Solid state generator for powerful radio frequency ion sources in neutral beam injection systems

Kraus, Werner; Fantz, U.; Heinemann, B.; Franzen, P.

doi:10.1016/j.fusengdes.2014.11.015

Cited by 38 publications

(22 citation statements)

References 11 publications

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“…Over many years the generators used were self-excited tube oscillators. Recently very promising experiments have been started with replacing them by transistorized amplifiers [6].…”

Section: Rf Sources For Negative Neutral Beam Injection Systems (Nnbi)mentioning

confidence: 99%

Towards large and powerful radio frequency driven negative ion sources for fusion

et al. 2017

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The ITER neutral beam system will be equipped with radio-frequency (RF) negative ion sources, based on the IPP Garching prototype source design. Up to 100 kW at 1 MHz is coupled to the RF driver, out of which the plasma expands into the main source chamber. Compared to arc driven sources, RF sources are maintenance free and without evaporation of tungsten. The modularity of the driver concept permits to supply large source volumes. The prototype source (one driver) demonstrated operation in hydrogen and deuterium up to one hour with ITER relevant parameters. The ELISE test facility is operating with a source of half the ITER size (four drivers) in order to validate the modular source concept and to gain early operational experience at ITER relevant dimensions. A large variety of diagnostics allows improving the understanding of the relevant physics and its link to the source performance. Most of the negative ions are produced on a caesiated surface by conversion of hydrogen atoms. Cs conditioning and distribution have been optimized in order to achieve high ion currents which are stable in time. A magnetic filter field is needed to reduce the electron temperature and coextracted electron current. The influence of different field topologies and strengths on the source performance, plasma and beam properties is being investigated. The results achieved in short pulse operation are close to or even exceed the ITER requirements with respect to the extracted ion currents. However, the extracted negative ion current for long pulse operation (up to 1 h) is limited by the increase of the co-extracted electron current, especially in deuterium operation.

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“…Over many years the generators used were self-excited tube oscillators. Recently very promising experiments have been started with replacing them by transistorized amplifiers [6].…”

Section: Rf Sources For Negative Neutral Beam Injection Systems (Nnbi)mentioning

confidence: 99%

Towards large and powerful radio frequency driven negative ion sources for fusion

et al. 2017

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“…A further improvement was to replace the initially used self-excited tube based oscillators for the RF power supply by two 150 kW solid-state RF amplifiers, each supplying two drivers switched in series. This change resulted in much more reliable operation at high power due to the stable frequency and a better matching to the source 8 .…”

Section: Figure 1 the Four Drivers Of The Elise Sourcementioning

confidence: 99%

Deuterium results at the negative ion source test facility ELISE

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Fantz

et al. 2018

Review of Scientific Instruments

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The ITER neutral beam system will be equipped with large RF driven negative ion sources, with a cross section of 0.9 m x 1.9 m, which have to deliver extracted Dion beams of 57 A at 1 MeV for one hour. On the ELISE test facility a source of half of this size is being operational since 2013. Goal of this experiment is to demonstrate a high operational reliability and to achieve the extracted current densities and beam properties required for ITER. Technical improvements of the source design and the RF system were necessary to provide reliable operation in steady state with an RF power of up to 300 kW. While in short pulses the required D-current density has almost been reached, the performance in long pulses is determined in particular in Deuterium by inhomogeneous and unstable currents of coextracted electrons. By refined caesium evaporation and distribution procedures, and reduction and symmetrization of the electron currents considerable progress has been made and up to 190 A/m 2 D -, corresponding to 66 % of the value required for ITER, have been extracted for 45 minutes.

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“…In order to improve the efficiency of the RF system and its reliability, state-of-the-art solid state RF generators (amplifier) were tested successfully at the test facility BATMAN equipped with the prototype source, i.e. one driver [28]. Compared with the so far used self-excited oscillators, which are also foreseen to be used at the ITER sources, their electrical efficiency is higher than 90% instead of 50-60% and they do not need water cooling.…”

Section: Rf-efficiency and Reliabilitymentioning

confidence: 99%

Towards powerful negative ion beams at the test facility ELISE for the ITER and DEMO NBI systems

et al. 2017

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The test facility ELISE represents an important step in the European R&D roadmap towards the neutral beam injection (NBI) systems at ITER. ELISE provides early experience with operation of large radio frequency (RF) driven negative hydrogen ion sources. Starting with first plasma pulses in March 2013, ELISE has meanwhile demonstrated stable 1 h plasma discharges with repetitive 10 s beam extraction pulses every 3 min in hydrogen and deuterium at the ITER required pressure of 0.3 Pa. Stable ion currents of 9.3 A and 5.8 A have been extracted using only one quarter of the available RF power and reducing the extraction voltage in order to control the co-extracted electrons. The best hydrogen pulse for the required 1000 s for hydrogen gave an extracted current of 21.4 A and resulted in an accelerated current of 17.9 A, using only 53 kW per driver. Linear scaling towards full RF power (90 kW/driver) predicts that the target value of the negative ion current (H‾: 33 A extracted, 23 A accelerated; D‾: 28 A extracted and 20 A accelerated) can be achieved or even exceeded. Issues in long pulse operation are the caesium dynamics and the stability of the co-extracted electron current, for which the caesium management and the magnetic field configuration are promising tools for optimisation. Operation at high RF power for long pulses has highest priority for the next experimental campaign. In parallel or in a later stage, ELISE could serve as a test bed for studies on a DEMO NBI system. Examples are concepts concerning RF efficiency, operation with largely reduced caesium consumption or with caesium alternatives, and neutralization of the accelerated ion beam by a laser neutralizer in order to improve efficiency and reliability of NBI systems. Lab scale experiments on these topics are carried out presently in parallel with ELISE operation.

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Solid state generator for powerful radio frequency ion sources in neutral beam injection systems

Cited by 38 publications

References 11 publications

Towards large and powerful radio frequency driven negative ion sources for fusion

Towards large and powerful radio frequency driven negative ion sources for fusion

Deuterium results at the negative ion source test facility ELISE

Towards powerful negative ion beams at the test facility ELISE for the ITER and DEMO NBI systems

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