We  report  on recent experiments  on  the  ASDEX  Upgrade  (AUG)  tokamak (major  radius R ≈1.65  m, minor radius a ≈ 0.5  m) with  third  harmonic  ICRF  heating  of deuterium  beam  ions. Prior  to  this  work,  the scheme has  been  developed and  applied on the JET tokamak, the largest currently operating tokamak (R ≈ 3 m, a ≈ 1 m), for fusion product studies and for testing alpha particle diagnostics in preparation of ITER [1]. The experiments  reported here demonstrate that this scheme can also be used in medium size tokamaks such as AUG despite their
reduced fast ion confinement.This  work  has  been  carried out   within   the 
framework   of   the   EUROfusion  Consortium  and  has  received  funding  from  the Euratom  research  and  training  programme  2014-2018 under grant agreement No 633053. The views and  opinions  expressed  herein  do  not  necessarily reflect those of the European Commission.Postprint (published version

ASDEX Upgrade

Bobkov, Volodymyr

EUROfusion MST1

Gallart, Daniel

Geiger, Benjamin

Johnson, Thomas

Mantsinen, Mervi

Meyer, Hendrik

Nocente, Massimo

Ochoukov, Roman

Odstrčil, Tomas

Perelli, Enrico

Rasmussen, Jens

Schneider, P. A.

Sharapov, Sergei

Tardini, Giovanni

Tardocchi, Marco

Vallejós, Pablo

Mantsinen, M.

Bobkov, V.

Gallart, D.

Geiger, B.

Johnson, T.

Meyer, H.

Nocente, M.

Ochoukov, R.

Odstrcil, T.

Perelli, E.

Rasmussen, J.

Schneider, P.

Sharapov, S.

Tardini, G.

Tardocchi, M.

Vallejós, P.

MPG.PuRe

Third harmonic ICRF heating of deuterium beam ions on ASDEX Upgrade

 Third harmonic ICRF heating of deuterium beam ions on ASDEX Upgrade M.J. Mantsinen1,2, Vl. Bobkov3, D. Gallart1, B. Geiger3, T. Johnson4, H. Meyer5, M. Nocente6, R. Ochoukov3, T. Odstrčil3, E. Perelli7, J. Rasmussen8, P.A. Schneider3, S. Sharapov5, G. Tardini3, M. Tardocchi6,7, P. Vallejós4 and the ASDEX Upgrade and EUROfusion MST1 Teams* 1Barcelona Supercomputing Center, Barcelona, Spain 2ICREA, Barcelona, Spain 3Max-Planck-Institut für Plasmaphysik, Garching, Germany 4KTH, Stockholm, Sweden 5CCFE, Culham Science Centre, Abingdon, UK 6Dipartimento di Fisica ‘G. Occhialini’, Università degli Studi di Milano-Bicocca, Italy 7Istituto di Fisica del Plasma ‘Piero Caldirola’, Milano, Italy 8Technical University of Denmark (DTU), Denmark *www.euro-fusionscipub.org/mst1  Introduction We report on recent experiments on the ASDEX Upgrade (AUG) tokamak (major radius R ≈ 1.65 m, minor radius a ≈ 0.5 m) with third harmonic ICRF heating of deuterium beam ions. Prior to this work, the scheme has been developed and applied on the JET tokamak, the largest currently operating tokamak (R ≈ 3 m, a ≈ 1 m), for fusion product studies and for testing alpha particle diagnostics in preparation of ITER [1]. The experiments reported here demonstrate that this scheme can also be used in medium size tokamaks such as AUG despite their reduced fast ion confinement.  Experimental set-up The experiments were carried out in H mode AUG plasmas with 2.5-5 MW of deuterium NBI with a maximum injection energy of 59-93 keV. A total of four discharges (cf. Table 1) were performed with ICRF power tuned to the central D resonance with an ICRF frequency of 41.8 MHz and the 0 phasing of the ICRF antennas. Experimental results and comparison with modelling The main plasma parameters of discharge 32331 are compared in Fig. 1 with those of discharge 32330 which was prepared in the same way but without ICRF power. The comparison of these discharges shows a clear increase in the neutron rate RNT with ICRF power, which was observed with two independent neutron detectors, i.e. an epithermal neutron detector [2] and a LaBr3 detector [3]. Both discharges were terminated by a disruption due to impurity accumulation, with an earlier disruption at t = 2.68 s in discharge 32331.  43rd EPS Conference on Plasma Physics P1.035 Table 1 Main parameters for AUG discharges with third harmonic ICRF heating of deuterium beam ions Parameter\Discharge 32331 32573 32604 32605 Magnetic field (T) 1.8 1.85 1.85 1.85 Plasma current (MA) 1.0 0.8 0.8 0.8 NBI power (MW) 2.6 5.1 5.0 5.0 NBI inj. energy (keV) 59 59 and 93 59 59 ICRF power (MW) 2.0 1.8 3.6 3.8  23412312341232.0 2.2 2.80122.4 2.6Time (s)Discharge 32331 (red) Discharge 32330 (blue)Core line integrated density (10e19/m3)Electron temperature (keV)NBI Power (MW)ICRF Power (MW)Neutron yield (a.u.) A detailed analysis of discharge 32331 with the TRANSP and PION codes shows that the measured RNT is up to a factor of 4-5 times larger than RNT due to beam-thermal and thermal fusion reactions. PION [4, 5] provides time-dependent modelling of combined ICRF and NBI heating, taking into account the absorption of ICRF power on the resonant D beam ions. It uses the measured plasma parameters and the NBI deposition as calculated by TRANSP as input. According to PION, the observed increase in RNT during ICRF heating is consistent with the acceleration of D beam ions with ICRF waves above the maximum injection energy. As we can see in Fig. 2, PION reproduces both the time behaviour and the observed relative increase in RNT. As the fast deuterium tail develops in the deuterium distribution function as ICRF power is absorbed by D, the single pass D damping more than doubles from about 20% at t = 2.2 s to 45% at t = 2.55 s for the toroidal mode number N = 12. According to PION, about 85%, 10%, and 5% of the ICRF power is absorbed by deuterons, direct electron damping and parasitic edge damping, respectively, at t = 2.55 s. The parasitic edge damping was included in the PION modelling in the same way is for earlier JET discharges [6, 7]. Figure 1 Main plasma parameters for AUG 1MA/ 1.8T discharge 32331 and reference discharge 32330 without ICRF power.    Discharge 32331 Figure 2 Measured (green) and simulated (black) RNT as given by PION for discharge 32331. The measured RNT has been scaled to match the simulated RNT at t = 2.25 s. Also shown is RNT as calculated by PION assuming zero ICRF power (red dashed line).  43rd EPS Conference on Plasma Physics P1.035 Further confirmation for the acceleration of fast deuterons above the injection energy was obtained with passive and active neutral particle analysers (NPAs) [8]. Significant deuterium fluxes above the maximum NBI injection energy were observed by the NPAs up to the maximum energy of 200 keV of the measurements (Fig. 3). No fast protons were detected, which is consistent with the applied scenario. The D ion distribution function as simulated by PION and SELFO [9] are broadly consistent with the measured NPA fluxes. According to both codes, the calculated D distribution function extended to the 1 MeV range and the fast ion losses remained small. The high-energy cut-off of ICRF induced velocity space diffusion due to finite Larmor radius effects [10,11] was about 1.2-1.5 MeV and roughly equal to the maximum energy of trapped deuterons that were confined in these plasmas.   Figure 3 Deuterium flux as measured with the passive NPA and the event rate measured by the active NPA for AUG discharge 32330 with NBI only and discharge 32331 with third harmonic heating of deuterium beam ions.   The main goal for the subsequent discharges was to establish more stable plasmas while maintaining efficient acceleration of D ions by ICRF waves. This was achieved in discharge 32573 with the changes to the discharge parameters as indicated in Table 1. Furthermore, the plasma electron density was increased to 5x1019 m-3 and three pulses of ICRF power were programmed while maintaining constant NBI, each long enough to reach steady-state plasma conditions. As we can see in Fig. 4, the neutron rate RNT clearly responded to the application of ICRF power. This result was confirmed with all three available independent neutron detectors, i.e. the epithermal neutron detector, the LaBr3 detector and a neutron spectrometer [12]. They showed an increase of a factor of 1.7-2.1 in RNT with respect to its level without ICRF power. However, the observed ICRF enhancement was found to be smaller than the factor of about 2.5 predicted by PION. The reasons for this difference are under investigation and may be related to interaction of fast ions with MHD modes such as the m = 2 / n =1 locked mode that persisted throughout the discharge. In the two remaining discharges 32604 43rd EPS Conference on Plasma Physics P1.035 and 32605, the ICRF power was increased while the maximum beam injection energy was reduced back to 59 keV as in discharge 32331. The latter change allowed better diagnosis of the fast D tail with the NPAs. The measured NPA deuterium fluxes were observed to increase with ICRF power, as expected from theory. At the highest coupled ICRF powers in discharge 32605, however, the observed ICRF enhancement of RNT was found to be smaller than that predicted by PION as for discharge 32573 above. Unfortunately, like discharge 32331 above, discharges 32604 and 32605 suffered from radiation events and impurity accumulation. Their comparison with discharge 32575 suggests that increasing the NBI energy, which leads to improved D single pass damping, is beneficial for the applied scheme on AUG. Finally, we note that according to PION, the deuterium energy content increased approximately by 30-50% with the application of ICRF power in these AUG discharges.  4682461 2 3 4 5 60123Time (s)Discharge 32573Core line integrated density (10e19/m3)NBI Power (MW)ICRF Power (MW)Neutron yield (a.u.) Conclusions Third harmonic ICRF heating of deuterium beam ions has been demonstrated on AUG for the first time. The acceleration of fast deuterons above the beam injection energy was confirmed by three independent neutron diagnostics and direct measurements with passive and active NPAs. The magnitude of the observed deuteron acceleration is consistent with modelling. The scheme provides a new tool for fast ion physics studies and diagnostic development on AUG. Acknowledgements This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under grant agreement No 633053. The views and opinions expressed herein do not necessarily reflect those of the European Commission. Figure 4 Overview of discharge 32573. The neutron yield is as measured by an epithermal neutron detector. References [1] S. Sharapov et al., Nucl. Fusion (in press) and references therein [2] G. Tardini et al., Nucl. Fusion 53 (2013) 063027 [3] M. Nocente M. et al., Nucl. Fusion 52 (2012) 063009 [4] L.-G. Eriksson, T. Hellsten and U. Willén, Nucl. Fusion 33 (1993) 1037 [5] L.-G. Eriksson and T. Hellsten, Phys. Scripta 55 (1995) 70 [6] L.-G. Eriksson et al., Nucl. 38 (1998) 265278 [7] M.J. Mantsinen et al., IAEA Technical Committee meeting on Energetic Particles, Vienna 2015 [8] P.A. Schneider, Rev. Sci. Instrum. 86 (2015) 073508 [9] T. Hellsten et al., Nucl Fusion 44 (2004) 892 [10] M.J. Mantsinen et al., Nucl. Fusion 39 (1999) 459 [11] A. Salmi et al. Plasma Phys. Control. Fusion 48 (2006) 717 [12] G. Tardini et al., J. Instrum. 7 (2012) C03004 43rd EPS Conference on Plasma Physics P1.035

English

We  report  on recent experiments  on  the  ASDEX  Upgrade  (AUG)  tokamak (major  radius R ≈1.65  m, minor radius a ≈ 0.5  m) with  third  harmonic  ICRF  heating  of deuterium  beam  ions. Prior  to  this  work,  the scheme has  been  developed and  applied on the JET tokamak, the largest currently operating tokamak (R ≈ 3 m, a ≈ 1 m), for fusion product studies and for testing alpha particle diagnostics in preparation of ITER [1]. The experiments  reported here demonstrate that this scheme can also be used in medium size tokamaks such as AUG despite their

reduced fast ion confinement.This  work  has  been  carried out   within   the 

framework   of   the   EUROfusion  Consortium  and  has  received  funding  from  the Euratom  research  and  training  programme  2014-2018 under grant agreement No 633053. The views and  opinions  expressed  herein  do  not  necessarily reflect those of the European Commission

UPCommons

Third harmonic ICRF heating of Deuterium beam ions on ASDEX Upgrade

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Third harmonic ICRF heating of Deuterium beam ions on ASDEX Upgrade

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