pulsed magnetic mirror device 1 D O 1 S Hwang 2 B K Jung 1 M Choi 1 G Baek 1 C Sung 1 KAIST 2 KAERI Korean Nuclear Society Spring Meeting Jeju Korea May 19 2022 ID: 1039660
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1. Design and construction ofpulsed magnetic mirror device 1D. O, 1S. Hwang, 2B. K. Jung, 1M. Choi, 1G. Baek, 1C. Sung1KAIST, 2KAERIKorean Nuclear Society Spring MeetingJeju, Korea, May 19, 2022E-mail: choongkisung@kaist.ac.kr1
2. 2KAIST FPDL O Dong GeunContentsIntroductionDesign of the KAIMIR systemInitial plasma operation testSummary / Future work
3. Schematics of plasma confinement in mirror geometry2IntroductionKAIST FPDL O Dong Geun3The needs for magnetic mirror plasma deviceMagnetic mirror geometry plasma device :Open magnetic field system / confine plasma by mirror force from the B field intensity change ()Advantage of magnetic mirror deviceSimple geometry, construction of device / Easier accessibility of diagnosticsContinuous operation, No current driveGas Dynamic Trap (GDT) : Achieved maximum Te ~ 900eV plasma generation1, in 2014From this result, research on the development of fusion based neutron source is actively on the wayMirror related studies are also ongoing in other countries ex) Wisconsin (WHAM) / China (KMAX)… [1] Bagryansky, P. A., et al. Physical review letters 114.20 (2015)[2] https://scfh.ru/en/papers/trap-f-o-r-fusion-/
4. IntroductionKAIST FPDL O Dong Geun4Development purpose of KAIst MIRror plasma system (KAIMIR) deviceBasic plasma physics study in magnetic mirror geometryPhysical analysis of instability in mirror plasma systemWave – plasma interaction in mirror plasma systemFusion / Industrial plasma application studyBase research for Fusion based neutron sourceResearch of industrial plasma sourceEdge plasma in fusion and divertor region physics studySchematic of KAIMIR deviceActual photograph of KAIMIR deviceExample of KAIMIR plasma discharge
5. Design of the pulsed plasma systemKAIST FPDL O Dong Geun5Overall systemDiameter 0.65m / length 2.48m cylindrical structure, consists of Source / Center / Expander ChamberGenerate center region 0.04~0.08T / mirror region 0.2~0.4T mirror geometry B field by Solenoid / Mirror coilApply arc plasma gun as a source, designed for ~5ms, pulsed high density plasma generation Drawing of KAIMIR device
6. Design of the pulsed plasma systemKAIST FPDL O Dong Geun6Magnetic field simulationBz along r = 0Mirror / Solenoid coil current : 150A / 150A in simulationNearly uniform at center of the chamber0.08T at center / 0.44T at mirror nozzle → Mirror ratio ~ 5Aims to Max. 300A current discharge to coil (150A in present)
7. Design of the pulsed plasma systemKAIST FPDL O Dong Geun7Magnetic field measurementMagnetic field measurement / simulation resultsby changing Axial location(Gauss meter calibration factor: 0.9)Magnetic field measurement / simulation resultsby changing coil current value (Location : mirror nozzle)Apply current 10A / 10A in mirror / solenoid coil, measure B field by axial locationMirror region 340G / center region 65G, formation of mirror ratio ~5, B field geometryB field measurement by changing coil current in the center of mirror coilVerified linear proportionality of B field intensity by current value changeMeasured / simulated data agree each other in Axial location / Current value
8. Design of the pulsed plasma systemKAIST FPDL O Dong Geun8Magnetic coil power systemPower moduleSeries connection of 2.7V / 2000F capacitor[60ea (Solenoid) / 80ea (mirror)]→ Max. possible voltage charge : 162V (Solenoid) / 216V (mirror)Applies power to four electromagnetic coils connected in parallelSteady magnetic field generation after ~0.1sTime evolution of Coil V / I / B field (solenoid coil, 10V, 0.5s pulse, measured center of the coil)
9. Design of the pulsed plasma systemKAIST FPDL O Dong Geun9Piezo-electric valvePlasma gunSource chamberCenterchamberExpanderPFNCathodeCath-anodeCollectorPlasma4kΩGas linePlasma gun installed at source chamber / Collector plate (295, Tungsten) installed at ExpanderGas injection : controlled by Piezo-electric valve (~ms response time)Gas type : Ar / HeBoth Plasma gun / Collector sustained by SUS pipe structure → Axial location adjustablePower of the plasma source applied by Pulse forming Network (PFN) system Plasma source / Collector
10. Design of the pulsed plasma systemKAIST FPDL O Dong Geun10PFN power systemPulse Forming Network (PFN)Pulsed plasma needs long (~ms) moderate high voltage pulse to gunMatching circuit / Load impedance, ladder-like connection→ flat square pulse to loadPFN power bank system specificationTrigger systemVoltage for sustaining plasma is lower than initiating plasma dischargeSudden (~100us) high voltage for breakdown→ Sustain plasma with PFN powerDischarge power from trigger system→ Sudden spark makes plasma column→ Plasma discharged from PFN PFNCathodeCath-anodeCollector PFN V / I simulation resultsTrigger
11. Initial plasma operation testKAIST FPDL O Dong Geun11PFN power systemTime evolution of Gun Voltage / Current PFNCathodeCath-anodeRCollector PFN –Plasma gun circuit schematicsCondition : PFN Voltage 800V / Trigger voltage 1600V caseMax. ~350V / ~1.6kA, Voltage / Current is applied to gun→ Plasma impedance ~ 0.22Ω (Not matched to expected 0.15Ω), Flat top : ~3ms (2~5ms)Plasma gun power : maximumCause of waveform change : Internal resistance of inductor / Imperfect impedance matching / Stray Resistance Gun current simulation considering Flat top
12. Initial plasma operation testKAIST FPDL O Dong Geun12TLP measurementConditionsMagnetic field : (mirror region : 0.4T / center region : 0.078T)TLP location : center chamber (-10cm from the center)PFN : 800V / Trigger : 1600VBase pressure ~3×10-7 Torr / Operating pressure ~ 1mTorrGas : ArgonTriple Langmuir Probe measurement resultParameter averaged in Flat top (2~5ms) ~ / ~4.4eVPreliminary measurement results,more analysis required to be confirmed Flat topTriple Langmuir Probe settingsCurrent measuring resistance : 10Ω / : 24V
13. Initial plasma operation testKAIST FPDL O Dong Geun13I-V curve / Ion saturation current measurementConditionsMagnetic field : (mirror region : 0.4T / center region : 0.078T)TLP location : center chamber (-10cm from the center) PFN : 800V / Trigger : 1600VBase pressure ~3×10-7 Torr / Operating pressure ~ 1mTorrGas : ArgonFlat topMeasurement of I-V characteristic curve, saturation currentDischarge plasma by changing Biasing voltage ()Measure current flowing at the probe tip for each shotsExtract current data at 2ms from the discharge, draw I-V curveFrom the I-V curve, Average ion saturation current at the Flat top (2~5ms)matches within ~25% from TLP data
14. KAIST FPDL O Dong Geun14Summary / Future workNew pulsed linear magnetic mirror plasma device is constructed in KAISTResearch interests : Basic mirror plasma physics and fusion / industrial applicationB field : center region 0.04~0.08T / mirror region 0.2~0.4T / Mirror ratio : 2.5 ~ 10Plasma source : Arc plasma gun, ~350V / 1.6kA in initial experimentsInitial plasma parameter measurement : ne~6.9×1019m-3 / Te~4.4eV (by TLP)Summary
15. KAIST FPDL O Dong Geun15Summary / Future workFuture workDiagnose plasma characteristics from experiments of diverse conditionCheck reproducibility of the experiments by repeating same shots in many different timingMeasure plasma parameter by changing location of Plasma gun and CollectorConduct electrode biasing in Collector and analyze the effect to the plasma parameterMeasure plasma characteristics by changing PFN / Trigger voltageStudy plasma parameter by changing magnetic field geometry configurationImprovement of KAIMIR plasma diagnosticsMicrowave interferometry – plasma line-integrated densityOES measurement – Plasma radiation spectrumDiamagnetic loop – Plasma internal energyProbe measurement - Modification of physical model / data processing
16. 16KAIST FPDL O Dong GeunThank you
17. Backup slideKAIST FPDL O Dong Geun17Magnetic coil specificationMirror coilCoil resistance : 1.026Ω / Inductance : 43.07mH / Number of turns : 360Coil diameter: 278mm / weight : 15.1kgInstall location : ±730mm / ±645mm (From center)L/R time (risetime) : 42msSolenoid coilCoil resistance : 0.746Ω / Inductance 15mH / Number of turns : 120Coil diameter : 620mm / weight : 10.9kgInstall location : ±388mm / ±138mm (From center)L/R time (risetime) : 20ms
18. Backup slideKAIST FPDL O Dong Geun18PFN power systemPFN systemSparker systemT1+T1-PFN-PFN+PFN power system circuit schematics
19. Backup slideKAIST FPDL O Dong Geun19CAD model of Plasma gun
20. Backup slideKAIST FPDL O Dong Geun20Power balance equationInput Power – Power lossAssumptionplasma volume as Stored energy Power efficiency of the gun to plasma ~ 50%~300V, 1.2kA power will be applied to gun in ~5ms , choose where R : mirror ratio / : ion Coulomb collision time In steady state, Order is similar with experimental results Power balance analysis
21. Backup slideKAIST FPDL O Dong Geun21Triple Langmuir probe design10mm100mm200mmControl box DAQCircuit diagramTLP Structure2.2M 10 (Gain) DC bias (24V)Isolation amplifierTungsten tip Triple Langmuir probe structure / circuit schematicsTriple Langmuir probe (TLP)~5ms pulsed plasma diagnostics → high temporal resolution requiredUtilize property of I-V characteristic curve of plasmafrom V / I value b/w probes, calculate plasma density / temperatureDirectly measures plasma parameters without any voltage sweepingAssume ideal I-V curve, measurement affected by DC bias and tip sizeProbe / circuit designAlumina tube : 100mm (Twice of predicted plasma radius)Metal tip : 0.3, exposed length 10mm, Tungsten wireVoltage measuring resistance : 2.2M (Make Floating tip current~0)Current measuring resistance : 10 (better SNR, Saturation/voltage drop)DC bias : 24V (Series connection of 12V lead-acid battery)Measured data varies with DC bias value,Need cross-check with another diagnostics
22. Backup slideKAIST FPDL O Dong Geun22Operation procedure / timingKAIMIR Nominal Operation procedure / timing settingsBase pressure ~3×10-7 Torr / Coil, PFN power bank chargedPiezo-electric valve is triggered→ Operating pressure ~1mTorrIGBT module of the coil is triggeredIGBT module of the PFN is triggeredPlasma is discharged from the PFN power-200ms0ms200ms-200ms ~ 100msfor both coil-100ms ~ -50msTime line0ms ~ 5msPlasmaDischargeB field generationGas injection