Physics design of the HNB accelerator for ITER

The physics design of the accelerator for the heating neutral beamline on ITER is now finished and this paper describes the considerations and choices which constitute the basis of this design. Equal acceleration gaps of 88 mm have been chosen to improve the voltage holding capability while keeping the beam divergence low. Kerbs (metallic plates around groups of apertures, attached to the downstream surface of the grids) are used to compensate for the beamlet–beamlet interaction and to point the beamlets in the right direction. A novel magnetic configuration is employed to compensate for the beamlet deflection caused by the electron suppression magnets in the extraction grid. A combination of long-range and short-range magnetic fields is used to reduce electron leakage between the grids and limit the transmitted electron power to below 800 kW.

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

[2]  V. Toigo,et al.  Status of PRIMA, the test facility for ITER neutral beam injectors , 2013 .

[3]  Piergiorgio Sonato,et al.  Flexible magnetic design of the MITICA plasma source and accelerator , 2013 .

[4]  A. Krylov,et al.  Experimental results from the Cadarache 1 MV test bed with SINGAP accelerators , 2006 .

[5]  D. J. Campbell,et al.  Chapter 1: Overview and summary , 1999 .

[6]  A Kojima,et al.  Vacuum insulation of the high energy negative ion source for fusion application. , 2012, The Review of scientific instruments.

[7]  K Tsuchida,et al.  Voltage holding study of 1 MeV accelerator for ITER neutral beam injector. , 2012, The Review of scientific instruments.

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

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

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

[11]  A. D. Lorenzia,et al.  Voltage holding optimization of the MITICA electrostatic accelerator , 2013 .

[12]  K. Watanabe,et al.  Long pulse acceleration of MeV class high power density negative H− ion beam for ITER , 2015 .

[13]  Piergiorgio Sonato,et al.  Optimization of the electrostatic and magnetic field configuration in the MITICA accelerator , 2013 .

[14]  R. V. Latham,et al.  High voltage vacuum insulation : basic concepts and technological practice , 1995 .

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

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

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

[18]  P. Sonato,et al.  Design of the MITICA neutral beam injector: from physics analysis to engineering design , 2013 .

[19]  Nicola Pilan,et al.  Magnetic Field Effect on Voltage Holding in the MITICA Electrostatic Accelerator , 2014, IEEE Transactions on Plasma Science.

[20]  D. Boilson,et al.  Voltage holding and dark currents in the Cadarache 1 MV ion beam facility , 2002, 20th International Symposium on Discharges and Electrical Insulation in Vacuum.

[21]  Pierluigi Veltri,et al.  Compensation of Beamlet Deflections and Focusing Methods in the Electrostatic Accelerator of MITICA Neutral Beam Injector , 2014, IEEE Transactions on Plasma Science.

[22]  C. Wimmer,et al.  Size Scaling of Negative Hydrogen Ion Sources for Fusion , 2015 .

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

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

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

[26]  L. Grisham,et al.  Beamlet deflection due to beamlet-beamlet interaction in a large-area multiaperture negative ion source for JT-60U. , 2008, The Review of scientific instruments.

[27]  R. S. Hemsworth,et al.  Compensations of beamlet deflections for 1 MeV accelerator of ITER NBI , 2013 .

[28]  T. Inoue,et al.  1 MV vacuum insulation for the ITER neutral beam injectors , 2010, 24th ISDEIV 2010.

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

[30]  M J Singh,et al.  Physics design of a 100 keV acceleration grid system for the diagnostic neutral beam for international tokamak experimental reactor. , 2010, The Review of scientific instruments.

[31]  N Pilan,et al.  Voltage holding prediction in multi electrode-multi voltage systems insulated in vacuum , 2011, IEEE Transactions on Dielectrics and Electrical Insulation.

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

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

[34]  R. S. Hemsworth,et al.  Design of neutral beam system for ITER-FEAT , 2001 .

[35]  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.

[36]  R. H. Bulmer,et al.  Sustained Spheromak Physics Experiment (SSPX): design and physics results , 2012 .

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

[38]  R. S. Hemsworth,et al.  Mo layer thickness requirement on the ion source back plate for the HNB and DNB ion sources in ITER , 2015 .

[39]  V. Toigo,et al.  The European contribution to the development of the ITER NB injector , 2011 .

[40]  C. Martens,et al.  Overview of the RF source development programme at IPP Garching , 2006 .

[41]  G Serianni,et al.  Concepts for the magnetic design of the MITICA neutral beam test facility ion accelerator. , 2012, The Review of scientific instruments.

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