scispace - formally typeset
Search or ask a question
Journal ArticleDOI

Pilot experiments for the International Thermonuclear Experimental Reactor active beam spectroscopy diagnostic

TL;DR: 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 the role of integrated data analysis for the conceptual layout of the change exchange recombination spectroscopy and MSE diagnostic.
Abstract: 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.

Summary (2 min read)

Introduction

  • 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.
  • A comprehensive package of active beam based spectroscopy tools for the International Thermonuclear Experimental Reactor(ITER) has been developed and a final summary was recently completed.
  • More quantitative studies and modeling will be required in this field.
  • The effects of carbon and beryllium coatings on reflectivity and polarization characteristics of metallic mirrors have been modeled and presented at several meetings(e.g., Ref. 7).

II. CXRS AND BES INSTRUMENTATION

  • Very early on it has been recognized that the substantial attenuation of the diagnostic beam requires high-optical throughput spectrometers in order to compensate for a low CX signal in the presence of huge background of continuum radiation.
  • The system’s etendue sA·V=4310−1 mm2 srd is preserved by the periscope fiber bundle assembly, and a DNB slab of about 1003100 mm is imaged for each radial channel onto the entrance slits1 35 mmd of individual spectrometers.
  • The role of the CXRS/ BES diagnostic as a multi-tasking requires the simultaneous measurement of the main ion species: helium ash at 468 nm, intrinsic impurities C and Ne at 529 nm, and bulk D and T ions at 650 nm(cf. Fig. 1).
  • The proposed scheme is to make use of color filters and different orders of the TRINITI echelle grating instruments for different representative wavelengths.
  • The detection of nonthermal broadband features depends critically on clear distinction of CX induced features and passive background.

III. MSE MEASUREMENTS BY RATIOMETRY

  • The combination of CXRS and beam emission spectroscopy5 is seen today as the sole path to obtain absolute ion densities(helium ash) on ITER.
  • A natural spin-off of BES on the DNB is to exploit the D-alpha spectrum and its amplitudes for magnetic diagnosis.
  • In fact, the complementary exploitation of the entire MSE polarization pattern will ultimately optimize signal accuracy and spatial resolution.
  • The pitch angleBp/Bt derived from the dipole intensity ratio of s andp group in MSE spectrum, which, in the case of statistical population, is determined by the angleq between direction of l.o.s. and Lorentz-vectorEL=v3B.
  • Is for the case of a simplified circular magnetic flux surface and the ITER CXRS top-port periscope.

IV. FIRST-MIRROR EXPERIMENTS ON TEXTOR

  • Metallic mirrors which are foreseen for ITER optical periscopes were recently investigated on TEXTOR.
  • The aim of the experiments was to investigate optical properties of plasma-facing mirrors in dependence on erosion, deposition, and particle implantation.
  • Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp.
  • The wavelength regime of measurements ranged from 250 to 2500 nm.
  • First experimental evaluations14 can be summarized as: (1) after plasma exposure the reflectivity was decreased by up to 35% in the deposition areas.

V. ACTIVE BEAM SPECTROSCOPY DATA ANALYSIS: CHEAP FOR ITER

  • A collateral activity to ongoing conceptual design and feasibility studies is dedicated to the development of suitable data analysis packages including spectral analysis and physics evaluation.
  • For ITER the concept of integrated data CX analysis implies a comprehensive diagnostic coverage of the main plasma ions(intrinsic and seeded impurities and bulk ions).
  • A new concept is to involve a full set of spectra representing, for example, a complete ion temperature profile and solve all spectra in one go.
  • Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp.

Did you find this useful? Give us your feedback

Content maybe subject to copyright    Report

Pilot experiments for the International Thermonuclear Experimental
Reactor active beam spectroscopy diagnostic
M. von Hellermann,
a)
M. de Bock, R. Jaspers, and K. Jakubowska
FOM-Institute for Plasma physics “Rijnhuizen,” Association EURATOM, Trilateral Euregio Cluster, 3430 BE
Nieuwegein, NL
R. Barnsley, C. Giroud, N. C. Hawkes, and K. D. Zastrow
UKAEA Culham Laboratory Euratom Association, Abingdon, United Kingdom
P. Lotte and R. Giannella
CEA Cadarache, Association Euratom, France
A. Malaquias
IAEA, Vienna, Austria
E. Rachlew
Euratom Association-VR, KTH Stockholm, Sweden
S. Tugarinov and A. Krasilnikov
TRINITI Troitsk, Russia
A. Litnovsky, V. Philipps, and P. Wienhold
Institute for Plasma Physics, FZ-Juelich, Euratom Association, 52425 Juelich, Germany
P. Oelhafen and G. De Temmerman
Institut für Physik, University of Basel, 4056 Basel, Switzerland
L. Shmaenok
Phystex, Vaals, NL and loffe Physical Technical Institute, St. Peterburg, Russia
(Presented on 19 April 2004; published 1 October 2004)
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. © 2004 American Institute of Physics. [DOI: 10.1063/1.1787950]
I. INTRODUCTION
A comprehensive package of active beam based spec-
troscopy tools for the International Thermonuclear Experi-
mental Reactor (ITER) has been developed and a final sum-
mary was recently completed.
1
The package encompasses
charge exchange recombination spectroscopy (CXRS)
2,3
for
the measurement of the main impurity ion densities (includ-
ing helium ash), ion temperature and torodial as well as po-
loidal plasma rotation. Quantitative use of beam emission
spectroscopy (BES)
4
based on comprehensive atomic model-
ing is proposed as an indispensable cross-calibration tool for
absolute local impurity density measurements
5
and monitor-
ing of the neutral beam power deposition profile. Finally, a
full exploitation of the motional Stark effect (MSE) pattern is
proposed to deduce local pitch angles, total magnetic fields
6,7
and radial electric fields. CXRS on slowing-down alphas as
demonstrated. on the Tokamak Fusion Test Reactor
8
is also
considered for the ITER DNB and HNB (100 keV/amu,
2.2 MW diagnostic neutral beam and 500 keV/amu, 17 MW
heating neutral beam respectively) and was discussed
recently.
2
More quantitative studies and modeling will be
required in this field. A similar diagnostic challenge refers to
the measurement of slowing-down beam ions as produced by
the HNB. Medium energy velocity distribution functions rep-
resenting slowing-down helium beam ions were observed at
the Joint European Tours (JET).
9
A number of issues have
been recognized over the last years which need to be ad-
dressed in advance of the next stage, the diagnostic “procure-
ment phase.” Four of those are addressed in this article.
(1) The optimization of spectral instruments and detectors
for the active beam spectroscopy diagnostic package
needs to be tested on existing fusion devices in order to
establish suitable combinations for high-resolution and
broadband applications. Moreover, multi-tasking recom-
mends practical maintainable instrumental solutions.
(2) A converging interest in motional Stark diagnostics,
beam emission spectroscopy, and charge exchange spec-
a)
Author to whom correspondence should be addressed; electronic mail:
mgvh@rijnh.nl
REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 75, NUMBER 10 OCTOBER 2004
0034-6748/2004/75(10)/3458/4/$22.00 3458 © 2004 American Institute of Physics
Downloaded 02 Jan 2007 to 134.94.122.39. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp

troscopy has highlighted the needs for characterization
of the polarization transfer properties of optical
periscopes.
(3) A central issue is the survival and protection of the first
mirrors used in observation periscopes. The effects of
carbon and beryllium coatings on reflectivity and polar-
ization characteristics of metallic mirrors have been
modeled and presented at several meetings (e.g., Ref. 7).
First results describing erosion effects of monocrystal-
line molybdenum mirrors were reported recently.
10
(4) Finally, data evaluation procedures are closely linked to
feasibility studies and will ultimately decide on achiev-
able performances.
II. CXRS AND BES INSTRUMENTATION
Very early on it has been recognized that the substantial
attenuation of the diagnostic beam requires high-optical
throughput spectrometers in order to compensate for a low
CX signal in the presence of huge background of continuum
radiation. For the case of a modulated DNB the effective
signal to noise is then determined by the ratio of CX signal
and fluctuation of the background. A crucial criterion for the
acceptance of CXRS as a viable tool for ITER is the capa-
bility of measuring local helium ash densities in the plasma
core. At TRINITI a high-optical-throughput, high-resolution
spectrometer was developed especially for CXRS
application.
11
A unique combination of a large f-number
F/3,f =480 mm, and high linear dispersion value D
=0.250.3 nm/mm make it a particularly suited instrument
for the envisaged ITER CXRS system. The system’s etendue
A· =4 10
−1
mm
2
sr is preserved by the periscope fiber
bundle assembly, and a DNB slab of about 100 100 mm is
imaged for each radial channel onto the entrance slit 1
5mm of individual spectrometers. The role of the CXRS/
BES diagnostic as a multi-tasking requires the simultaneous
measurement of the main ion species: helium ash at 468 nm,
intrinsic impurities C and Ne at 529 nm, and bulk D and T
ions at 650 nm (cf. Fig. 1). The proposed scheme is to make
use of color filters and different orders of the TRINITI ech-
elle grating instruments for different representative wave-
lengths. Pilot experiments are required addressing achievable
sensitivities, stray-light suppression, and color control. A
critical issue will also be the spectral purity of the underlying
continuum radiation and its quantum noise photon statistics
in order to verify predicted spectral signal-to-noise reactor
(SNR) values (cf Ref. 1). The detection of nonthermal broad-
band features depends critically on clear distinction of CX
induced features and passive background.
III. MSE MEASUREMENTS BY RATIOMETRY
The combination of CXRS and beam emission
spectroscopy
5
is seen today as the sole path to obtain abso-
lute ion densities (helium ash) on ITER. BES refers here
explicitly to a quantitative exploitation of measured and
modeled line intensities and wavelength separations and not
to the measurement of plasma fluctuations. A natural spin-off
of BES on the DNB is to exploit the D-alpha spectrum and
its amplitudes for magnetic diagnosis. This will be comple-
mentary to MSE polarimetry on the HNB.
6,12,13
In fact, the
complementary exploitation of the entire MSE polarization
pattern will ultimately optimize signal accuracy and spatial
resolution. Whereas the viewing geometry of the HNB MSE
periscopes is optimized for a maximum sensitivity to a rota-
tion of the polarization pattern, the DNB periscopes will only
be sensitive to changes of the angle between Lorentz-field
vector and viewing line. For the ITER magnetic field B
t
=5.2 T, and a DNB energy of 100 keV/amu, the MSE com-
ponents (6
and 3
components, respectively) will be well
separated and the SNR compared to the background
fluctuation level (assuming photon statistics of continuum
radiation) should be in excess of 50 (see also Refs. 1 and 2).
The pitch angle B
p
/B
t
derived from the dipole intensity
ratio of
and
group in MSE spectrum, which, in the case
of statistical population, is determined by the angle
be-
tween direction of l.o.s. and Lorentz-vector E
L
=
v
B
I
I
=
sin
2
1 + cos
2
.
Maximum sensitivity for observation angles
close to 45°.
For the ITER CXRS top-port periscope the angle
on axis
B
p
=0 is 32.6°. Figure 2 shows q values derived from ratio
I
/I
for the case of a simplified circular magnetic flux sur-
face and the ITER CXRS top-port periscope. In contrast to
polarimetry, no active or passive polarizing element is in-
volved in ratiometry. However, a key issue will be isotropic
reflection factors ensuring the preservation of I
/I
for the
entire observation system including multiple mirrors in the
periscope, the fiber link, and finally in the spectrometer it-
self. A MSE ratiometry pilot experiment is presently imple-
mented on TEXTOR in ITER-like geometry.
IV. FIRST-MIRROR EXPERIMENTS ON TEXTOR
Metallic mirrors which are foreseen for ITER optical
periscopes were recently investigated on TEXTOR. The aim
of the experiments was to investigate optical properties of
plasma-facing mirrors in dependence on erosion, deposition,
and particle implantation.
FIG. 1. Schematic layout of CXRS/
BES/MSE spectroscopic instrumenta-
tion. Multi-tasking of periscopes for
simultaneous evaluation of CXRS
(impurity and bulk ions), BES on
injected neutrals and finally for MSE
ratiometry.
Rev. Sci. Instrum., Vol. 75, No. 10, October 2004 Plasma diagnostics 3459
Downloaded 02 Jan 2007 to 134.94.122.39. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp

Large polycrystalline metal mirrors (molybdenum and
tungsten) on inclined target holders were exposed in the
scrape-off layer (SOL) plasma of TEXTOR in both erosion
and deposition-dominated zones. The accumulated plasma
exposure time of mirrors was about 900 s. Particle energies
and particle affluence were of the same order of magnitude
as those expected for ITER. Figure 3 shows a schematic
layout of the mirror test and one sample exposed in the
deposition-dominated zone. The reflectivity was measured
before and after exposure in the SOL. The wavelength re-
gime of measurements ranged from 250 to 2500 nm. First
experimental evaluations
14
can be summarized as:
(1) after plasma exposure the reflectivity was decreased by
up to 35% in the deposition areas. The reflectivity was
increased by 12% in the plasma near zones (erosion
zones);
(2) fringes due to constructive and destructive interference
are observed if /4 corresponds to the optical thickness
of a deposited film;
(3) the degradation of reflectivity of the exposed mirror
samples is likely due to film growth observed on the
mirror surface; and
(4) the increase of reflectivity of mirrors noticed on some
areas is possibly due to annealing effects during the tem-
perature excursions and/or cleaning by plasma ions.
V. ACTIVE BEAM SPECTROSCOPY DATA ANALYSIS:
CHEAP FOR ITER
A collateral activity to ongoing conceptual design and
feasibility studies is dedicated to the development of suitable
data analysis packages including spectral analysis and phys-
ics evaluation. At JET the self-consistent CX evaluation
package CHEAP (charge exchange analysis package) is
used routinely and is potentially applicable in inter-shot
performance.
The CHEAP concept is based on a comprehensive
atomic modeling
15
of all emission processes (beam emission,
active and passive charge exchange recombination) making
use of a full set of data for the plasma environment. An
essential first step is the introduction of a common mapping
grid for all physical parameters. This strategy has enabled us
to treat the beam-plasma interaction (i.e., beam stopping and
beam emission processes) in a consistent fashion. Multiple
step processes and contributions from excited states are taken
into account. For ITER the concept of integrated data CX
analysis implies a comprehensive diagnostic coverage of the
main plasma ions (intrinsic and seeded impurities and bulk
ions). From this point of view, the issue of CX measurement
of helium ash densities on ITER is inseparable from a simul-
taneous measurement of all ions. Moreover, the issue of a
density measurement is linked directly to a measurement of
ion temperature and plasma rotation.
Highlights of future activities in this field are listed
below:
(1) Super Fit: The present strategy of spectral analysis is
usually based on a step-by-step process addressing each
spectrum individually. A new concept is to involve a full
set of spectra representing, for example, a complete ion
temperature profile and solve all spectra in one go.
(2) Integrated Data Analysis: From a similar point of view, a
spectral analysis is ultimately to be seen as part of a
global data consistency strategy. Ion temperature and
density lead to ion pressure and combined with electron
pressure to a match of kinetic and diamagnetic energy
which can be used as a constraint on spectral analysis.
(3) The stochastic occurrence of plasma edge line emission,
e.g., edge localized modes ELMs is a potential hazard to
a perfect background suppression scheme using beam
modulation. In this case, complex spectra will have to be
evaluated requiring advanced atomic modeling and suit-
able extraction tools.
1
M. von Hellermann, “Active Charge Exchange Spectroscopy (CXRS) and
Beam Emission Spectroscopy BES+MSE with Diagnostic Neutral
Beam (DNB) (under EFDA contract; not publicly available, contact:
mgvh@rijnh.nl)
2
M. von Hellermann, C. Giroud, N. C. Hawkes, R. Jaspers, A. Krasilnikov,
P. Lotte, G. McKee, A. Malaquias, M. O’. Mullane, E. Rachlew, S.
FIG. 2. Safety factor q as derived from MSE intensity ratio for different
minor radii and ITER top-portconfiguration. Note, a simplified case off cir-
cular flux geometry has been assumed for illustration purposes.
FIG. 3. (Color) Large polycrystalline metal mirrors (molybdenum and tung-
sten) on inclined target holders were exposed in the SOL plasma of TEX-
TOR in both erosion and deposition-dominated zones.
3460 Rev. Sci. Instrum., Vol. 75, No. 10, October 2004 von Hellermann
et al.
Downloaded 02 Jan 2007 to 134.94.122.39. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp

Tugarinov, and K.-D. Zastrow, 30th EPS Conf. Contr. Fus. Pl. Phys., St.
Petersburg, 2003, ECA Vol. 27A, O-4.2D.
3
A. Malaquias, A. Costley, A. Gorshkov, N. Hawkes, M. v. Hellermann,
M. Kuldkepp, P. Lotte, E. Rachlew, S. Tugarinov, G. Vayakis, and C.
Walker, 15th Topical Conference on High Temperature Plasma Diagnos-
tics, San Diego, 19 April 2004.
4
W. Mandl, R. Wolf, M. von Hellermann, and H. P. Summers, Plasma Phys.
Controlled Fusion 35, 1373 (1993).
5
M. von Hellermann, R. Jaspers, H. P. Summers, and K-D. Zastrow, Ad-
vanced Diagnostics for Magnetic and Inertial Fusion, edited by P. E.
Stott, A. Wootton, G. Gorini, E. Sindoni, and D. Batani (Plenum, New
York, 2001),p.205.
6
P. Lotte, M. Von Hellermann, A. Malaquias, R. Giannella, N. Hawkes, E.
Rachlew, R. Jaspers, P. Nielsen, S. Tugarinov, and C. Walker, in Ref. 2,
P1–183.
7
A. Malaquias, M. von Hellermann, P. Lotte, S. Tugarinov, and V. Voit-
senya, in Ref.2 .
8
G. McKee, R. J. Fonck, B. Stratton, R. Budny, Z. Chang, and A. Ramsey,
Nucl. Fusion 37, 501 (1997).
9
M. von Hellermann, W. G. F. Core, J. Frieling, L. D. Horton, R. W. T.
König, W. Mandl, and H. P. Summers, Plasma Phys. Controlled Fusion
35, 799 (1993).
10
K. Vukolov and V. Voitsenya, Sixth ITPA Topical Group Meeting on ITER
Diagnostics, Part I, Naka, Japan, February 2004.
11
S. Tugarinov, A. Krasilnikov, V. Dokouka, R. Khayrutidinov, I. Beigman,
I. Tolstikhina, L. Vainshtein, M. von Hellermann, and A. Malquias, Rev.
Sci. Instrum. 74, 2075 (2003).
12
N. C. Hawkes, A. Malaquias, P. Lotte, M. von Hellermann, M. Brix, R.
Giannella, M. Kuldkepp, E. Rachlew, C. Negus, and E. Surrey, Fifth ITPA
Topical Group Meeting on ITER Diagnostics, St. Petersburg, Russia, 16
July 2003.
13
F. Levinton, R. Fonck, G. Gammel, R. Kaita, H. Kugel, E. Powell, and D.
Roberts, Phys. Rev. Lett. 63, 2060 (1989).
14
P. Wienhold, A. Litnovsky, V. Philipps, P. Oelhafen, G. De Temmerman,
W. Schneider, and B. Emmoth. (unpublished).
15
http://adas.phys.strath.ac.uk..
Rev. Sci. Instrum., Vol. 75, No. 10, October 2004 Plasma diagnostics 3461
Downloaded 02 Jan 2007 to 134.94.122.39. Redistribution subject to AIP license or copyright, see http://rsi.aip.org/rsi/copyright.jsp
Citations
More filters
Journal ArticleDOI
TL;DR: In this paper, the authors describe the requirements for high reliability in the systems (diagnostics) that provide the measurements in the ITER environment, which is similar to those made on the present-day large tokamaks while the specification of the measurements will be more stringent.
Abstract: In order to support the operation of ITER and the planned experimental programme an extensive set of plasma and first wall measurements will be required. The number and type of required measurements will be similar to those made on the present-day large tokamaks while the specification of the measurements—time and spatial resolutions, etc—will in some cases be more stringent. Many of the measurements will be used in the real time control of the plasma driving a requirement for very high reliability in the systems (diagnostics) that provide the measurements. The implementation of diagnostic systems on ITER is a substantial challenge. Because of the harsh environment (high levels of neutron and gamma fluxes, neutron heating, particle bombardment) diagnostic system selection and design has to cope with a range of phenomena not previously encountered in diagnostic design. Extensive design and R&D is needed to prepare the systems. In some cases the environmental difficulties are so severe that new diagnostic techniques are required. a Author to whom any correspondence should be addressed.

309 citations

Journal ArticleDOI
TL;DR: The use of an injected neutral beam -either a dedicated diagnostic beam or the main heating beams - to localize and enhance the spectroscopic measurements described in Chap. 5 has been exploited for a number of key physics measurements, in particular detailed profile information on ion parameters, the radial electric field, plasma current density, and turbulent transport.
Abstract: In this chapter we discuss the various diagnostic techniques in which active spectroscopy plays a role. The use of an injected neutral beam - either a dedicated diagnostic beam or the main heating beams - to localize and enhance the spectroscopic measurements described in Chap. 5 has been exploited for a number of key physics measurements, in particular detailed profile information on ion parameters, the radial electric field, plasma current density, and turbulent transport. The ability to make these detailed measurements has been a key element in the development of improved plasma performance. The neutral beam techniques have been extended by the use of such beam analogs as laser beams, gas puffs, and pellet injection for specific measurements. In each case we describe the general principle behind the measurement and include several successful examples of their implementation, briefly touching on some of the more important physics results. We conclude with a few remarks about the relevance and re...

53 citations

Journal ArticleDOI
TL;DR: In this article, problems arising from high power ECRH under conditions of incomplete absorption are discussed, and individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation.
Abstract: Problems related to the development of diagnostics for steady state fusion plasma experiments are discussed. The paper concentrates on those necessities already appearing in current non-burning plasma fusion experiments when extending pulse lengths beyond 10 s, i.e. thermal load, erosion, deposition and long-time signal integration in magnetic diagnostics. Problems arising from high power ECRH under conditions of incomplete absorption are outlined. Individual standard diagnostic systems are discussed to identify their specific problems as well as the opportunities connected with long pulse operation. Burning plasma experiments characterized by intense n- and γ-radiation are briefly reviewed for reasons of completeness, dealing with radiation induced processes in windows, fibres, cables and mirrors. Methods of data handling, real time monitoring and plasma control are outlined.

50 citations


Cites background from "Pilot experiments for the Internati..."

  • ...Large polycrystalline metal mirrors of Mo and W have been exposed in the SOL plasma of TEXTOR mounted on inclined target holders [269]....

    [...]

  • ...Experiments have shown that thin films (10 nm) of C-H or Be can strongly modify the reflectance of mirrors as well as its polarization characteristics [268, 269]....

    [...]

Journal Article
TL;DR: In this paper, a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams is described.
Abstract: We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the pi(3) and sigma(1) lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6 degrees from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the D(alpha) transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

25 citations

Journal ArticleDOI
TL;DR: A version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split D(alpha) emission from the neutral beams, recently installed on the DIII-D tokamak.
Abstract: We describe a version of a motional Stark effect (MSE) diagnostic based on the relative line intensities and spacing of Stark split Dα emission from the neutral beams. This system, named B-Stark, has been recently installed on the DIII-D tokamak. To find the magnetic pitch angle, we use the ratio of the intensities of the π3 and σ1 lines. These lines originate from the same upper level and so are not dependent on the level populations. In future devices, such as ITER, this technique may have advantages over diagnostics based on MSE polarimetry. We have done an optimization of the viewing direction for the available ports on DIII-D to choose the installation location. With this placement, we have a near optimal viewing angle of 59.6° from the vertical direction. All hardware has been installed for one chord, and we have been routinely taking data since January 2007. We fit the spectra using a simple Stark model in which the upper level populations of the Dα transition are treated as free variables. The magnitude and direction of the magnetic field obtained using this diagnostic technique compare well with measurements from MSE polarimetry and EFIT.

23 citations

References
More filters
Journal ArticleDOI
TL;DR: Tugarinov et al. as discussed by the authors used active charge exchange recombination spectroscopy (CXRS) for the measurement of low-Z impurities in a fully diagnosed plasma to increase the overall data consistency and reduce the statistical error of each single impurity density determination.
Abstract: 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.

19 citations

Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Pilot experiments for the international thermonuclear experimental reactor active beam spectroscopy diagnostic" ?

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.