Gehre, O.

Gruber, O.

Lackner, K.

Müller, E.

Stäbler, A.

Wagner, F.

English

MPG.PuRe

The power dependence of r<sub>E</sub> in the h-mode of ASDEX

THE POWER DEPENDENCE OF TE LN Tl 1E H—MODE OF ASDEXF. Wagner, 0. Gruber. O.Gcln‘e, K. Lackner, ER. Muller, and A. Stiiblei‘Max-Planckdnstitut fur PlasmaphysikEURA'I‘OM Association, D—8046 Giuching. Fed. Rep. otGermanyINTRODUCTION: The global energy confinement time I a of H-mode plasmasis found in ASDEX to be power independent for hydrogen injection intodeuterium plasmas / 1 /. DUI—D reports the same behaviour tor deuteriuminjection into deuterium plasmas / 2 /. These findings are contrary to thosefrom JET / 3 / and JET-2M / 4 /. where degradation of IE in the H-niode isobserved as in the L—mode. This causes great uncertainty in predictingH—mode confinement of next - generation tokamak experiments. In this paperwe try to analyze the power dependence of IE in the quiescent H—mode. H’ incomparison with regular H-mode results. The Hit—mode. may display theintrinsic H-mode confinement properties because ELMs do not additionallycontribute to the energy losses. The power scaling studies of JET were donewithout ELMs, but the published results of ASDEX and DIN—l) were obtainedwith ELMs.POWER SCALING OF I TN THE Hit-MODE: Under the conditions I =0.32MA.Bt=22T power scans in tie quiescent H-mode were possible in ASDFBX both forHO— and D07 injection into deuterium plasmas in the restricted power range of1.75 S PNT S 3.5 MW. Without ELMs an additional difficulty in the IE analysisarises because the Ht-phase does not reach the steady state. During the beampulse the lit-phase is terminated by a thermal quench caused by largeimpurity radiation which finally matches the power input. 1 globally as well aslocally in the plasma centre J and which initiates an intermediate l_.vphase / 5 /.The duration of the Hit—phase depends on the heatingr power and increasesfrom 95ms at 1.75MW to 125ms at 3.5MW. During?T the H‘“-phase the particlecontent increases linearly at a rate corresponding to 2—3 times the beamfuelling. The impurity radiation increases nearly exponentially After theH”"-transition. [3 ) increases once more owing to the improved confinement;when the impurity radiation starts to affect the. energy balance, tip rolls overand decreases already during the l'I"“-phase.Because of the non-steady—state conditions and the central radiation issue. theIE analysis was done in three steps: IE is evaluated according to IE ‘ ’= E HPtot ~ (IE /dt ) to correct for the lack of stationarity. These values allow thecomparison with those from other experiments. In a second step the followingrelation is used:‘ tr _i prad (p) pdpdrrE<2)=rE(1)-ii— ............................ j- 1])tr t pheat (p) pdpdrEqu. ll) corrects for the radiation power emitted in the radial zone where theradiation - and heating power densities overlap. Mere edge radiation does notlead to a correction, The. IEl ) values should represent the actual transportproperties of the quiescent H*-mode. There is a certain arbitrariness in thechoice of ”3(2) as it is strongly varying with time. In a final step, full transportanalysis ( using TRANSP l is done for two H‘“-discharges, the one with thelowest and the one with the highest heating power, to have a further check onthe data and the analysis.Figure 1 shows the power dependence of the global confinement times 1713(1) andI (3) in the Hit-mode, evaluated as described above in comparison with 1: rva ues of the regular H—inode with ELMs. As H-phases with ELMs reachsteady state. IE is calculated in this case simply from TE = E / Ptot' While thel-l—mode does not show any distinct power dependence ( IE (ms) : 52.2'PlMWl‘O'OS) with H0 into D+. the quiescent H-mode does. The following powerdependence is obtained for the H*- phase ( based, howeygru on 4 data pointsonly M: TEl1l=86'P'O-45 ibl‘ H0 into 13+ and 1313(1): 132 oP-O- In for D0 into 13+. Thecurve in Fig. 1 is the power fit to the D0 into D+ cases; the horizontal lineguides the eye to the results obtained with ELMs.Figure 2 shows the time dependence of IE as obtained from the full transportanalysis and of IE” l. The confinement times are plotted from the OH—phaseinto the L— and finally into the H*—phase. The results are. shown for the extremepower cases, The TE values in Fig 2 are obtained taking into account theradiation losses and correspond to IE( ) as obtained from equ.( l/ 5 /.In summary we also find in ASDEX a power dependence ofTE in the quiescentH*-mode as in JET. As such a dependence is not observed in the regularH~mode. it can be speculated that IE in this case is predominantli determinedby the energy losses caused by ELMs superimposed on the heat trap port lossesso that the overall confinement time is power—independent. We iall try toanalyze this possibility in the following.THE EFFECT OF ELMs ON THE GLOBAL CONFINEMENT: As ELMs are anexternal mode. the global confinement is affected Figure 3 shows a dischargewhere quiescent phases follow those with ELMs. As soon as ELMs set in. theparticle and energy contents decrease It is difficult to assess the energy lossesperjELM. From the changes in slope of the [5p trace in Fig. 3 we conclude thatT (“EL (representing the ELM losses) is about 110 ms.T 1e energy lost at an ELM can be determined in three ways: All ca}: bemeasured direct by using the equilibrium coils, which are placed Within ihevacuum vessel and which have sufficient time response. Typically 5 ‘7? of theenergy content is lost by an ELM. Another possibility is to determine the energyloss via the effect of an ELM on the plasma profiles. For n(; and Te continuousmeasurement is possible. An ELM affects both InP and Te from the plasma edgeto about 1‘ = 15 cm. The relative amplitude increases with radius for 119 and T6in about the same way with Ane / ne : .r.’\Te / Te = 10% at r:30cni.(0n theassumption that the T1 profile is affected in the same way by an ELM, we canintegrate the energy loss and conclude that about 8 ‘Z= of the energy is lost. Afinal possibility to evaluate the energy loss of an ELM is by measuring thepower flux into the divertor chamber onto the target. plate. This measurementis rather inaccurate and can only serve as a consistency check. Typically anELM leads to power deposition at the target plate with a peak power density ofabout 1 kVV/cmz and a width of about 4 cm. The duration of increased energyloss during an ELM is approximately 0.4 ms; the energy loss is assessed to”(7‘3about 10 kJ in rough agreement with the other estimates. The particle loss perELM is typically 1 ' 1019 corresponding to ANC / NE. 2 5%.The repetition time of ELMs depends somewhat on the heating power. At lowpower ELMs appear erratically and the ELM pefiod fluctuates. At high power,ELMs appear in a more regular form and the repetition time becomes constantat about 6 ms. It was not possible to determine the amplitude distribution ofthe ELMs. The low-power, high—frequency ELMs are clearly smaller inamplitude, Assuming a constant. ELM amplitude of AE / E of 6‘74 and arepetition time tELM = 6 ms and superimposing these losses onto the transportlosses ( see Fig.1 ) we can (calculate the power dependence of the globalconfinement time: I C = rElZl'l + AF] / E ° t . M'l. The results calculated inthis way are also plEtted in Fig. 1. They rougll—i y agree with the measured IEdata obtained with ELMs.SUMMARY: First the global energy confinement time is shown to decreasewith power when the l-l-mode is operated in the quiescent H—phase as in «JET .This conclusion is drawn, however, from a rather weak experimental basisbecause of our limitations in operating the H-mode without ELMs . It is shownthat the lack of power dependence in the regular HAmode with ELMs could bedue to the power—dependent microscopic transport losses being superimposedon those caused by ELMS.The ratio between TE in the quiescent H—mode ofASDEX and JET (both with D0-> 13+) is about 20, which is a factor of 2 more than the ratio of the currents,indicating an additional size. scaling given approximately by the major radius.REFERENCES:/ 1 / A. Stabler, F. Wagner, et al.,4th Intern. Symp. on Heating inTor. Plasmas. Rome (1984), Vol. I, p. 3./2/ KH. Burrell, S. Ejima, et al., Phys. Rev. Lett. 59( 1987 J 432./3 / M. Keilhacker. M. Bishop, et al., Proc. 14th Europ. Cont. on Contr.Fusion and Plasma Phys, Madrid, part III, p. 1339 (1987)./4/ K. Odajima, A. Funahashi, et al., 11. Intern. Conf. on Plasma Phys.and Contr. Nucl. Fusion Research, IAEA, Vienna. Vol. I (1987) p.151./5/ O. Gruber, W. Jilge, et al., Proc. 12th Europ. Conf. on Contr. Fusionand Plasma Phys, Budapest, part I, p. 18 (1985).FIGURE CAPTIONS:FIG. 1 Global energy confinement time in the quiescent (H*) and the regular(H) H-mode with ELMs versus heating power. The curve is a power fitto the D0 —> D‘l' case, the horizontal line guides the eye to theH-cases with H0 -> D+- The circles are calculated from the H0 -> D+IE values with the radiation correction.FlG.2 Energy confinement time (TE) and replacement time (T JlZlJ of two 11*discharges with different heating powers, as obtained 350m TRANSP.FIGB Line - density 116, divertor H radiation and [31301 for a discharge withintermittent quiescent and IfiJM - active phases.'31 OFi . 1g 150 ‘A 100 'wELuP50 ‘X H0 —> D+ ( H )a D°->D+(H*) o H0->D+(H*)I H0 —> D+ ( H‘ ) radiation corrected0 calculated from (I) with ELMs simulated0 ' l ' I ' l0.0 1 .0 2.0 3.0PTOT (MW)0'15 #11513 Fig. 2IEBSmi,_. 0.10-_.31LUP0.05-1.10 1.20 1.300.15# HAN'[EBSUDJ \\/Ir—/0“0-———_J IEIBOEITHVfE ............. I // T's-”WILup.)0.05-0 34123.48 MW105 1:10 105 LZC 1'05

http://hdl.handle.net/21.11116/0000-0009-428D-E

The power dependence of r<sub>E</sub> in the h-mode of ASDEX

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