Abstract
Currents driven by radio frequency (rf) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER.
| Original language | English (US) |
|---|---|
| Article number | 225001 |
| Journal | Physical review letters |
| Volume | 121 |
| Issue number | 22 |
| DOIs | |
| State | Published - Nov 30 2018 |
All Science Journal Classification (ASJC) codes
- Physics and Astronomy(all)
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Suppression of Tearing Modes by Radio Frequency Current Condensation. / Reiman, A. H.; Fisch, N. J.
In: Physical review letters, Vol. 121, No. 22, 225001, 30.11.2018.Research output: Contribution to journal › Article › peer-review
TY - JOUR
T1 - Suppression of Tearing Modes by Radio Frequency Current Condensation
AU - Reiman, A. H.
AU - Fisch, N. J.
N1 - Funding Information: The rf current condensation effect identified here increases the efficiency of rf current drive stabilization, allowing the stabilization of larger islands for a given rf power, and it reduces the sensitivity of the stabilization to radial misalignment of the ray trajectories relative to the island O-line. Also, a broad rf driven current aiding the maintenance of steady state can provide stabilization through condensation, even in the absence of a stabilizing geometric effect. The local power deposition and electron acceleration are highly sensitive to the perturbation of the local temperature in an island. Moreover, the nonlinear feedback on the power deposition increases the temperature perturbation. The combination of the nonlinearly enhanced temperature perturbation with the rf current sensitivity to the temperature produces the rf current condensation effect. Our calculations here neglected the effects of wave depletion, which have been left for future investigation. If account is taken of wave depletion in launching the rf waves, the effect can further increase the concentration of the rf current near the O-line, and can thereby further increase the stabilization efficiency. Also neglected were more peaked unperturbed deposition profiles and additional sources of heating in the islands, which would lower some of the thresholds calculated here. Despite approximations, what is clear is that the current condensation effect is both new and important. Signatures of the phenomena predicted here should be observable in more precise temperature measurements in island interiors, through comparisons of different methods of rf current drive, through more careful analyses of saturated island widths, and through comparisons to island formation in the rf overdrive regime. Apart from the academic interest of the fold bifurcation, it leads to the practical applications of increased stabilization efficiency, and decreased saturated island widths through hysteresis. The threshold for the current condensation effect has been encountered in present-day experiments, and will very likely be encountered in ITER. The condensation effect is particularly effective in stabilizing large islands, where the increased efficiency may be crucial for the minimization of disruptivity on ITER, which in turn could impact the economical advancement of tokamak fusion. The authors would like to acknowledge conversations with Ms. Ge Dong and Mr. Eduardo Rodriguez. This work was supported by DOE Contract No. DE-AC02-09CH11466. [1] 1 P. C. de Vries , M. F. Johnson , B. Alper , P. Buratti , T. C. Hender , H. R. Koslowski , and V. Riccardo , Nucl. Fusion 51 , 053018 ( 2011 ). NUFUAU 0029-5515 10.1088/0029-5515/51/5/053018 [2] 2 P. C. de Vries , Phys. Plasmas 21 , 056101 ( 2014 ). 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PY - 2018/11/30
Y1 - 2018/11/30
N2 - Currents driven by radio frequency (rf) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER.
AB - Currents driven by radio frequency (rf) waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. Present analyses of stabilization assume that the local electron acceleration is unaffected by the presence of the island. However, the power deposition and electron acceleration are sensitive to the perturbation of the temperature. The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and can lead to a bifurcation of the solution to the steady-state heat diffusion equation. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. The threshold for the effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER.
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U2 - 10.1103/PhysRevLett.121.225001
DO - 10.1103/PhysRevLett.121.225001
M3 - Article
C2 - 30547647
AN - SCOPUS:85057797562
VL - 121
JO - Physical Review Letters
JF - Physical Review Letters
SN - 0031-9007
IS - 22
M1 - 225001
ER -