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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, )(

1

2

2

LRS

L

R

j j

pj

j j

pj

+=

W--=

W+-=

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www

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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.