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TJ-II: impact of impurities on turbulence: Difference between revisions
TJ-II: impact of impurities on turbulence (view source)
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''' Proposal ''' | ''' Proposal ''' | ||
The present proposal focuses on studying the impact of impurities on the turbulence | The present proposal focuses on studying the impact of impurities on the properties of turbulence and the transport it drives. In particular, the controlled injection of impurities with low to moderate charge state (either with TESPEL or Laser Blow Off (LBO)) is desired. In order to provoke observable changes in the characteristics of the plasma turbulent behavior and performance, the impurities must be injected at non-tracer concentration, i.e. <math>Z^2 n_Z/n_i\sim 1</math>, with <math>Z</math> the charge state of the impurity, <math>n_Z</math> the impurity density and <math>n_i</math> the density of the main ions. To estimate the amount of impurities introduced and their localization, an estimate of the effective charge as well as the tomographic reconstruction of the radiation monitor signals will be of key importance. In that sense, the present proposal can greatly benefit from the conclusions of the proposal [http://fusionwiki.ciemat.es/wiki/TJ-II:_Zeff_measurement_using_visible_bremsstrahlung_(VB)_with_NBI_heating_(II)] | ||
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In order to assess the impact of the impurity injections in the plasma performance and turbulence, monitoring the time the evolution of the electron and ion temperature (<math>T_e</math> and <math>T_i</math>, respectively), as well as the diagmagnetic energy, will be essential. Ideally, <math>T_e</math> and <math>T_i/</math> should be measured at a radial position near to the that with largest impurity concentration and strongest impurity density gradient. If that information cannot be experimentally determined, a position from the inner core and mid-plasma radius will be chosen. Doppler Reflectometry (DR) fluctuation measurements radial profiles will be necessary in order to assess the changes in the amplitude of the turbulent density fluctuations. For modeling purposes, Thomson Scattering (TS) electron density (<math>n_e</math>) and temperature profiles shall be measured at a time instant of the discharge. Whenever available, a <math>T_i</math> radial profiles will be highly valuable. | In order to assess the impact of the impurity injections in the plasma performance and turbulence, monitoring the time the evolution of the electron and ion temperature (<math>T_e</math> and <math>T_i</math>, respectively), as well as the diagmagnetic energy, will be essential. Ideally, <math>T_e</math> and <math>T_i/</math> should be measured at a radial position near to the that with largest impurity concentration and strongest impurity density gradient. If that information cannot be experimentally determined, a position from the inner core and mid-plasma radius will be chosen. Doppler Reflectometry (DR) fluctuation measurements radial profiles will be necessary in order to assess the changes in the amplitude of the turbulent density fluctuations. For modeling purposes, Thomson Scattering (TS) electron density (<math>n_e</math>) and temperature profiles shall be measured at a time instant of the discharge. Whenever available, a <math>T_i</math> radial profiles will be highly valuable. | ||
As the impact on the plasma foreseen after the injection is expected to depend on how the impurities distribute radially, either forming a peaked or a hollow density profile, two plasma scenarios are to be looked at: a plasma scenario with predominantly ion-root ambipolar electric field throughout the hole plasmas, which should lead impurities to peak; and plasma scenario under broader core electron root and transition to ion root in the outer half of the plasma column. Whether those two scenarios are accessed by scanning the ECRH power and plasma density or by adding NBI to the heating scheme is left for discussion, and the decision will depend on how the different heating schemes constraint the quality and | As the impact on the plasma foreseen after the injection is expected to depend on how the impurities distribute radially, either forming a peaked or a hollow density profile, two plasma scenarios are to be looked at: a plasma scenario with predominantly ion-root ambipolar electric field throughout the hole plasmas, which should lead impurities to peak; and plasma scenario under broader core electron root and transition to ion root in the outer half of the plasma column. Whether those two scenarios are accessed by scanning the ECRH power and plasma density or by adding NBI to the heating scheme is left for discussion, and the decision will depend on how the different heating schemes constraint the quality and availability of the diagnostics data. | ||
Required resources: | |||
Number of plasma discharges or days of operation: 40 shots | |||
Essential diagnostic systems: spectroscopic system, Bolometric arrays, X-Ray detectors, Doppler reflectometer, HIBP, VUV spectrometer, NPA system, ECE, Thomson Scattering. | |||
Type of plasmas: standard configuration (100_44_64), ECRH (possibly NBI too). Scan of density and ECRH power on a shot-to-shot basis, so that we the scenario of the different set of discharges transit from CERC to predominantly ion root conditions. In each shot, the injection of a different impurity source will be carry out in ideally stationary conditions. | |||
Specific requirements on wall conditioning if any: to be discussed. | |||
External users: need a local computer account for data access: no | |||
Any external equipment to be integrated? Provide description and integration needs: None. | |||
== Preferred dates and degree of flexibility == | == Preferred dates and degree of flexibility == | ||
Preferred dates: (format dd-mm-yyyy) | Preferred dates: (format dd-mm-yyyy) | ||