Bondarenko, I.S.

Chmyga, A.A.

Deshko, G.N.

Dreval, N.B.

Khrebtov, S.M.

Komarov, A.D.

Kozachek, A.S.

Krupnik, L.I.

Nedzelskiy, I.S.

Наукова електронна бібліотека періодичних видань НАН України (Vernadsky National Library of Ukraine)

PLASMA DIAGNOSTICSBEAM INJECTION SYSTEMS FOR THE HIBP PLASMA DIAGNOSTICS OF THE IPP NSC “KHARKOV INSTITUTE OF PHYSICS AND TECHNOLOGY”I.S. Bondarenko, A.A. Chmyga, G.N. Deshko, N.B. Dreval, S.M. Khrebtov, A.D. Komarov, A.S. Kozachek, L.I. KrupnikInstitute of Plasma Physics, National Scientific Centre “Kharkov Institute of Physics and Technology”, 61108 Kharkov, UkraineI.S. NedzelskiyAssociação EURATOM/IST, Centro de Fusão Nuclear, Instituto Superior Técnico, 1049-001 Lisboa, PortugalPACS: 52.70.Nc1. INTRODUCTIONAmong a lot  of  contactless methods the plasma corpuscular  diagnostics  one  takes  from  leading  places. With the help of plasma probing by ion and neutral beams it  is  possible  to  receive  information  about  space distribution  of  a  potential,  density,  plasma  electron temperature,  impurity  ions  and  poloidal  magnetic  field (axial  current)  space  distributions  in  plasma  of  modern fusion  devices.  Now  we  have  two  main  directions  of plasma corpuscular diagnostics – heavy ion beam probing (HIBP)  [1] and  light  atomic  beam  probing  diagnostic systems (BES) [2].The heavy ion beam probing diagnostic systems allow  obtaining  information  about  the  plasma  potential space distribution,  density,  and electron temperature and plasma axial current distribution. This method is based on the  heavy  ion  (Cs  or  Tl)  beam  injection  in  a  plasma volume and the secondary ion beam current  and energy registration  usually  by  means  of  a  300 Proca–Green electrostatic  energy  analyzer.  This  diagnostics  required high accuracy of primary and secondary ion beams energy measurements and high stability (not less than 10-5) of ion beam energy, so the injector and analyzer power supplies voltage. The easy neutral beam diagnostics based on Li or Na beam injection  in  plasma  volume  and  registration  a spectral characteristics of a probing beam radiation allows investigating  plasma  and  impurity  ions  density  space distribution  in  peripheral  area  of  modern  thermonuclear devices. This method has a potential possibility to measure poloidal  and  toroidal  magnetic  fields.  This  diagnostics required high intensity of the probing beam (up to 10 mA), but not so high stability of beam energy.  The corpuscular  diagnostic  systems consist  of two  main  parts  –  an  injector  of  a  primary  beam  and analyzing device of a secondary signal from plasma. A main  task  of  an  injector,  for  all  types  of  diagnostic complexes,  is  to  supply  a  probing  beam  density  in researched  area  of  plasma  sufficient  for  reliable registration  of  a  secondary  signal.  The  injector  is  also consists  of  two  parts  the  emitter-extractor  unit  (ion source) and a shaping-focusing system.2. EMITTER-EXTRACTOR UNIT AND SHAPING-FOCUSING SYSTEMThe emitter-extractor unit scheme is shown at Fig.1. This quasipierce emitter-extractor unit was elaborated in IPP NSC KIPT and is  using  now (with  not  significant modifications) in injectors of HIBP diagnostic complexes of  modern  fusion  devices,  such  as  TJ-II  (CIEMAT, Spain), Т-10 (RSC, Russia), ТUМАN-3М (PhTI, Russia), ISTTOK (CFN/IST, Portugal), and in light neutral beam injector  (BES)  at  ASDEX  Upgrade  tokamak,  (IPP, Germany).        This design allows rather simple changing of the emitter (3) and heating filament (4).Fig.1. Ion injector emitter–extractor unit:1. Extractor electrode2. Pierce electrode3. Solid state thermo ionic emitter4. Heating filament5. Filament enclose6. Filament holder 7. Emitter flange Problems of Atomic Science and Technology. 2002. № 5. Series: Plasma Physics (8). P. 145-147                      145The calculations and experimental investigations of this unit shows, that in order to obtain maximum ion current, without ion current to the extractor, it’s necessary to have the following relations between electrode dimensions:Dextr= dem-extr                                                         (1),Dext / dem =1.5                                    (2),whereDextr  - extractor hole diameter; dem – emission surface diameter; dem-extr  -emitter-extractor gap. In  this  case Chaild  –  Lengmour law for  flat  diode  can describe the relationship between ion current density and extractor voltage:22/381054,5dUj⋅⋅=−µ ,                        (3),where d = dem-extr , µ  - ion atomic mass.The  optimal  extractor  cone  angle  (1)  is  900, pierce electrode - 1200. The pierce electrode (2) may have an electrical contact with emitter surface, or may be no – in  that  case  one  can  apply  the  positive  potential  to  it (some hundred volts) to plug out the ion beam.Solid-state  thermo  ionic  emitters  (3),  elaborated  in IPP NSC KIPT consists of metal  (Ta, W) support  with backing emitter material – alkali ion aluminosilicate (Li, Na,  K,  Cs)  [3,  4],  we use  also  ceolite  for  Tl,  and Cs. These emitters allow obtaining the ion current density in steady state mode up to 10 mА/сm2 and some  А/сm2 in pulse mode. Working resource – 25 mА.hour/gram.A shaping-focusing system based on multy-electrode accelerating tube with potential distribution which allows to have soft operation of ion beam focusing point.3. INJECTOR SYSTEMSFig. 2 presents the ion injector for HIBP system of TI-II fusion device [5].Fig.2.  Cs +  HIBP diagnostic system injector of TJ-IIstellarator:1. Emitter–extractor unit2. Focusing electrode3. Accelerating tube4. Faraday cup5. Deflecting plates6. Wire detectorThe space potential distribution, which necessary for ion beam accelerating and focusing into determined point  of  stellarator  plasma  was  assigned  by  resistive divider of accelerating tube. The initial ion beam focusing is carried out by three-electrode lens, consists of extractor electrode, focusing electrode (2), and some first rings of accelerating  tube  (3),  after  that  the  ion  beam  is accelerating to determined energy. Ion current and focus distance  control  is  carried  out  by  means  of  extractor potential and emitter temperature (filament current). Injector  power  supply,  elaborated  in  IPP  NSC KIPT,  consists  of  4  sources:  accelerating  voltage (+200кV,  1  mА),  extracting  voltage  (-4  кV,  1  mА), modulation  voltage  (+600  V,  1  mА),  emitter  filament heating voltage (12 V, 15 А), assembled in a mutual box. This power supply guarantee high stability of accelerating voltage  (not  worse  than  10-5),  which  is  necessary  for plasma potential measurements by HIBP method. Ion current measurements carried out by Faraday cup (4). The FC design allows to measure the ion current between  stellarator  pulses  and  to  transmit  ion  beam to plasma in determined period of time. This design prevents ion beam coming into stellarator vacuum chamber during a  period  of  magnetic  field  arising,  then  consists  a conditions for run away electron current appearance. This current appears due to a secondary ion-electron emission from vacuum chamber wall and leads to plasma discharge breakdown. The ion beam space control  is  carrying out by deflecting plates (5), and beam profile measurements - by wire detector (6).This  injector  allows  to  having  primary  Cs  ion beam current up to 100 mkA with beam diameter 4 mm. It’s  more  than  enough  for  steady  secondary  ion  beam registration.  The  secondary  ion  current  on  analyzer detector  plates  is  now  100  –  300  nA,  it’s  2  order  of magnitude more than plasma loading. The same types of injectors are working now at HIBP  diagnostic  systems  of  tokamaks  Т-10  (300  кV, 30mкА,  Tl+ beam),  ТUМАN-3М (80  кV,  80 mкА,  K+ beam) and ISTTOK.               Fig.3 shows potential distribution in HIBP injector of ISTTOK tokamak [6], one can see the initial ion beam focusing area by three-electrode lens (I – III) and accelerating area (IV). 146Fig.3. Potential space distribution in ISTTOK tokamak injectorISTTOK injector  system can  operate  with  two mutually  replacing  ion sources–  solid  state  and plasma sources. Plasma ion source allows injecting into plasma practically  any  kind  of  ions  and  also  two  or  more component  ion beams with  the  aim of  plasma electron temperature  measurements.  With  Cs+ solid-state  source this injector produces up to 20 mkA, 20 keV beam with 3mm diameter and 1,7 mrad divergence at 1,3 m from the accelerating tube. It can operate with a mono-cusp plasma ion souce also,  and produces  up to  40 mkA Xe+ beam with the same 3 mm diameter but  16-mrad divergence. The  respective  current-to-voltage  characteristics  are shown in Fig.4.Fig.4. ISTTOK injector current-to-voltage characteristicsMPIS – mono-cusp plasma ion source,SSTS –solid-state thermo ionic source,a – emitter diameter, d – emitter extractor gap4. CONCLUSIONA long – focus primary ion beam HIBP injectors described in this report. They were based on accelerating tubes  with  resistively  dividers.  These  systems  have  a possibility  of  a  soft  control  of  focusing  distance  and primary  beam  density  by  means  of  extractor  voltage control.  This  feature  is  very  important  for  supplying  a probing  beam  density  in  researched  area  of  plasma sufficient for reliable registration of a secondary signal.Now  authors  are  working  under  new  types  of emitter – extractor units, based on Li and Na solid state thermo ionic emitters in order to obtain ion current up to several dozen milliamps for beam - emission spectroscopy (BES),  and  several  –  component  ion  beams  for  plasma electron temperature measurements by HIBP method.  This work was supported by STCU Grant № P-102.REFERENCES1. Yu.N. Dnestrovskij, A.V. Melnikov, L.I. Krupnik, I.S. Nedzelskij, “Development of Heavy Ion Beam Probe Diagnostics”, IEEE Transactions on Plasma Science, vol. 22, № 4, p. 310-331, 1994. 2. E. Wolfrum, F. Aumayr, D. Wutte, HP. Winter, E. Hintz, D. Rusbuldt, R.P. Schorn,   “Fast Lithium-Beam Spectroscopy of Tokamak Edge Plasmas, Review of Scientific Instruments, vol. 64, № 8,  p. 2285-2292, 1993.3. I.A. Stepanenko, A.D. Komarov, A.S. Kozachek et al., “Investigation of Natural Minerals Thermo Ionic Emission” Radiotechnics and Electronics, v.38, № 12, p.2225-2227, 1993.4. L.I.Krupnik, N.V.Samohvalov, Yu.V. Trofimenko ”Advantage of Natrium Atoms Usage in a Beam Emission Spectroscopy (BES) and Obtaining of Stable and Intensive Ion Emission from Aluminosilicate Emitters”, Plasma Physic, v.20, № 2, p.186-188, 1994.5. L.I. Krupnik, I.S. Bondarenko, A.A. Chmyga, M.B. Dreval, S.M. Khrebtov, A.D. Komarov, A.S. Kozachok, C. Hidalgo, I. Garcia-Cortes, L. Rodriguez-Rodrigo, A.V. Melnikov, P. Goelho, M. Gunha, B. Goncalves, A. Malaquias, I.S. Nedzelskij, C.A.F. Varandas, “The First Operation of the Advanced Heavy Ion Beam Probing Diagnostic on the TJ-II Flexible Heliac”, Fusion Engineering and Design, v. 56-57, p. 935-939, 2001.6. J.C. Cabral, A. Malaquias, I.S. Nedzelskiy, C.F. Varandas, I.S. Bondarenko, O.O. Chmyga,  M.B. Dreval, S.M. Khrebtov, O.D. Komarov, O.S. Kozachok,  “Improvement of the Injector System for ISTTOK HIBP Diagnostic Complex”, 8 Ukrainian Conference and School on Plasma Physics and Controlled Fusion, Alushta, September 11-16, Book of Abstracts, p. 184, 2000.147148

Beam injection systems for the HIBP plasma diagnostics of the IPP NSC “Kharkov Institute of Physics and Technology”

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Beam injection systems for the HIBP plasma diagnostics of the IPP NSC “Kharkov Institute of Physics and Technology”

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