Improvement of angular momentum confinement with density peaking on ASDEX

Kallenbach, A.; Mayer, H. M.; Fußmann, G.; Buechese, R.; Gruber, O.; Klueber, O.; Mertens, V.; Vollmer, O.; Zohm, H.

doi:10.1088/0029-5515/30/4/006

Cited by 20 publications

(15 citation statements)

References 26 publications

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“…The impurity toroidal velocity is obtained from charge exchange recombination spectroscopy (CXRS), with the C V I 529.05nm CX line. It is routinely measured on ASDEX Upgrade by two CXRS systems, CHR [38] and the older system CER [39,40]. In neoclassical theory, a difference is predicted between the main ion toroidal velocity and the impurity toroidal velocity [41].…”

Section: The Radial Force Balancementioning

confidence: 99%

The radial electric field and its associated shear in the ASDEX Upgrade tokamak

et al. 2006

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Abstract. The radial electric field (E r ) and its shear (∂E r /∂r) are believed to be fundamental for turbulence suppression in magnetically confined plasmas. Doppler reflectometry offers a direct method of obtaining E r and ∂E r /∂r measurements. It is a type of microwave radar technique which uses the back-scatter of microwaves from a radial position in the plasma where the refractive index equals zero. In this paper, the use of Doppler reflectometry for E r measurements is investigated. The technique is extended for ∂E r /∂r measurements by simultaneously probing the plasma with two microwave beams at different frequencies. E r and ∂E r /∂r measurements are presented for a wide variety of plasma conditions. The measurements show that E r and its associated shear are linked to plasma confinement. Their absolute values increase with confinement at the plasma edge. Furthermore, the measurements show dependence on the applied plasma auxiliary heating and the plasma shape. The E r shear results suggest that negative shear is more influential than positive shear, in contradiction with several theoretical models.

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Section: The Radial Force Balancementioning

confidence: 99%

The radial electric field and its associated shear in the ASDEX Upgrade tokamak

et al. 2006

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“…Hc, 52.50.Gj The high ion temperature enhanced confinement regime has been observed for super shots in TFTR [1], hot ion modes in JET and in 3], and counter-NBI modes in ASDEX [4] and in JFT-2M [5]. These enhanced confinement regimes observed in many tokamaks are correlated with density peaking.…”

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confidence: 93%

High Ion Temperature Mode in Heliotron-E

et al. 1996

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A high ion temperature T i mode is observed for neutral beam heated plasmas in Heliotron-E. This high T i mode plasma is characterized by a peaked ion temperature profile and is associated with a peaked electron density profile produced by neutral beam fueling with low wall recycling. The observed improvement in ion heat transport can be related to the radial electric field shear rather than to the rotation velocity shear in the bulk plasma.PACS numbers: 52.55. Hc, 52.50.Gj The high ion temperature enhanced confinement regime has been observed for super shots in TFTR [1], hot ion modes in JET and in 3], and counter-NBI modes in ASDEX [4] and in JFT-2M [5]. These enhanced confinement regimes observed in many tokamaks are correlated with density peaking. However, no observation of the high ion temperature enhanced confinement regime has been reported in heliotron/torsatron or stellarator devices. Theoretically, radial electric field shear or plasma rotation shear is expected to improve confinement by suppressing microturbulence in the plasma. Then weaker particle pinch effects and a smaller improvement of energy confinement are predicted in heliotron/torsatron or stellarator devices than those in tokamaks because of strong damping of the plasma rotation due to helical ripple (only radial electric field shear due to plasma rotation shear is considered in this model) [6]. Experimentally, both bulk poloidal rotation and radial electric field were directly measured in an H-mode plasma in DIII-D [7]. These measurements clearly show that the bulk plasma is somewhat unrelated to the radial electric field due to a large diamagnetic drift (y u is in the ion diamagnetic direction which is not expected from E 3 B drift because E r is negative). However, which of these, the electric field shear or the velocity shear, suppresses the turbulence has not yet been clarified because both radial electric field and velocity shear unfortunately exist in the same region in the plasma in H mode but not in L mode. Therefore it is an important issue to investigate whether density peaking and improved confinement are realized and whether a radial electric field or plasma rotation shear can reduce heat transport in heliotron/torsatron and stellarator devices. A preliminary result of the high ion temperature mode in Heliotron-E has been reported [8]. In this Letter we present the observation of high ion temperatures and an enhanced confinement regime in the Heliotron-E device and discuss the mechanism of enhanced confinement.The Heliotron-E is an axially asymmetric heliotron/torsatron with poloidal period number l 2, toroidal period number m 19, major radius R 2.2 m, magnetic field B 1.9 T, and averaged minor radius a 21.4 cm [9]. Heliotron-E has several nearly perpendicular neutral beams with 0 ± (five ion sources, 1.5 MW), 11 ± (three ion sources, 1

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“…Charge exchange spectroscopy ͑CXS͒ has been developed as a tool to measure ion temperature profiles [1][2][3][4][5][6][7][8][9] and plasma rotation and also the radial electric field using radial force balance. [10][11][12] In a heliotron/torsatron, there is no large toroidal rotation because of parallel viscosity in the toroidal direction.…”

Section: Introductionmentioning

confidence: 99%

Measurements of poloidal rotation velocity using charge exchange spectroscopy in a large helical device

Ida

Kado

Liang

2000

Review of Scientific Instruments

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Absolute measurements of poloidal rotation velocity with the accuracy up to 1 km/s ͑2 pm in wavelength͒ were done using charge exchange spectroscopy in a large helical device. Radial profiles of the absolute Doppler shift of charge exchange emission with a beam are obtained from spectra measured with four sets of optical fiber arrays that view downward and upward at the poloidal cross section with and without neutral beam injection. By arranging the optical fiber from four arrays close to each other at the entrance slit, the apparent Doppler shift due to aberrations of the spectrometer and due to interference of the cold component ͑the charge exchange between He-like oxygen and thermal neutrals 8 pm from the charge exchange emission with a beam͒ can be eliminated from the measurements. The measured poloidal rotation velocity is 1-3 km/s in the electron diamagnetic direction at half of the plasma minor radius.

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Improvement of angular momentum confinement with density peaking on ASDEX

Cited by 20 publications

References 26 publications

The radial electric field and its associated shear in the ASDEX Upgrade tokamak

The radial electric field and its associated shear in the ASDEX Upgrade tokamak

High Ion Temperature Mode in Heliotron-E

Measurements of poloidal rotation velocity using charge exchange spectroscopy in a large helical device

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