Extraction of volume-produced H− ions from a multicusp source

Leung, K. N.; Ehlers, K. W.; Bacal, M.

doi:10.1063/1.1137215

Cited by 210 publications

(79 citation statements)

References 17 publications

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“…The positive effect of biasing the plasma grid in negative ion sources is known since the 1980s and is used in many different ion sources [9][10][11][12][13] ; the general effect on the source performance has been reported also for the BATMAN (Bavarian Test Machine for Negative Ions) test facility in earlier publications 6,14 . Variation of the bias voltage changes the potential profile in the sheath in front of the plasma grid from an electron repelling case at low bias towards an electron attracting sheath at high bias.…”

Section: Introductionmentioning

confidence: 99%

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

Wimmer

Fantz

NNBI-Team³

2016

Journal of Applied Physics

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Large-scale sources for negative hydrogen ions, capable of delivering an extracted ion current of several ten amperes, are a key component of the neutral beam injection system of the upcoming ITER fusion device. Since the created heat load of the inevitably co-extracted electrons after magnetic separation from the extracted beam limits their tolerable amount, special care must be taken for the reduction of coextracted electrons -in particular in deuterium operation, where the larger amount of co-extracted electrons often limits the source performance. By biasing the plasma grid (PG, first grid of the extraction system) positively with respect to the source body the plasma sheath in front of the PG can be changed from an electron repelling towards an electron attracting sheath. In this way, the flux of charged particles onto the PG can be varied, thus changing the bias current and inverse to it the amount of co-extracted electrons. The PG bias affects also the flux of surface-produced H − towards the plasma volume as well as the plasma symmetry in front of the plasma grid, strongly influenced by an ⃗ E × ⃗ B drift. The influence of varying PG sheath potential profile on the plasma drift, the negative hydrogen ion density and the source performance at the prototype H − source is presented, comparing hydrogen and deuterium operation. The transition in the PG sheath profile takes place in both isotopes, with a minimum of co-extracted electrons formed in case of the electron attracting PG sheath. The co-extracted electron density in deuterium operation is higher than in hydrogen operation, which is accompanied by an increased plasma density in deuterium.

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Section: Introductionmentioning

confidence: 99%

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

Wimmer

Fantz

NNBI-Team³

2016

Journal of Applied Physics

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“…During Cs-seeded operation, the PE's material is changed to molybdenum from copper in order to keep its temperature higher than the copper PE using heat input from the plasma, since controlling the temperature of the PE surface plays an important role in increasing the H − production rate [4][5][6]. Dipole magnets referred to as filter magnets are located at the extraction region of the chamber to create a magnetic filter field [7] perpendicular to the central axis of the chamber. The magnetic filter field is optimized so as to maximize the arc efficiency, defined as the ratio of the beam current to the arc power in Cs-free operation [2].…”

Section: Apparatusmentioning

confidence: 99%

Development of a 20 mA negative hydrogen ion source for cyclotrons

Etoh

Onai

Arakawa

et al. 2017

AIP Conference Proceedings

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Effect due to plasma electrode adsorbates upon the negative ion current and electron current extracted from a negative ion source AIP Conference Proceedings 1869, 030025 (2017) Abstract. A cesiated DC negative ion source has been developed for proton cyclotrons in medical applications. A continuous H − beam of 23 mA was stably extracted at an arc power of 3 kW. The beam current gradually decreases with a constant arc power and without additional Cs injection and the decay rate was about 0.03 mA (0.14%) per hour. A feedback control system that automatically adjusts the arc power to stabilize the beam current is able to keep the beam current constant at ±0.04 mA (±0.2%).

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“…•In 1983, a novel method of extracting volume-produced H" ions directly from a multicusp source was reported by Leung et al 14 The multicusp plasma generator has demonstrated its ability to produce large volumes of uniform and quiescent plasmas with good gas and electrical efficiency. 1 ^ A schematic diagram of the apparatus is shown in Fig.…”

Section: Surface-produced H" Ion Sourcesmentioning

confidence: 99%

Development of high current and high brightness negative hydrogen ion sources

Leung

1989

Nuclear Instruments and Methods in Physics Research Section B:

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Negative hydrogen ions have found important applications in particle accelerators and in fusion research. These ions can be generated from two different types of ion sources -the surface conversion source and the volume production source. Recent experiments demonstrate that H" current exceeding 1 A can be obtained from both types of ion sources. Because of the lower H" ion temperature and the fact that they can be operated without cesium, volume H" sources are highly desired. However, further technology must be developed on the control of electrons and the reduction of gas flow i-IntroductionThe use of H" ions for accelerator applications was first proposed by Alvarez in 1951. 1 Since then, H" have found important applications in cyclotrons and tandem accelerators, in fueling storage rings of high energy accelerators, and in generating energetic neutral beams (E > 150 keV) for heating and for current drive in fusion plasmas. Negative hydrogen ions can be formed by double charge exchange processes or by direct extraction from a negative ion source. In general, two distinct types of H" ion sources can be identified: (1) surface conversion sources -in which the H" ions are generated by particle collisions with low work function surfaces, and (2) volume production sources -in which the negative ions are produced by electron-molecule and electron-ion collision processes in the volume of a discharge plasma. Because of the smaller beam omittance and the fact that they can be operated without cesium, volume H~ sources are now being developed by various high energy and fusion laboratories in the world. This article reviews the development and some of the latest technology of these two types of negative ion sources. It can be seen that in just twenty years, H" ion beams have been improved from several milli-ampere to more than 1 ampere. II. Surface-produced H" ion sourcesThere are two major types of surface conversion H" ion sources. One type uses a Penning discharge geometry (for example the planotron source)or an E x B discharge configuration (for example the magnetron source). The second type employs the multicusp plasma generator as the discharge chamber. This source was originally developed at Lawrence Berkeley Laboratory for neutral beam application. Recently, it has been used as an H" -2-source for particle accelerators at Los Alamos National Laboratory and at KEK in Japan.In 1972, the Novosibirsk group discovered that the yield of H" ions was increased from 5 to 20 mA by adding cesium to the hydrogen discharge in a planotron source. H" current density greater than 3 A/cm 2 has been achieved in milli-second pulses. 2 The function of the cesium is twofold: first, it acts as a sputtering agent, and second, it lowers the work function of the target surface so as to enhance the negative ion formation.In Novosibirsk, a multi-slit planotron source with one dimensional In normal operation, cesium is introduced into the discharge so as to lower the work function of the converter and consequently enhance the H"yiel...

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Extraction of volume-produced H− ions from a multicusp source

Cited by 210 publications

References 17 publications

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

Extraction of negative charges from an ion source: Transition from an electron repelling to an electron attracting plasma close to the extraction surface

Development of a 20 mA negative hydrogen ion source for cyclotrons

Development of high current and high brightness negative hydrogen ion sources

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