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[[File:TJ-II_Helium_beam.png|300px|thumb|right|The TJ-II Helium beam diagnostic]]
[[TJ-II]] possesses a supersonic Helium beam diagnostic.
 
The beam source consists of a fast-pulsed piezoelectric valve with a nozzle of
[[TJ-II]] possesses a supersonic Helium beam diagnostic based on the line ratio method.
0.3 mm diameter and a parabolic profile skimmer with a diameter
<ref>[http://link.aip.org/link/?RSINAK/72/602/1 B. Brañas et al., ''Atomic beam diagnostics for characterization of edge plasma in TJ-II stellarator'', Rev. Sci. Instrum. '''72''', 602 (2001)]</ref>
of 0.5 mm.
<ref>[http://link.aip.org/link/?RSINAK/75/3478/1 A. Hidalgo et al., ''Multipulse supersonic helium beam diagnostic in the TJ-II stellarator'', Rev. Sci Instrum. '''75''', 3478 (2004)]</ref>
The mean beam velocity is 1500 m/s.
<ref>[http://dx.doi.org/10.1016/j.jnucmat.2009.01.290 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]</ref>
The density of He atoms at the measurement region is estimated to be of
the order of &lt; 10<sup>11</sup> cm<sup>-3</sup>.
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).
<ref>B. Brañas et al., ''Atomic beam diagnostics for characterization of edge plasma in TJ-II stellarator'', [[doi:10.1063/1.1319868|Rev. Sci. Instrum. '''72''', 602 (2001)]]</ref>
A Collisional Radiative (CR) model for the line emission intensity ratios is used
to deduce electron densities and temperatures.
<ref name="Hidalgo">A. Hidalgo et al., ''Multipulse supersonic helium beam diagnostic in the TJ-II stellarator'', [[doi:10.1063/1.1779617|Rev. Sci Instrum. '''75''', 3478 (2004)]]</ref>
<ref name="Guzman">F. Guzmán et al, ''On the determination of edge Ti profiles by a supersonic He beam in TJ-II'', [[doi:10.1016/j.jnucmat.2009.01.290|Journal of Nuclear Materials '''390-391''' (2009) 1127-1130]]</ref>
It provides profiles of the electron temperature and density in the plasma edge at a repetition rate of up to 200 Hz.
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 &phi; = 355.3&deg; ([[TJ-II:Sectors|sector]] C8).
It is located at &phi; = 355.3&deg; ([[TJ-II:Sectors|sector]] C8).
[[File:TJ-II_Helium_beam.png|300px|thumb|right|The TJ-II Helium beam diagnostic. The laser can be crossed with the Helium beam for LiF measurements of the excited He population <ref name="Hidalgo" /> and validation of the CR model.]]


== Data description ==
== Data description ==
The Helium beam pulse shape is stored in the [[TJ-II:Shot database|TJ-II database]] with the name 'HELIO_HAZ'.
The Helium beam pulse shape is stored in the [[TJ-II:Shot database|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).
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).
[[File:TJ-II He beam.jpg|400px|thumb|left|Photo of He beam diagnostic (top port)]]  
[[File:TJ-II He beam.jpg|400px|thumb|left|Photo of Helium and [[TJ-II:Lithium Beam|Lithium]] beam diagnostics (top ports)]]  


== References ==
== References ==
<references />
<references />
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