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High harmonic fast wave heating efficiency enhancement and current drive at longer wavelength on the National Spherical Torus Experimenta)
a)Paper JI1 5, Bull. Am. Phys. Soc. , 142 (2007).
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View: Figures


Image of FIG. 1.
FIG. 1.

High harmonic fast wave propagation characteristics for total magnetic field at the antenna location on NSTX [toroidal field , plasma current ]. (a) Perpendicular wavenumber vs density for parallel wavenumbers , , and . (b) The tangent of the propagation angle relative to the direction of vs density. The onset density is and .

Image of FIG. 2.
FIG. 2.

Central electron temperature and stored electron energy vs time with RF power modulation for toroidal wavenumbers equal to (a) , (b) , and (c) . [ , , , and helium plasma.] Line average density is also shown for comparison between the shots ( is in units of on the left scale).

Image of FIG. 3.
FIG. 3.

Comparison of time plots of stored electron energy obtained at (solid curve) and (dashed curve) for . Exponential fits to the last RF pulses [Eq. (1) ] give electron heating efficiencies of 40% and 22% for and , respectively. [Conditions for are those of Fig. 2 . Conditions for are , and helium (Ref. 10 ).]

Image of FIG. 4.
FIG. 4.

(a) Time dependence of electron stored energy with maximum modulated RF power of , one with (solid curve), and the other with (dashed curve). (b) Edge electron density ( in front of Faraday shield) vs time. The onset density for and perpendicular propagation is indicated by the horizontal dashed lines.

Image of FIG. 5.
FIG. 5.

(a) Time dependence of total stored energy for a pulsed RF power of vs the phase between antenna straps [ corresponds to co-CD phasing ]. (b) Change in total stored energy at {just prior to injection of the diagnostic neutral beam pulse [dashed vertical line in Fig. 5(a) ]} showing the fall-off of heating at longer wavelengths, . ; , helium.

Image of FIG. 6.
FIG. 6.

Thomson scattering profiles vs antenna phase for in Fig. 5 for (a) electron temperature , (b) electron density , and (c) electron pressure . ( for all antenna phases, .) increases and broadens and decreases with increasing .

Image of FIG. 7.
FIG. 7.

ray tracing calculated by , projected on to (a) the toroidal midplane and (b) a poloidal section. Calculations utilized temperature and density profiles from shot 123440 (solid green ray) and 123435 (dashed red ray). These shots were used in the experiment for ( phase) launch and and ( phase) launch, respectively, of Fig. 5 . The point on each ray where 80% of the RF power has been absorbed by the plasma is indicated by the colored dot.

Image of FIG. 8.
FIG. 8.

Decay of central electron temperature for antenna phase of after preheating the electrons to at to provide single pass damping of the wave (Fig. 7 ). ; , helium plasma.

Image of FIG. 9.
FIG. 9.

Onset density and angle of ray propagation comparison between NSTX and ITER. The ITER ion cyclotron antenna concept dimensions give toroidal wavenumber values of and for 90° and 180° strap-to-strap phasing, respectively, for a magnetic field at the antenna of and an operating frequency of .

Image of FIG. 10.
FIG. 10.

(a) MSE pitch angle profiles vs major radius measured at the time slice for the antenna phase cases of , , and no-RF in Fig. 5 . L equilibrium reconstruction polynomial fits are also shown. (b) Toroidal current density vs the square root of normalized poloidal flux obtained by fitting the measured pitch angles to the magnetic surfaces local to the measurements. The integrated current for relative to the no-RF case is and relative to the case is .

Image of FIG. 11.
FIG. 11.

The prediction of RF driven toroidal current density for the antenna phasing case of Fig. 10 using (a) the two-dimensional full wave code (peak toroidal spectral ray , toroidal wavenumber ) and (b) the three-dimensional full wave code (101 toroidal wavenumbers). For a heating efficiency , the integrated current is and for single mode and 101 mode cases, respectively. The current is decreased by a factor of from the no-trapping case.

Image of FIG. 12.
FIG. 12.

A three-dimensional wave field amplitude (101 toroidal modes) for the antenna phasing case of Fig. 10 . Fields are indicated for the toroidal midplane and poloidal cross sections at the center of the antenna and 180° away.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: High harmonic fast wave heating efficiency enhancement and current drive at longer wavelength on the National Spherical Torus Experimenta)