Baruzzo, M.

Belonohy, E.

Buchanan, J.

Carvalho, I.

King, D. B.

Viezzer, Eleonora

Weisen, H.

English

idUS. Depósito de Investigación Universidad de Sevilla

Mixed Hydrogen-Deuterium plasmas on JET ILW: H-mode confinementand isotope mixture controlD. B. King1, E. Viezzer2, M. Baruzzo3, E. Belonohy1, J Buchanan1, I Carvalho4, K. Cave-Ayland1,I. Coffey5, C.D. Challis1, E.G. Delabie6, A. Drenik7, L. Garzotti1, J.Hillesheim1, L Horvath8,E.Joffrin9, D. Keeling1, K. Kirov1, C.F. Maggi1, M. Maslov1, S. Saarelma1, E.R. Solano10,M. Stamp1, D. Valcarcel1, H.Weisen11and JET contributors*Eurofusion Consortium JET, Culham Science Centre, Abingdon, OX14 3DB, UK1 Culham Centre for Fusion Energy, Abingdon, UK, 2 University of Seville, Seville, Spain, 3Consorzio RFX, Padova, Italy, 4 Instituto de Plasmas e Fusão Nuclear, Instituto SuperiorTécnico, Universidade de Lisboa, P-1049-001, Lisboa, Portugal, 5 Queens University, Belfast,UK, 6 Oak Ridge National Laboratory, Oak Ridge, USA, 7 Max-Planck-Institut furPlasmaphysik, Garching b. Munchen, Germany, 8 University of York, York, UK, 9 CEA,Caderache, France, 10 CIEMAT, Madrid, Spain, 11 EPFL, Lausanne, SwitzerlandPrevious results on fusion experiments have shown that plasma properties such as confine-ment and ELM frequency depend on the isotopic mass [1]. However, the behaviour of mixedisotope plasmas is less understood, particularly in JET-ITER Like Wall (JET-ILW). A study ofhydrogen-deuterium (H-D) H-mode plasmas in JET-ILW strengthens the physics basis for ex-trapolations to JET deuterium-tritium (D-T) operation, supports the development of strategiesfor isotope ratio control for the future D-T campaign and provides stringent tests for plasmatransport models. Beyond JET the fuelling behaviour of mixed isotope plasmas and the be-haviour of hydrogen majority plasmas is relevant for ITER.Experiments in mixed hydrogen-deuterium (H-D) plasmas have been performed on JET tostudy the effect of isotope composition on plasma properties, in particular the H-mode confine-ment. This work is part of a wider study of the isotope effect on JET including the confinementof pure H and D plasmas [2] and the effect of isotope on L-H transition in [3].In order to carry out the experiment it was necessary to develop a method for controllingthe isotope ratio. On JET the fuelling actuators are gas puffing, neutral beam injection (NBI),pellets and wall recycling. A control method using feedback and feedforward gas injection wasdeveloped with edge diagnostics based on Balmer-Alpha emission as the sensor.* See the author list of “Overview of the JET results in support to ITER” by X. Litaudon et al., Nucl. Fusion57 (2017) 10200144th EPS Conference on Plasma Physics O3.112NBI  (D) Power (MW)Gas Fuelling (1022  el/s)H/(H+D)         0.0    2.0    4.0    6.0    8.0106    Watt         0.0    1.0    2.0    3.0    4.0    5.01021   trons/s44 46 48 50SEC0.00.20.40.60.81.0JET Data Display9123491234 NBI/PTOTSeq=7 (0)91234 GASH/G09RSeq=129 (0)91234 GASH/G11RSeq=129 (0)91234 KS3B/HTHDSeq=15 (0)91234 KT5P/HTHDSeq=67 (0)91234 PROC/FH_SCALED1Edge gauge Edge spectroscopyCore (estimate)DeuteriumHydrogen1Pulse 91234, Bt = 1.7T, Ip = 1.4MAFigure 1: Real time control of isotope ratio in edge andcoreTo estimate the core isotope mixturea relationship between the neutron rateand core deuterium content was devel-oped. This was done by analysing puredeuterium pulses over a range of den-sities and temperatures then scaling theneutron rates from these pulses accord-ing to the deuterium content. It can beseen in Fig. 1 that the core isotope ratiois within 10% of the measured edge ra-tio (which is the estimated error of thecore isotope calculation).Scans of isotope mixture were per-formed in plasmas of fixed plasma cur-rent (1.4MA), toroidal field (1.7T), totalgas fuelling rate (1-1.1x1022el/s) and plasma shape (with strike points in the corner of the di-vertor) using predominantly NBI heating of either deuterium or hydrogen. These parameterswere chosen so that comparisons could be made with other, pure isotope experiments. Type-IELMy H-mode pulses of this type were successfully performed with the isotope ratio varyingfrom 1.05< Me f f <1.8 and 8MW<Pinput<10MW. Data from pure isotope plasmas is availablefrom [2] to complete the full range of isotope ratio. The dependence of thermal stored energyvs effective mass is shown in Fig.2.BT = 1.7T, IP=1.4MA, PNBI=8−10MWFigure 2: Thermal stored energy calculatedby TRANSP vs effective mass for mixedisotope plasmas (blue) and pure isotopeplasmas (red)Figure 3 shows the ne-Te diagram for variousisotope ratios at one gas puff level (1-1.1 × 1022el/s). The NBI power varied between 8 and 10 MW.As the isotope ratio changes from predominantly D(H/(H+D) < 0.25) to predominantly H (H/(H+D) >0.75) the datapoints move along constant pressure,exchanging density and temperature. This is consis-tent with the findings in full D and full H plasmas[2]. Note that the full D and H plasmas indicatedin figure 3 have been performed at a wider rangeof NBI power (6-13MW) and gas fuelling of 0.8 ×1022 el/s. At constant gas, H plasmas feature lower44th EPS Conference on Plasma Physics O3.112density and need a much larger gas puff to reach thesame pedestal density, consistent with results on ASDEX Upgrade [4]. As shown in figure 3,for the power range specified above the temperature in D is higher compared to H, indicatingthat in order to achieve similar pedestal temperatures more power is required in H.n (10 m )e19 -30 4 51 2 3T(keV)e1.00.60.40.20.8ρpol = 0.95Gas 1.1 × 10 e /s22 -H/(H+D) > 0.750.4 < H/(H+D) < 0.660.25 < H/(H+D) < 0.4H/(H+D) < 0.25Full DFull H0.01.2 kPa1.2 kPa1.0 kPa0.8 kPa0.5 kPaFigure 3: Pedestal density and temperature for pulsesacross range of isotope ratio and pure isotope pulsesacross a range of input power and gas fuelling.To determine the rate at which thecore and edge isotope ratio could varya discharge was performed where thegas fuelling was switched from D to Hduring the type-I ELMy H-mode phase,while other parameters were kept thesame as in the isotope ratio scan. Thistest was performed with both divertorand main chamber gas fuelling. It canbe seen from Fig 4 that in both casesthe core isotope ratio closely followsthe edge isotope ratio. The main cham-ber case appears to change more rapidlybut this could be due to the proximity ofthe diagnostic to the divertor gas puff.This pulse also contains 20% H NBI power so the difference could either be related to diagnos-tic, gas fuelling position or beam fuelling. It takes ∼ 10 energy confinement times (calculatedusing TRANSP [5]) for the plasma composition to change from ∼ 5% to ∼ 50% hydrogen.When changing gas species the effect on the plasma behaviour is much faster than the effecton overall plasma composition. Fig. 4 also shows the ELM behaviour (from Beryllium emis-sion) when the gas isotope is changed. The valve response is 100ms and within 200ms of thegas switch there is a change in ELM behaviour, the ELM frequency changes from 70Hz to50Hz. This could either be related to the small change in isotope ratio or the effect of neutrals.It has been shown that the plasma confinement in mixed isotope plasmas does not vary sig-nificantly with isotope ratio between 1.2< Me f f <.1.8 and that the density and temperature varyacross this isotope range. There is a more significant change in confinement near pure isotopes(consistent with [2]), this is also supported by the change in ELM frequency for small change inisotope ratio in the pulse with changing gas fuelling. Due to the proximity to the L-H threshold(expected to be 8-9MW for pure hydrogen at these parameters) it is still unclear whether thestored energy variation is a change in the confinement behaviour or due to the changes in L-H44th EPS Conference on Plasma Physics O3.112threshold power as seen in [3]. The strong effect of small amounts of minority isotopes showshow it is vital for isotope studies to be carried out at high isotope purity.Gas Fuelling (1022  el/s)H/(H+D)Be Emission Outer divertor spectroscopyInner divertor spectroscopyCore (estimate)H/(H+D)ELM freq 70Hz ELM freq 50HzDeuterium Hydrogen     0.10.20.30.40.5     0.10.20.30.40.5         0.0    0.5    1.0    1.5    2.0    2.5    3.01013   p/scm2sr46 47 48 49s    0.0    0.2    0.4    0.6    0.8    1.01022   trons/sJET Data Display91215, 9127491215 KS3B/HTHDSeq=15 (0)91215 PROC/FH_SCALED191215 KS3D/HTHDSeq=12 (0) Uid=chain191274 KS3B/HTHDSeq=19 (0)91274 PROC/FH_SCALED191274 KS3D/HTHDSeq=10 (0) Uid=chain191215 EDG8/TBEOSeq=9 (0)91215 GASH/C31RSeq=151 (0)91215 GASH/C32RSeq=151 (0)Bt = 1.7T, Ip = 1.4MAPulse 91215Pulse 91274Figure 4: Change in isotope ratio with gas fuelling usingdivertor fuelling (first pane) and main chamber fuelling(second pane), ELM behaviour with isotope change fordivertor fuelled discharge (third pane) and gas fuellinglevel (bottom pane).It has been demonstrated that iso-tope control in JET ILW can be suc-cessfully performed and that many con-finement times were required to fullychange the isotope ratio. This couldhave consequences for potential burn-control methods on fusion reactors. Fi-nally, it has been shown that gas fu-elling dominates the core isotope com-position of these pulses with beam fu-elling a much smaller effect. Further ex-periments in H-D at higher input powerand plasma current would allow extrap-olation to higher performance JET-ILWplasmas and to larger plasmas such asITER.This work has been carried outwithin the framework of the EUROfu-sion Consortium and has received funding from the Euratom research and training programme2014-2018 under grant agreement No 633053 and from the RCUK Energy Programme [grantnumber EP/I501045]. The views and opinions expressed herein do not necessarily reflect thoseof the European Commission.References[1] G. Saibene et al, Nucl. Fusion 39, 1133 [2] (1999)[2] C Maggi this conference[3] J Hillesheim this conference[4] F.M. Laggner et al,Physics of Plasmas 24, 056105 (2017)[5] R.J. Goldston et al, J. Comp. Phys 43 (1981) 6144th EPS Conference on Plasma Physics O3.112

Mixed Hydrogen-Deuterium plasmas on JET ILW: H-mode confinement and isotope mixture control

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Mixed Hydrogen-Deuterium plasmas on JET ILW: H-mode confinement and isotope mixture control

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