Acknowledgements• USDOEgrantNo.DE-FG02-00ER54610

• M.C.Milleretal.,RevSci.Instrum.83,10E332(2012)

• Marushchenko et al., Comput.Phys.Commun.185,165(2014)

• Hansonetal.,Nucl.Fusion49,075031(2009)• I.H.Hutchinson,Prin.ofPlasmaDiagnostics(2e),CUP

TheCompactToroidalHybridExperiment

• CTHisa5field-periodtorsatrondesignedtoinvestigateplasmainstabilityanddisruptionsoverawiderangeofoperatingconditions

• ThehybridfeatureofCTHistheabilitytoaddtoroidalcurrent,whichgivessignificantcontroloverthetransformprofile.

DESIGNRo =0.75m

av =0.29m

ap ≤0.20m

Bo ≤0.7T

Ip ≤80kA

PECRH=15kWPOHM ~ 200kW

PLASMAPARAMETERSshottime~ 0.1s

ne ≤5x1019 m-3

Te ≤200eV

<b> ≤0.2%

0.02≤≤0.35

V3FITSensitivityAnalysis

• foragivendensityprofile,V3FITshowshow sensitivityofreconstructiondependsonthenewlocationsofthebeams

TRAVISBeamRefractionStudy

• beamdeflectiontendstobehighestwhereverthereisbothahigherdensityandastrongdensitygradient

• TRAVIScodewasusedtoanalyzepossiblebeamlocationstominimizethedeflectionofthebeamfromretro-reflector(δZ)

Summary

• interferometerupgradehasbeensuccessfullydesigned,builtanddemonstrated.

• newchannelisincorporatedinequilibriumreconstructions

• planningtousenewdensitymodeltoanalyzeverticalinstability

• performanceissuesofthenewchannelwillbeaddressedbyfurtherrefiningthefrequencymodulationprogram

SystemPerformance

• channel4line-integrateddensityconsistentwithotherchannelsassumingup-downsymmetricdischarge

• 4independentbeamsgivemoredetailsofshotevolution

• noiseisachallengeforthenewchannel.(4)Nowitiswell-controlled.

BASICS• Plasmaretardsmm-wavebeam~ densityà phasemodulation

• Thedetector(SHM)measurestheintensityoftheinterferencefringes

• Thetotal phasedelaywrittenintermsoftheline-averagedplasmadensity:

• 1fringeshiftà ∆𝜙%&'()* = 2𝜋 à ~ 3.0×104& electrons/m3

InterferometryinPlasmaDiagnosis

ADVANTAGES

• non-perturbativemeasurement

• subharmonicreferencelegfeedsdirectlyintomixer– easyalignmentofdetector

CHALLENGES

• refractionofbeamoutofretro-reflectorà lossofsignal

• rapidtransient-inducederrorsinfringecounting(fringejumps)

V3FITMulti-BeamComparison

Startedwiththeassumptionthatmoredataisbetter.

Compared3,4and5-beamconfigurations

• Weestimatedpotentialreductionintheerrorsinequilibriumreconstructioninexpandingsignalstoa4and5-beamsystem

• Computed“fractionalerror”(𝛼)basedonknownandreconstructeddensityprofiles

• mainresult isthereisverylittledifferencebetweenthe4-beamand5-beamsystemsintermsofreducingerrorsinreconstruction

𝛼 ≡∫ 𝑑𝑠|𝑛<=>?=(𝑠) − 𝑛CDE>=(𝑠)|4'

∫ 𝑑𝑠𝑛<=>?=(𝑠)4'

plasmadensity

[x10

18 m

-3]

shot#18102253

References

t=1.630sOhmicrise

t=1.650s

Ohmicplateau

shot#18102253

EquilibriumReconstruction

• firstequilibriumreconstructionsusingupgradedinterferometer basedonsimplelinesegmentmodelfordensity

Height(Z)[m]

majorradius(R)[m]

Height(Z)[m]

majorradius(R)[m]

n e(x10

18)[m

-3]

fluxcoordinate(s)

n e(x10

18)[m

-3]

fluxcoordinate(s)

UpgradedInterferometerOverviewMOTIVATION

• newconfigurationprovides2additionalindependentdiagnosticsignalswhichshouldprovidemuchimproveddensityprofileresolutionforstudyingMHDinstabilitiesanddisruptions

newSHMdetector

voltage-controlledoscillator

amplifier-multiplierchain

14.5 cm

7.3 cm

0.0 cm

-11.1 cm

chan 1

chan 2

chan 3

chan 4

10.2 cm

0.0 cm

-10.2 cm

mm-wavepowerline

parabolicmirror

Sub-HarmonicMixer

detectors

HDPEwindow

retroreflectors

chan 1

chan 2

chan 3

Improvementsinnewdesign• asymmetricpositionseliminateredundancy

• beamscoverhigherfractionofplasmavolume

• higherfrequencymitigatesdensitylimit

CTHspecialdesignfeaturesSubharmonicMixer(SHM)design• referencelegsupplieddirecttoSHMfacilitatesalignmentandreducesconversionloss

Double-passhorizontallaunch• allowssingle-portaccesstoplasma

Chirpingoffrequencycontrol• frequencymodulationrequiredforphaseshiftcalculationinsingle-sourceinterferometer

Limitationsoforiginaldesign• symmetricoff-axisbeamsareredundantdata

• beamscoversmallerfractionofplasmavolume

• double-passdesignimposesalimitonmaximumdensity

UpgradeModifications

• mm-wavebeamat280GHzand10mW

• Improvedbeamconfiguration

• beamrefractionanalysiswasdoneonthreegeneralclassesofprofiles- broad,peakedandhollow

• higherfrequencybeamhaslowerrefraction

• newhigherfbeamplacedwherebeamlossbydeflectionisminimizedforfullsystem

• signaleffectiveness(𝐸GH)isameasureofthesensitivityofmodelparameterstovariationsinagivensignal.

• RESULT - fullanalysisshowsbeamspacingprovidescoveragewithgoodsensitivityoverfullplasmavolumeforbroad,peakedandhollowdensityprofiles.

TheCTHCoilSet

𝐸GH ≡𝑑(𝑙𝑛𝜎HK)𝑑(𝑙𝑛𝜎G)

t=1.610sECRHphase

Height(Z)[m]

majorradius(R)[m]

n e(x10

16)[m

-3]

fluxcoordinate(s)

shot#18102253