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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!
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 3
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).
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 4
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?
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 5
Absolutely-calibrated visible/NIR spectrometers measure synchrotron emission on C-Mod
2.7 T 7.8 T
11
60
82
40
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11
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11
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90
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5.4 T
• RE densities are difficult to reproduce, so we are not interested in the absolute amplitude.
• Instead, we are interested in the spectral shape.
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 6
2.7 T 7.8 T
11
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5.4 T
• 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
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 7
*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
APS DPP 2016 – Research in Support of ITER – A. Tinguely 9
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
APS DPP 2016 – Research in Support of ITER – A. Tinguely 10
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]
11
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.
APS DPP 2016 – Research in Support of ITER – A. Tinguely 12
Synchrotron emission limits the mono-energetic RE energy
3 November 2016
• 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.
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 13
Summary of Results
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 14
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).
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 15
References
Backup slides
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3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 17
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
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 18
2.7 T 7.8 T
11
60
82
40
24
11
60
82
40
26
11
60
90
20
16
5.4 T
• 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
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 19
Compare synchrotron emission at three magnetic fields
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 20
Evolving RE energy distribution is observed in SE spectra time evolution
1160824026
Quiescent RE flattop
1160824026
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 21
SE polarization data is also available1
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3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 22
Modelling efforts have had limited success
1160512011
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]
1160512011
3 November 2016 APS DPP 2016 – Research in Support of ITER – A. Tinguely 23
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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3 November 2016 25
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