Neutralisation and transport of negative ion beams: physics and diagnostics

Neutral beam injection is one of the most important methods of plasma heating in thermonuclear fusion experiments, allowing the attainment of fusion conditions as well as driving the plasma current. Neutral beams are generally produced by electrostatically accelerating ions, which are neutralised before injection into the magnetised plasma. At the particle energy required for the most advanced thermonuclear devices and particularly for ITER, neutralisation of positive ions is very inefficient so that negative ions are used. The present paper is devoted to the description of the phenomena occurring when a high-power multi-ampere negative ion beam travels from the beam source towards the plasma. Simulation of the trajectory of the beam and of its features requires various numerical codes, which must take into account all relevant phenomena. The leitmotiv is represented by the interaction of the beam with the background gas. The main outcome is the partial neutralisation of the beam particles, but ionisation of the background gas also occurs, with several physical and technological consequences. Diagnostic methods capable of investigating the beam properties and of assessing the relevance of the various phenomena will be discussed. Examples will be given regarding the measurements collected in the small flexible NIO1 source and regarding the expected results of the prototype of the neutral beam injectors for ITER. The tight connection between measurements and simulations in view of the operation of the beam is highlighted.

[1]  M Cavenago,et al.  Deflection compensation for multiaperture negative ion beam extraction: analytical and numerical investigations , 2014 .

[2]  J. R. Conrad,et al.  Beamlet steering by aperture displacement in ion sources with large acceleration‐deceleration ratio , 1980 .

[3]  G. Serianni,et al.  Study of a high power hydrogen beam diagnostic based on secondary electron emission. , 2016, The Review of scientific instruments.

[4]  F. Molon,et al.  Design, installation, commissioning and operation of a beamlet monitor in the negative ion beam test stand at NIFS , 2015 .

[5]  G. Chitarin,et al.  Numerical simulations of the first operational conditions of the negative ion test facility SPIDER. , 2016, The Review of scientific instruments.

[6]  R. Girnius,et al.  Production of fast H/sup 0/ atoms by stripping H/sup -/ ions in gas and vapor targets , 1980 .

[7]  F. Murtas,et al.  Conceptual design of a neutron diagnostic for 2-D deuterium power density map reconstruction in MITICA , 2017 .

[8]  J. H. Whealton.  Effect of beamlet‐beamlet interaction on ion optics of multiaperture sources , 1978 .

[9]  Y. Hirano,et al.  Electron density profile measurements at a self-focusing ion beam with high current density and low energy extracted through concave electrodes. , 2014, The Review of scientific instruments.

[10]  R. S. Hemsworth,et al.  Detailed design optimization of the MITICA negative ion accelerator in view of the ITER NBI , 2015 .

[11]  R. S. Hemsworth,et al.  Overview of the design of the ITER heating neutral beam injectors , 2017 .

[12]  A. Pimazzoni,et al.  Analysis of diagnostic calorimeter data by the transfer function technique. , 2016, The Review of scientific instruments.

[13]  K. Usui,et al.  Achievement of 500 keV negative ion beam acceleration on JT-60U negative-ion-based neutral beam injector , 2011 .

[14]  H. P. L. de Esch,et al.  Negative ion beam halo mitigation at the 1 MV testbed at IRFM , 2011 .

[15]  M. Cavenago.  Integrodifferential models of electron transport for negative ion sources , 2015 .

[16]  R. Pasqualotto,et al.  Tomographic diagnostic of the hydrogen beam from a negative ion source , 2011 .

[17]  M. Cavenago.  Moderately converging ion and electron flows in two-dimensional diodes. , 2012, The Review of scientific instruments.

[18]  G. Serianni,et al.  A first characterization of the NIO1 particle beam by means of a diagnostic calorimeter , 2017 .

[19]  U. Fantz,et al.  Spectroscopy—a powerful diagnostic tool in source development , 2006 .

[20]  P. Zaccaria,et al.  Design and R&D for manufacturing the MITICA Neutraliser and Electron Dump , 2013 .

[21]  P. Strehl.  Beam instrumentation and diagnostics , 2006 .

[22]  Yujiro Ikeda,et al.  Present status of the negative ion based NBI system for long pulse operation on JT-60U , 2006 .

[23]  Jérôme Paméla,et al.  A model for negative ion extraction and comparison of negative ion optics calculations to experimental results , 1991 .

[24]  L. Garrigues,et al.  Modeling of plasma transport and negative ion extraction in a magnetized radio-frequency plasma source , 2017 .

[25]  M. Bacal,et al.  Negative hydrogen ion production mechanisms , 2015 .

[26]  R. Sah,et al.  Electron beam probe for charge neutralization studies of heavy ion beams , 1982 .

[27]  E. Surrey,et al.  Beam Induced Effects in the ITER Electrostatic Residual Ion Dump , 2009 .

[28]  G. Serianni,et al.  Design and analyses of a one-dimensional CFC calorimeter for SPIDER beam characterisation , 2010 .

[29]  R. Pasqualotto,et al.  The tomographic diagnostic of ITER neutral beam injector , 2013 .

[30]  G. Serianni,et al.  Benchmark of numerical tools simulating beam propagation and secondary particles in ITER NBI , 2015 .

[31]  P. Allison,et al.  Beam Potential Measurement of an Intense H- Beam by Use of the Emissive Probe Technique , 1985, IEEE Transactions on Nuclear Science.

[32]  L. S. Simonenko,et al.  Excitation of ion oscillations of a plasma by a fast beam of negative ions , 1974 .

[33]  R. S. Hemsworth,et al.  Status of the ITER heating neutral beam system , 2009 .

[34]  G. Serianni,et al.  Simulation of diatomic gas-wall interaction and accommodation coefficients for negative ion sources and accelerators. , 2016, The Review of scientific instruments.

[35]  V. Gorshkov,et al.  Physical Processes in Compensated Beams of Negative Ions and Problems of Transport of the Beams , 2007 .

[36]  R. S. Hemsworth,et al.  Gas flow and related beam losses in the ITER neutral beam injector , 2006 .

[37]  E. Pitcher,et al.  H/sup /minus// beam neutralization measurements with a gridded-energy analyzer, a noninterceptive beam diagnostic , 1988 .

[38]  O. Naito,et al.  Heating and non-inductive current drive by negative ion based NBI in JT-60U , 2000 .

[39]  C. Taliercio,et al.  Design of a visible tomography diagnostic for negative ion RF source SPIDER , 2013 .

[40]  B. H. Wolf,et al.  Handbook of Ion Sources , 1995 .

[41]  Piergiorgio Sonato,et al.  Design and R&D of Thermal Sensors for ITER Neutral Beam Injectors , 2014, IEEE Transactions on Plasma Science.

[42]  Francis F. Chen,et al.  Introduction to Plasma Physics and Controlled Fusion , 2015 .

[43]  A. Holmes.  NEGATIVE HYDROGEN ION BEAMS , 1992 .

[44]  Chr. Day,et al.  3D Monte Carlo vacuum modeling of the neutral beam injection system of ITER , 2010 .

[45]  T. Kulevoy,et al.  Development of Small Multiaperture Negative Ion Beam Sources and Related Simulation Tools , 2009 .

[46]  K. Halbach.  Design of permanent multipole magnets with oriented rare earth cobalt material , 1980 .

[47]  Pierluigi Veltri,et al.  Tomographic reconstruction of the beam emissivity profile in the negative ion source NIO1 , 2016 .

[48]  V. Antoni,et al.  Development of an energy analyzer as diagnostic of beam- generated plasma in negative ion beam systems , 2017 .

[49]  M. Droba,et al.  Beam transport and space charge compensation strategies (invited). , 2016, The Review of scientific instruments.

[50]  R. Pasqualotto,et al.  Modeling and design of a beam emission spectroscopy diagnostic for the negative ion source NIO1. , 2014, The Review of scientific instruments.

[51]  Masaki Osakabe,et al.  Compensation of beam deflection due to the magnetic field using beam steering by aperture displacement technique in the multibeamlet negative ion source , 2001 .

[52]  M Brombin,et al.  SPIDER beam dump as diagnostic of the particle beam. , 2016, The Review of scientific instruments.

[53]  E. Surrey.  Gas heating in the neutralizer of the ITER neutral beam injection systems , 2006 .

[54]  Pierluigi Veltri,et al.  Evaluation of power loads on MITICA beamline components due to direct beam interception and electron backscattering , 2013 .

[55]  R. S. Hemsworth,et al.  Physics design of the HNB accelerator for ITER , 2013 .

[56]  A. Masiello,et al.  Design and R&D for manufacturing the beamline components of MITICA and ITER HNBs , 2015 .

[57]  I. Soloshenko,et al.  Stabilization of ion–ion instability with the aim of improvement transportation characteristics of a negative ion beam , 2002 .

[58]  G. Serianni,et al.  Applicability of inverse heat flux evaluation to thermographic measurements in SPIDER , 2017 .

[59]  A. Ivanov,et al.  Conversion of negative hydrogen ions into atoms in a hydrogen-plasma target , 1980 .

[60]  U. Fantz,et al.  Long pulse H- beam extraction with a rf driven ion source on a high power level. , 2010, The Review of scientific instruments.

[61]  G. Chitarin,et al.  First negative ion beam measurement by the Short-Time Retractable Instrumented Kalorimeter Experiment (STRIKE). , 2014, The Review of scientific instruments.

[62]  G. Serianni,et al.  The influence of grid positioning on the beam optics in the neutral beam injectors for ITER , 2016 .

[63]  G. Serianni,et al.  Solutions to mitigate heat loads due to electrons on sensitive components of ITER HNB beamlines , 2016 .

[64]  P. Zaccaria,et al.  Physics and engineering design of the accelerator and electron dump for SPIDER , 2011 .

[65]  A. Forrester,et al.  Large Ion Beams: Fundamentals of Generation and Propagation , 1988 .

[66]  G. Serianni,et al.  Negative Ion Extraction With Finite Element Solvers and Ray Maps , 2008, IEEE Transactions on Plasma Science.

[67]  B. Heinemann,et al.  Beam diagnostic tools for the negative hydrogen ion source test facility ELISE , 2013 .

[68]  T. Ropponen,et al.  IBSIMU: a three-dimensional simulation software for charged particle optics. , 2010, The Review of scientific instruments.

[69]  T. Imai,et al.  Experimental comparison between plasma and gas neutralization of high-energy negative ion beams , 2004 .

[70]  P. Mukhin,et al.  NEUTRALIZER OF INTENSE ION BEAMS. , 1967 .

[71]  V. Toigo,et al.  The PRIMA Test Facility: SPIDER and MITICA test-beds for ITER neutral beam injectors , 2017 .

[72]  Chr. Day,et al.  Cryopump design development for the ITER Neutral Beam Injectors , 2009 .

[73]  T. S. Green.  Intense ion beams , 1974 .

[74]  W. Deluca,et al.  NONDESTRUCTIVE BEAM PROFILE DETECTION SYSTEMS FOR THE ZERO GRADIENT SYNCHROTRON. , 1968 .

[75]  H. D. Esch,et al.  Electron dumps for ITER HNB and DNB beamlines , 2010 .

[76]  R. S. Hemsworth,et al.  Recent improvements to the ITER neutral beam system design , 2012 .

[77]  M. Spolaore,et al.  In-vacuum sensors for the beamline components of the ITER neutral beam test facility. , 2016, The Review of scientific instruments.

[78]  N. Wells.  The development of high-intensity negative ion sources and beams in the USSR. Technical report , 1981 .

[79]  B. Ruf,et al.  Benchmark of the SLACCAD code against data from the MANITU testbed at IPP , 2013 .

[80]  Piergiorgio Sonato,et al.  Experimental Validation of the 3-D Molecular Flow Code AVOCADO , 2014, IEEE Transactions on Plasma Science.

[81]  E. Pitcher,et al.  H¯ Beam Neutralization Measurements with a Gridded-Energy Analyser, a Noninterceptive Beam Diagnostic , 1988 .

[82]  V. A. Zhil’tsov,et al.  The development of a negative ion beam plasma neutralizer for ITER NBI , 2000 .

[83]  I. Soloshenko.  Problems of intense negative ion beam transport (invited) , 2004 .

[84]  Stanley Humphries,et al.  Charged Particle Beams , 1990 .

[85]  P. Veltri,et al.  Design of the new extraction grid for the NIO1 negative ion source , 2015 .

[86]  M Brombin,et al.  Final design of thermal diagnostic system in SPIDER ion source. , 2016, The Review of scientific instruments.

[87]  A. Chutjian,et al.  Electron scattering by molecules II. Experimental methods and data , 1983 .

[88]  R Pasqualotto,et al.  Modeling and simulation of a beam emission spectroscopy diagnostic for the ITER prototype neutral beam injector. , 2014, The Review of scientific instruments.

[89]  Y. Takeiri,et al.  Optics of the NIFS negative ion source test stand by infrared calorimetry and numerical modelling. , 2016, The Review of scientific instruments.

[90]  U. Fantz,et al.  Upgrade of the BATMAN test facility for H− source development , 2015 .

[91]  Masaki Osakabe,et al.  High-power and long-pulse injection with negative-ion-based neutral beam injectors in the Large Helical Device , 2006 .

[92]  V. Toigo,et al.  A substantial step forward in the realization of the ITER HNB system: The ITER NBI Test Facility , 2017 .

[93]  V. Antoni,et al.  Preliminary studies for a beam-generated plasma neutralizer test in NIO1 , 2017 .

[94]  Y. Mizutani,et al.  Experimental study of ion beamlet steering by aperture displacement in two-stage accelerator , 1980 .

[95]  Kazuhiro Watanabe,et al.  Operation of the negative-ion based NBI for JT-60U , 1998 .

[96]  K. Tsumori,et al.  Ion beam transport: modelling and experimental measurements on a large negative ion source in view of the ITER heating neutral beam , 2016 .

[97]  P. Sonato,et al.  The Full-Size Source and Injector Prototypes for ITER Neutral Beams , 2016 .

[98]  G. Gorini,et al.  Diagnostics of the ITER neutral beam test facility. , 2012, The Review of scientific instruments.

[99]  G Serianni,et al.  Comparative study of beam losses and heat loads reduction methods in MITICA beam source. , 2014, The Review of scientific instruments.

[100]  F. Molon,et al.  Negative ion beam characterisation in BATMAN by mini-STRIKE: Improved design and new measurements , 2015 .

[101]  E.Yu. Klimenko,et al.  The next step in the development of a negative ion beam plasma neutralizer for ITER NBI , 2001 .

[102]  Giuseppe Gorini,et al.  nGEM neutron diagnostic concept for high power deuterium beams , 2012 .

[103]  M. Bigi,et al.  Status of NIO1 construction , 2011 .

[104]  E. Surrey.  Space Charge Neutralization in the ITER Negative Ion Beams , 2007 .

[105]  V. Antoni,et al.  Effects of Negative Ion Source Characteristics on Beam Optics: The Case of SPIDER , 2012, IEEE Transactions on Plasma Science.

[106]  Emanuele Sartori,et al.  AVOCADO: A numerical code to calculate gas pressure distribution , 2013 .

[107]  P. McNeely,et al.  Neutral depletion in an H− source operated at high RF power and low input gas flow , 2011 .

[108]  D. Aprile,et al.  Cancellation of the ion deflection due to electron-suppression magnetic field in a negative-ion accelerator. , 2014, The Review of scientific instruments.

[109]  J. H. Whealton.  Linear optics theory of ion beamlet steering , 1977 .

[110]  T. Adachi,et al.  Fast data acquisition system of a non-destructive profile monitor for a synchrotron beam by using a microchannel plate with multi-anodes , 1991 .

[111]  V Antoni,et al.  Status of the ITER neutral beam injection system. , 2008, The Review of scientific instruments.

[112]  V. Bardakov,et al.  Peculiarities of measuring ion energy distribution in plasma with a retarding field analyzer. , 2015, The Review of scientific instruments.

[113]  Ian G. Brown,et al.  The Physics and technology of ion sources , 1989 .

[114]  S. Mochalskyy,et al.  Beam formation in CERNs cesiated surfaces and volume H− ion sources , 2016 .

[115]  E. Surrey,et al.  The beam driven plasma neutralizer , 2013 .

[116]  Mieko Kashiwagi,et al.  Results of the SINGAP neutral beam accelerator experiment at JAEA , 2009 .

[117]  P. Sonato,et al.  Modeling of Beam Transport, Secondary Emission and Interactions With Beam-Line Components in the ITER Neutral Beam Injector , 2014, IEEE Transactions on Plasma Science.

[118]  R. Gutser,et al.  Negative hydrogen ion transport in RF-driven ion sources for ITER NBI , 2009 .

[119]  L. Grisham.  Lithium jet neutralizer to improve negative hydrogen neutral beam systems , 2007 .

[120]  R. Pasqualotto,et al.  A wire calorimeter for the SPIDER beam: Experimental tests and feasibility study , 2015 .

[121]  L. S. Simonenko,et al.  Gas focusing of a negative-ion beam , 1974 .

[122]  O. Delferrière,et al.  Investigation of ion beam space charge compensation with a 4-grid analyzer. , 2016, The Review of scientific instruments.

[123]  A. Goncharov,et al.  Investigation of ion Langmuir oscillations in a plasma--fast ion beam system , 1973 .

[124]  G Serianni,et al.  Study of space charge compensation phenomena in charged particle beams. , 2012, The Review of scientific instruments.

[125]  A. Holmes.  Theoretical and experimental study of space charge in intense ion beams , 1979 .

[126]  J. Pozimski,et al.  Radial distribution of space-charge force in compensated positive-ion beams (invited) , 1998 .

[127]  G. Serianni,et al.  Simulation of space charge compensation in a multibeamlet negative ion beam. , 2016, The Review of scientific instruments.

[128]  R. S. Hemsworth,et al.  Heat load estimation in the duct and blanket module region of the HNB during various operating scenarios of the ITER machine , 2013 .

[129]  G Serianni,et al.  First experiments with the negative ion source NIO1. , 2016, The Review of scientific instruments.

[130]  N. Pomaro,et al.  Characterization, test and interpretative simulations of one-dimensional Carbon Fiber Composite prototype for SPIDER experiment , 2013 .

[131]  M. Cavenago.  Extraction layer models for negative ion sources , 2017 .

[132]  G. Serianni,et al.  Simulation of the gas density distribution in the large vacuum system of a fusion-relevant particle accelerator at different scales , 2015 .

[133]  E. Sartori,et al.  Transmission of electrons inside the cryogenic pumps of ITER injector. , 2016, The Review of scientific instruments.

[134]  G. A. Cottrell.  Tomography of neutral beams , 1984 .

[135]  M. Spolaore,et al.  Preliminary design of electrostatic sensors for MITICA beam line components. , 2016, The Review of scientific instruments.

[136]  G. Serianni,et al.  Spatial characterization of the space charge compensation of negative ion beams , 2013 .

[137]  B. Duval,et al.  Negative ion source development for a photoneutralization based neutral beam system for future fusion reactors , 2016 .

[138]  Pierluigi Veltri,et al.  Experimental validation of an innovative deflection compensation method in a multi-beamlet negative-ion accelerator , 2017 .

[139]  G. Cottrell.  Optical profilometry of intense neutral beams , 1982 .

[140]  G. Dimov,et al.  Conversion of a beam of negative hydrogen ions to atomic hydrogen in a plasma target at energies between 0.5 and 1 MeV , 1975 .

[141]  T. Imai,et al.  Suppression of fast electron leakage from large openings in a plasma neutralizer for N-NB systems , 2006 .

[142]  D. Leitner,et al.  Space-charge compensation measurements in electron cyclotron resonance ion source low energy beam transport lines with a retarding field analyzer. , 2014, The Review of scientific instruments.

[143]  R. S. Hemsworth,et al.  Modeling of secondary emission processes in the negative ion based electrostatic accelerator of the International Thermonuclear Experimental Reactor , 2008 .

[144]  A. Lifschitz,et al.  Numerical study of beam propagation and plasma properties in the neutralizer and the E-RID of the ITER Neutral Beam Injector , 2014 .

[145]  J. Ludvig,et al.  Electron-beam diagnostic for space-charge measurement of an ion beam - eScholarship , 2003 .