRH) or Neutral-Beam Injection (NBI) is applied, the ion distribution functions are distorted and the Maxwellian representation used for the ion temperature estimate is not necessarily justified, typically leading to an overestimate of the thermal component of the ion temperature. By using a coupled wave / Fokker-Planck numerical solver to calculate the actual ion distribution functions under the influence of external heating and the resulting neutron yield, the fast and thermal components of the bulk ion distributions can be disentangled and a 'thermal-only' ion temperature consistent with the neutron measurements can be extracted. An example of this procedure for the WEST tokamak with ICRF heating will be presented and the differences between the results obtained with respect to the simplified Maxwellian-based procedure will be discussed. [ABSTRACT FROM AUTHOR]

The retarding field analyzer (RFA) is considered to be one of the most effective tools to measure ion temperature (Ti) in the plasma boundary. However, there are some inaccuracies in the measured Ti by RFA caused by impurities in the plasma. In this paper, the influence of impurities on the measured Ti by RFA have been analyzed in hydrogen isotope plasmas with both low-Z and high-Z impurities. The analytical results show that Ti is underestimated in H+ (also D+ and T+) plasma when the fuel ion charge is taken as the charge number and the analyzed Ti in H+ plasma are all larger than that in D+ and T+ plasmas, exhibiting the isotope effect. With the concentration of low-Z impurity (ηl) increasing, the analyzed Ti decreases and is underestimated by about 20% with ηl ~ 12%. Following a comparison of different charge numbers and masses of low-Z impurities, it is found that larger charge numbers and smaller masses of low-Z impurities lead to greater underestimation of the analyzed Ti. High-Z impurities make almost no impact on the Ti, due to their small current contribution. Moreover, the Ti is measured by RFA and edge rotational diagnostic (ERD) systems through experiments. The results show good agreement with the analytical evaluations. [ABSTRACT FROM AUTHOR]

Isobaric tags have been widely used for the identification and quantification of proteins in mass spectrometry-based proteomics. The mass-balanced, 1H/2H isotope-coded dipeptide tag (MBIT) is a multifunctional isobaric tag based on N-acetyl-Ala-Ala dipeptide containing an amine-reactive linker that conjugates the tag to the primary amines of proteolytic peptides. MBITs provide a pair of isotope-coded quantitation signals separated by 3 Da, which enables 2-plex quantification and identification of proteins in the 15-250 fmol range. Various MBITs diversified at the N-acetyl group or at the side chain of the first alanine provide a pair of bs ions as low-mass quantitation signals in a distinct mass window. Thus, a combination of different MBITs allows multiplex quantification of proteins in a single liquid chromatography-mass spectrometry experiment. Unlike other isobaric tags, MBITs also offer a pair of ys ions as high-mass quantitation signals in a noise-free region, facilitating protein quantification in quadrupole ion trap mass spectrometers. Uniquely, bS ions, forming N-protonated oxazolone, undergo unimolecular dissociation and generate the secondary low-mass quantitation signals, aS ions. The yield of aS ions derived from bS ions can be used to measure the temperature of bS ions, which enables a reproducible acquisition of the peptide tandem mass spectra. Thus, MBITs enable multiplexed quantitation of proteins and the concurrent measurement of ion temperature using bS and aS signal ions as well as the isobaric protein quantitation in resonance-type ion trap using yS (complement of bS) signal ions. This review provides an overview of MBITs with a focus on the multi-functionality that has been successfully demonstrated in the peptide tandem mass spectrometry. © 2014 Wiley Periodicals, Inc. Mass Spec Rev 34: 209-218, 2015. [ABSTRACT FROM AUTHOR]