Beamline Optimization for 100-keV Diagnostic Neutral Beam Injector for ITER

• Published in: IEEE transactions on plasma science Vol. 38; no. 3; pp. 242 - 247
• Main Authors: Bandyopadhyay, M., Singh, M.J., Rotti, C., Chakraborty, A., Hemsworth, R.S., Schunke, B.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01.03.2010; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: beam transmission; Beamline components (BLCs); diagnostic; Electrostatics; Exact sciences and technology; Hydrogen; Ion beams; ITER; Magnetic confinement and equilibrium; neutral beam (NB); Niobium; Optical control; Optical losses; Optimization; Packaging; Physics; Physics of gases, plasmas and electric discharges; Physics of plasmas and electric discharges; Plasma; Plasma properties; Procurement; Propagation losses; Resonance; Spectrum analysis; Tokamaks; Toroidal magnetic fields; Transport properties; Charge exchange; ITER tokamak; Hydrogen; Ionic current; beam transmission; Optimization; Ion optics; Design; Magnetic confinement; Hydrogen ions; Focusing; Injector; Ion sources; Beam transport; Confined plasma; diagnostic; Procurement; Thermonuclear reactors; Neutral beam; Beamline components (BLCs); Ion beams; Beam currents; Negative ions; Plasma transport processes; ITER; neutral beam (NB); Magnetic fields
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2009.2035623

The 100-kV negative-hydrogen-ion-source-based diagnostic neutral beam (NB) (DNB) injector, which forms a part of the Indian (IN) procurement package for ITER, targets a delivery of ~18-20 A of neutral hydrogen-atom beam current into the ITER torus for charge exchange resonance spectroscopy diagnostics. Considering stripping losses, a ~70-A negative ion current is required to be extracted from the ion source, which leads to a production of 60 A of accelerated ion beam. Subsequent process of neutralization, electrostatic ion separation, and transport to the duct leads to a large separation between the points of generation of the ion beam to the point of delivery of the NB into the torus (~23 m). This forms one of the most important constraints for the transport of NBs to ITER. The requirements are not only for a stringent control over ion optics, the transport to electrostatic separator, minimum loss of beam due to intercepting elements, low reionization loss, and focusing to control interception losses but also for adequate compensation of residual magnetic fields to overcome magnetic field induced deflections also form important design issues for a reasonable transmission efficiency. Due to multiparameter dependence, it becomes necessary to assess the different scenarios using numerical codes. In the present case, the assessment has been carried out for the DNB using the beam-transport codes PDP, BTR, and the MCGF codes which are developed by the Russian Federation. An optimized configuration of the beamline has been arrived at on the basis of these code-enabled studies. These parameters are the following: listing of the vertical and horizontal focal lengths as 20.6 m, a spacing between ground grid and neutralizer of 1 m, and positioning of residual-ion dump at a distance of 0.75 m from the neutralizer exit. Further, optimizing the gas feed to the source and neutralizer leads to a final transmission of ~35% of the extracted beam power to the torus. This paper shall present the methodology, the issues concerned, and the final configuration which forms the basis for the present engineering.