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Lower hybrid current drive experiments on Alcator C-Mod: Comparison with theory and simulationa)
a)Paper JI1 3, Bull. Am. Phys. Soc. , 141 (2007).
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10.1063/1.2904569
/content/aip/journal/pop/15/5/10.1063/1.2904569
http://aip.metastore.ingenta.com/content/aip/journal/pop/15/5/10.1063/1.2904569
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Stainless steel grill used to inject LHRF power in Alcator C-Mod. Grill consists of four rows of 22 phased waveguides per row.

Image of FIG. 2.
FIG. 2.

The vacuum power spectra vs parallel refractive index , launched by a single row of the LH coupler in Fig. 1 . The blue solid line, green dashed line, and the red dash-dotted line correspond to relative waveguide phasings of 60°, 90°, and 120°, respectively.

Image of FIG. 3.
FIG. 3.

Layout of sightlines for the 32 chord, horizontally viewing hard x-ray camera on Alcator C-Mod.

Image of FIG. 4.
FIG. 4.

Measured decrease in loop voltage vs time for increasing LH power levels. All traces correspond to a series of discharges in Alcator C-Mod, where and .

Image of FIG. 5.
FIG. 5.

Change in loop voltage vs normalized power for a range of plasma and LHRF parameters in Alcator C-Mod [ , , ].

Image of FIG. 6.
FIG. 6.

Normalized loop voltage drop vs normalized power for three different relative waveguide phasings. Solid circles correspond to 60° phasing (launched ), square symbols correspond to 90° phasing (launched ), and open circles correspond to 120° phasing (launched ).

Image of FIG. 7.
FIG. 7.

Analysis of LHCD results from Alcator C-Mod using the Fisch–Karney theory (Ref. 23). Normalized power required to support the inductive energy in the plasma vs the wave parallel phase velocity normalized to the Dreicer velocity .

Image of FIG. 8.
FIG. 8.

Value of parallel refractive index at absorption [ (absorbed)] vs the launched parallel refractive index [ (launched)] as derived from fitting the Alcator C-Mod LHCD data to the Fisch–Karney theory (see Fig. 7 ).

Image of FIG. 9.
FIG. 9.

Time traces for a discharge in Alcator C-Mod where there is significant noninductive LH current drive. Top row of traces show the plasma current ( ) and peak electron density vs time ( ). Middle row of traces show the LH power ( ) and the peak electron temperature ( ) vs time ( ). Bottom row of traces show the plasma and loop voltage vs time ( ).

Image of FIG. 10.
FIG. 10.

(a) Electron density from Thomson scattering vs normalized radius for the discharge in Fig. 9 at . (b) LH wave accessibility for 60° phasing vs major radial position ( ), using Eq. (6) , the density profile in Fig. 10(a) , and the equilibrium reconstruction at .

Image of FIG. 11.
FIG. 11.

(a) Contours of the nonthermal LH-driven electron distribution function from a simulation for the discharge parameters in Fig. 9 . Distribution function contours correspond to a normalized minor radius of . (b) Comparison of measured and simulated (without radial diffusion) hard x-ray spectra for the discharge in Fig. 9 at . Experimentally measured spectra are shown as solid lines and the simulated spectra are shown as dashed lines. The black, blue, and red curves correspond to the , , and detector energies, respectively.

Image of FIG. 12.
FIG. 12.

(a) Comparison of LHRF deposition profiles from a simulation of the C-Mod discharge in Fig. 9 at . The blue curve corresponds to the simulation without radial diffusion and the red curve corresponds to the simulation with a radial diffusion operator of the form given by Eqs. (7) with . (b) Comparison of LHRF current density profiles from the simulation shown in (a). The blue curve corresponds to the simulation without radial diffusion and the red curve corresponds to the simulation with radial diffusion. (c) Comparison of measured and simulated hard x-ray spectra. The solid black line corresponds to the measured spectra at (the detector bin), the solid blue line corresponds to the simulated spectra without diffusion, and the dashed blue line corresponds to the simulated spectra with radial diffusion.

Image of FIG. 13.
FIG. 13.

Measurements of LH current profile modification in Alcator C-Mod from the MSE diagnostic. The red traces correspond to an ohmic reference plasma with no LH power and the tan, blue, and green traces correspond to three consecutive discharges with LH power applied at the level. Time traces for the LH power and loop voltage are shown in the top panels and time traces for the MSE measurement of pitch angle are shown in the middle and bottom panels for four channels corresponding to and .

Image of FIG. 14.
FIG. 14.

(a) Electron density from Thomson scattering vs normalized radius for discharge 1070828018 at . (b) LH wave accessibility for 75° phasing vs major radial position ( ), using Eq. (6) , the density profile in (a), and the equilibrium reconstruction at .

Image of FIG. 15.
FIG. 15.

(a) Comparison of the measured current density profile from the MSE diagnostic (red diamonds) with the simulated current density (ohmic plus LH) from (blue line) for discharge 1070828018 at . Also shown for reference is the LH current density profile from a simulation corresponding to a zero DC electric field. (b) Comparison of the measured and simulated hard x-ray spectra for discharge 1070828018 at . The experimentally measured spectrum at (the energy bin) corresponds to the solid black line and the simulated spectrum corresponds to the solid blue line and includes radial diffusion.

Image of FIG. 16.
FIG. 16.

Full-wave LH field simulation for Alcator C-Mod plasma [ , , , ]. The simulation was performed using the parallel solver with 980 radial elements and 1023 poloidal modes. Shown are the contours of the .

Image of FIG. 17.
FIG. 17.

(a) LHRF power density profile from the field solver for the Alcator C-Mod plasma shown in Fig. 16 and using linear electron Landau damping. (b) LHRF power density profile from a simulation of the C-Mod plasma in Fig. 12(a) using a narrow distribution of rays with linear electron Landau damping. The power densities in (a) and (b) are normalized to of absorbed power.

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2008-04-25
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Lower hybrid current drive experiments on Alcator C-Mod: Comparison with theory and simulationa)
http://aip.metastore.ingenta.com/content/aip/journal/pop/15/5/10.1063/1.2904569
10.1063/1.2904569
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