Diagnostic Neutral Beam Research Articles

The ITER neutral beam front end components integration

The neutral beam (NB) system for ITER is composed of two heating neutral beam injectors (HNBs) and a diagnostic neutral beam injector (DNB). A third HNB can be installed as a future up-grade. This paper will present the design development of the components between the injectors and the tokamak; the so-called ‘front end components’: the drift duct consists of the NB bellows and the drift duct liner, the vacuum vessel pressure suppression system box (VVPSS box), the absolute valve, and the fast shutter. These components represent the key links between the ITER tokamak and the vessels of the NB injectors. The design of these components is demanding due to the different loads that these components will have to stand.The paper will describe the different design solutions which have to be implemented regarding the primary vacuum confinement, the power handling capability and the remote maintenance operations. The sizes of the components are determined by the large cross section of the neutral beam. The power handling capability is driven by the anticipated re-ionization of the neutral beam and the electromagnetic fields in this region. The drift duct bellows (with an inner diameter of 2.5m) shall guarantee a leak tight vacuum enclosure during the vertical and radial displacements of the ITER vacuum vessel. The conductance of the VVPSS box must be maximized in the available space. The absolute valve remains a challenging development. The total leak rate through the valve must be ≤1×10−8Pam3/s when the valve is closed. Due to the radiation environment, the seals of the gate valve will be metallic. An R&D program has been launched to develop a suitable metallic seal solution with the required dimensions. The maximum allowed closing time for the fast shutter shall be less than 1s. For all these components the leak tightness will be guaranteed by a welded lip seal and the mechanical stability by bolted structures.

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.

The Beam Profile Calculation for Diagnostic Neutral Beam on HT-7 Tokamak

A new calculation method is introduced for convergence beam intensity. The program based on this method is prepared for beam intensity distribution and beam power calculation. Taking the HT-7 DNB as a reference, the beam profile calculated by program is similar with that of Gaussian fit of experimental data.

Measurements with magnetic field in the National Spherical Torus Experiment using the motional Stark effect with laser induced fluorescence diagnostic

The motional Stark effect with laser-induced fluorescence diagnostic (MSE-LIF) has been installed and tested on the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Lab. The MSE-LIF diagnostic will be capable of measuring radially resolved profiles of magnetic field magnitude or pitch angle in NSTX plasmas. The system includes a diagnostic neutral hydrogen beam and a laser which excites the n = 2 to n = 3 transition. A viewing system has been implemented which will support up to 38 channels from the plasma edge to past the magnetic axis. First measurements of MSE-LIF signals in the presence of small applied magnetic fields in neutral gas are reported.

Thermal and hydraulic performance of the helium-operated shutter protecting the first mirror of the ITER diagnostics

The ITER core charge exchange recombination spectroscopy (core CXRS) is a diagnostic system designed to collect the light emitted from interaction of the Diagnostic Neutral Beam (DNB) with the core plasma and guides it via a mirror labyrinth through the Upper Port Plug toward a fiber bundle, which then transmits the light to a set of spectrometers for spectral analysis. The first mirror (M1), being the most important part of the optical system which defines workability of the entire CXRS, works in direct view of the plasma. The latter strongly impacts the mirror causing its surface erosion and deposition with degradation of the optical capability. The fast shutter (FS) is supposed to play the main role in reducing the time of the first mirror exposition to the plasma. The performed work is focused on the detailed thermal and hydraulic analyses of the main components of the M1 protecting device (blades, arms and actuator) and its cooling and pneumatic systems. The performed analysis confirms, in general, the workability of the helium-operated shutter and verifies the pneumatic actuation concept proposed for the M1 protecting device.

DNB exit scraper—Concept and engineering

The 100kV negative hydrogen ion source based Diagnostic Neutral Beam (DNB) injector is part of the Indian procurement for ITER. The DNB is designed to deliver an 18–20A hydrogen neutral beam to the ITER plasma. The exit scraper (ES) defines the profile of the beam after it leaves the calorimeter, the last Beam Line Components (BLCs) during operation. BTR11Developed by the Russian Research Centre, Kurchatov Institute, Moscow, Russia. and PDP1 codes are used to obtain the optimum entry and exit opening dimensions of the ES, so as to deliver the maximum power to the tokamak plasma, and to limit the power to downstream components due to beam interception, to protect front end components from the interception of re-ionized devious particles. Each horizontal heat transfer (HT) panel of ES receives a total power of 85kW for each symmetric 10mrad beam (worst case scenario) with peak power density of 1.17MW/m2. The thermo hydraulic design is carried out to withstand the heat flux due to the beam interception on the ES. The mechanical design of the ES is carried out by considering the spatial constraints in the DNB system and the remote handling (RH) system. In the present design, the copper heat transfer panels are directly bolted to the structural member. Protection shall be incorporated to ensure that there is no exposure of the bolt head. The thermo-mechanical analysis has been carried out for the normal, off-normal (accidental/worst-case) events of the ITER DNB. During normal operation, the maximum possible von Mises stress of the order of 62.4MPa can be expected on the bottom heat transfer panel, and the corresponding deflection of the structure is of the order of 0.62mm. All the stress checks were carried out with respect to the Structural Design Criteria for In-vessel Components (SDC-IC) criterion. The paper shall present the ES design highlighting its salient features.

Fluctuation BES measurements with the ITER core CXRS prototype spectrometer

The ITER core CXRS diagnostic system collects the light emitted from the interaction of the diagnostic neutral beam with the core plasma and guides it via a mirror labyrinth through the upper port plug #3 towards a fiber bundle, which then transmits the light into a set of spectrometers for spectral analysis. In order to test the accessibility of the special parameter range required for the ITER measurement, a prototype spectrometer was built and operated successfully at the TEXTOR tokamak. In addition to the He/Be, C/Ne and H/D/T regular spectral channels, a fluctuation beam emission spectroscopy (BES) system has been integrated to measure core MHD activity, and validate corresponding ITER simulation results. The fluctuation system can be operated as an alternative to the spectral BES measurement, and has 8 spatial channels sampled at 2MHz. In this paper, we present details of the fluctuation BES system and its interface to the ITER prototype spectrometer along with simulation and measurement results at TEXTOR. We show that the measurement fully confirms the simulation results on achievable photon current at the detector and on the signal to noise ratio.

Status of ITER neutral beam cell remote handling system

The ITER neutral beam cell will contain up to three heating neutral beams and one diagnostic neutral beam, and four upper ports.Though manual maintenance work is envisaged within the cell, when containment is breached, or the radiological protection is removed the maintenance must be conducted remotely.This maintenance constitutes the removal and replacement of line replaceable units, and their transport to and from a cask docked to the cell. A design of the remote handling system has been prepared to concept level which this paper describes including the development of a beam line transporter, beam source remote handling equipment, upper port remote handling equipment and equipment for the maintenance of the neutral shield. This equipment has been developed complete the planned maintenance tasks for the components of the neutral beam cell and to have inherent flexibility to enable as yet unforeseen tasks and recovery operations to be performed.

A high etendue spectrometer suitable for core charge eXchange recombination spectroscopy on ITER

A feasibility study for the use of core charge exchange recombination spectroscopy on ITER has shown that accurate measurements on the helium ash require a spectrometer with a high etendue of 1mm(2)sr to comply with the measurement requirements [S. Tugarinov et al., Rev. Sci. Instrum. 74, 2075 (2003)]. To this purpose such an instrument has been developed consisting of three separate wavelength channels (to measure simultaneously He/Be, C/Ne, and H/D/T together with the Doppler shifted direct emission of the diagnostic neutral beam, the beam emission (BES) signal), combining high dispersion (0.02 nm/pixel), sufficient resolution (0.2 nm), high efficiency (55%), and extended wavelength range (14 nm) at high etendue. The combined measurement of the BES along the same sightline within a third wavelength range provides the possibility for in situ calibration of the charge eXchange recombination spectroscopy signals. In addition, the option is included to use the same instrument for measurements of the fast fluctuations of the beam emission intensity up to 2 MHz, with the aim to study MHD activity.

Feasibility of non-thermal helium measurements with charge exchange spectroscopy on ITER

The use of active charge exchange recombination spectroscopy (CXRS) as a diagnostic for fusion-produced alpha particles on ITER is constrained by the signal-to-noise ratio, which is determined by the intensity of the line of interest, the optical throughput of the diagnostic, the neutral beam penetration, and the intensity of bremsstrahlung radiation. The CX spectral line for fast ions has been modelled together with the expected background emission and we present the signal-to-noise ratios calculated as a function of the diagnostic design parameters. Combining the CXRS data from both the heating and the diagnostic neutral beams on ITER, information on fast ions with energies up to 1 MeV can be obtained for the parameters of the ITER core CXRS diagnostic design. To achieve this, energy binning of the signal is used (100 keV bins or larger), in order to improve the signal-to-noise ratio, with a time resolution of 2 s. The time resolution of the measurement can be improved using a higher throughput spectrometer, but this is ultimately limited by the amount of light from the neutral beam that can be collected. Despite the challenges and the fact that the results are not as optimistic as previously assumed, it is concluded that useful information on fast helium density profiles can be obtained using CXRS on ITER.

Use of the focusing multi-slit ion optical system at RUssian Diagnostic Injector (RUDI)

The upgrade of the diagnostic neutral beam injector RUDI in 2010 was performed to increase the beam density at the focal plane in accordance with the requirements of charge-exchange recombination spectroscopy diagnostics. A new focusing ion-optical system (IOS) with slit beamlets and an enlarged aperture was optimized for 50% higher nominal beam current and reduced angular divergence with respect to the previous multi-aperture IOS version. The upgraded injector provides the beam current up to 3 A, the measured beam divergence in the direction along the slits is 0.35°. Additionally, the plasma generator was modified to extend the beam pulse to 8 s.

The European Supplied Components of the ITER Vacuum Pumping Systems

The ITER Vacuum Pumping systems are designed to pump hydrogen isotopes, including tritium, helium and impurities. The EU is responsible for the in-kind supply of 8 torus-, 2 cryostat-, 3 Heating Neutral Beam-(HNB) and 1 Diagnostic Neutral Beam-(DNB) cryopumps, their 14 Cold Valve Boxes (CVBs) and the cryolines between them as well as the Leak Detection and Localization (LD&L) systems. The design of these systems has progressed well in the past with the exception of LD&L, where the results of a significant R&D program are required to define the design. The torus and cryostat cryopumps incorporate an inlet vacuum valve capable of controlling the pumping speed and require to be sufficiently instrumented for performance and inventory control. In order to fully define the related Procurement Arrangements (PA) and minimize any technological, programmatic or cost risks, a 1:1 Pre-Production cryopump (PPC) has been planned to be built and tested as well as a series of necessary R&D activities will need to be performed. These activities will address all technological challenges, specify the instrumentation needs of these Vacuum Pumping systems and analyze their performance, incorporating also all safety provisions and remote handling requirements.

Note: Multi-point measurement of |B| in the gas-dynamic trap with a spectral motional Stark effect diagnostic

An upgraded spectral motional Stark effect diagnostic has been installed on the gas-dynamic trap (GDT) experiment to enable spatially resolved measurement of |B|. A new low-noise charge-coupled device detector, combined with enhancements of the diagnostic neutral beam, allows single-shot profile measurements. Previously only single-point motional Stark effect measurements were possible, and detector noise severely limited measurement precision, requiring multi-shot averaging. The plasma pressure profile in GDT is derived from the measured diamagnetic modification of |B| and used to examine the conditions of stable plasma confinement at high plasma pressure.

Design optimization of the 100 kV HV bushing for ITER-DNB

The 100 kV bushing of the Diagnostic Neutral Beam (DNB) injector is a cylindrical feedthrough which forms the interface between the gas insulated transmission line and the torus primary vacuum and provides all necessary services to the beam source. All conventions for safety, voltage holding requirement, vacuum compatibility and the choice of materials have been addressed in the design. Finite Element Analyses (FEAs) for the electrostatic and the structural configuration is carried out to validate the design of the High Voltage Bushing (HVB). Several iterations and optimizations of the stress shields are carried out to meet electrostatic criteria, especially at the triple point (the ceramic, metal and vacuum joint), which is critical for good voltage holding. Structural analyses is carried out to assess the stress distribution in the fiber reinforced plastic insulator, the alumina insulator and the integrated HVB for different load cases like operational orientation (horizontal), normal operation and accidental case. Design is further validated for seismic conditions for Seismic Loading-2 (SL-2).

Electromagnetic transients simulation using a shell approach for ITER cCXRS upper port plug due to plasma vertical displacement events

Transient electromagnetic (EM) analysis is presented focusing on main components of the ITER core charge exchange recombination spectroscopy (cCXRS) port plug developed by Forschungszentrum Jülich (FZJ), ITER-NL and UKAEA(CCFE) in 2009. The cCXRS primary function is to transfer the light in the visible part of spectra emitted by interaction of the plasma ions with a diagnostic neutral beam. The TYPHOON software package has been used for the EM analysis. The code is dedicated for simulation of transient electromagnetic processes using a shell approach in the integral–differential formulation to represent conducting structures with a set of multi-connected shells arbitrary located in a space. The advantage of the shell approach is a higher flexibility in modelling detailed structures as compared with widely used 3D models. On the other hand, the shell approach requires ultimate care in modelling relatively thick structures. These issues are discussed in the paper. Two vertical displacement events (VDE) which seem to result in the largest EM loads on the main cCXRS components have been agreed with FZJ and simulated. Transient electromagnetic processes caused by different sources have been considered separately, and then superimposed to obtain the total solution. Three types of transient processes for each type of VDE have been analyzed: (1) due to variations of a toroidal plasma current, shape and position and due to variations of poloidal field coils (PFC) and central solenoid (CS) currents, (2) due to variations of the Halo current and (3) due to variations of a toroidal magnetic flux of plasma. The analysis covers two options for electrical contact between the main shell (MS) of the port plug and the blanket shield module (BSM). The results are supposed to be used for benchmarking with independent 3D EM models developed for the upper port plug.

Spectroscopic Determination of the Species Fractions and the Power Profiles of the Diagnostic Neutral Beam on the HT-7 Tokamak

Spectroscopic Determination of the Species Fractions and the Power Profiles of the Diagnostic Neutral Beam on the HT-7 Tokamak

An Indian test facility to characterise diagnostic neutral beam for ITER

The diagnostic neutral beam (DNB) line shall be used to diagnose the He ash content in the D–T phase of the ITER machine using the charge exchange recombination spectroscopy (CXRS). Implementation of a successful DNB at ITER requires several challenges related to the production, neutralization and transport of the neutral beam over path lengths of 20.665 m, to be overcome. The delivery is aided if the above effects are tested prior to onsite commissioning. As DNB is a procurement package for INDIA, an ITER approved Indian test facility, INTF, is under construction at Institute for Plasma Research (IPR), India and is envisaged to be operational in 2015. The timeline for this facility is synchronized with the RADI, ELISE (IPP, Garching), SPIDER (RFX, Padova) in a manner that best utilization of configurational inputs available from them are incorporated in the design. This paper describes the facility in detail and discusses the experiments planned to optimise the beam transmission and testing of the beam line components using various diagnostics.

ITER DNB ion source movement mechanism

The 100 kV negative hydrogen ion source based Diagnostic Neutral Beam (DNB) injector, a part of Indian (IN) Procurement Package for ITER. DNB is expected to deliver 18–20 A of hydrogen neutral beam to the ITER plasma through a narrow blanket aperture of size 0.40( H) × 0.45( V) m 2, at a distance ∼20.67 m from the ion source position. Due to long transport length, a small misalignment of the ion source will cause significant transmission loss of the beam and produce asymmetric heat load on the beamline components and on the duct assembly. Mechanical misalignment and deflection due to tokamak stray magnetic field are also envisaged and therefore ion source positional adjustment is needed during DNB operation. This can be addressed by making provisions for the desired vertical and horizontal movements in the ion source support structure. Two independent translations for horizontal angular and linear misalignment adjustment are achieved by means of “master–slave” configuration arrangement in the support structure. The force analysis of the movement mechanism of the ion source support structure is carried out analytically by statics and generates inputs for an engineering design of such movement mechanism and discussed in the manuscript.

Development of Focused Neutral Beams with Small Angular Divergence for Plasma Heating and Diagnostics

A series of neutral beam injectors for plasma heating and diagnostics in modern magnetic fusion devices has been developed in the Budker Institute of Nuclear Physics. In ion sources of these injectors arc discharge or RF plasma boxes are used. Ion optical systems are optimized to produce ion beams with a low enough angular divergence. In order to provide beam focusing, the grids are formed as spherical segments. Such ballistically focused beams are further neutralized in a gas target and subsequently are used to heat or diagnose plasma. Obtained diagnostic neutral beams with precise focusing are widely used to measure plasma parameters by beam emission spectroscopy methods in tokamaks, stellarators, reversed field pinches and open traps. High power focused beams with small divergence are also necessary for heating of localized regions of plasma and in the devices with narrow access ports through which only small size, high power density beams can be transported. Transition to steady state operation regime of the injectors is discussed.

Performance of Diagnostic Neutral Beam for the HT-7 Tokamak

Diagnostic neutral beam (DNB), combined with spectral diagnostics, is employed to measure the ion temperature in HT-7. The factors affecting the extracted beam are studied in the experiment for the high performance diagnostic neutral beam. A 6.5 A extracted hydrogen current at 43 keV of 100 ms was obtained after optimization. The extracted beam has a proton ratio as high as 40%, and can penetrate into the core plasma after neutralization to measure the ion temperature effectively.