Experimental Results from Three-ion Species Heating Scenario on Alcator C-Mod
J. Wright, S. Wukitch, E. Edlund,Y.O. Kazakov, Y. Lin, M. Porkolab,
D. Van Eester, J. Ongena, B15-12 Team and JET contributors*
IAEA, Kyoto, Oct 2016
*See the author list of “Overview of the JET results in support to ITER” by X. Litaudon et al. to be published in Nuclear Fusion Special issue: overview and summary reports from the 26th Fusion Energy Conference (Kyoto, Japan, 17-22 October 2016)./
New Heating scenario for efficient heating and pseudo-alphas verified on Alcator C-Mod
• First verification of three ion species heating scenario [Kazakov NF 032001 (2015)] on Alcator C-Mod in fall 2015 experimental campaign.
• ICRF only heating produced MeV 3He ion populations – suitable as a pseudo-alpha population
• Observed heating efficiency was significantly greater than D(3He) minority heating on C-Mod.
• Additional experiments in 2016 on JET and Alcator C-Mod also observed effects of MeV 3He ions.
Field-aligned4-strapantennaatJport(78MHz)
Two2-strapantennasatD-port(80.5MHz)andE-port(80MHz)
Adding second minority to improve absorption• Polarization at the minority resonance
can be further improved by using an additional smaller minority [KazakovNF 55 (2015)].
• H(D)((3He)) case in Alcator C-Mod with ~70% H, 30% D, 0%--0.2%--3% 3He.
• Without 3He, TORIC predicts 90% electron heating, 10% D. In reality, mostly edge losses from parasitic effects
• With 3He, 90% 3He heating, 10% electron
TOMCAT predictions of absorption [Kazakov, RF 2015 Invited Talk]
E+ maximized at L-cutoff
• L-cutoff location can be controlled by adjusting H-D ratio. (H res out of plasma on low field side.)
• Put L-cutoff near minority 3He resonance to have near 100% E+ polarization at ion-cyclotron resonance!
• Not possible with only two species.
Concentration scan of 3He
Quick transition to 3He heating, then gradual fall-off to dominant electron heating.
w/o 3He
With 3He
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Phasecontrastimagingsystem(PCI)
• Plasmadensityfluctuationsintroducephasevariationstothelaserbeam.
• Laserphasevariationsareconvertedtointensityvariationsbyal/4phaseplate.
• Acoustic-opticalfrequencyshiftertomodulatethelaserbeamtohaveabeat-frequencyneartheRFfrequency(heterodynescheme).
• RFwavescanbemeasuredinthissetupatthebeatfrequency[E.Nelson-Melby etal,PRL90,155004(2003)].
• Thesystemhasrecentlybeenupgradedtohavehighersensitivityathighfrequenciesandbettercalibration.
7
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R
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Determine3HelevelfromthedoubleMClocationsasmeasuredbyPCI
Double mode conversion layers at N||2= S
• Top:PCIRFsignallevelcontoursvs.R andt.Bottom:StixL/S/Rcurves.• PCIhas32channels,coveringaboutmajorradiusfrom0.64mto0.74m.• FromthelocationoftheMClayersà X[3He]» 0.7%andX[H]»70%forthisshot.
80 MHz RF signal from E antenna, shown in PCI spectra at ~880 kHz after heterodyne modulation. Amplitude related to Erfamplitude, phase give kRinformation.
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Alfvenactivitiesindicatethegenerationoffastions
• Reversed Shear Alfven Eigenmodes (RSAEs) observed on PCI
• Indicates presence of energetic ions (> 200 keV) [Edlund PoP056106 2009]
• Sawtooth crash ejects ions from plasma
• PCI measures fast wave and mode converted waves.
• Coincide with RF heating
Freq (Hz)
Major R(m)
RF Power (MW)
Total Power
E antenna (80 MHz)
D antenna (80.5 MHz) J antenna (78 MHz)
PCI measurement of D antenna waves
PCI spectrogram showing RSAEs
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TAEsseentoevolveduringlongsawteeth showevidenceofMeVions
• Twotornadomodesseenonleft20ms afterlastsawtooth consistentwith20ms timetobuildupMeVtailin3Hedistribution(Shot1160901023).
• Rightplotshows3Hedistributionwith400keV coreand5MeVtailassuming4MWcore-coupledICRFpowerfromAORSA+CQL3Dmodeling.
• Thedistributiondropsoffatabout3MeVwherepromptlossremovesionsfromthetokamak.
E("He) = 0.5 ##$%&'()*+
2800 MeV =0.7 MeV [Coppi PF 1988]
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Fokker-Planckmodelingshowsenergetictailandcoreheating
• Temperatureprofileontheleftshowscoreheating.• Ontheright,local3Hetailtemperatureisshown.
Unorm velocitycorrespondstoEmax=6MeV
keV
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IncreaseinefficiencyofICRFplasmaobserved
• ComparisonwithsimilarD(3He)shotdemonstratesmoreefficientheatingwithH–D(3He).
• TypicalchangeinstoredenergyforD(3He)is25%to50%higherwiththreespeciesscenariothanminorityheating,
• whileusingafactorof10less3He.
0.6 0.7 0.8 0.9 1.0
1
2
3
4
PICRF [MW]
0.08
0.12
0.04
Wmhd [MJ]
3
4
5
Te0 [keV]
1160
8230
03, 1
1609
0100
9
Time [s]
D(3He)H-D(3He)
12
● Efficient plasma heating at very low X[3He] ~ 0.2%successfully demonstrated in H-D mix plasmas
● Isotopic ratio H/(H+D) was varied in the range 0.74-0.93:good wave absorption at such low 3He levels
Pulse #90758
+π/2 phasing
X[H] ~ 0.9*H/(H+D) ~ 80%
X[3He] ~ 0.2%
H-D mixture
TestingD-(3He)-HICRHscenarioonJET:effectiveplasmaheating
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#90752: X[3He] ~ 0.2-0.3% (dipole ICRF phasing)
PICRH
PNBI
Te0
TestingD-(3He)-HICRHscenarioonJET:effectofICRHantennaphasing
#90755: X[3He] ~ 0.1-0.3% (+π/2 ICRF phasing)
PICRH
PNBI
Te0
● Benefit of launching waves in the co-current direction using +π/2 antenna phasing(smaller |k||| + RF-induced pinch effect; see M. Mantsinen et al., PRL (2002))
● Sawtooth stabilization: period of sawtooth oscillations depends on the adopted phasing
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TestingD-(3He)-HICRHscenarioonJET:fast-iongeneration
Observation of characteristic gamma-lines from 3He + 9Be nuclear reactions
Reconstructed gamma-ray emission profile for pulse #90753: X[H] ~ 70-75%, X[3He] ~ 0.2%, PRF = 4MW (2MW, dipole + 2MW, +π/2)
Excitation of TAE modes
● More localized wave absorption with +π/2 phasing● Lines with Eγ > 4.44MeV are efficiently excited if the 3He energy increases from 1MeV to 2MeV● TAE excitation, fTAE ~ 320-340kHz, nTAE = 5-7 → E[3He] ~ 2-3MeV (energy estimate)
Analysis: T. Craciunescu (INFLPR), V. Kiptily (CCFE), M. Nocente (IFP-Milano), S. Sharapov (CCFE) et al.
Conclusions• Three-ion ICRF scenarios have been demonstrated
on Alcator C-Mod and JET to provide efficient method of heating minority species to MeV energies suitable for use as a pseudo-alpha population for confinement studies.
• Modeling of ion temperatures with full wave and Fokker-Planck codes also predicts MeV ion energies.
• May provide a fast-ion source in W7-X [See Kazakov, P4 this afternoon] and in non-activated ITER.