Investigation of triggering mechanisms for internal transport barriers in alcator c mod
Download
1 / 10

Investigation of triggering mechanisms for internal transport barriers in Alcator C-Mod - PowerPoint PPT Presentation


  • 68 Views
  • Uploaded on
  • Presentation posted in: General

Investigation of triggering mechanisms for internal transport barriers in Alcator C-Mod. K. Zhurovich C. Fiore, D. Ernst, P. Bonoli, M. Greenwald, A. Hubbard, D. Mikkelsen * , E. Marmar, J. Rice MIT Plasma Science and Fusion Center * Princeton Plasma Physics Laboratory APS DPP Meeting

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha

Download Presentationdownload

Investigation of triggering mechanisms for internal transport barriers in Alcator C-Mod

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Investigation of triggering mechanisms for internal transport barriers in alcator c mod

Investigation of triggering mechanisms for internal transport barriers in Alcator C-Mod

K. Zhurovich

C. Fiore, D. Ernst, P. Bonoli, M. Greenwald, A. Hubbard, D. Mikkelsen*, E. Marmar, J. Rice

MIT Plasma Science and Fusion Center

*Princeton Plasma Physics Laboratory

APS DPP Meeting

Philadelphia, PA

October 31, 2006


Motivation

Motivation

Inward pinch

Core

Edge

Outward diffusion

Background:

  • Internal transport barriers (ITBs) can be routinely produced in C-Mod steady enhanced Dα (EDA) H-mode plasmas by applying ICRF at |r/a| ≥ 0.5 (off-axis heating)

  • They are observed primarily in the electron particle channel and are marked by the steepening of the density and pressure profiles following the L-H transition

    Framework:

  • During normal plasma operation inward neoclassical Ware pinch is balanced by the outward diffusion caused by the microturbulent modes, resulting in a flat density profile


Motivation1

Motivation

Background:

  • Internal transport barriers (ITBs) can be routinely produced in C-Mod steady enhanced Dα (EDA) H-mode plasmas by applying ICRF at |r/a| ≥ 0.5 (off-axis heating).

  • They are observed primarily in the electron particle channel and are marked by the steepening of the density and pressure profiles following the L-H transition.

    Framework:

  • During normal plasma operation inward neoclassical Ware pinch is balanced by the outward diffusion caused by the microturbulent modes, resulting in a flat density profile

Inward pinch

Core

Edge

Outward diffusion

  • Suppressing turbulent diffusion allows the pinch to overcome, resulting in a peaked density profile

  • Longer modes (ITG) are responsible for transport

  • Shifting the ICRF resonance outward flattens the temperature profile and decreases the mode’s drive


Plasma parameters itb vs non itb

Plasma parameters (ITB vs. non-ITB)

6.3 T

ITB

line-integrated density (1020 m-2)

line-integrated density (1020 m-2)

density peaking =

density peaking

RF power (MW)

RF power (MW)

time (s)

time (s)

5.6 T

non-ITB

  • Magnetic field scan: shift the RF resonance location on shot-to-shot basis

  • Plasma current adjusted proportionally to keep q95 constant

  • Sharp threshold in BT consistent with previous observations


Pre itb electron temperature gradient

Pre-ITB electron temperature gradient

Near ITB foot location

Just inside ITB foot

ITB

non-ITB

  • Temperature scale length is calculated from ECE measurements

  • Averaging has been done over steady portions of the discharges (pre-ITB phase for ITB discharges)

  • R/LT decreases as the ICRF resonance position is moved outward by raising the magnetic field

  • This decrease is observed just inside the ITB foot location for ITB discharges


Change in electron temperature gradient

Change in electron temperature gradient

70 MHz

on-axis

80 MHz

off-axis

R=0.78m

Te (keV)

ITB foot

R=0.83m

time (s)

time (s)

Te (keV)

R/LT

time (s)

R (m)

  • Dual frequency ICRF setup

  • ITB develops during the off-axis heating phase

  • Temperature measurements are done by high resolution (32 channels) ECE system

  • Temperature scale length is derived from channels around the ITB location

  • Profiles are shown at times corresponding to 100% on-axis heating, 50%-50% on- and off-axis, and 100% off-axis heating

  • R/LT decreases in the region of ITB as the ICRF resonance moves off axis


Ion temperature profile measurements

Ion temperature profile measurements

ITB

non-ITB

ITB

  • Ion temperature is measured by high resolution x-ray system (HIREX)

  • Central ion temperature is derived from neutron rate measurements

  • Ion temperature profile gets flatter as ICRF resonance is moved off axis


Ion temperature profile transp simulation

Ion temperature profile (TRANSP simulation)

Te

Ti

RF (x10)

(Watts/cm3)

Te

Ti

RF (x10)

(Watts/cm3)

Te

Ti

RF (x10)

(Watts/cm3)

Te

Ti

RF (x10)

(Watts/cm3)

  • Ti is calculated by TRANSP to match the neutron rate (using feedback corrected multiplier on χneo to obtain χi)

  • Ion temperature profile gets broader as ICRF resonance is move outward

  • This trend is consistent with experimental observations

ITB


Itg growth rate profiles

ITG growth rate profiles

non-ITB

ITB

  • ITG/ETG growth rate profiles are calculated by linear gyrokinetic stability code GS2 based on TRANSP analysis

  • No difference in ETG growth rates and spectra for ITB vs. non-ITB cases

  • The region of stability for ITG modes gets wider as ICRF resonance is moved outward

  • kρi spectra are similar for all runs and peak at ~0.3-0.4


Conclusions

Conclusions

  • Experimental evidence: electron and ion temperature profiles get flatter as ICRF resonance location is shifted off-axis

  • Ti profiles as calculated by TRANSP exhibit similar trend with the absolute deviation from the electron temperature being small

  • Using TRANSP Ti profiles linear GS2 calculations show that region of stability to ITG modes gets wider as ICRF resonance is move outward

  • Suppressing ITG turbulence can be a dominant factor in the triggering mechanisms for off-axis ICRF heated ITBs in C-Mod


ad
  • Login