Parameter dependences of the experimental nitrogen concentration required for detachment in ASDEX... more Parameter dependences of the experimental nitrogen concentration required for detachment in ASDEX Upgrade and JET S. Hendersona, M. Bernertb,D. Bridab,M. Cavedonb,P. Davidb, R. Duxb,C. Girouda, A. Hubere, A. Kallenbachb, B. Lomanowskic, A. Meigsa, F.Reimoldd, M. Wischmeierb, S. Wieseneand the EUROfusion MST1 team†, ASDEXUpgrade team††, and JET team†††aUKAEA, CCFE, Culham Science Centre, Abingdon, OX14 3DB, UKbMax-Plank-Institut für Plasmaphysik, D-85748 Garching, GermanycOak Ridge National Laboratory, Oak Ridge, TN 37831, USAdMax-Plank-Institut für Plasmaphysik, D-85748 Greifswald, GermanyeForschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung-Plasmaphysik, D-52425 Jülich, GermanyEmail: stuart.henderson@ukaea.ukSubstantial seeding ofimpurities into the divertor has been used for a long time intokamaks to reduce the power and particle fluxes impacting on the divertor targets and is one of the main techniques to be utilised on ITER to allow safe, steady state divertor ...
Plasma rotational velocity measurements may be applied to the test of plasma theory, to the asses... more Plasma rotational velocity measurements may be applied to the test of plasma theory, to the assessment of the effects of plasma perturbations, and as substitutes for electric field measurements. For these applications, we developed a plasma rotation diagnostic based on the measurement of the Doppler shift of impurity spectra. In ohmic plasmas, the measurement is complicated by the small size of the velocity induced line shift compared with the line width. To overcome this problem, our diagnostic system is configured to observe each of two plasma regions at several times during a single shot using a single array detector. This procedure can eliminate the need for a separate absolute wavelength calibration if the regions are properly chosen and can minimize the effects of detector noise and shot-to-shot plasma variation. The two chords selected for observation can be changed from shot to shot. The details of the novel optical system are described. As an example of the technique, rotational velocity profiles for ohmic plasmas perturbed by a radial, resonant magnetic field are presented.
Tungsten erosion was quantified during inter/intra-ELM periods in He-dominated JET-ILW plasmas by... more Tungsten erosion was quantified during inter/intra-ELM periods in He-dominated JET-ILW plasmas by optical emission spectroscopy. The intra-ELM tungsten sputtering in helium plasmas, which dominates the total W source, prevails by a factor of about 4 over inter-ELM sputtering in the investigated ELM frequency range from 90 Hz–120 Hz. He ions are mainly responsible for the W erosion during the ELMs in He plasmas. The strong in/out asymmetry of the ELM-induced W erosion is observed in He plasmas even at high ELM frequencies beyond 100 Hz. In Ohmic/L-mode plasmas and during the H-mode inter-ELM plasma phases both He2+ and Be2+ ionic species are major contributors to the W erosion. Their contribution depends on the electron temperature in the divertor: for Te > 15 eV both species cause significant W sputtering, for Te < 15 eV, Be 2+ ions are solely responsible for the W erosion. Tungsten erosion during in both inter and intra-ELM periods in He-dominated plasmas are significantly larger than in deuterium plasmas. It is 15–25 times larger during the inter-ELM phase and in L-mode discharges at Te = 25–30 eV. On the other hand, the ELM-induced W source is by a factor of 3 larger than in D plasmas.
All major JET systems have been fully commissioned for D - T and the DTE1 series of experiments h... more All major JET systems have been fully commissioned for D - T and the DTE1 series of experiments has started with the D - T fuel mixture and operating conditions foreseen for ITER. In the area of ITER physics, significant results have been produced in both D - D and D - T. In D-D, the L - H threshold power database has been extended, the bounds on edge-electron temperature and density in ELMy H-modes have been defined and the advantages of Types I and III ELMy discharges have been compared. In D - T plasmas, the isotope effect on H-mode threshold power and transport has been determined so that a more accurate assessment can be made of the ignition margin and heating requirements for ITER. Trace tritium experiments have provided first particle transport measurements and an assessment of the ITER reference ion-cyclotron resonance-frequency heating scenarios has been started. In the area of fusion performance, record D - D neutron yields have been obtained by controlling the plasma and current profiles in hot ion ELM-free H-modes and optimized shear modes. In D - T, internal transport barriers have been readily established in optimized shear discharges and Alfvén eigenmodes have been observed.
Substantial seeding of impurities into the divertor has been used for a long time in tokamaks to ... more Substantial seeding of impurities into the divertor has been used for a long time in tokamaks to reduce the power and particle fluxes impacting on the divertor targets and is one of the main techniques to be utilised on ITER to facilitate stationary divertor operation [1]. There have been attempts to predict how the impurity concentration required for detachment should scale with different plasma parameters, such as the power crossing the separatrix, Psep, and the upstream separatrix density, ne,sep [2 − 4]. In [3] the machine size scaling enters through theminor radius, amin, due to the dependence on the poloidal magnetic field. Including the LH threshold scaling provides a dependence on B T R[4]. Since there are no experimental results to test these scaling laws, this work uses spectroscopy to measure the divertor nitrogen concentration, cN , in the outer divertor to examine the parameter dependencies both within and across the ASDEX Upgrade (AUG) and JET tokamaks.
Since the last IAEA conference, the scientific programme of JET has focused on the qualification ... more Since the last IAEA conference, the scientific programme of JET has focused on the qualification of the integrated operating scenarios for ITER and on physics issues essential for the consolidation of design choices and the efficient exploitation of ITER. Particular attention has been given to the characterization of the edge plasma, pedestal energy and edge localized modes (ELMs), and their
ABSTRACT The analysis of equilibrium conditions might be irrelevant to determine the importance o... more ABSTRACT The analysis of equilibrium conditions might be irrelevant to determine the importance of a certain set of atomic data. We show, that in non-equilibrium and optically thick plasmas intercombination transitions between highly excited states as well as higher order dielectronic satellite transitions are of extraordinary importance for diagnostics. In optically thin equilibrium plasmas, however, they are almost negligible. Numerical examples are presented for neutral helium in attached/detached plasmas as well as for dense laser produced plasmas.
Rotation velocities were measured in two Ohmically heated discharges and compared to neoclassical... more Rotation velocities were measured in two Ohmically heated discharges and compared to neoclassical predictions evaluated with measurements of Ti, ni, and Er. Hydrogen fueled one of the discharges, and helium was the principal fuel for the other. For both discharges, poloidal rotation is consistent with the momentum balance equation. In contrast, current neoclassical theory predicts the toroidal rotation velocity only
Parameter dependences of the experimental nitrogen concentration required for detachment in ASDEX... more Parameter dependences of the experimental nitrogen concentration required for detachment in ASDEX Upgrade and JET S. Hendersona, M. Bernertb,D. Bridab,M. Cavedonb,P. Davidb, R. Duxb,C. Girouda, A. Hubere, A. Kallenbachb, B. Lomanowskic, A. Meigsa, F.Reimoldd, M. Wischmeierb, S. Wieseneand the EUROfusion MST1 team†, ASDEXUpgrade team††, and JET team†††aUKAEA, CCFE, Culham Science Centre, Abingdon, OX14 3DB, UKbMax-Plank-Institut für Plasmaphysik, D-85748 Garching, GermanycOak Ridge National Laboratory, Oak Ridge, TN 37831, USAdMax-Plank-Institut für Plasmaphysik, D-85748 Greifswald, GermanyeForschungszentrum Jülich GmbH, Institut für Energie-und Klimaforschung-Plasmaphysik, D-52425 Jülich, GermanyEmail: stuart.henderson@ukaea.ukSubstantial seeding ofimpurities into the divertor has been used for a long time intokamaks to reduce the power and particle fluxes impacting on the divertor targets and is one of the main techniques to be utilised on ITER to allow safe, steady state divertor ...
Plasma rotational velocity measurements may be applied to the test of plasma theory, to the asses... more Plasma rotational velocity measurements may be applied to the test of plasma theory, to the assessment of the effects of plasma perturbations, and as substitutes for electric field measurements. For these applications, we developed a plasma rotation diagnostic based on the measurement of the Doppler shift of impurity spectra. In ohmic plasmas, the measurement is complicated by the small size of the velocity induced line shift compared with the line width. To overcome this problem, our diagnostic system is configured to observe each of two plasma regions at several times during a single shot using a single array detector. This procedure can eliminate the need for a separate absolute wavelength calibration if the regions are properly chosen and can minimize the effects of detector noise and shot-to-shot plasma variation. The two chords selected for observation can be changed from shot to shot. The details of the novel optical system are described. As an example of the technique, rotational velocity profiles for ohmic plasmas perturbed by a radial, resonant magnetic field are presented.
Tungsten erosion was quantified during inter/intra-ELM periods in He-dominated JET-ILW plasmas by... more Tungsten erosion was quantified during inter/intra-ELM periods in He-dominated JET-ILW plasmas by optical emission spectroscopy. The intra-ELM tungsten sputtering in helium plasmas, which dominates the total W source, prevails by a factor of about 4 over inter-ELM sputtering in the investigated ELM frequency range from 90 Hz–120 Hz. He ions are mainly responsible for the W erosion during the ELMs in He plasmas. The strong in/out asymmetry of the ELM-induced W erosion is observed in He plasmas even at high ELM frequencies beyond 100 Hz. In Ohmic/L-mode plasmas and during the H-mode inter-ELM plasma phases both He2+ and Be2+ ionic species are major contributors to the W erosion. Their contribution depends on the electron temperature in the divertor: for Te > 15 eV both species cause significant W sputtering, for Te < 15 eV, Be 2+ ions are solely responsible for the W erosion. Tungsten erosion during in both inter and intra-ELM periods in He-dominated plasmas are significantly larger than in deuterium plasmas. It is 15–25 times larger during the inter-ELM phase and in L-mode discharges at Te = 25–30 eV. On the other hand, the ELM-induced W source is by a factor of 3 larger than in D plasmas.
All major JET systems have been fully commissioned for D - T and the DTE1 series of experiments h... more All major JET systems have been fully commissioned for D - T and the DTE1 series of experiments has started with the D - T fuel mixture and operating conditions foreseen for ITER. In the area of ITER physics, significant results have been produced in both D - D and D - T. In D-D, the L - H threshold power database has been extended, the bounds on edge-electron temperature and density in ELMy H-modes have been defined and the advantages of Types I and III ELMy discharges have been compared. In D - T plasmas, the isotope effect on H-mode threshold power and transport has been determined so that a more accurate assessment can be made of the ignition margin and heating requirements for ITER. Trace tritium experiments have provided first particle transport measurements and an assessment of the ITER reference ion-cyclotron resonance-frequency heating scenarios has been started. In the area of fusion performance, record D - D neutron yields have been obtained by controlling the plasma and current profiles in hot ion ELM-free H-modes and optimized shear modes. In D - T, internal transport barriers have been readily established in optimized shear discharges and Alfvén eigenmodes have been observed.
Substantial seeding of impurities into the divertor has been used for a long time in tokamaks to ... more Substantial seeding of impurities into the divertor has been used for a long time in tokamaks to reduce the power and particle fluxes impacting on the divertor targets and is one of the main techniques to be utilised on ITER to facilitate stationary divertor operation [1]. There have been attempts to predict how the impurity concentration required for detachment should scale with different plasma parameters, such as the power crossing the separatrix, Psep, and the upstream separatrix density, ne,sep [2 − 4]. In [3] the machine size scaling enters through theminor radius, amin, due to the dependence on the poloidal magnetic field. Including the LH threshold scaling provides a dependence on B T R[4]. Since there are no experimental results to test these scaling laws, this work uses spectroscopy to measure the divertor nitrogen concentration, cN , in the outer divertor to examine the parameter dependencies both within and across the ASDEX Upgrade (AUG) and JET tokamaks.
Since the last IAEA conference, the scientific programme of JET has focused on the qualification ... more Since the last IAEA conference, the scientific programme of JET has focused on the qualification of the integrated operating scenarios for ITER and on physics issues essential for the consolidation of design choices and the efficient exploitation of ITER. Particular attention has been given to the characterization of the edge plasma, pedestal energy and edge localized modes (ELMs), and their
ABSTRACT The analysis of equilibrium conditions might be irrelevant to determine the importance o... more ABSTRACT The analysis of equilibrium conditions might be irrelevant to determine the importance of a certain set of atomic data. We show, that in non-equilibrium and optically thick plasmas intercombination transitions between highly excited states as well as higher order dielectronic satellite transitions are of extraordinary importance for diagnostics. In optically thin equilibrium plasmas, however, they are almost negligible. Numerical examples are presented for neutral helium in attached/detached plasmas as well as for dense laser produced plasmas.
Rotation velocities were measured in two Ohmically heated discharges and compared to neoclassical... more Rotation velocities were measured in two Ohmically heated discharges and compared to neoclassical predictions evaluated with measurements of Ti, ni, and Er. Hydrogen fueled one of the discharges, and helium was the principal fuel for the other. For both discharges, poloidal rotation is consistent with the momentum balance equation. In contrast, current neoclassical theory predicts the toroidal rotation velocity only
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