New Results from the Globus-M Spherical Tokamak

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1 New Results from the Glous-M Sphericl Tokmk V.K. Gusev 1), V.M. Amoskov ), A.S. Anniev 1), E.A. Azizov 3), A.G. Brsukov ), V.A. Belykov ), S.E. Bender ), I.N. Chugunov 1), A.V. Dech 1), V.V. Dychenko 1), V.E. Golnt 1), M.A. Irzk 1), S.V. Krikunov 1), Yu.A. Kostsov ), E.A. Kuznetsov 3), V.M. Leonov ), R.G. Levin 1), S.Yu. Medvedev ), V.B. Minev 1), A.B. Mineev ), O.A. Minyev 1), E.E. Mukhin 1), A.N. Novokhtskii 1), M.I. Ptrov 1), A.A. Petrov 3), V.G. Petrov 3), Yu.V. Petrov 1), K.A. Podushnikov 1), V.V. Rozhdestvenskii 1), N.V. Skhrov 1), O.N. Shcherinin 1), V.N. Scheritskii 3), E.I. Terukov 1), G.N. Tilinin ), S.Yu. Tolstykov 1), V.I. Vsiliev ), M.I. Vildjuns 1), N.I. Vinogrdov 1), A.V. Voronin 1), V.A. Ygnov 3) 1) A.F. Ioffe Physico-Technicl Institute, St. Petersurg, Russi ) D.V. Efremov Reserch Institute of Electrophysicl Apprtus, St. Petersurg, Russi 3) TRINITI, Troitsk, Moscow Region, Russi ) Nucler Fusion Institute, RRC Kurchtov Institute, Moscow, Russi ) M.V. Keldysh Institute for Applied Mthemtics, Moscow, Russi e-mil contct of min uthor: Astrct. New results from the Glous-M sphericl tokmk re presented. High plsm current of.36 MA, high toroidl mgnetic field of. T nd other importnt plsm chrcteristics were chieved. Descried re the opertionl spce nd plsm stility limits in the OH regime. The fctors limiting opertionl spce (MHD instilities, runwy electrons, etc.) re discussed. New experiments on plsm fuelling re descried. First results of experiments with coxil plsm gun injector re presented. Initil results of plsm wll interction study re outlined. First results otined with new dignostic tools instlled on the tokmk re presented. An uxiliry heting system test ws performed. Preliminry results of simultions nd experiments re given. 1. Introduction. Glous-M is the first Russin sphericl tokmk (ST), commissioned in 1999 t the A.F. Ioffe Institute, St. Petersurg. Recently the chieved prmeters in the OH regime were significntly improved through progress in vcuum technology, power supplies nd control system modifiction. A plsm current vlue of.36 MA ws otined with centrl solenoid poloidl flux of.3 W, oth vlues eing out 7% of the design vlue. The mgnetic field strength reched. T (9%). The progress in plsm current mplitude nd durtion increse since 1999 is shown in Fig.1. The plsm current rmp-up rte reched 17 MA/s. The vlue of the Ejim-Wesley coefficient ws K E-W.66 in dischrges with optimized prmeters. The prmeters chieved in the lst two yers in the OH regime re dequte for trnsition to uxiliry heting nd et limit study. The properties of OH plsms, with emphsis on opertionl limits nd experimentl tools for plsm performnce increse, re descried elow in detil.,s N$ D F E 7LPH PV FIG.1. Plsm current evolution in the OH regime due to progress in vcuum conditioning nd power supply technology. () cpcitor tteries, () thyristor rectifiers in single swing nd (c) in doule swing regime. F

2 . Opertionl spce nd stility limits. The opertionl spce of Glous-M in the OH regime is presented in Fig.. There re three well-known orders limiting the opertionl spce: the low q, low density (runwys) nd high density (Greenwld) orders. The two density orders re shown in the figure s stright lines. The high density limit ehvior in the OH regime looks similr to tht of other STs, e.g. START [1]. In the experiments with plsm fuelling y gs puff from the low field side, it ws possile to come close to the Greenwld limit (n/n Gr.8) t lower plsm current nd t the current rmpdown phse. Further density increse ws limited, presumly, y resistive, low n MHD modes. However, due to the higher mgnetic field in Glous-M, the solute vlue of chieved verge density ws high enough, (7 8) 1 19 m -3. The low density order of opertionl spce is defined y runwy ehvior. The ehvior of runwys in STs differs from conventionl tokmks due to strong toroidl electric field vrition cross the plsm column (E // ~1/R) nd higher vlues of E //. It is descried in []. The min fetures of runwy ehvior in Glous-M re s follows: (i) plsm current crried y runwys t low densities is not significnt, I run /I Pl 1 1%, (ii) the sptil distriution of runwy production rte nd runwy em shpe is hollow, with the mximum shifted to the periphery. This feture rodens the opertionl spce eyond the runwy order, nd limits the mximum energy of runwys (< MeV) nd their lifetime (< ms). Also, runwy genertion during mjor disruption is not recorded, in T F\O spite of the rther high prllel electric field induced during the disruption,? // 1 V/m. Plsm current mplitude ws limited y the lowest sfety fctor (q cyl.9, q 9 = ) tht could e chieved in toroidl field rmp-down experiments. The increse of plsm stility to kink (n=1,,3) nd llooning modes is explined y rodening of the plsm pressure profile in the configurtion with q() > 1 [3]. Fig.3 represents the plsm prmeter ehvior in the toroidl field rmp-down experiment, during which the toroidl et β T 1% ws chieved. 3. Plsm fuelling experiments. First experiments on plsm fuelling with novel fuelling source were performed. The method is directed injection of plsm jet into the tokmk. To Q H % 7 P 7 D]XPRYD OLPLW *UHHQZDOG OLPLW FIG.. Opertionl spce (Hugill digrm) of OH regime in Glous-M. Ip (ka) B (mt) (. u.) q 9 li et, % et 3 -,,,,7,6, 1 1 Plsm Current Mirnov Signl Ed ge sfety f cto r q 9 (EFIT) In te rnl Ind u ct nc e Normlized Bet Toroidl et Toroidl Field FIG.3. Time evolution of sfety fctor, QRUPDOL]HG DQG WRURLGDO GXULQJ WRURLGDO ILHOG rmp-dwn experiment.

3 penetrte deep into the mgnetic field, the plsm jet hs to hve high plsm density nd high directed velocity. This mens tht the prticle collision frequency in the jet plsm must e higher thn the cyclotron frequency. Also, the specific kinetic energy must e high s compred with the mgnetic field pressure. For the experiments in Glous-M (B T. T), the density of the injected plsm must e higher thn 1 1 m 3 nd velocity of ~7 km/s must e chieved. A doule stge source (plsm gun) [] ws used in the experiment. The source genertes jet of plsm with density exceeding 1 m 3 with totl numer of chrged prticles in the rnge of The pulse durtion is. ms nd the ioniztion efficiency reches 9%. The jet velocity of the hydrogen plsm vried etween 1 nd km/s. Although this ws lower thn necessry for penetrtion, the experimentl results showed significnt difference from conventionl fuelling methods. Fig. demonstrtes plsm initition with the help of the injector. Insted of the gs puff used in the conventionl scenrio (lso shown in Fig.), plsm jet ws injected into the empty vcuum vessel shortly efore inductive voltge ws pplied. One cn see tht the plsm I (ka) Plsm current, Shot 3386, nl,1 1 (cm - ) U (V) U (V) Line integrted density, R = cm 1 Tp - Mirnov signl Mirnov signl FIG.. Inductive plsm initition with different fuelling methods: - ZLWK SODVPD LQMHFWLRQ û7 p - time of the plsm gun shot), - with gs puffing prefill. I (ka) nl,1 1(cm-) nl,1 1(cm-) nl,1 1 (cm - ) Plsm current, Shot 3381, 3389 Tg Tp Line integrted density, R = cm Line integrted density, R = cm Line integrted density, R = cm FIG.. Comprison of the plsm injection () to the gs SXII E IXHOOLQJ PHWKRGV û7 g - gs puff intervl, û7 p - plsm gun shot. FIG.6. Penetrtion of the plsm jet with km/s speed into toroidl mgnetic fields of different strength (from left to right B T () = T,. T,.1 T,. T).

4 current rmps up fster nd to higher vlue t the sme loop voltge (sme mgnetic flux consumption). It is lso seen tht mgnetic turulence during current rmp-up is lower in the cse of injection. Fig. shows plsm density wveforms during gs-puff fuelling nd plsm jet injection into n OH dischrge. It is seen tht density increses in ~. ms fter injection compred to ~1 ms during gs puff. Fig.6 shows video frmes of plsm jet injection into the empty vessel of Glous-M with only toroidl mgnetic field pplied. One cn see the deeper penetrtion of plsm jet with equl velocities into the lower toroidl field. The effect of plsm jet current interction with nonhomogeneous mgnetic field (the plsm em is pushed to the lower B T region) is lso seen in the photos.. Plsm wll interction study. Experiments re imed to optimize the choice of mteril for the in-vessel protection pltes (cron or tungsten) nd increse the effectiveness of the oroniztion technology. For this purpose, the investigtion of the fundmentl properties of films deposited onto vessel wlls during oroniztion nd study of in-vessel mteril redeposition hs strted. First results re presented in []. It ws found tht n morphous film structure is creted fter oroniztion. It contins oron, cron nd hydrogen. The hydrogen content goes down with king. The physicl properties of the film re like those of semiconductors. The next nlysis will e done fter few hundred plsm shots. Essentil chnges of the initil film structure re expected. Preliminry dt (need to e confirmed) showed the cretion of dimond-like film t the surfce of silicon proes plced in the X-point region.. Plsm dignostics development. New dignostic systems hve een instlled, including poloidl rry of Mirnov coils (8 units); four chnnel pyroelectric olometer for rdition loss recording; time of flight (rdr) reflectometer for edge density profile recording in the rnge of m -3. A pper on new dignostic tools is under preprtion. Fig.7 shows the density profile vrition recorded y rdr reflectometer during injection of plsm jet. One cn see drmtic chnge in peripheril density ehvior following the injection pulse. The density grdient recorded y the device incresed ~3. times during 1 ms. The Thomson scttering system is under finl ssemly. A lser pulse trin from the proing lser output is shown in Fig.8. FIG.7. Density profile vrition in shot # 367 recorded y rdr reflectometer during injection of plsm jet t 6. ms. khz 66Hz khz FIG.8. Thomson scttering proing lser pulse trin of pulses with vrile repetition rte. Averge output energy ~ J/pulse. 6. Auxiliry plsm heting. One of the RF plsm heting scenrios of Glous-M is nonresonnt trnsit time mgnetic pumping (TTMP) sorption of fst mgnetosonic wve t ω/ω ci 8-1 (HHFW heting). To simulte the propgtion nd sorption of the plsm wves in the higher ion cyclotron hrmonic frequency rnge in STs, full-wve electromgnetic code is under development. A simultion model is descried in [6]. As

5 result of simultions, the RF field distriution in the plsm volume nd RF power sorption cn e computed. Fig.9 represents the sored RF power density verged on ech mgnetic surfce for the Glous-M conditions. First ntenn-plsm mtching experiments were performed in Glous-M utilizing set of equipment developed for the RF heting progrm. It consists of n RF genertor of ion cyclotron frequency rnge, 7 MHz, with ultimte power up to 1. MW. Pulse durtion is up to ms. The single strip ntenn is supplied with Frdy screen, protected y oron nitride nd instlled into the vcuum vessel. In the first experiments, input RF power through one ntenn will not exceed kw. Two stus produce ntenn mtching with the plsm nd the genertor mechniclly step y step. The results of one of the first, low power ( kw) shots re shown in Fig.1. Assemly of the NB injector for the energy of 3 kev nd 1. MW power hs een completed. Numericl simultions of neutrl em sorption y the Glous-M plsm were performed. The first em of deuterium neutrls with power level of ~. MW ws otined flux coordinte 7. Conclusions. The Glous-M ST could stly operte in wide rnge of densities nd sfety fctor vlues. The plsm creted during n ohmic heting dischrge hs ll the necessry fetures for the trget plsm to e used in uxiliry heting, high et experiments. A possile wy to increse OH plsm performnce is connected with development of plsm fuelling methods nd deeper investigtion of plsm-wll interction processes. The first results on plsm fuelling showed the necessity to increse plsm jet velocity to 7 1 km/s nd the numer of prticles to 1, which will e done soon. Unlike the compct toroid injection method, plsm jet does not contin noticele impurities, which results in lower plsm impurity flux. New dignostic tools hve een commissioned nd first dt re encourging. Auxiliry heting experiments hve egun. The work is supported y the Ministry of Industry, Science nd Technology nd the Ministry of Atomic Energy of the Russin Federtion, s well s y RFBR grnts , , nd [1] A. Sykes, Tech. Physics, (1999) 17. [] V.K. Gusev, et l., Proc. of 9 th EPS Conf. on Plsm Phys. nd Contr. Fusion, Montreux, P.1 (). [3] V.K. Gusev, et l., Proc. of 8 th EPS Conf. on Contr. Fusion nd Plsm Phys., Funchl, ECA, vol.a (1) [] A.V. Voronin, K.G. Helllom, Plsm Phys. nd Contr. Fusion, 3 (1) 183. [] N.V. Skhrov, et l., Proc. of 9 th EPS Conf. on Plsm Phys. nd Contr. Fusion, Montreux, P.78 (). [6] V.K. Gusev, et l., Proc. of nd IAEA-TCM on Sphericl Tori nd 17 th Int. Sphericl Torus Workshop, São José dos Cmpos, SP, Brzil (1). sored RF power density,.u. 1 FIG.9. Asored RF power density verged on ech mgnetic surfces for B T =.6 T, I P =.3 MA, n e ()=1 m -3, T e ()=. kev, k=1.8, δ=.16, f=3 MHz. Plsm current (ka); shot #377 1 Integrl plsm density (1E18mE-) 1 Incident RF power (.u.) Reflected RF power (.u.) H-lf emission (.u.) CIII emission (.u.) FIG.1. Evolution of plsm prmeters during the ntenn-plsm mtching experiment. B T ()=. T, f= MHz, P RF = kw.