LIF diagnostic for measuring beam transport magnetic fields
- Naval Research Lab., Washington, DC (United States). Plasma Physics Div.
A novel, spatially-resolved, non-intrusive diagnostic is being developed to measure magnetic fields associated with intense ion beam propagation through a low-pressure gas, as is envisioned for light ion-driven ICF. The diagnostic uses laser-induced fluorescence (LIF), and is varied to measure either small or large fields. Small fields (B < 200 G), as expected in ballistic transport with solenoidal lens focusing using 1 Torr gas, produce Zeeman shifts, {Delta}{lambda}{sub z}, smaller than the transition linewidth, {Delta}{lambda}. High sensitivity for the low-B measurement is achieved by a variation on the Babcock technique using LIF spectroscopy. LIF from a J = 1{r_arrow}0 transition in a probe species is viewed parallel to B. In this case {Delta}M=0 fluorescence is not visible, and {Delta}M={+-}1 fluorescence is right- and left-circularly polarized, and can be measured separately using polarization filters. If a narrow-bandwidth pump laser is tuned to a half-maximum point of the unsplit transition line, the B-field shifts one of the {Delta}M={+-}1 absorption transitions into resonance with the laser and shifts the other further out of resonance. For small fields, the difference in the fluorescence signals of the two polarization is proportional to {Delta}{lambda}{sub z} and B. Large fields (B > 200 G), as expected in self-pinched transport using 10 to 100 mTorr gas, produce {Delta}{lambda}{sub z} larger than {Delta}{lambda}. The small-B technique can be adapted to measure large B by adding an etalon to act as a narrow-band optical filter of LIF. The etalon transmission curve then transduces {Delta}{lambda}{sub z} to a change in detected intensity, analogously to the absorption line profile in the small-B technique. Results of proof-of-principle experiments using calibrated B-fields, and plans for fielding the diagnostic on Gamble-II are presented.
- Sponsoring Organization:
- Sandia National Labs., Albuquerque, NM (United States)
- OSTI ID:
- 338483
- Report Number(s):
- CONF-970559-; TRN: 99:005796
- Resource Relation:
- Conference: 24. IEEE international conference on plasma science, San Diego, CA (United States), 19-23 May 1997; Other Information: PBD: 1997; Related Information: Is Part Of IEEE conference record -- Abstracts; PB: 354 p.
- Country of Publication:
- United States
- Language:
- English
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