Development Of 1MW-CW Gyrotron For ITER
JA-KO Joint Workshop on RF Heating and Current Drive in Fusion PlasmasNational Fusion Research Institute (NFRI), Daejeon, Korea, Jan. 14–15, 2008Development of 1MW-CW Gyrotronfor ITERA. Kasugai, K. Kajiwara, K. Takahashi, N. Kobayashi,and K. SakamotoJapan Atomic Energy Agency (JAEA)
Status of 170GHz gyrotron performance 1hour/0.6MWDemonstration of steady state operationBurning of plasma in ITER( 400s) Output Power (MW) 1.0MW/800s/55% Satisfied basicrequirement of ITERgyrotron(1.0MW/500s/50%)Achievement of target ofITER gyrotronITER 20032006- 2005 Pulse Duration (s)
Contents1. ECH system in ITER2. Gyrotron technologies & improvements3. Experimental resultsCW operationScenario to high efficiency operation4. Summary
ECH system in ITERITERIn ITER, 170GHz 24MW ElectronCyclotron Wave system is plannedfor plasma heating/Current drive/ Instability suppression.Japan:Equatorial launcher& 8-GyrotronsPlasma radius : 6.2mQ value: 10 Burn time: 400 500sFusion power : 500MWMost Important Technical IssueEstablishment of reliable &high power & CW GyrotronFinal Target of ITER Gyrotron:Demonstration of 170GHz,1MW, 500s, 50% efficiency
Gyrotron TechnologyArtificialdiamond windowEnergy recoveryDistribution function of e-beam55% 37%25keVLong pulse operationLow loss tangentHigh thermal conductivityCavity inputCavity outputAt collector0keV Energy 72keVHigh power cavityHigher oscillation mode170GHz/1MW(TE31,8)ElectronbeamOutput RF at windowITER gyrotronField pattern at cavity (oscillation)
Major Improvements of the Gyrotron Optimization of launcher & mirrorsOscillation mode: TE31,8 (Cavity)For high efficiency& reduction ofstray RFLauncher& mirrors Output: Gaussian beamElectron beam quality For high oscillation efficiencyHigh quality beamMIG & EmitterunwantedelectronsGyrotronCathode before AfterHigh pitchfactoroperationBeam current controlFor Stable oscillationBeam Current (A)Stepconfiguration40 Control of cathodeheater powerWith pre-programmingcontrol of heater30 20 Without controlof heater10 0 -2000200 400 600 800 1000 1200Time (s)
Experimental Result of 170GHz GyrotronRF Profile at the WindowMeasured RF output profile agreed well with the design.DesignMeasurement byIR cameraP 0.6MWFlame time 1/ 120 sWindow temperaturemeasured throughviewing port of MOUMeasured stray radiation was reduced to 2% of output powerby optimization of the launcher & mirrors.
RF Transmission Line for Long Pulse ExperimentDirectionalCouplerRFInside of MOURFCu plate for coolingMOUPre-loadRFRFgyrotron1MW Dummy load63.5mm evacuated W/G 7m(ITER size)
Stable One Hour OperationDepressed Collector Volt.(20kV/div)StablepowersupplyAnode Volt.(20kV/div)Cathode Volt.(20kV/div)StablebeamcurrentBeam Current (10A/div)Light from Gyrotron (a.u.)Constantpower0.6 MW/1hour (steady stateoperation) was achievedOutput Energy 2.1GJNoarcingGoodpressure teady State OperationVacuum Pressure(1x10-8torr/div)Stable oscillationNo arcing and good vacuum10-5 Pa during operation No problem of cooling capacitybecause of low stray radiationRF Power (0.6MW)Window Center Temp1 hour/3600 sClear prospect for applicationto the ITER ECH system
Aging History up to 3600s OscillationPulse Duration (s)40003500350030003000Power 0.6MW(170GHz)250025002000200015001500World recordbefore 2006/4Outgas inside thegyrotron was low level.10001000500500001st phase(9 days)High depressedcollector voltage 28kV&Low stray radiation2nd phase(5 days)It was possible toextend the pulseduration rapidly.Working Day for Pulse Extension0.8s3600s : Short aging time within 2 weeks
Try to High Efficiency OperationReverse rotational modes(TE-28,9,TE-27,9) were not observed0.6MW/1hr operationSoft self-excitationregion (Low Efficiency)Hard self-excitationregion (High Efficiency)Clear hysteresiseffect on Bc scanHard self-excitation region 56%0.8 0.6170GHz TE30,80.4167GHz 0.20.0 ,8TE31Soft selfexcitationVb 72.5kV,Vcpd 25.5kV, Ib 30A6.6First demo by Bc scan with CW operation 0.6MW/1hroperation (fix)In hard self-excitationregion, TE31,8 can’texcite directly.Output PowerPower (MW)Output(MW)By decreasing Bcwith keepingoscillation1.06.62 6.64 6.66 6.68 6.7Cavity field, Bc (T)
Scenario for High Efficiency Operation(1) (2)(1) Increase of anode voltage ( )(2) Decrease of cavity fieldAnode Voltage (kV)43.042.542.0Ia0.8MW0.6MWTE31,841.040.5Hard selfexcitation region40.039.06.620.5MWCavityField(1)Beam CurrentRFInitialOsciTE30,86.64Cathode Volt.Soft selfexcitation region41.539.5Anode Volt.(2)0.7MW56%Depressed Collector Volt.6.666.686.706.72Cavity field (T)It is proved accessibility to maximumtheoretical efficiency by active control.Collector TempPower0s100s
1MW/800s/55% operationV-CPD ( 24.5kV)Ib 30A (0.8MW)V-Anode (-6.3kV)V-Cathode (-48.3kV)Beam Current (38A)Pout (1.01MW)800s ( 1MW)Cavity Field (6.625T)Collector Temp( 100 C)Arc signal (a.u.)Increase of beam currentIb 38A(1MW)1MW/800s/55% attainedwith triode operation.The development missionof ITER (1MW, 500s, 50%)was attained.Vacuum Pressure (max. 8x10-8torr)Oscillation Time (s)
Power Balance of 1MW OperationTotal measured powerGenerated RF powerat cavity (A B)Collector heat loadRF Loss in the Gyrotron (A)relief windowsDC Break ceramic insulatorMirrors (1st 3rd)Launcher & JacketBeam tunnelGyrotron body & 4th mirrorCavityGyrotron Output (B)Dummy LoadMiter BendsWaveguideMOU1853.7CollectorHeat .6534.51024.39682.7845.6(unit : kW)MOURF Loss in the GyrotronInput Beam PowerGyrotronOutputMBWGDummyLoadGlobal efficiency: 55%Input Beam PowerInput power and generated RFpower and collector heat loadare balanced.
Quick Start of 800kW operationInitial current 38ADepressed CollectorVoltage ( 27kV) 800kWwithin 100msAnodeVoltage ( -3kV)Beam Current ( 30A)Zoom upRF signalCathodeVoltage ( -45kV)RF signal (a.u.)-5s0s5sBc: fixedAnode Voltage:-4 -3kV after 100msOutput Power (kW)Collector Temperature (88 C)800600 55.5%40020000100200300 400 500Time (s)600700800
Oscillation characteristics in Hard self-excitation regionLong pulse operation ( 300s)Power100No saturation0.8800.6Total Effi.600.4Osci. Effi.400.2Vacc. 72kV, Vanode optimized,VCPD optimized,Cavity Field Optimized01020304020050Beam Current (A)This result indicates that advanced operationscenario is available for each beam current.Oscillation Efficiency (%)1.00.0Efficiency on hard selfexcitation region issignificantly improved incomparison with soft selfexcitation region.120Efficiency (%)Output Power (kW)(MW)1.2Comparison hard & softself-excitation regionLong Pulse(hard selfexcitation)Short Pulse(soft self-excitation)Beam Current (A)
Total Shot NumberNumber of shotsOperation:Apr., 2006 Jan. 2008Total Energy: 144GJ 10s 30s 100s 300s 1000s 3000sNumber of Shots 1MW: 20 shotsPulse width (s)Total Shots Number 10s : 1000 shotsNo damage & No problem of oscillationDemonstration of higher reliability
SummaryIn development of 170GHz ITER gyrotron 1.0MW/800s/55%Oscillation in hard self-excitation regionby active parameter controlBasic objective for ITER gyrotron wasattained with triode operation. 1hour/0.6MWstable steady state operation.
Burn time : 400 500s Fusion power : 500MW. Artificial diamond window ITER gyrotron Higher oscillation mode 170GHz/1MW (TE31,8) 55% At collector Distribution function of e-beam Cavity input Cavity output Energy 37% 25keV 0keV 72keV Electron beam Energy recovery High power cavity Long pulse operation Low loss tangent High thermal conductivity Gyrotron Technology Output RF at window Field .
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