Off-axis neutral beam current drive for advanced scenario development in DIII-D

Murakami, M.; Park, J.M.; Petty, C. C.; Luce, T. C.; Heidbrink, W. W.; Osborne, T.H.; Prater, R.; Wade, M. R.; Anderson, P.M.; Austin, M. E.; Brooks, N.H.; Budny, R.; Challis, C.; DeBoo, J. C.; deGrassie, J.S.; Ferron, J. R.; Gohil, P.; Hobirk, J.; Holcomb, C.T.; Hollmann, E. M.; Rao, Hong; Hyatt, A.W.; Lohr, J.; Lanctot, M. J.; Makowski, M. A.; McCune, D.; Politzer, Peter; Scoville, J.T.; John, H.E. St.; Suzuki, Takahiro; Taylor, T.S.; West, W.P.; Unterberg, E.A.; Zeeland, M. A. Van; Yu, J. H.

doi:10.1088/0029-5515/49/6/065031

Cited by 53 publications

(44 citation statements)

References 25 publications

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“…The work reported here is a continuation of previous work, in both modeling and experiment, on the use of offaxis neutral beam injection [15][16][17][18][19] and on increasing the b N stability limit through broadening of the current and pressure profiles. Modeling of the effect of broadening the pressure profile is discussed in Refs.…”

Section: Introductionmentioning

confidence: 80%

“…The fast ion stored energy fraction decreases slightly as a result of the difference in n e and T e between the axis and the mid-radius, but the total neutral-beam-driven current remains the same as a result of reduced electron shielding at mid-radius. 19 The result is slightly lower b N to achieve the same b Nth . With less neutral-beam-driven current density in the region near the axis, q core increases [ Fig.…”

Section: -7mentioning

confidence: 96%

“…The vertical injection angle can be varied, but all cases with off-axis injection described here used the two off-axis sources at the maximum tilt angle, 16.4 deg, which results in a peak in the neutral-beam-driven current density (J B ) from these sources atq between 19 0.4 and 0.5. In discharges where off-axis neutral beam injection was used, the direction of B T was reversed from the standard DIII-D direction in order to maximize 19 the off-axis J B . In these cases, the standard discharge shape was inverted vertically in order to maintain the ion rB T drift in the direction away from the X point.…”

Section: Discharge Production and Analysismentioning

confidence: 99%

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Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

et al. 2013

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The initial experiments on off-axis neutral beam injection into high noninductive current fraction (f NI ), high normalized pressure (b N ) discharges in DIII-D [J. L. Luxon, Fusion Sci. Technol. 48, 828 (2005)] have demonstrated changes in the plasma profiles that increase the limits to plasma pressure from ideal low-n instabilities. The current profile is broadened and the minimum value of the safety factor (q min ) can be maintained above 2 where the profile of the thermal component of the plasma pressure is found to be broader. The off-axis neutral beam injection results in a broadening of the fast-ion pressure profile. Confinement of the thermal component of the plasma is consistent with the IPB98(y,2) scaling, but global confinement with q min > 2 is below the ITER-89P scaling, apparently as a result of enhanced transport of fast ions. A 0-D model is used to examine the parameter space for f NI ¼ 1 operation and project the requirements for high performance steady-state discharges. Fully noninductive solutions are found with 4 < b N < 5 and bootstrap current fraction near 0.5 for a weak shear safety factor profile. A 1-D model is used to show that a f NI ¼ 1 discharge at the top of this range of b N that is predicted stable to n ¼ 1, 2, and 3 ideal MHD instabilities is accessible through further broadening of the current and pressure profiles with off-axis neutral beam injection and electron cyclotron current drive. V C 2013 AIP Publishing LLC.

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Section: Introductionmentioning

confidence: 80%

Section: -7mentioning

confidence: 96%

Section: Discharge Production and Analysismentioning

confidence: 99%

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Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

et al. 2013

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“…The counter beams produce more trapped particles than co beams and the perpendicular beams produce more trapped particles than tangential beams. For off-axis injection, the fast-ion population depends on the helicity of the field line [42]. For injection with a negligible poloidal field, the initial pitch of the velocity vector relative to the field is χ 0 v φ /v = R tan /R.…”

Section: Off-axismentioning

confidence: 99%

Beam-ion confinement for different injection geometries

Heidbrink¹,

Murakami²,

Park³

et al. 2009

Plasma Phys. Control. Fusion

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The DIII-D tokamak is equipped with neutral beam sources that inject in four different directions; in addition, the plasma can be moved up or down to compare off-axis with on-axis injection. Fast-ion data for eight different conditions have been obtained: co/counter, near-tangential/near-perpendicular and on-axis/offaxis. Neutron measurements during short beam pulses assess prompt and delayed losses under low-power conditions. As expected, co-injection has fewer losses than counter, tangential fewer than perpendicular and on-axis fewer than off-axis; the differences are greater at low current than at higher current. The helicity of the magnetic field has a weak effect on the overall confinement. Fast-ion D α (FIDA) and neutron measurements diagnose the confinement at higher power. The basic trends are the same as in low-power plasmas but, even in plasmas without long wavelength Alfvén modes or other MHD, discrepancies with theory are observed, especially in higher temperature plasmas. At modest temperature, two-dimensional images of the FIDA light are in good agreement with the simulations for both on-axis and off-axis injection. Discrepancies with theory are more pronounced at low fast-ion energy and at high plasma temperature, suggesting that fast-ion transport by microturbulence is responsible for the anomalies.

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“…NBCD current is theoretically predicted to depend on the NB injection angle to the magnetic field line [14,15]. In order to study the effect of NB injection angle, the direction of the toroidal magnetic field B t and the vertical shift of the plasma were scanned in DIII-D, as shown in figure 4(c).…”

Section: Resultsmentioning

confidence: 99%

Experimental investigation and validation of neutral beam current drive for ITER through ITPA Joint Experiments

Suzuki¹,

Akers²,

Gates³

et al. 2011

Nucl. Fusion

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Joint experiments investigating the off-axis neutral beam current drive (NBCD) capability to be utilized for advanced operation scenario development in ITER were conducted in four tokamaks (ASDEX Upgrade (AUG), DIII-D, JT-60U and MAST) through the international tokamak physics activity (ITPA). The following results were obtained in the joint experiments, where the toroidal field, B t , covered 0.4-3.7 T, the plasma current, I p , 0.5-1.2 MA, and the beam energy, E b , 65-350 keV. A current profile broadened by off-axis NBCD was observed in MAST. In DIII-D and JT-60U, the NB driven current profile has been evaluated using motional Stark effect diagnostics and good agreement between the measured and calculated NB driven current profile was observed. In AUG (at low δ ∼ 0.2) and DIII-D, introduction of a fast-ion diffusion coefficient of D b ∼ 0.3-0.5 m 2 s −1 in the calculation gave better agreement at high heating power (5 MW and 7.2 MW, respectively), suggesting anomalous transport of fast ions by turbulence. It was found through these ITPA joint experiments that NBCD related physics quantities reasonably agree with calculations (with D b = 0-0.5 m 2 s −1 ) in all devices when there is no magnetohydrodynamic (MHD) activity except ELMs. Proximity of measured off-axis beam driven current to the corresponding calculation with D b = 0 has been discussed for ITER in terms of a theoretically predicted scaling of fast-ion diffusion that depends on E b /T e for electrostatic turbulence or β t for electromagnetic turbulence.

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Off-axis neutral beam current drive for advanced scenario development in DIII-D

Cited by 53 publications

References 25 publications

Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

Progress toward fully noninductive discharge operation in DIII-D using off-axis neutral beam injection

Beam-ion confinement for different injection geometries

Experimental investigation and validation of neutral beam current drive for ITER through ITPA Joint Experiments

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