Negative ion source development for fusion application (invited)

Abstract

Giant negative ion sources, producing high-current of several tens amps with high energy of several hundreds keV to 1 MeV, are required for a neutral beam injector ͑NBI͒ in a fusion device. The giant negative ion sources are cesium-seeded plasma sources, in which the negative ions are produced on the cesium-covered surface. Their characteristic features are discussed with the views of large-volume plasma production, large-area beam acceleration, and high-voltage dc holding. The international thermonuclear experimental reactor NBI employs a 1 MeV-40 A of deuterium negative ion source, and intensive development programs for the rf-driven source plasma production and the multistage electrostatic acceleration are in progress, including the long pulse operation for 3600 s. Present status of the development, as well as the achievements of the giant negative ion sources in the working injectors, is also summarized.

Magnetic filter field dependence of the performance of the RF driven IPP prototype source for negative hydrogen ions

“…This, however, seems to be a problem especially for the small IPP prototype source; low pressure operation down to 0.2 Pa was possible in the large 1/2-size ITER source (1 m × 1 m) at the IPP RADI test facility even with a magnetic field strength comparable to the values here [30]. A similar dependence of the operating pressure from the volume to surface area ratio was seen for the arc driven sources [10]. Figure 8 shows the maximum achieved extracted current density and the minimum achieved ratio of co-extracted electron to ion current in dependence on some parameters of the magnetic field configurations, i.e.…”

“…in sources operating with surface production of the negative ions, is the magnetic filter field (see [4,8] for the RF driven negative ion source, and [9][10][11][12][13][14] for the arc driven sources). The magnetic filter field separates the plasma production zone (in the RF source the so-called driver where the RF is coupled in) from the extraction zone near the first grid of the acceleration system, the plasma grid.…”

Performance of multi-aperture grid extraction systems for an ITER-relevant RF-driven negative hydrogen ion source

“…From the experiences obtained in the last three decades in different experiments worldwide [4][5][6][12][13][14][15][16], the maximum achievable current density under these extreme conditionslow pressure, low extraction voltage, low amount of co-extracted electrons-is in the range of 200-300 A m −2 for deuterium and 300-400 A m −2 for hydrogen (as the amount of co-extracted electrons is much lower in hydrogen, a larger ion current density can be achieved by reducing the filter field strength). These high negative ion current densities could only be achieved until now with caesium seeding of the source.…”

Long-pulse production of high current negative ion beam by using actively temperature controlled plasma grid for JT-60SA negative ion source

“…In order to achieve such high-energy high-current beams with long-pulse, a lot of R&D has been carried out to overcome the common critical issues of the negative ion production, the beam optics and the voltage holding capability in the world [3][4][5].…”