HT-7 May,2003

Differential Residual Gas Analysis During Plasma Discharge in HT-7 Superconductor Tokamak

IndexAbstract1.Introduction2, HT-7 differential RGA and setup3.Ananlysis and results3.1, The ratio of D/H during plasma discharge 3.2, Neutral D2 behavior during plasma discharge 3.3, Neutral impurities and hydrogen behavior during plasma discharge 3.4, Impurities after plasma with disruption 4,conclusions

abstract;H2O, D2O, CO, CO2, CH3, O2, -;1) ,DH;2) ;3),;

2, HT-7 differential RGA and setup HT-7 Tokamak inner chamber:The volume 4870L. One belt and two poloidal graphite limiter; Total surface of graphite limiter is about 0.8m2. The vacuum system: two turbo molecular pumping stations and two cryopump stations; The ultimate pressure is lower than 1.010-5Pa. Vacuum reaches 1.0~210-5Pa between plasma shots.

The differential RGA system: one turbo pump system, one gauge and one Quadruple Mass Spectrometer (QMS). Connected to the main HT-7 chamber by one 1m long bellows tube, baked to 100oC to prevent the wall from absorbing the little and transit particles. Nominal pumping speed : 600l/s. The background pressure: 2.010-8Pa without backing. After connected with main chamber, the background pressure is 1.010-6Pa as the pressure in main chamber is 1.010-6Pa and bellows tube was baked to 100oC.The ratio of pressure between two chambers: 80.

1,sensitively after plasma discharge;2,neutral gas,3,during plasma discharge,measure neutral particles.4,not good space and time resolution during plasma discharge; 5,maximum acquisition data frequency is 16.5ms/point with big noise for only one q/m;6,after plasma termination, gas was recombined and transiently produced by plasma impact to the wall.

3.Ananlysis and results 3.1, the ratio of D/H during plasma discharge 3.2, neutral D2 behavior during plasma discharge 3.3 neutral impurities and hydrogen behavior during plasma discharge 3.4 Impurities after plasma with disruption

3.1,the ratio of D/H during plasma discharge 3.1.1IntroductionAfter plasma discharge termination the ionized D or H was recombined to molecules. The ratio of D2 to H2 in deuterium plasma discharge was measured according to the their increased pressure after the discharge termination. The D/H ratio is a average value in one shot.The pressure ratio of m/q=4 to m/q=2 by RGA is 20 while the main HT-7 chamber was just filled with deuterium without breakdown, which is considered as the background to analyze.

3.1.2 the change of D/H ratio during first day of campaign and before 1st boronization Fig 1 the D/H ratio change during first day of campaign and before 1st boronization.1, At the first 30 shots in the campaign the ratio of D/H is near 1 or lower. 2, With increase plasma density, the ratio of D/H became unstable. 3, During plasma discharge with main parameters as IP=140~160KA, ne11019/m3 , t=1~2s, before the first time boronization the average value of D/H ratio is about 6.33.

3.1.3 D/H ratio changing after the 2rd boronization

At early, H/D>10;D/H ratio increases 1 around 50 shots. After about 80 shots, the D/H ratio reaches 2. The D/H ratio increased approx linear.Reflects boron film characteristics changed In the campaign, longer than 40s plasma discharges were reached as the D/H is about 0.31 after 1stboronization.Fig2. D/H ratio changing after 2 boronization

D/H ratio changing after the 4rd boronizationAt early, H/D~10;D/H ratio increases 1 around 50 shots. After about 80 shots, the D/H ratio reaches 2. The D/H ratio increased approx linear.Same as after 2rd boronizationIn the campaign, longer than 60s plasma discharges were reached as the D/H is about 1 after 4stboronization.

3.2, neutral D2 behavior 3.2.1, D2 in shot 56766 ne=0.51019/m3 in shot 56766 D2 partial pressure in differential chamber reaches 7.4710-6Pa after filling. Then it goes down quickly to about 1.110-7 Pa at the time of gas breakdown and was stable during whole plasma discharge. After plasma discharge termination, the pressure increased to 110-5Pa.Fig3.The partial pressure change of deuterium in shot 56766

3.2.2 analysis and resultsAt starting filling, deuterium existed as molecules. Then it was ionized. But during whole plasma discharge pulse, deuterium was nearly steady at the edge plasma by the interaction of plasma and first wall surface. After plasma termination the pressure of the neutral D increasing very much by recombined from D+.

3.3 neutral impurities and hydrogen behavior during plasma discharge3.3.1 introduceFor carbon-based materials, the formation of hydrocarbons, CO, CO2 leads to enhance the erosion yields, even at room temperature [1].Carbon interacts with thermal atomic hydrogen over a broad temperature range, extending do to a room temperature forming mainly CH3, and a wide range of higher hydrocarbon [3][4]. D2O formed by exchanging H with D+ from water is useful to know exchanging process. Also O2 is important impurity in the other impurities formation procedure. So H2O, D2O, CO, CO2, CH3, O2 are main impurities in carbon limiter HT-7 device during plasma discharge.

3.3.2 the partial pressure change in differential chamber of m/q=28 during shot 56781 plasma discharge

partial pressure rises from 310-8Pa to 510-8Pa at breakdown, then stable at 4.510-8Pa last about 15s, later grows up slowly to 710-8Pa before plasma termination. After plasma discharge termination, it arises to 4.610-7Pa. Fig4 the partial pressure change in differential chamber of m/q=28 during shot 56781 plasma discharge

3.3.3 Hydrogen and impurities partial pressure change in differential chamber in shot 56775Hydrogen behavior is similar with deuterium. But during plasma pulse, its partial pressure increased from 410-7Pa in first 25s, and reached a stabilized value 1.010-6Pa. After plasma termination, abundant CO and CO2 were formed. D2O and CH3 delayed stabilization a few seconds. C3H3 and O2 go back to background very fast. Fig5 Impurities M/q=2,4,15,18,20,28,44,39,32 during 56775 shot.

3.3.4, analysis and resultsImpurities:increasing at the beginning of the discharge, then stable, later rising again till discharge termination and quickly increasing after discharge termination. Stabilization of neutral impurities and deuterium means that interaction between plasma edge and wall reach almost steady. After discharge termination, because of strong power dispersing on the wall and recombination the impurities pressure increase sharply. a lots of high energy particles impact with graphite limiter and abundant C was erosion and ionizedAfter deuterium breakdown, D+ start impacting with graphite limiter and wall . surface and abundant H accumulated at surface or combined in boron film was sputtered. Most of it was ionized. Also hydrogen trapped in carbon released. However, after plasma termination, which kind impurity is main impurity is not easy to study. There are many factors to influence the impurities forming, such as particles energy, wall temperature, which need to be studied deeply.

3.4 Impurities after plasma with disruption in shot 56176The m/q=28 partial pressure increased to 310-6Pa; higher than normal plasma termination as in fig5. D2O and O2 partial pressure increased very much, which is different with in fig5. By compared with shot 56177 without disruption by other diagnostics, C and O impurities during disruption is at high level. C and O were combined to form CO and remained partial oxygen. Fig6 main particles partial pressure increased after plasma with disruption in shot 56176.Fig7 impurities level measured by other diagnostics and compared between shot 56176 and 56177.

4,conclusionsTo measure the particles change in real time during plasma discharge is very helpful to know what happened about neutral impurities during plasma discharge. The Residual Gas Analysis (RGA) system provides an effective and easy implementation method to study edge neutral impurities and hydrogen behavior. To measure the fast partial pressure increase of impurities at the time of plasma discharge termination, which is useful for understanding the damage of the first wall surface by the interaction of plasma and materials. The rate of D/H during plasma discharge can be calculated by the data of molecules of recombined particles after plasma termination. By comparing with other diagnostics, we can get more detailed information of plasma edge physics. Need to study deeply and improve the differential system.

Reference[1] Poschenrieder, W., Venus, G., ASDEX Team, J.Nucl. Mater.111&112(1982) 29[2] G.Federici, J.Nucl.Fusion,VOL.41.(2001)1968[3]Horn, A.,et al., Chem. Phys.Lett. 231(1994)193[4]Vietzke,E., et al.,J.Nucl. Mater. 280(2000)39

Residual gas &Limiter Temperature&power flux

May 7,2003

Measurement point in p-limiterBelt limiter A-17,B-18,C-19,D-20

Power flux calculationW continuous powerQ-transient power3-thermocouple place

Shot 58065 to 58072 RGA measure m/q=28 pressure at 16.5ms/point. almost no change in 10 shots before 56065Increased slowly from 58065 to 58067;In shot 58068,69,70 increased to 3E-6;Almost no change in shot 58071 and 58072; Diagnostic signal58069,58070 without disruption; lower Vis(10),O2,OV.58067,58068 with disruption;Apparent Vis(10),O2,OV.Temp.Temp. curve at biggest temp.changed points shows no big different.(Maybe same reason in shot 56176).

RGA data and Plasma parameters

Temperature comparedConclusions:1,Temp. measurement points are not enough to get detail information about all wall temp. changing.2,Impurities produced in discharge with disruption maybe remain to next shots by soft adhered to wall.3,easy cleaned.

Shot 56778 to 56781First round shots longer than 30s;RGA data and Plasma parameters;Temp. voltage Data in shot 56778 to 56781;Temp.data and calculate heating flux deposited on limiter surface in shot 56779Analysis

RGA data and Plasma parametersM/q=28 peak higher than 7.5E-7Pa;After shot 56780, reach 1.2E-6Pa; Almost same Vis(10),O2,OV signal in three shots;

Voltage of thermocouples (mv) In shot:56776 to 56781 Temp.Higher than 20mv cannt be saved;Cannt show total data in many shots;Measurement point limited;From the flat longer to estimate highest Temp. change;Channel 12 is highest Temp. increasing point in most shots; (2,11)Temp. data in shot 56779 is nearly complete.

Temp.and Power of heating in 567791,Temp. voltage increasing-Channel 12, fast at 5s;and continues.Till 30s, reach 20mv.-Channel 11, fast at stat, than stable increasing with lower speed.-Most channel, at stable lower speed.-Almost same decreasing trance.2,Power of heating on limiter surface(2&12)-Channel 2, almost near 1MW/m2;-Channel 12, highest over 10MW/m2; and two times near 10MW/m2.s; lowest 2MW/m2.s; -At 30s, Temp. to 630 and 150 respectively.3,transit and steady power deposition have differential effect.Accumulated.

Shot 61576 to 61579 Shot 61579 is longest discharge in HT-7.RGA data and Plasma parametersVoltage of Temp. in shot 61578&61579Temp. comparing from 61573 to 61579Temp.and Power of H&C in 61578Compare between 56779&61578

RGA data and Plasma parametersShot 61576&61577,Higher m/q=28 peak after plasma discharge. 61577 reach 1.5E-6Pa;Shot 61578&61579, even no increasing; RGA data is consisted with Vis(10),O2,OV signal.IPA and heating power.(stability and lower).

Voltage of Temp. in shot 61578&61579Temp.data is near complete;Two shots have nearly Temp. performance;highest Temp.is near 300oC(9.5mv) at channel 2;In 61578,12&2,fast Temp.increased at first and slowly later; other point temp. steady slowly increased.

Temp. comparing from 61573 to 61579Fig1 show highest Temp. increasing (channel 20 in belt limiter) in different shot;Fig2 show Temp.increasing at channel 2 point in different shot.Shot 61575,61576,61577 have higher Temp. over measurement range.Shot 61576 flat is longest.In 61578&61579, fast increasing at channel 2&11 was restrained.

Temp.and Power of H&C in 615781,Channel 2&5(1s average):-Channel 2, fast at 1s; highest power flux 7MW/m2; Then was restrained, no power for short time;then power flux increased to 1MW/m2.-Channel 5, Temp. stably increased with lower speed. power flux lower than 2MW/m2.-2, 12 channels(5s average):-channel 11, highest power flux 3.5MW/m2.-most point, power flux lower and stable.-cooling power flux near 1MW/m2.s at 200oC(include convection-self diffusion and water cooling, and radiation);Right!-as limiter temp.dropped, cooling power decreased.3,transient and steady power deposition have differential effect.--Accumulated.4,transient power deposition is main procedure.

1s average for 12 channelsTemperature on belt limiter 1,steady, very slow speed;2,radiation

Power on poloidal limiter surface61578(Just for reference!)two Poloidal limiter surface 0.237384m2Average power flux ~540kw/m2Power ~120kw-Higher than LHCD power 110kw.Very litter temp. change on belt limiter.

56779&61578

Compare between 56779&61578

5677961578Max.power flux(1s average)10.5MW/m27MW/m2Power depositionContinues higherLower after 10sTemperature630OC at 30sHighest 300OCchannel122,11M/q=28 pressure3E-6Pa after dischargeNo apparent changeAuxiliary heating power(LHCD)148KW110KWIPA60KA32KADischarge pulse50s60sDisplace signalbigSmallVis,O2,OVSome peaksmooth

2MW/m2 10MW/m2T1(x) 3mm;T2(x)-10mm;.

Conclusions: 1, raw data detectedDifferential RGA : 1,sensitively after plasma discharge;2,neutral gas,3,during plasma discharge,increased but little;4,not good space and time resolution during plasma discharge; 5,maximum acquisition data frequency is 16.5ms/point with big noise for only one q/m;6,after plasma termination, gas was recombined and transiently produced by plasma impact to the wall.Temp. measurement: 1, measurement points are not enough to explain residual gas;2,data received and saved lost some useful parts in many shots;3,cannt save temp.data as its voltage is higher than 20mv.

2,Temp. increasing1,Maximum temp. change point is different, alternated at channel 2,11,12;2, Max. temp. exceeded 20mv in many shots longer than 40s;3,Better restrain the temp.increasing at channel 2 in longest shot(61578&61579);4,Except for max. temp. change channel, other channels have same performance, at lower stable speed increasing;5,Temp. increasing is accumulated by transient power impact and steady dispersal;6,Temp. increasing time at longer pulse discharge is same as plasma long.7,havent intensity impact evidence at longer plasma discharges termination;

3,Power deposited and removed1,Power deposited flux on limiter surface exceeded 10MW/m2.s at channel 12 in shot 56779.2, in 61578 shot A,Channel 2&5(1s average):-Channel 2, fast at 1s; highest power flux 7MW/m2; Then was restrained, no power for short time;later power flux increased to 1MW/m2 again.-Channel 5, Temp. stably increased with lower speed. power flux lower than 2MW/m2. B, 12 channels(5s average):-channel 11, highest power flux 3.5MW/m2.. -most points, power flux lower and stable. -cooling power flux near 1MW/m2 at 200oC(include convection-self diffusion and water cooling, and radiation);-as limiter temp.dropped, cooling power decreased.

4, Power on poloidal limiter surface61578(Just for reference!) two Poloidal limiter surface 0.237384m2Average power flux ~540kw/m2Power ~120kw-Higher than LHCD power 110kw.(Strange: by reference, estimate about half power deposited on limiter)No temp. change on belt limiter.The calculation have principle wrong, just for reference.

5,residual q/m=28 impurity 1,From 56776 to 56781(first round longer than 30 shots )M/q=28 peak higher than 7.5E-7Pa;After shot 56780 termination, reach 1.2E-6Pa;2,From 61576 to 61579(61579 longest shot in HT-7)Shot 61576&61577,Higher m/q=28 peak after plasma discharge. 61577 reach 1.5E-6Pa;Shot 61578&61579, even no increasing; 3,during plasma discharge,increased but little; 4,after plasma termination, gas was recombined and transiently produced by plasma impact to the wall.5,RGA data is consisted with Vis(10),O2,OV signal in most shots.

6,relationsResidual gas m/q=28 related surface temp. and plasma parameters (include auxiliary, power displacement,long,density,temperature and so on).Complex procedure.For two longest shots 61578&61579, with lower IPA, Auxiliary heating power(LHCD)and displacement, temperature havent continues fast increasing and q/m=28 peak is even no change(see compare between 56779&61578). Can not draw very precise inductions.Need more data.

7, remained questions1, transient power flux at plasma termination;2,find temp. evidence about disruption;3,precise calibration thermocouple.

Note!1,power flux is different at same channel by 1s or 5s average,which caused from signal noise and average time.2,thermocouples calibration is by table in the book. Not very precise!

Vacuum Calibration In HT-7

Calibration system4 turbo-pump stations (for air)1500l/s600l/s2*450l/s2 cyro-pump stationsAir 5800l/s;H2 13200l/s;He 6000l/s;water 17300l/sStandard gas chamber2.3l

principleP*S*t=(P2-P1)*vP-balance pressure in HT-7 inner chamber;P2-p1-standard chamber pressure change;V-standard chamber volume; t-filling time

Pump speed for D2,H2,He,N2

Compare

gasCyropump5-5~10-410-4~10-310-3~10-2>10-2heliumwithout 1700-5600

Conclusions1, HT-7 pump system have lowest pump speed for nitrogen than for other gas. Pump speed for N2 is also lower than turbo pump nominal pump speed 2,Graphite limiter and wall serve as big pump for deuterium, hydrogen and helium.3,Big pump speed for D2, H2 and He, higher than estimated.

1# 2#,differential chamber DL-7 VS MaxigaugeThree gauges calibration by N2

ResultsVery good liner relation;For 2# DL-7 gauge, it is different between with and without Cyro-pump working; This means gas diffusion in HT-7 chamber(is it influence plasma discharge?How to reach gas balance in chamber by filling and pumping?).One inflexion states DL-7 gauge filament omitting current changed.The dispersal point in curve caused by different standard gas.

Volume of HT-7 chamberThis is average value.4.87m3

M/q=3,4 for D2 and He by QMS calibration For helium and deuterium, P3 have good liner relation with P4.P3 of deuterium is higher than of helium as the P4 is same.The calibration maybe useful to distinguish helium from deuterium during plasma discharge.

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