TJ-II:Helium Beam

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TJ-II possesses a supersonic Helium beam diagnostic. The beam source consists of a fast-pulsed piezoelectric valve with a nozzle of 0.3 mm diameter and a parabolic profile skimmer with a diameter of 0.5 mm. The mean beam velocity is 1500 m/s. The density of He atoms at the measurement region is estimated to be of the order of < 1011 cm-3. Three He emission lines (667.2, 706.5 and 728.1 nm) are simultaneously detected by means of a beam-splitter system and a set of three 16-channel photomultiplier arrays (Hamamatsu, model R5900U-20-L16) with interference filters (FWHM = 1 nm). [1] A Collisional Radiative (CR) model for the line emission intensity ratios is used to deduce electron densities and temperatures. [2] [3] It provides profiles of the electron temperature and density in the plasma edge at a repetition rate of up to 200 Hz.

It is located at φ = 355.3° (sector C8).

The TJ-II Helium beam diagnostic. The laser can be crossed with the Helium beam for LiF measurements of the excited He population [2] and validation of the CR model.

Data description

The Helium beam pulse shape is stored in the TJ-II database with the name 'HELIO_HAZ'. The detected line emission signals are stored with the names 'He_xxx_yy', where 'xxx' is the wavelength in nm (667, 706, or 728), while 'yy' is the position (from 01 through 16).

Photo of Helium and Lithium beam diagnostics (top ports)


  1. B. Brañas et al., Atomic beam diagnostics for characterization of edge plasma in TJ-II stellarator, Rev. Sci. Instrum. 72, 602 (2001)
  2. 2.0 2.1 A. Hidalgo et al., Multipulse supersonic helium beam diagnostic in the TJ-II stellarator, Rev. Sci Instrum. 75, 3478 (2004)
  3. F. Guzmán et al, On the determination of edge Ti profiles by a supersonic He beam in TJ-II, Journal of Nuclear Materials 390-391 (2009) 1127-1130