TJ-II: impact of impurities on turbulence: Difference between revisions

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'''Motivation.'''
'''Motivation.'''


In the context of analytical theory, the stabilizing role of impurities on Ion-Temperature-Gradient (ITG) driven instability has been known for decades, see e.g. <ref>R. R. Domínguez and M. N. Rosenbluth, Nuclear Fusion '''29''' 844 (1989).</ref>, where the derived linear dispersion relation shows that the increase of the impurity concentration has a positive impact on the critical gradient of the toroidal ITG mode and its growth rate. Numerically, and approaching the problem quasi-linearly, in  <ref>R. R. Domínguez and G. M. Staebler, Nuclear Fusion '''33''' 51 (1993).</ref> the benign impact of increasing the effective charge, <math>Z_{\text{eff}}</math>, on ITG stability is demonstrated, albeit for the simplified slab geometry. In contrast, at the time that the impact is found beneficial for the stability of the ITG mode, it is found deleterious for Trapped Electron Modes (TEMs) in the work just cited. And, importantly, the stabilizing role on ITG vanishes when the impurity density profile is hollow, as found <ref>J. Q. Dong and W. Horton, Phys. Plasmas '''2''' 3412 (1995)</ref>.
In the context of analytical theory, the stabilizing role of impurities on Ion-Temperature-Gradient (ITG) driven instability has been known for decades, see e.g. <ref>R. R. Domínguez and M. N. Rosenbluth, Nuclear Fusion '''29''' 844 (1989).</ref>, where the derived linear dispersion relation shows that the increase of the impurity concentration has a positive impact on the critical gradient of the toroidal ITG mode and its growth rate. Numerically, and approaching the problem quasi-linearly, in  <ref>R. R. Domínguez and G. M. Staebler, Nuclear Fusion '''33''' 51 (1993).</ref> the benign impact of increasing the effective charge (<math>Z_{\text{eff}}</math>) on ITG stability was confirmed, albeit for the simplified slab geometry. In contrast, at the time that the impact is found beneficial for the stability of the ITG mode, it is found deleterious for Trapped Electron Modes (TEMs) in the work just cited. And, importantly, the stabilizing role on ITG vanishes when the impurity density profile is hollow, as found in <ref>J. Q. Dong and W. Horton, Phys. Plasmas '''2''' 3412 (1995)</ref>. Works like the ones just mentioned point out to a more complex description of microturbulence in plasmas, when in its full multi-species character is taken into account.


The interest in these early works and on the question itself about the active role of impurities on the overall turbulence behavior has been brought to the front line of stellarator research by recent W7-X experiments <ref>R. Lunsford ''et al'' Phys. Plasmas '''28''' 082506 (2021) </ref>. In the cited work, the conclusions highlight the increase of up to a 30% in the central ion temperature that follows after the injection of non-trace amounts of Boron. Given the limitations found in W7-X to achieve high core ion temperature <ref>M. N. A. Beurskens ''et al''., Nuclear Fusion '''61''' 116072 (2021)</ref>, with the exception of scenarios with reduced turbulence where W7-X, the motivation to study systematically the means to reduce the turbulence ion heat transport is strongly motivated. In contrast with the afore-mentioned analytical and numerical works, that employ approximations of different kind or consider simplified geometries, the possibility to study the problem numerically in all its complexity is at hand. Multi-species gyrokinetic simulations with the codes stella<ref>M. Barnes ''et al''., J. Comp. Phys '''391''' 365 (2019)</ref>, have just become affordable recently and, indeed, have been reported in the stellarator literature for the first time in <ref>J. M. García-Regaña ''et al''., J. Plasma Phys. '''87'''(1) 855870103 (2021)</ref>.
The interest in these early works and on the question itself about the active role of impurities on the overall turbulence behavior has been brought to the front line of stellarator research by recent W7-X experiments <ref>R. Lunsford ''et al'' Phys. Plasmas '''28''' 082506 (2021) </ref>. In the cited work, the conclusions highlight the increase of up to a 30% in the central ion temperature that follows after the injection of non-trace amounts of Boron. Given the limitations found in W7-X to achieve high core ion temperature <ref>M. N. A. Beurskens ''et al''., Nuclear Fusion '''61''' 116072 (2021)</ref>, with the exception of scenarios with reduced turbulence where W7-X, the motivation to study systematically the means to reduce the turbulence ion heat transport is strongly motivated. In contrast with the afore-mentioned analytical and numerical works, that employ approximations of different kind or consider simplified geometries, the possibility to study the problem numerically in all its complexity is at hand. Multi-species gyrokinetic simulations with the codes stella<ref>M. Barnes ''et al''., J. Comp. Phys '''391''' 365 (2019)</ref>, have just become affordable recently and, indeed, have been reported in the stellarator literature for the first time in <ref>J. M. García-Regaña ''et al''., J. Plasma Phys. '''87'''(1) 855870103 (2021)</ref>.

Revision as of 13:36, 19 January 2022

Description of the activity

Motivation.

In the context of analytical theory, the stabilizing role of impurities on Ion-Temperature-Gradient (ITG) driven instability has been known for decades, see e.g. [1], where the derived linear dispersion relation shows that the increase of the impurity concentration has a positive impact on the critical gradient of the toroidal ITG mode and its growth rate. Numerically, and approaching the problem quasi-linearly, in [2] the benign impact of increasing the effective charge () on ITG stability was confirmed, albeit for the simplified slab geometry. In contrast, at the time that the impact is found beneficial for the stability of the ITG mode, it is found deleterious for Trapped Electron Modes (TEMs) in the work just cited. And, importantly, the stabilizing role on ITG vanishes when the impurity density profile is hollow, as found in [3]. Works like the ones just mentioned point out to a more complex description of microturbulence in plasmas, when in its full multi-species character is taken into account.

The interest in these early works and on the question itself about the active role of impurities on the overall turbulence behavior has been brought to the front line of stellarator research by recent W7-X experiments [4]. In the cited work, the conclusions highlight the increase of up to a 30% in the central ion temperature that follows after the injection of non-trace amounts of Boron. Given the limitations found in W7-X to achieve high core ion temperature [5], with the exception of scenarios with reduced turbulence where W7-X, the motivation to study systematically the means to reduce the turbulence ion heat transport is strongly motivated. In contrast with the afore-mentioned analytical and numerical works, that employ approximations of different kind or consider simplified geometries, the possibility to study the problem numerically in all its complexity is at hand. Multi-species gyrokinetic simulations with the codes stella[6], have just become affordable recently and, indeed, have been reported in the stellarator literature for the first time in [7].

Proposal

In the present proposal the impact of impurities on the background turbulence will be studied.

International or National funding project or entity

Include funding here (grants, national plans)

Description of required resources

Required resources:

  • Number of plasma discharges or days of operation:
  • Essential diagnostic systems:
  • Type of plasmas (heating configuration):
  • Specific requirements on wall conditioning if any:
  • External users: need a local computer account for data access: yes/no
  • Any external equipment to be integrated? Provide description and integration needs:

Preferred dates and degree of flexibility

Preferred dates: (format dd-mm-yyyy)

References

  1. ↑ R. R. Domínguez and M. N. Rosenbluth, Nuclear Fusion 29 844 (1989).
  2. ↑ R. R. Domínguez and G. M. Staebler, Nuclear Fusion 33 51 (1993).
  3. ↑ J. Q. Dong and W. Horton, Phys. Plasmas 2 3412 (1995)
  4. ↑ R. Lunsford et al Phys. Plasmas 28 082506 (2021)
  5. ↑ M. N. A. Beurskens et al., Nuclear Fusion 61 116072 (2021)
  6. ↑ M. Barnes et al., J. Comp. Phys 391 365 (2019)
  7. ↑ J. M. García-Regaña et al., J. Plasma Phys. 87(1) 855870103 (2021)

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