In 2020 a modernized tokamak T-15MD (R=1.5 m, a=0.67 m, κ=1.8, Ipl≤2 MA, Bt≤2 T, discharge duration ≤10 s, Paux≤24 MW) will be launched in the National Research Center “Kurchatov Institute”. For this installation, a modern Charge eXchange Recombination Spectroscopy (CXRS-diagnostics) has been developed. It can function both on a diagnostic injector (EDNB=60 keV) and heating injector (ENBI=80 keV) . CXRS-diagnostics of T-15MD can be used to measure local values of the following plasma parameters with high spatial (≈1 cm) and temporal (≈1 ms) resolutions: ion temperature (Ti), density of main gas and light impurities nuclei (nz), toroidal and poloidal rotation velocity (Vpol, Vtor) and the fast-ion spectrum. The composition of the CXRS-diagnostic complex and its schematic is presented. Its main components are the DNB (H, 60 keV, 150 kW), four spectrometers (two of them based on Echelle gratings, one based on holographic grating and another utilizes both types of gratings), and EMCCD-cameras. The attenuation of the diagnostic beam in the plasma is calculated considering its ionization and charge exchange by the main gas and impurities (C, O), as well as electron impact ionization. The intensities of active and passive components of λ=5291 Åline of C5+ ion are calculated considering the line fine structure, Doppler, and Zeeman effects. The active and passive signals emitted by C5+ ion are estimated for toroidal and poloidal registration systems. It is established that the acquisition time of 1 – 3 ms is enough to achieve the valid signal level to measure Ti with a statistical error ≈ 3 %. The calculated ratio between the active and passive CXRS-signal in the plasma center is 2.2 – 3.7. Measurement error is estimated for λ=5291 ÅCX-line and calculations show low measurement errors for Ti and nz (around 2 – 5 %), Vpol and Vtor (around 2 km/s). This indicates that CXRS-diagnostics have potential to provide reliable and accurate measurements of the named plasma parameters on T-15MD.

CXRS diagnostics supply a set of important plasma parameters of fusion plasmas. According to the system requirements, the CXRS diagnostics in ITER should supply plasma velocity (poloidal and toroidal), impurity ion densities and ion temperatures. The ITER CXRS-edge diagnostic system must measure these parameters over the outer half of the plasma radius. The use of CXRS in ITER encounters serious challenges. In the paper the decisions made to overcome these difficulties for ITER CXRS-edge diagnostics system are described. Testing results of single-crystal Mo prototypes of first mirror are presented. The results of image quality modelling of optical scheme, where the in-vacuum optics uses only mirrors and all lenses are in the air part rather far from plasma, are presented. The results of laboratory test of the device developed for CXRS-edge on the base of transmission holographic gratings are presented.

The development of cleaning optics and deposition-mitigating techniques is a key factor in the construction and operation of optical diagnostics in ITER. The cleaning of optical surface by pulsed radiation from a fiber laser is an effective method that can recover optical properties of the mirror surface. The possibility of cleaning metallic mirrors from films with complex composition by pulsed radiation from a fiber laser has been experimentally researched. It has been shown that high initial reflection characteristics of optical elements can be recovered by choosing regimes of radiation effect on the deposited surface. Efficient cleaning is ensured by radiation with the power density of less than 107 W/cm2. At this relatively low power density, pollutions are removed in a solid phase and the thermal effect on the mirror is insignificant. Preliminary experiments of the metal mirrors cleaning by fiber laser radiation have demonstrated the possibility of hardware implementation techniques. Experiments on transport of laser radiation to the metal mirror by using a system of lens and cleaning showed the possibility of a hardware implementation of methods applicable in the geometry of the port-plug ITER.

Since the first feasibility studies of active beam spectroscopy on ITER in 1995 the proposed diagnostic has developed into a well advanced and mature system. Substantial progress has been achieved on the physics side including comprehensive performance studies based on an advanced predictive code, which simulates active and passive features of the expected spectral ranges. The simulation has enabled detailed specifications for an optimized instrumentation and has helped to specify suitable diagnostic neutral beam parameters.Four ITER partners share presently the task of developing a suite of ITER active beam diagnostics. which make use of the two 0.5 MeV/amu 18 MW heating neutral beams and a dedicated 0.1 MeV/amu, 3.6 MW diagnostic neutral beam. The IN ITER team is responsible for the DNB development and also for beam physics related aspects of the diagnostic. The RF will be responsible for edge CXRS system covering the outer region of the plasma (1 > r/a > 0.4) using an equatorial observation port, and the EU will develop the core CXRS system for the very core (0 < r/a < 0.7) using a top observation port. Thus optimum radial resolution is ensured for each system with better than a/30 resolution. Finally, the US will develop a dedicated MSE system making use of the HNBs and two equatorial ports. With appropriate modification, these systems could also potentially provide information on alpha particle slowing-down features..On the engineering side, comprehensive preparations were made involving the development of an observation periscope, a neutron labyrinth optical system and design studies for remote maintenance including the exchange of the first mirror assembly, a critical issue for the operation of the CXRS diagnostic in the harsh ITER environment.Additionally, an essential change of the orientation of the DNB injection angle and specification of suitable blanket aperture has been made to avoid trapped particle damage to the first wall. (C) 2010 Elsevier B.V. All rights reserved.

In burning plasma fusion devices, fast ion transport plays a central role in the performances of the machines. Moreover the losses of energetic particles might cause severe damages on plasma facing components. Therefore real time measurements of fast ion transport would provide valuable information for safe and reliable plasma operations. In this paper, we examine the feasibility of a monitoring system based on active charge exchange recombination spectroscopy making use of the 0.5 MeV/amu ITER heating neutral beams for detecting fast (4)He(+2) (alphas) particles in ITER plasmas. There are two time scales relevant to fast ion dynamics: the first is the slowing down time of the distribution function which is of the order of 1 s, and the second is the time scale of burstlike transport events such as collective Alfven mode excitations, which--for typical ITER plasma parameters--can be as low as 0.2-1 ms. To detect such fast events a broadband high-throughput spectrometer is needed, while for the reconstruction of the alpha velocity distribution function a higher resolution spectrometer and longer integration time are necessary. To monitor a spatial redistribution of fast particles due to the propagation of the instability, it is proposed to use a limited number of spatial channels, looking at the charge exchange He II spectra induced by the heating beams, whose energy matches the slowing down energies of fast particles. The proposal is to share the motional stark effect periscope on equatorial port 3 [A. Malaquias et al., Rev. Sci. Instrum. 75, 3393 (2004)] adding additional fibers and suitable instruments. A signal to noise ratio of 5 could be achieved with a spatial resolution of a/15 and a time resolution of 5 ms, in a broad spectral band of 100 A, corresponding to the spectral broadening of the line emitted by alpha particles with energies DeltaE < or = 1.5 MeV. Fast H and D ion populations created by heating neutral beam or ion cyclotron resonance heating are expected to produce significantly lower charge exchange signal levels and can only be monitored on substantially longer time scales as it is expected because of the strong energy difference with respect to the heating neutral beam and the consequently low charge exchange cross sections.

A reassessment of the proposed package of beam aided diagnostic systems for ITER has led to a number of new developments. As a result of a joint development effort and comprehensive optimisation studies it was decided to use two separate diagnostic observation periscope assemblies both dedicated to CXRS (Charge Exchange Recombination Spectroscopy) and BES (Beam Emission Spectroscopy), which will exploit a Diagnostic Neutral Beam injected radially into the plasma: A ‘Core CXRS’ system (EU) which covers dominantly the inner half of the confined plasma, and an ‘Edge CXRS’ system (RF) which ensures a high radial resolution in the outer half of the plasma. The Core system utilises an upper port periscope (U-port-3), and two periscopes located in an equatorial port (E-port-3) are envisaged for the Edge CX system. The equatorial port is shared with a dedicated MSE (Motional Stark Effect) system for the measurement of magnetic field pitch angles making use of the Heating Neutral Beams. A complementary MSE approach is proposed for the exploitation of intensity line ratios as measured by the BES data from upper and equatorial ports. More recently, at the 10 ITPA meeting on ITER diagnostics at Moscow in April 2006, it was proposed to share the use of Core and Edge periscopes with the new ITER partner India, and introduce a package of Beam related diagnostics in order to optimise instrumentation for CXRS and BES. The optical layouts of the two periscope systems have been recently reviewed and alignment and instrumentation schemes were developed. A comprehensive multi-parameter spectral modelling effort based on an ITER reference scenario (ne(0)=10m, Te(0)=Ti(0)=20keV, B=5.2T, Zeff=1.6) the actual observation geometry, and modelling of atomic processes, has enabled an update of expected performances in terms of measurement accuracies, time and spatial resolution. Summarising the results of the performance study we can conclude that the measurement of radially resolved profiles of ion temperature, plasma rotation and ion densities, including that of the helium ash, are a realistic feasibility and expected parameter errors are compatible with the specifications laid down in the ITER “Measurement requirement table”. Moreover, spectral Signal-To-Noise numbers well above 10 are expected for the main part of the confined plasma, that is for 0.2

A status report is given on recent joint activities on the ITER CXRS and BES diagnostic package. Expected measurement performances are reviewed as well as comprehensive discussions are led on an integral approach to the implementation of Core and Edge CXRS observation periscopes. The “first mirror” location, its operational temperature, maintenance issues, and optimization of optical imaging are addressed. In parallel to more technical aspects, particular attention has also been given to the development of common evaluation and modeling tools. One part of this work is linked to the modeling of spectra for existing fusion devices and their CXRS diagnostics and extrapolation to the ITER environment. The purpose of this effort is to provide tools for the optimization of spectroscopic instrumentation, and moreover, the specifications of a suitable diagnostic beam.

An overview is given of the present design of the active beam spectroscopy diagnostics for the ITER. Present spatial resolution and signal-to-noise indicate that, in principle, all proposed measurements are possible covering the entire plasma minor radius. Calculations show that the mirror based periscopes and the impurity coating of the first mirror affect the signal strength and the polarization characteristics of the measured spectra having an impact in the measurement accuracy. On-line calibration techniques and methods to access the first mirror status are addressed.

Supporting pilot experiments and activities which are currently considered or already performed for the development of the International Thermonuclear Experiment Reactor active beam spectroscopy diagnostic are addressed in this article. Four key issues are presented including optimization of spectral instrumentation, feasibility of a motional Stark effect (MSE) evaluation based on line ratios, “first-mirror” test-bed experiments at the tokamak TEXTOR, and finally the role of integrated data analysis for the conceptual layout of the change exchange recombination spectroscopy and MSE diagnostic.

Active charge exchange recombination spectroscopy (CXRS) is used in most of the present fusion experiments as a proven tool for local measurements of the main ions in the plasma [R. Isler, Plasma Phys. Controlled Fusion 36, 171 (1994)]. A comprehensive diagnostic coverage of intrinsic and injected impurities is essential for any self-consistent plasma simulation and prediction of plasma performance. In particular, for the assessment of local helium ash densities [M. von Hellermann et al., Plasma Phys. Controlled Fusion 35, 799 (1993)], CXRS will play a key role for future fusion devices such as ITER. However, it should be emphasized that any helium ash analysis is only viable in a fully diagnosed plasma, that is, all other ions need to be measured as well. Two fundamental limitations are considered in the following assessment. First is the detectability of a weak CX signal against a strong background of plasma continuum radiation. A second, equally important requirement is the accuracy with which local neutral beam densities can be established in order to derive absolute ion densities from the extracted active CX signals. The second problem can be approached either by experimental data from beam emission spectroscopy (M. von Hellerman et al., Conference on Advanced Diagnostics for Magnetic and Inertial Fusion Varenna, Sept. 2001), or calculated by beam attenuation codes using electron and both bulk and impurity ion density profiles. This report includes a description of the CXRS measurement concept, the experimental and optical scheme of measurements for ITER (S. Tugarinov et al., Conference on Advanced Diagnostics for Magnetic and Inertial Fusion, Varenna, Sept. 2001), and the main conclusions and recommendation that we have made from the results of a signal-to-noise (SN) value calculations. The main conclusions are the following: CXRS at ITER appears to be a viable diagnostic tool and the projected diagnostic neutral beam will provide adequate SN ratios for spectral analysis. A comprehensive approach to helium ash measurement, making use of a simultaneous measurement of the main low-Z impurities, will considerably increase the overall data consistency and will also significantly reduce the statistical error of each single impurity density determination. Three periscopes located in upper port for the intrinsic impurity measurements will also provide ion temperature, plasma rotation, and deuteron density profiles.

Natural diamond detector (NDD) performance was studied up to a neutron fluence of 10(15) neutron/cm(2). The variations of the NDD spectrometric response to incident alpha-particles from Am-241 source after exposure to fast neutron fluences up to 3 x 10(16) n/cm(2) were examined. No significant variations up to the level of 10(14)n/cm(2) were observed. Degradation of charge collection efficiency at higher fluences is reported. No remarkable increase of the NDD leakage current and count rate change had been observed up to a neutron fluence of 3 x 10(16)n/cm(2). The charge collection efficiency variations of neutron irradiated diamond spectrometer were studied ex situ under gamma-rays, beta-radiation and visible light excitation. Charge collection efficiency restoration up to 75% level and the NDD performance stabilization by extrinsic low-intensity visible light (550 nm < lambda < 800 nm) or intrinsic excitations have been demonstrated. (C) 2002 Elsevier Science B.V. All rights reserved.

Partial pressure neutral gas measurements have been made using a commercial Penning gauge in conjunction with an “active spectrometer.” In prior work utilizing band pass filters and conventional spectrometers, trace concentrations of the hydrogen isotopes H, D, T and of the noble gases He, Ne, and Ar were determined from characteristic spectral lines in the light emitted by the neutral species of these elements. For all the elements mentioned, the sensitivity was limited by spectral contamination from a pervasive background of molecular hydrogen radiation. The active spectrometer overcomes this limitation by means of a digital lock-in method and correlation with reference spectra. Preliminary measurements of an admixture containing a trace amount of neon in deuterium show better than a factor of 20 improvement in sensitivity over conventional techniques. This can be further improved by correlating the relative intensities of multiple lines to sets of reference spectra.

Recent measurements of the two-dimensional (2-D) spatial profiles of divertor plasma density, temperature, and emissivity in the DIII-D tokamak [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] under highly radiating conditions are presented. Data are obtained using a divertor Thomson scattering system and other diagnostics optimized for measuring the high electron densities and low temperatures in these detached divertor plasmas (ne⩽1021 m−3, 0.5 eV⩽Te). D2 gas injection in the divertor increases the plasma radiation and lowers Te to less than 2 eV in most of the divertor volume. Modeling shows that this temperature is low enough to allow ion–neutral collisions, charge exchange, and volume recombination to play significant roles in reducing the plasma pressure along the magnetic separatrix by a factor of 3–5, consistent with the measurements. Absolutely calibrated vacuum ultraviolet spectroscopy and 2-D images of impurity emission show that carbon radiation near the X-point, and deuterium radiation near the target plates contribute to the reduction in Te. Uniformity of radiated power (Prad) (within a factor of 2) along the outer divertor leg, with peak heat flux on the divertor target reduced fourfold, was obtained. A comparison with 2-D fluid simulations shows good agreement when physical sputtering and an ad hoc chemical sputtering source (0.5%) from the private flux region surface are used.

In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma separates the first wall from the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also,serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be required in the next generation of tokamaks, for without it the divertor engineering requirements are very demanding. To successfully demonstrate a radiative divertor, a highly radiative condition with significant volume recombination must be achieved in the divertor, while maintaining a low impurity content in the core plasma.Divertor plasma properties are determined by a complex interaction of classical parallel transport, anomalous perpendicular transport, impurity transport and radiation, and plasma-wall interaction. In this paper we will describe a set of experiments on DIII-D designed to provide detailed two-dimensional documentation of the divertor and SOL plasma. Measurements have been made in operating modes where the plasma is attached to the divertor strike plate and in highly radiating cases where the plasma is detached from the divertor strike plate. We will also discuss the results of experiments designed to influence the distribution of impurities in the plasma using enhanced SOL plasma flow. Extensive modelling efforts will be described which are successfully reproducing attached plasma conditions and are helping to elucidate the important plasma and atomic physics involved in the detachment process.

This paper presents a comparison of the total radiated power profile and impurity line emission distributions in the SOL and divertor of DIII-D. This is done for ELMing H-mode plasmas with heavy deuterium injection (partially detached divertor operation, PDD) and those without deuterium puffing. Results are described from a series of dedicated experiments performed on DIII-D to systematically measure the 2D (R, Z) structure of the divertor plasma. The discharges were designed to optimize measurements with new divertor diagnostics including a divertor Thomson scattering system. Discharge sequences were designed to produce optimized data sets against which SOL and divertor theories and simulation codes could be benchmarked. During PDD operation the regions of significant radiated power shift from the inner divertor leg and SOL to the outer leg and X-point regions. Dα emission shifts from the inner strikepoint to the outer strikepoint. Carbon emissions (visible CII and CIII) shift from the inner SOL near the X-point to a distributed region from the X-point to partially down the outer leg during moderate D2 puffing. In heavy puffing discharges the carbon emission coalesces on the outer separatrix near the X-point and for very heavy puffing it appears inside the last closed flux surface above the X-point. Calibrated spectroscopic measurements indicate that hydrogenic and carbon radiation can account for all of the radiated power. Lα and CIV radiation are comparable and when combined account for as much as 90% of the total radiated power along chords viewing the significant radiating regions of the outer leg.

by M.E. Fenstermacher, R.D. Wood, S.L. Allen, N.H. Brooks, D.A. Buchenauer, T.N. Carlstrom, J.W. Cuthbertson, E.J. Doyle, T.E. Evans, P.-M. Garbet, R.W. Harvey, D.N. Hill, A.W. Hyatt, R.C. Isler, G. Jackson, R.A. James, R. Jong, C.C. Klepper, C.J. Lasnier, A.W. Leonard, M.A. Mahdavi, R. Maingi, W.H. Meyer, R.A. Moyer, D.G. Nilson, T.W. Petrie, G.D. Porter, T.L. Rhodes, M.J. Schaffer, R.D. Stambaugh, D.M. Thomas, S. Tugarinov, M.R. Wade, J.G. Watkins, W.P. West, and D.G. Whytej