Analysis of Runaway Electron Synchrotron Emission in ... · Analysis of Runaway Electron...
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Analysis of Runaway Electron Synchrotron Emission in Alcator C-Mod A. Tinguely 1 , R. Granetz 1 , M. Hoppe 2 , A. Stahl 2 , O. Embréus 2 Thursday, 3 November 2016 Research in Support of ITER APS DPP, San Jose, CA 1 Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 2 Chalmers University of Technology, Gothenburg, Sweden Supported by USDoE award DE-FC02-99ER54512.
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Analysis of Runaway ElectronSynchrotron Emission
in Alcator C-ModA. Tinguely1, R. Granetz1, M. Hoppe2, A. Stahl2, O. Embréus2
Thursday, 3 November 2016
Research in Support of ITER
APS DPP, San Jose, CA
1Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA2Chalmers University of Technology, Gothenburg, Sweden
Supported by USDoE award DE-FC02-99ER54512.
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 2
Runaway electrons may severely damage ITER
[1] V.V. Plyusnin, et al. NF 46, 277-284 (2006).
Relativistic “Runaway” Electrons (REs):
• Energies > 10 MeV
• Current ≤ 60% of Ip [1]
• In ITER, RE beams of 9 MA!
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Runaway electrons may severely damage ITER
dp
dt= 𝐅𝐄 + 𝐅𝐂
𝐧
𝐩𝟐+ 𝐅𝐀𝐋𝐃 𝐩∥, 𝐩⊥, 𝐁
Electric forceO(5-10) [2]
Radiation reactionO(3-15)
Collisional drag O(1)
Relativistic “Runaway” Electrons (REs):
• Energies > 10 MeV
• Current ≤ 60% of Ip [1]
• In ITER, RE beams of 9 MA!
[1] V.V. Plyusnin, et al. NF 46, 277-284 (2006).[2] R.S. Granetz, et al. PoP 21, 072506 (2014).
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Consider an electron with energy E = 40 MeV and pitch = 0.1 in three different magnetic fields.
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).
[3]
Does synchrotron emission limit the maximum energy of REs?
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Absolutely-calibrated visible/NIR spectrometers measure synchrotron emission on C-Mod
2.7 T 7.8 T
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• RE densities are difficult to reproduce, so we are not interested in the absolute amplitude.
• Instead, we are interested in the spectral shape.
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2.7 T 7.8 T
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• Select one time-slice near maximum emission during and steady plasma parameters.
• Take the ratio of two spectra and normalize.
Absolutely-calibrated visible/NIR spectrometers measure synchrotron emission on C-Mod
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*Relative to the reference spectra
Positive slope
• More brightness at longer wavelengths
• Shifted toward the red
Negative slope
• More brightness at shorter wavelengths
• Shifted toward the blue
Compare synchrotron emission at three magnetic fields
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).[4] J.H. Yu, et al. PoP 20, 042133 (2013). APS DPP 2016 – Research in Support of ITER – A. Tinguely 8
Compare synchrotron emission at three magnetic fields
Mono-energetic/pitch [3,4]
5.4 T
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Compare synchrotron emission at three magnetic fields
Mono-energetic/pitch [3,4]
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).[4] J.H. Yu, et al. PoP 20, 042133 (2013).
E = 28 MeVpitch = 0.1
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E = 28 MeVpitch = 0.1
≠
Mono-energetic/pitch [3,4]
Compare synchrotron emission at three magnetic fields
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).[4] J.H. Yu, et al. PoP 20, 042133 (2013).
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely
[3]
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B = 5.4 T, pitch = 0.1
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).
Decreasing RE energy decreases synchrotron emission amplitude and shifts toward the red
To keep the brightness the same, an increase in magnetic field requires a decrease in energy.
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Synchrotron emission limits the mono-energetic RE energy
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• Per particle, synchrotron emission increases and shifts toward shorter wavelengths with increasing magnetic field and energy (for fixed pitch).
• Measured synchrotron brightnesses at three magnetic fields (2.7 T, 5.4 T, and 7.8 T) have similar spectral shapes.
• Assuming a mono-energetic RE beam at a fixed pitch, an increase in synchrotron emission per particle (from an increase in magnetic field) reduces the energy.
Synchrotron emission is limiting the energy of REs.
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Summary of Results
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Preliminary results from synthetic diagnostic SOFT [5] show good agreement with experiment
[5] Correspondence with M. Hoppe and the Chalmers Plasma Physics Group (2016).
[1] V.V. Plyusnin, et al. NF 46, 277-284 (2006).
[2] R.S. Granetz, et al. PoP 21, 072506 (2014).
[3] I.M. Pankratov. Plasma Phys. Reports 25, 2 (1999).
[4] J.H. Yu, et al. PoP 20, 042133 (2013).
[5] M. Hoppe, Chalmers Plasma Physics Group (private communication, 2016).
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References
Backup slides
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Absolutely-calibrated visible/NIR spectrometers (~300-1000 nm) measure SE on C-Mod.
SE
C-Mod ITER
Btor (T) 5.4 (2 – 8) 5.3
ne (1020 m-3) 1 (0.2 – 4) 1.0
Top View
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2.7 T 7.8 T
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• Select one time-slice near maximum emission during steady plasma parameters.
• Take the ratio of two spectra and normalize.
Absolutely-calibrated visible/NIR spectrometers measure synchrotron emission on C-Mod
E/Ec = 14 𝛕𝐫𝐚𝐝 = 11
E/Ec = 11 𝛕𝐫𝐚𝐝 = 2.2
E/Ec = 1.5 𝛕𝐫𝐚𝐝 = 4.6
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Compare synchrotron emission at three magnetic fields
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Evolving RE energy distribution is observed in SE spectra time evolution
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Quiescent RE flattop
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SE polarization data is also available1
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Modelling efforts have had limited success
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1160512011Time-dependent CODE [a,b]:• Uses linearized kinetic equation• Includes avalanche sources• Works for a few C-Mod shots
[a] M. Landreman, et al. CPC 185, 847 (2014).[b] A. Stahl, et al., to appear in NF. arXiv:1601.00898v3 [physics.plasm-ph][c] A. Stahl, et al. PoP 20, 093302 (2013).
μW
/mm
2/n
m/s
r
[c]
[c]
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Preliminary results from synthetic diagnostic SOFT [5] show good agreement with experiment
[5] Correspondence with M. Hoppe and the Chalmers Plasma Physics Group (2016).
SOFT simulation of RE beam:• C-Mod EFIT flux
reconstruction• Camera view geometry• Radius = 16 cm• Energy = 24 MeV• Pitch = 0.10
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