First absolute measurements of fast-ion losses in the ASDEX Upgrade tokamak (original) (raw)
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Nuclear Fusion
Absolute flux of fast ion losses induced by tearing modes have been measured by means of fast ion loss detectors (FILD) for the first time in RF heated plasmas in the ASDEX Upgrade tokamak. Up to 30 M W/m 2 of fast ion losses are measured by FILD at 5 cm from the separatrix, consistent with infra-red camera measurements, with energies in the range of 250 − 500 keV and pitch angles corresponding to large trapped orbits. A resonant interaction between the fast ions in the high energy tail of the ICRF distribution and a m/n = 5/4 tearing mode leads to enhanced fast ion losses. Around 9.3 ± 0.7 % of the fast ion losses are found to be coherent with the mode and scale linearly with its amplitude, indicating the convective nature of the transport mechanism. Simulations have been carried out to estimate the contribution of the prompt losses. A good agreement is found between the simulated and the measured velocity space of the losses. The velocity space resonances that may be responsible for the enhanced fast ion losses are identified.
Fast-ion losses due to high-frequency MHD perturbations in the ASDEX upgrade tokamak
Physical review letters, 2008
Time resolved energy and pitch angle measurements of fast ion losses correlated in frequency and phase with high frequency magnetohydrodynamic (MHD) perturbations have been obtained for the first time in a magnetic fusion device and are presented here. A detailed analysis of fast ion losses due to Toroidal Alfvén Eigenmodes (TAEs) has revealed the existence of a new core localized MHD perturbation, the Sierpes mode. The Sierpes mode is a non-Alfvénic instability which dominates the losses of fast ions in ICRH heated discharges. The internal structure of both, TAEs and Sierpes mode has been reconstructed by means of highly-resolved multichord soft X-ray measurements.
Study of fast-ion losses in experiments on neutral beam injection on the Globus-M spherical tokamak
Plasma Physics Reports, 2011
The paper presents a review of the main results on the heating of plasma ions and behavior of fast ions in experiments on neutral beam injection (NBI) carried out in 2003-2010 on the Globus M spherical tokamak. It is noticed that, along with significant success achieved in NBI plasma heating, there is experi mental evidence indicating significant losses of the power injected into the plasma. Most probably, the power is lost due to so called first orbit losses, i.e., losses of fast ions that are produced in plasma after ionization of beam atoms and occur in unconfined trajectories. Until recently, the absence of appropriate diagnostic equip ment did not allow one to verify this hypothesis. The use of the ACORD M charge exchange analyzer directed tangentially to the plasma column made it possible to measure the spectra of fast ions slowed down in plasma and confirm the assumption on the presence of substantial orbit losses of fast particles (~25-50% of the beam power). In addition to the review of the experimental results, the paper presents analysis of orbit losses on the basis of 3D simulations of fast ion trajectories in plasma. The results of experiments on studying the influence of the magnitude of the tokamak magnetic field on the confinement of fast ions are also pre sented. Along with computer simulations, these experiments made it possible to formulate recommendations on the reduction of orbit losses in the Globus M tokamak.
Fast ion JET diagnostics: Confinement and losses
AIP Conference Proceedings, 2008
A study of magnetically confined fast ions in tokamaks plays an important role in burning plasma research. To reach ignition and steady burning of a reactor plasma an adequate confinement of energetic ions produced by NBI heating, accelerated with ICRF and born in fusion reactions is essential to provide efficient heating of the bulk plasma. Thus, investigation of the fast ion behaviour is an immediate task for present-day large machines, such as JET, in order to understand the main mechanisms of slowing down, redistribution and losses, and to develop optimal plasma scenarios. Today's JET has an enhanced suite of fast ion diagnostics both of confined and lost ions that enable to significantly contribute to this important area of research. Fast ion populations of p, d, t, 3 He and 4 He, made with ICRF, NBI, and fusion reactions have been investigated in experiments on JET with sophisticated diagnostics in conventional and shear-reversed plasmas, exploring a wide range of effects. This paper will introduce to the JET fast-ion diagnostic techniques and will give an overview of recent observations. A synergy of the unique diagnostic set was utilised in JET, and studies of the response of fast ions to MHD modes (e.g. tornado modes, sawtooth crashes), fast 3 He-ions behaviour in shearreversed plasmas are impressive examples of that. Some results on fast ion losses in JET experiments with various levels of the toroidal field ripple will be demonstrated.
Upgrade of the diagnostic neutral beam injector for the TCV tokamak
Fusion Engineering and Design, 2003
A diagnostic neutral beam injector (DNBI) [CRPP report LRP 710/01, CRPP-EPFL, 2001; EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365] has been installed on tokamak à configuration variable (TCV) [Plasma Phys. Control Fusion, 36 (1994) B277; Plasma Phys. Control Fusion, 43 (2001) A161; Plasma Phys. Control Fusion, to be published] for the purpose of providing local measurements of plasma ion temperature, velocity and impurity density by Charge eXchange recombination spectroscopy (CXRS) [EPS Conf. Contr. Fusion Plasma Phys., 25A (2001) 365].
Alpha particle losses from Tokamak Fusion Test Reactor deuterium–tritium plasmas
Physics of Plasmas, 1996
Because alpha particle losses can have a significant influence on tokamak reactor viability, the loss of deuterium-tritium alpha particles from the Tokamak Fusion Test Reactor ͑TFTR͒ ͓K. M. McGuire et al., Phys. Plasmas 2, 2176 ͑1995͔͒ has been measured under a wide range of conditions. In TFTR, first orbit loss and stochastic toroidal field ripple diffusion are always present. Other losses can arise due to magnetohydrodynamic instabilities or due to waves in the ion cyclotron range of frequencies. No alpha particle losses have yet been seen due to collective instabilities driven by alphas. Ion Bernstein waves can drive large losses of fast ions from TFTR, and details of those losses support one element of the alpha energy channeling scenario.
The Review of scientific instruments, 2014
The proton detector (PD) measures 3 MeV proton yield distributions from deuterium-deuterium fusion reactions within the Mega Amp Spherical Tokamak (MAST). The PD's compact four-channel system of collimated and individually oriented silicon detectors probes different regions of the plasma, detecting protons (with gyro radii large enough to be unconfined) leaving the plasma on curved trajectories during neutral beam injection. From first PD data obtained during plasma operation in 2013, proton production rates (up to several hundred kHz and 1 ms time resolution) during sawtooth events were compared to the corresponding MAST neutron camera data. Fitted proton emission profiles in the poloidal plane demonstrate the capabilities of this new system.