TJ-II:Helium Beam

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 He beam diagnostic (top port)

References

[1] B. Brañas et al., Atomic beam diagnostics for characterization of edge plasma in TJ-II stellarator, Rev. Sci. Instrum. 72, 602 (2001)

[Hidalgo-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)

[Guzman-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

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[2]

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