4,378
edits
TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II: Difference between revisions
TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II (view source)
Revision as of 13:09, 27 March 2018
, 27 March 2018Admin moved page TJ-II: Evaluation of Neoclassical transport correction terms in TJ-II to TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II without leaving a redirect
m (Admin moved page TJ-II: Evaluation of Neoclassical transport correction terms in TJ-II to TJ-II:Evaluation of Neoclassical transport correction terms in TJ-II without leaving a redirect) |
|||
| (6 intermediate revisions by 3 users not shown) | |||
| Line 15: | Line 15: | ||
'''Background''' | '''Background''' | ||
Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., '' | Neoclassical transport is widely considered to determine radial energy transport in high-temperature plasmas of stellarators up to a certain radial position <ref> A. Dinklage et al., ''Inter-machine validation study of neoclassical transport modelling in medium- to high-density stellarator-heliotron plasmas'', Nucl. Fusion, 53 (2013), 6. </ref>. In particular, for low-density ECH-heated stellarator plasmas, the levels of electron energy transport predicted by neoclassical simulations <ref> J. L. Velasco et al., ''Study of the neoclassical radial electric field of the TJ-II flexible heliac'', Plasma Physics and Controlled Fusion 56 (2012) 015005 </ref> are comparable to those estimated in the experiment, e.g. <ref name=Tallents> S. Tallents et al., ''Transport analysis in an electron cyclotron heating power scan of TJ-II plasmas'' 2014 Plasma Physics and Controlled Fusion 56 07502 </ref>, and the measured density and power dependence of the energy confinement time <ref> E. Ascasíbar et al., ''Magnetic configuration and plasma parameter dependence of the energy confinement time in ECR heated plasmas from the TJ-II stellarator'', Nucl. Fusion 45 (2005), 276 </ref> is in reasonable agreement with neoclassical predictions (assuming that the electrons are in the 1/nu transport regime). In this experiment, we would like to take a closer look to the parameter dependence of the energy flux and, in particular to the Er dependence. | ||
Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>. | Going beyond the plain comparison, for selected discharges, between the neoclassical predictions of radial fluxes and the experimental measurements is relevant for two reasons. For starters, it allows to identify and characterize possible systematic deviations. More interestingly, in a real plasma, the particles are not in a pure regime (e.g. the 1/nu, as mentioned above, sqrt(nu), plateau, etc), but in a mixture of regimes, since for a given temperature they are approximately distributed according to a Maxwellian. Studying the parameter dependence of the energy flux can allow to identify to what extent the different regimes contribute to transport in real conditions. This may something relevant, e.g. if, when optimizing a magnetic configuration with respect to neoclassical transport, reducing the transport level of one particular regime is incompatible with reducing that of other regimes. Currently, this kind of analysis is already under development in the W-7X optimized stellarator <ref> J. A. Alonso et al., ''Ion heat transport in low-density W7-X plasmas'', 44th EPS Conference on Plasma Physics, Belfast, Northern Ireland, June 26- 30, 2017 </ref>. | ||
| Line 30: | Line 30: | ||
First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values. | First, the radial electric field will be measured on a series of standard configuration ECH plasmas with constant heating power and increasing densities around the root transition critical density. This scan should provide a set of discharges with constant Te profiles (ECH alignment adjustment may be required to ensure that) and changing ne profiles. The range of densities will be selected by adjusting the heating power value in order to allow the DR in the rho ~ [0.3-0.8] range. Some trade-off maybe necessary to ensure good TS profile data. Ti will be measured at the plasma core by the NPA. At least, 10 different Er profiles should be measured this way, with some intermediate radial region being covered by all density values. | ||
Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range. | Second, a fixed density value will be selected such that an equivalent scan can be carried out by small increments of PECH. In this scan, the radial region probed by the reflectometer remains constant, as density profiles can be made roughly constant, while Te profiles will change. The density must be such that good TS data is collected, the root transition takes place for a power roughly around that of a gyrotron at full power and DR probes the [0.3-0.8] range. | ||
Finally, one of the previous scans could be repeated in a high ripple configuration in order to check the impact on the measurements of the increased transport. | |||
== Description of required resources == | == Description of required resources == | ||
| Line 37: | Line 37: | ||
* Number of plasma discharges or days of operation: | * Number of plasma discharges or days of operation: | ||
10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan). | 10 Er profiles are required (in order to produce an empirical qe,r (Er) curve with reasonable resolution) for each scan. This means an absolute minimum of 20 discharges. Since fine tunning may required in ECH alignment and fueling in order to achieve constant profiles, two full days of operation will probably be required (one per scan). Ideally, both days would be separated in time in order to properly evaluate the results. | ||
* Essential diagnostic systems: | * Essential diagnostic systems: | ||
| Line 47: | Line 47: | ||
* Type of plasmas (heating configuration): | * Type of plasmas (heating configuration): | ||
Standard configuration (100_44_64) with ECH heating. | Standard configuration (100_44_64) with ECH heating. For the high ripple scan, additional shots would be carried out in ECH heated plasmas in 100_32_60 configuration. | ||
* Specific requirements on wall conditioning if any: | * Specific requirements on wall conditioning if any: | ||
| Line 69: | Line 69: | ||
[[Category:TJ-II internal documents]] | [[Category:TJ-II internal documents]] | ||
[[Category:TJ-II experimental proposals]] | [[Category:TJ-II experimental proposals Spring 2018]] | ||