V. V. Kolmogorov

Upgrade of the diagnostic neutral beam injector for the TCV tokamak

Abstract A diagnostic neutral beam injector (DNBI) [CRPP report LRP 710/01, CRPP-EPFL, 2001; EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365] has been installed on tokamak a configuration variable (TCV) [Plasma Phys. Control Fusion, 36 (1994) B277; Plasma Phys. Control Fusion, 43 (2001) A161; Plasma Phys. Control Fusion, to be published] for the purpose of providing local measurements of plasma ion temperature, velocity and impurity density by Charge eXchange recombination spectroscopy (CXRS) [EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365]. The system recently underwent a technical upgrade, which allowed to increase the full neutral beam current density by a factor of two (from 0.5 to 1 A at 52 keV injection energy) and to extend the operational range of the diagnostic. This was achieved by means of a new, larger ion source, with an increased extraction area and corresponding enhancements of the power supplies.

Ion source with LaB6 hollow cathode for a diagnostic neutral beam injector

In this article ion source capable of providing 8 A, 54 keV proton beam in maximum 3 s pulses is described. A general description of the diagnostic injector based on this ion source is also given. The ion beam is extracted and accelerated by a four-electrode multiaperture ion-optical system. In the ion source, hydrogen (deuterium) plasma is generated by an arc discharge plasma box with a hot LaB6 cathode. The plasma jet diverging from a small anode orifice enters the plasma expansion volume with a peripheral multipole magnetic field and after partial reflection from this field forms a uniform plasma emitter of 160 mm in diameter in the plasma grid plane. The plasma box operates with an arc current of 350–700 A, providing more than 75% of full energy specie in the extracted ion beam. The ion beam is subsequently neutralized in a hydrogen target with ∼50% efficiency and is focused 4 m downstream from the ion source that is provided by a spherical shape of the grids. The beam angular divergence is 0.6°. The ...

Commissioning of heating neutral beams for COMPASS-D tokamak.

Two neutral beam injectors have been developed for plasma heating on COMPASS-D tokamak (Institute of Plasma Physics, Prague). The 4-electrodes multihole ion-optical system with beam focusing was chosen to provide the low divergence 300 kW power in both deuterium and hydrogen atoms. The accelerating voltage is 40 kV at extracted ion current up to 15 A. The power supply system provides the continuous and modulated mode of the beam injection at a maximal pulse length 300 ms. The optimal arrangement of the cryopanels and the beam duct elements provides sufficiently short-length beamline which reduces the beam losses. The evolution of the impurities and molecular fraction content is studied in the process of the high voltage conditioning of the newly made ion sources. Two injectors of the same type have been successfully tested and are ready for operation at tokamak in IPP, Prague.

Results of upgrade of the diagnostic neutral beam injector for the TCV tokamak

A diagnostic neutral beam injector has been developed at BINP for beam emission spectroscopy measurements in TCV tokamak, Lausanne, Switzerland. The beam has been commissioned in 1999. It operates with a beam energy of up to 50 keV, equivalent neutral beam current (for hydrogen) up to 1 A and pulse duration up to 2 s. Plasma in the ion source is produced by inductively coupled 4.6 MHz radio-frequency discharge. Ions are extracted and accelerated by a four-grid ion optical system with 163 circular 4 mm i.d. apertures. The beam is to provide local measurements of plasma ion temperature, velocity, and impurity densities through active charge exchange recombination spectroscopy. The beam parameters of the diagnostic injector enabled to carry out the measurements at plasma density up to 5×1019 m−3. In order to improve signal to noise ratio in the charge exchange recombination spectroscopy (CXRS) measurements and extend the operational density up to 1020 m−3, the diagnostic injector has been upgraded in 2002. A...

Status of the GDT Experiment and Future Plans

In the recent experiments, on-axis transverse beta exceeding 0.4 in the fast ion turning points near the end mirrors has been achieved in the GDT experiment with 4 MW injection of 15-17 keV deuterium neutral beams at the center of the device. Neither enhanced transverse losses of the plasma nor anomalies in the fast ion scattering and slowing down were observed. The measured beta value is close to that needed in the versions of the GDT-based 14 MeV neutron source. At the same time, the electron temperature for given injection power and pulse duration is limited to 100-130eV. Its further increase is planned after upgrade of the injection system and increase of the magnetic field at the center of device up to 0.3T. Upgrade of the injection system assumes that neutral beam power incident on to the plasma will be increased up to 9-10 MW and pulse duration is extended from 1.2 to 5 ms. According to the results of numerical simulations, for the extended pulse duration a plasma steady state will be achieved with electron temperature of 250-320 eV, depending upon the assumptions on the transverse energy loss rate. Future experiments on the GDT-upgrade are discussed in the paper.

Installation and Operation of New Long Pulse DNB on Alcator C-Mod

A 50 kV, 7 amp, long-pulse (1.5-3.0 s) diagnostic neutral beam (DNB) built by the Budker Institute of Nuclear Physics in Novosibirsk has been installed on the Alcator C-Mod tokamak. The DNB is used for multiple diagnostics, including motional Stark effect (MSE), charge-exchange recombination spectroscopy (CXRS), and beam emission spectroscopy (BES). Facility required power is 1 MVA and is provided by a 5 kV electrical service. The 1.25 m3 DNB vacuum chamber is pumped using a 500 l/s turbo molecular pump, and two 50,000 l/s liquid helium cryo pumps. Mass flow controllers regulate the hydrogen gas flow to the source anode and cathode. A heated lanthanum hexaboride emitter is used for the arc cathode in order to provide an enhanced lifespan. The beam is extracted from a plasma arc source and accelerated by a set of perimeter-cooled molybdenum grids. Accelerated ions are partially neutralized in a gas cell, and the un-neutralized fraction is diverted by a bending magnet into a water cooled dump. A water cooled, instrumented movable calorimeter provides a target for test and conditioning shots. The neutralized beam is injected through a port duct into the C-Mod tokamak, and has a diameter specification of ~6 cm at the full-width half-maximum (FWHM) at the plasma. Spectroscopic measurements during initial commissioning have shown a full extracted energy fraction (at the source) of ~70% of beam current. Due to the high energy delivery capability of this diagnostic beam there is a risk of overheating the tokamak inner wall. A beam interlock system will incorporate the tokamak pulse state, plasma density, toroidal field, tokamak gas pressure, and an optical pyrometer aimed at the tokamak inner wall

Development of an RF-Ion Source for Plasma Diagnostic in the Magnetic Fusion Devices with Long Pulse Duration

A diagnostic neutral beam injector based on radiofrequency ion source has been developed at BINP, Novosibirsk for plasma diagnostics in magnetic fusion devices including magnetic mirrors with pulse duration up to several seconds, plasma density up to 1020 m-3 and plasma radius ~0.5m. It was observed that properties of the ceramic plasma box considerably changed after several hours of integrated operational time. After that, the proton specie in the beam essentially decreases. Eventually the proton component of the beam decreases approximately by 10% (from 60% down to 50% by current). This problem can be resolved by protection of the ceramic wall by a Faraday shield. We investigated the shield, which was made of aluminium tube with longitudinal slits and with a diameter close to that of the inner ceramic wall of the plasma box. This paper discusses the results of the beam composition measurements after installation of the Faraday shield.

Control System for the 1 MW Neutral Beam Injector

This paper presents general description of hardware and software of the neutral beam injector control system. The system is developed for control of the neutral beam injector which operates with 15-25 keV deuterium and hydrogen beams of 2 s maximum duration. It performs injection parameters calculation according to the desired beam power vs time curve, synchronizes and protects the injector subsystems and acquires its data during the shot. It also controls the injector operation between the shots. The system is based on an industrial computer with National Instruments PCIe boards: two PCIe-7842R reconfigurable input-output modules and a PCIe-6323 data acquisition module. An in-house developed interfacing module (cross-box) as well as serial to fiber optic converters are used for galvanic isolation and electrical compatibility with the injector subsystems. User interface software and PCIe boards programmable logic firmware are implemented in LabVIEW. Injection calculations and results acquired are represented with MATLAB. INTRODUCTION An 1 MW neutral beam injector has been designed and built by the Budker Institute of Nuclear Physics (Novosibirsk, Russia) for the TCV tokamak of the Swiss Plasma Center (Lausanne, Switzerland) [1]. The injector parameters are shown in the Table 1. It operates in the pulsed mode and is aimed to produce deuterium and hydrogen neutral beams with an ability of the beam on/off modulation with millisecond resolution and of gradually varying the power injected into tokamak. Table 1: Neutral Beam Injector Parameters Parameter Value Max power injected in tokamak 1 MW Beam power range 30 – 100 % Beam power stability ± 5 % Beam energy range 15 – 25 keV Max injection pulse duration 2 sec. Time delay between consecutive pulses 5 – 30 min. The injector consists of an ion source connected to a vacuum tank where the gas neutralizer, bending magnet, residual ion dumps and moving calorimeter are mounted. The injector subsystems are located in two areas: gas system, ignition system, vacuum system, thermocouple modules of movable calorimeter and ion dumps and some parts of the RF supply are mounted near the injector in the tokamak zone. The rest parts including high-voltage supply system, power supplies for the ion source grids and bending magnet, RF supply electronics as well as control system equipment are located in the electronics zone being 50 meters away. CONTROL SYSTEM The system to control the injector was decided to be based on an industrial computer with a set of embeddable input-output modules. As injector operates in pulsed mode all its subsystems must be synchronized carefully during the injection pulse (shot). Also care should be taken of monitoring the subsystems status between the shots. Total number of channels required to control the injector operation is as follows:  24 analog input channels with the rate of 5 kSamp/s for monitoring the subsystems operation during the shot;  8 analog output channels with 10 kSamp/s rate to control subsystems parameters during the shot;  16 digital output channels with the maximum rate of 10 kSamp/s used for subsystems synchronization during the shot;  16 digital input channels with 10 kSamp/s maximum rate used as interlocks during the shot and between the shots as well;  up to 40 digital input/output channels with the rate of less than 1 Samp/s to control and monitor the injector subsystems between the shots. Since the control system equipment is distanced from the injector itself and partly from its subsystems, it was decided to isolate the system galvanically and connect with distant injector elements using optical lines and communication interfaces to avoid interference and crosstalks from injector and tokamak operation. Hardware Shown on the Fig. 1 is the injector control system block diagram. A SuperLogics industrial computer SL-3UH77EB-GK with Windows 7 OS is chosen to run the control system software. It uses three PCI Express data acquisition modules by National Instruments as peripherals. Two of them are PCIe-7842R [2]: these reconfigurable input-output modules are based on a userprogrammable Virtex-5 FPGA. Each module also has 16bit resolution analog outputs with independent rate of up to 1 MSamp/s and analog inputs up to 200 kSamp/s. Another module used is PCIe-6323 data acquisition device [3] with 32 analog inputs of 16-bit resolution and 250 kSamp/s rate. Synchronization between PCIe modules is implemented by means of RTSI bus. ___________________________________________ * This work supported in part by the Swiss National Science Foundation. †V.V.Oreshonok@inp.nsk.su THPSC077 Proceedings of RuPAC2016, St. Petersburg, Russia ISBN 978-3-95450-181-6 712 C op yr ig ht

Ion Source for 10 sec Diagnostic Neutral Beam

The ion source for along pulse operating diagnostic neutral beam injector has been developed. The ion source has to form an 8 A, 60 keV hydrogen ion beam. The ion source consists of an RF-plasma driver and a four grids ion-optical system. Both ion-optical system and plasma driver have an augmented water-cooling system. Geometry of the ion-optical system was optimized by the numerical simulations in order to achieve the minimal beam angular divergence. The performance of the developed water-cooling system of the ion source was numerically simulated. Design of the developed ion source and experimental and numerical simulations results are presented in the paper.