The negative ions of hydrogen atom (H^-) are formed by dissociative attachment of cold electrons to the vibrationally excited molecules. This volume production process of H^- depends on the density of the vibrationally excited molecules and the cold electrons in the plasma. In order to produce the H^- effectively, we have proposed a designed system of a magnetized sheet plasma crossed with a vertical gas-flow and an electron-emitter made of tungsten filaments [1-2]. The magnetized sheet plasma is well suited for the production of negative ions because the electron temperature in the central region of the plasma is as high as 15 -20 eV, while in the circumferential region of plasma, a low temperature of 1 eV with obtained. The vibrationally excited hydrogen molecules result from the deexcitation of electronic excited hydrogen molecules by the collision of hydrogen molecules with hot electron (T_e=10-15 eV) in the central region of the sheet plasma. Also, vibrationally excited hydrogen molecules are attributed to recombinative desorption of hydrogen atoms on the end-target is made of W or Ta. The density of H^- is measured by changing the emission current I_E of the electron-emitter and the temperature of the end-target. The value of n_H^- was determined by a probe-assisted laser photodetachment method. Under a secondary hydrogen gas puffing into a hydrogen plasma, n_H^- have a maximum value (n_H^- = 2 × 10¹⁷ m^-3) at the gas pressure of 3 mTorr and the peak position of n_H^- is localized at the circumference of the sheet plasma. Also, n_H^- increases and becomes eight times larger than of the initial condition when I_E of the electron emitter increases from 0 to 25 A.

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