Impurity transport and plasma rotation in the ISX-B tokamak

Isler, R.C.; Murray, L. E.; Crume, E.C.; Bush, C. E.; Dunlap, J. L.; Edmonds, P.H.; Kasai, S.; Lazarus, E. A.; Murakami, M.; Neilson, G.H.; Paré, V.K.; Scott, S.D.; Thomas, C. E.; Wootton, A. J.

doi:10.1088/0029-5515/23/8/003

Cited by 90 publications

(90 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In the NBI case, the transport appears to more like neo-classical impurity transport, and in some instances, strong inward convection is seen. This sort of behavior has also been observed in tokamaks 9 2) Soft x-ray brightness profiles for silicon injection into a deuterium ECH plasma (top), with code predictions (bottom). r/a Figure 4 …”

Section: (4) Conclusionsupporting

confidence: 53%

Transport of injected impurities in Heliotron E

et al. 1984

View full text Add to dashboard Cite

Impurities have been injected into Heliotron E in order to study the transport properties of currentless plasmas. In ECH-produced plasmas, the observed impurity transport can be described by purely anomalous diffusion, with a coefficient of the order of D = 2000-5000 cm 2 • s" 1 . During neutral beam operation, the impurity transport can be characterized by considerably weaker diffusion, combined with inward convection. Convection velocities as large as a few hundred centimetres per second are inferred.

show abstract

Section: (4) Conclusionsupporting

confidence: 53%

Transport of injected impurities in Heliotron E

et al. 1984

View full text Add to dashboard Cite

show abstract

“…The different transport behavior was explained on the basis of neoclassical impurity transport in a situa-tion with momentum input and plasma rotation. 5 The energy confinement time T£, however, was found to degrade like that of L-mode plasmas heated with co-NI.…”

Section: Improved Confinement With Counter Neutral Injection Into Asdexmentioning

confidence: 94%

Improved confinement with counter neutral injection into ASDEX

et al. 1988

View full text Add to dashboard Cite

Counter injection into ASDEX leads to good particle, momentum, and also energy confinement with XE -80 ms at 1 MW (43 ms for co-injection). The improved confinement develops gradually during the heating phase and correlates with a simultaneous peaking of the density profile. The ion heat transport has to be reduced for a consistent transport analysis, in agreement with theoretical expectations. The sawtooth instability flattens the density profile and transiently reduces the energy content.PACS numbers: 52.55.Fa, 52.50.Gj An important goal of tokamak research is the development of plasma regimes with good confinement under auxiliary heating conditions to provide well established scenarios for the upcoming deuterium-tritium experiments. An important and challenging task is the understanding of the energy and particle transport in a tokamak plasma. In particular, it is the electron transport which is much higher than neoclassical theory predicts and which shows an unexplained variation with plasma parameters. But there is also accumulating experimental evidence that the ion heat transport is enhanced as well above the neoclassical expectation. 1 The effort to increase the plasma temperatures by auxiliary heating generally causes the electron transport to increase even further, resulting in the degraded confinement properties of the L mode. An alternative to the L-mode confinement is the H mode which shows good confinement properties even at high heating power 2 (L denotes low and H high confinement properties).In this paper we report on another operational regime characterized by good confinement properties. It develops when neutral injection as an auxiliary heating method is applied in the counter direction (against the direction of the plasma current). The injection of energetic neutral atoms into the plasma is presently the most successful and reliable auxiliary heating method. The orbits of the energetic ions after ionization depend strongly on the injection geometry. In case of counter injection (ctr-NI) the power and particle deposition profiles are broader and the fraction of ions which is lost during the slowing down phase is somewhat larger. There have been many attempts in the past to study ctr-NI heated plasmas and to compare their characteristics with those under co-injection (co-NI). 3,4 The main results were that particle confinement improves and remarkable differences in impurity transport have been noted. While co-NI reduces the impurity concentration, ctr-NI causes the impurities to accumulate in the plasma center. The different transport behavior was explained on the basis of neoclassical impurity transport in a situa-tion with momentum input and plasma rotation. 5 The energy confinement time T£, however, was found to degrade like that of L-mode plasmas heated with co-NI.On ASDEX we observe improved particle confinement with ctr-NI both affecting the bulk plasma (leading to a density increase without any external gas puffing only fueled by the beam) and giving rise to low-Z and high-Z impurity acc...

show abstract

“…Experimentally, it has previously been shown on TEXT [3], as well as other devices [4][5][6], that in fact the confinement of impurities actually increases prior to disruptions at the high-density limit. The implications of this for the Haas and Thyagaraja model [l] need to be addressed.…”

Section: Brower Et Al Replymentioning

confidence: 99%

Broweret al. reply

Brower

Bravenec

et al. 1992

Phys. Rev. Lett.

View full text Add to dashboard Cite

Brower et al. Reply:The phenomenological model described in the Comment [1] represents a novel interpretation of the long-time precursors to high-density-limit disruptions observed on TEXT [2]. The prediction that D e and V e have the same poloidal resistivity dependence and, consequently, that the ratio D e /V e and the density profile are invariant to changes in rj^, is most interesting. Relating microturbulence to anomalous poloidal resistivity, however, provides no information on the specific instability mechanism responsible for the density fluctuation levels. Our paper offers evidence that an ion-pressuregradient-driven mode may be driving changes in the transport, perhaps driven more unstable by impurity accumulation [2,3] and/or changes in the parameter rj, (experimentally unknown). This is further supported by data from helium-and pellet-fueled discharges where the ion feature in the fluctuation spectra is absent and the disruption limit is exceeded. In particular, for highdensity helium-gas-fueled discharges, the electron particle diffusivity in the core plasma (D e = \A m 2 /s) is significantly reduced when compared to the hydrogen-gasfueled equivalent (D e =2.2 m 2 /s).With respect to impurities, the theory of Haas and Thyagaraja [1] predicts that along with the measured degradation of heat and particle confinement, impurity confinement should also deteriorate. Experimentally, it has previously been shown on TEXT [3], as well as other devices [4][5][6], that in fact the confinement of impurities actually increases prior to disruptions at the high-density limit. The implications of this for the Haas and Thyagaraja model [l] need to be addressed. Although the authors' original interpretation that increased microturbulence, perhaps an n, instability, leads to confinement degradation and eventually a disruption via the Greenwald scenario [7] is unchanged, a potential relationship to anomalous poloidal resistivity represents an intriguing possibility which warrants further investigation.

show abstract

Impurity transport and plasma rotation in the ISX-B tokamak

Cited by 90 publications

References 26 publications

Transport of injected impurities in Heliotron E

Transport of injected impurities in Heliotron E

Improved confinement with counter neutral injection into ASDEX

Broweret al. reply

Contact Info

Product

Resources

About