Detection of fusion neutrons from a deuterium-proton mixed plasma in the GAMMA 10 Tandem Mirror

Abstract

Neutron diagnostics are applied to a deuterium plasma mixed with protons in the central cell of the GAMMA 10 tandem mirror [Inutake et al., Phys. Rev. Lett. 55, 939 (1985)]. The deuterium ions are heated with a slow ion cyclotron wave tuned to the fundamental deuterium resonance near the mid-plane of the central cell while the plasma is sustained with the fundamental resonance heating of protons in the minimum-B anchor cells. The measurement is based on in situ calibration to determine the transmission efficiency through machine walls and the counting efficiency of the detection system for neutrons emitted from 252Cf with energy close to that in the deuterium–deuterium (D–D) fusion reaction. The observation shows that the count rate of neutrons increases with diamagnetism, and this relation is accounted for in terms of fusion reaction between deuterium ions with a transverse temperature exceeding 10 keV. Discrepancies among ion temperatures determined with different diagnostics are mostly attributed to insufficient knowledge of the profiles of plasma parameters. The results indicate that the neutron measurement can be added as a powerful diagnostic tool for hot ions if combined with more detailed profile measurements.

Progress in potential formation and findings in the associated radially sheared electric-field effects on suppressing intermittent turbulent vortex-like fluctuations and reducing transverse losses

“…The central cell has a length of 6 m and a fixed limiter with a diameter of 0.36 m, and the magnetic-field intensity at the midplane B z = B m is 0.405 T with a mirror ratio R m of 5.2. Two systems of ion-cyclotron heating (ICH; 200 kW at 4.47 or 6.36 MHz, as well as 100 kW at 9.9 or 10.3 MHz) are employed for the central-cell hot-ion production and the anchor stabilization, respectively [31][32][33]. The plug and barrier cells are axisymmetric mirrors; they have an axial length of 2.5 m (B m = 0.497 T and R m = 6.2).…”

“…The plug and barrier cells are axisymmetric mirrors; they have an axial length of 2.5 m (B m = 0.497 T and R m = 6.2). Microwaves at 28 GHz are injected in the extraordinary mode into the plug and the barrier regions [21][22][23]31] to produce an ion-confining potential φ c , and a thermal-barrier potential φ b , respectively.…”

“…Recently, three-time progress in the formation of φ c including a new record of 2.1 kV in the plug region (filled circles in figure 2), in comparison to φ c attained 1992-2002 [27][28][29] (open circles in figure 2), has been achieved in a hot-ion mode [27][28][29][30][31][32] having bulk-ion temperatures T i = several kiloelectronvolts. The advance in the potential formation leads to the finding of remarkable effects of sheared E r (E r = dE r /dr c ≈ several 10 kV m −2 ) or sheared r (i.e.…”

“…kV-order plasma-confining potentials [14,15,21,22] and a hotion mode yielding fusion neutrons with T i = 10-20 keV [31].…”

Generalization and consolidation of scaling laws of potential formation and associated effects in the GAMMA 10 tandem mirror

“…The main tandem mirror operations from 1979 to 2000 in GAMMA 10 have been characterized in terms of (a) A high potential mode having kV order plasma confining potentials [1-4] (b) A hot ion mode yielding deuterium-deuterium (D-D) fusion produced neutrons with 10-20 keV bulk ion temperatures [5,6].…”