Experimental study of negative ion profiles in H2-MAR plasmas in divertor simulator MAP-II

Kado, S.; Kajita, Shin; Yamasaki, Daisuke; Iida, Yoshihiro; Xiao, Bingjia; Shikama, T.; Oishi, Tetsutarou; Okamoto, Atsushi; Tanaka, Satoru

doi:10.1016/j.jnucmat.2004.10.142

Cited by 18 publications

(23 citation statements)

References 19 publications

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“…Carbonfiber-composites (CFC) are used in many tokamaks as divertor material. Negative ion production on the carbon tiles has to be considered to correctly account for the heat load received by the divertor 17,18,19 . Indeed, the mutual neutralization of H -and H + and the subsequent molecular radiation participate in the heat load balance.…”

Section: A-introductionmentioning

confidence: 99%

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

et al. 2012

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In previous works, surface-produced negative-ion distribution-functions have been measured in H 2 and D 2 plasmas using graphite surfaces (HOPG). In the present paper we use the SRIM software to interpret the measured negative-ion distribution-functions. For this purpose the distribution-functions of backscattered and sputtered atoms arising due to the impact of hydrogen ions on a-CH and a-CD surfaces are calculated. The SRIM calculations confirm the experimental deduction that backscattering and sputtering are the mechanisms of the origin of the creation of negative ions at the surface. It is shown that the SRIM calculations compare well with the experiments regarding the maximum energy of the negative ions and reproduce the experimentally observed isotopic effect. A discrepancy between calculations and measurements is found concerning the yields for backscattering and sputtering. An explanation is proposed based on a study of the emitted-particle angulardistributions as calculated by SRIM. A-IntroductionThe ITER project and its successor DEMO (first nuclear-fusion based power plant prototype) aim at demonstrating power production by magnetic confinement nuclear fusion. Plasma start-up and continuous operation in the case of a tokamak reactor require very efficient heating and non-inductive current drive systems. Neutral beam injection (NBI) which uses high power beams of fast neutral atoms of hydrogen isotopes to heat the plasma is a promising candidate. In most existing NBI systems on contemporary fusion experiments a beam of positive ions is extracted from a conventional ion source, accelerated to energies of the order of 100 keV and neutralized via charge exchange in a background of neutral hydrogen. Due to the much larger physical dimensions the NBI systems for both ITER and DEMO require neutral beam energies in the 1 to 2 MeV range where the neutralization of positive ions becomes very inefficient and only the negative ions can be neutralized with sufficient yield. Hence the development of high current negative ion sources (50A D-beam for ITER) is crucial to the development of the ITER and DEMO NBI systems. The highcurrent-density negative-ion source for ITER 1 is currently the subject of intense research

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Section: A-introductionmentioning

confidence: 99%

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

et al. 2012

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“…A detailed description of MAP-II is provided in some studies, for example, Refs. [2,4]. MAP-II consists of differentially pumped dual chambers, a source chamber, and a target chamber, which are connected by a drift tube.…”

Section: Methodsmentioning

confidence: 99%

“…The laser photodetachment (LPD) method has been used in combination with an electrostatic probe for measuring the negative-ion density in various plasmas such as negative-ion sources [1] and divertor simulators [2][3][4]. In this method, an electrostatic probe is placed in a laser beam channel, and the increase in the electron density caused by the laser-induced photodetachment process, H − + hν → H+e, is detected as the variation in the electron current.…”

Section: Introductionmentioning

confidence: 99%

Magnetized Features of Sheath and Collection Region of Photodetached Electrons in Negative Ion Measurement

Kajita

Kado

Tanaka

2006

Contrib. Plasma Phys.

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The magnetized features of the sheath and collection region of photodetached electrons (PDE's) are experimentally studied in the linear divertor simulator MAP-II. The thickness of the electron sheath formed around a cylindrical electrostatic probe is measured by analyzing the variation in the temporal evolution of the laser photodetachment (LPD) signal. The effect of the magnetic field on the electron sheath thickness along the field is revealed by comparing the experimental result to the theoretical thickness derived using the Child-Langmuir (CL) law. The length of the collection region of PDE's is measured in several magnetized regimes by using the recently developed eclipse-LPD method. The physical meaning of this collection region is discussed based on the measured electron sheath thickness and the length of the collection region. Finally, the necessary conditions for applying the LPD technique in magnetized plasmas are discussed.

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“…The Eclipse-LPD [11] was applied. The hollow profile of the negative ion is a typical one in the divertor simulator where the negative hydrogen ions are destructed in the hot plasma column through an electron impact detachment process [3]. Therefore, the measurement of the flow and thermal velocities of the negative ions is performed at the radius r = 4.0 cm.…”

Section: Parallel Flow Obtained From the Recovery Timementioning

confidence: 99%

“…The laser photodetachment (LPD) method assisted by an electrostatic probe has been widely used for the measurement of negative ion density in so-called negative ion sources [1] and fusion divertor/edge plasma simulators [2,3]. Since this method has the potential to measure the velocity of the negative ions, a considerable amount of attention has been paid to the temporal behavior of LPD signals in an attempt to apply it to the study of negative ion sources [4,5]: i.e., optimizing the condition of beam emittance or magnetic filter.…”

Section: Introductionmentioning

confidence: 99%

A Concept of Negative Ion Flow Velocity Measurement Using a Laser Photodetachment Velocimetry (LPDV)

Kado

Kajita

Shikama

et al. 2006

Contrib. Plasma Phys.

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A concept of the thermal and flow velocities measurement for negative ions by means of a laser photodetachment technique, laser photodetachment velocimetry (LPDV), is presented. The difference in the temporal evolution of the photodetached excess electron current between the upstream and the downstream regions corresponds to the flow velocity, while the average of the recovery times corresponds to the thermal velocity, namely the negative ion temperature. Initial results in a divertor/edge plasma simulator MAP(material and plasma)-II suggest that the parallel flow velocity is small in the periphery of the linear plasma column where the negative ions exist. The negative ion temperature is similar to that of helium ion obtained for helium discharges.

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Experimental study of negative ion profiles in H2-MAR plasmas in divertor simulator MAP-II

Cited by 18 publications

References 19 publications

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

Production of negative ions on graphite surface in H2/D2 plasmas: Experiments and srim calculations

Magnetized Features of Sheath and Collection Region of Photodetached Electrons in Negative Ion Measurement

A Concept of Negative Ion Flow Velocity Measurement Using a Laser Photodetachment Velocimetry (LPDV)

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