scholarly journals Side emissions during EC injection for PDI studies in FTU tokamak

2019 ◽  
Vol 203 ◽  
pp. 02005 ◽  
Author(s):  
Alessandro Bruschi ◽  
Edoardo Alessi ◽  
Benedetta Baiocchi ◽  
William Bin ◽  
Ocleto D’Arcangelo ◽  
...  
Keyword(s):  
Pump Wave ◽  
Rotation Frequency ◽  
Thomson Scattering ◽  
Parametric Decay ◽  
Spectral Reconstruction ◽  
Different Types ◽  
Threshold Excitation ◽  
Low Threshold ◽  
Collective Thomson Scattering ◽  
Fine Time

The evidence of Parametric Decay Instabilities (PDI) excited by the ECH power injected in O-Mode has been explored in FTU Tokamak, using the Collective Thomson Scattering (CTS) diagnostic. The experiments show evidences to support the hypothesis of low-threshold excitation of waves generated by PDI mechanisms, formerly proposed in the case of 2nd harmonic X-mode injection in TEXTOR and ASDEX-U. Theoretical analysis predicts low-threshold parametric decay also for O-mode pump-wave injection, which can be injected in FTU at frequencies close to the first Harmonic EC resonance. Experiments were made at different magnetic fields, injecting the 140 GHz probe and observing the emission from the second antenna of the EC launcher in poloidally symmetric and asymmetric configurations, in presence of MHD islands. The signal is detected by the CTS radiometers, with a fast digitizer allowing the spectral reconstruction at very fine time and frequency scales. Different types of emissions are studied in detail, comparing them with the magnetic island rotation frequency in different plasma conditions. In order to locate the plasma volume originating the emissions, a new antenna and receiving line has been installed.

scholarly journals Anomalous absorption in ECRH experiments due to the parametric low-threshold excitation of localized UH waves

2019 ◽  
Vol 203 ◽  
pp. 01002
Author(s):  
Alexei Yu. Popov ◽  
Evgeniy Z. Gusakov
Keyword(s):  
Pump Wave ◽  
Low Frequency ◽  
Extraordinary Wave ◽  
Anomalous Absorption ◽  
Magnetic Island ◽  
Parametric Decay ◽  
Threshold Excitation ◽  
Power Threshold ◽  
Low Threshold ◽  
Low Frequency Waves

We describe the theoretical model which interprets the anomalous phenomena, i.e. the generation of backscattering signal observed in the ECRH experiments at TEXTOR, TCV, TJ-II, ASDEX-UG, LHD and FTU, as a consequence of the excitation of the parametric decay instability (PDI) leading to anomalous damping of the pump wave. The PDI power-threshold is shown to be extremely low due to the localization of both or one daughter upper hybrid (UH) waves in presence of a nonmonotonic (hollow) density profile, which is often observed in the ECRH experiments due to the magnetic island or the density pump-out effect. In the case of the extraordinary wave pump the model predicts substantial (up to 25%) anomalous absorption in the electron channel and explains the anomalous ion acceleration by the generation of secondary low frequency waves which directly transfer the pump power to the ion component. The possibility of anomalous absorption of the O-mode pump in the ECRH experiment due to the parametric excitation of trapped UH wave is also discussed and the anomalous absorption rate at the 10% level is predicted.

scholarly journals Observation and Modelling of the Onset of Parametric Decay Instabilities during Gyrotron Operation at ASDEX Upgrade

2019 ◽  
Vol 203 ◽  
pp. 02007 ◽  
Author(s):  
S.K. Hansen ◽  
S.K. Nielsen ◽  
J. Stober ◽  
J. Rasmussen ◽  
M. Stejner ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Theoretical Model ◽  
Wave Scattering ◽  
Thomson Scattering ◽  
Toroidal Magnetic Field ◽  
Parametric Decay ◽  
Fast Acquisition ◽  
Collective Thomson Scattering ◽  
High Degree ◽  
Millimeter Wave Scattering

We investigate parametric decay instabilities (PDIs) occurring for gyrotron radiation near the upper hybrid resonance at the ASDEX Upgrade tokamak. The PDIs are observed through anomalous millimeter-wave scattering which is recorded using the high-resolution, fast acquisition collective Thomson scattering system installed at ASDEX Upgrade, and an experiment in which such observations are made during a scan of the toroidal magnetic field is performed. A previously published theoretical model is used to calculate the gyrotron power necessary to excite PDIs in the experiment; the theoretical model is capable of predicting whether or not PDIs will be observed at a given toroidal magnetic field with a high degree of accuracy.

scholarly journals Modification of the collective Thomson scattering radiometer in the search for parametric decay on TEXTOR

2012 ◽  
Vol 83 (11) ◽  
pp. 113508 ◽  
Author(s):  
S. K. Nielsen ◽  
M. Salewski ◽  
W. Bongers ◽  
S. B. Korsholm ◽  
F. Leipold ◽  
...  
Keyword(s):  
Thomson Scattering ◽  
Parametric Decay ◽  
Collective Thomson Scattering

scholarly journals Mitigation of EC breakdown in the gyrotron transmission line of the ITER Collective Thomson Scattering diagnostic via a Split Biased Waveguide

2019 ◽  
Vol 14 (11) ◽  
pp. C11009-C11009 ◽  
Author(s):  
A.W. Larsen ◽  
S.B. Korsholm ◽  
B. Gonçalves ◽  
H.E. Gutierrez ◽  
E. Henriques ◽  
...  
Keyword(s):  
Transmission Line ◽  
Thomson Scattering ◽  
Collective Thomson Scattering ◽  
Thomson Scattering Diagnostic

Ion temperature measurements in a tokamak by collective Thomson scattering

1991 ◽  
Vol 69 (4) ◽  
pp. 1993-1998 ◽  
Author(s):  
M. R. Siegrist ◽  
R. Behn ◽  
D. Dicken ◽  
B. P. Duval ◽  
J. Hackmann ◽  
...  
Keyword(s):  
Thomson Scattering ◽  
Temperature Measurements ◽  
Ion Temperature ◽  
Collective Thomson Scattering

Scattering of electromagnetic waves by anomalous fluctuations of a magnetized plasma

1990 ◽  
Vol 43 (2) ◽  
pp. 165-172 ◽  
Author(s):  
V. N. Pavlenko ◽  
V. G. Panchenko
Keyword(s):  
Cross Section ◽  
Electromagnetic Waves ◽  
Pump Wave ◽  
Density Fluctuations ◽  
Scattering Cross Section ◽  
Magnetized Plasma ◽  
Lower Hybrid ◽  
Scattering Cross ◽  
Parametric Decay ◽  
Ion Acoustic

Fluctuations and scattering of transverse electromagnetic waves by density fluctuations in a magnetized plasma in the presence of parametric decay of the pump wave are investigated. The spectral density of electron-density fluctuations is calculated. It is shown that the differential scattering cross-section has sharp maxima at the ion-acoustic and lower-hybrid frequencies when parametric decay of the lower-hybrid pump wave occurs. We note that scattering at the ion-acoustic frequency is dominant. When the pump-wave amplitude tends to the threshold strength of the electric field the scattering cross-section increases anomalously, i.e. there is critical opalescence.

RAMI analysis of the Collective Thomson Scattering system front-end – Part2 – reliability block diagram analysis

2021 ◽  
Vol 171 ◽  
pp. 112593
Author(s):  
Diogo Rechena ◽  
Virgínia Infante ◽  
Elsa Henriques ◽  
Søren B. Korsholm ◽  
Axel W. Larsen ◽  
...  
Keyword(s):  
Block Diagram ◽  
Thomson Scattering ◽  
Scattering System ◽  
Reliability Block Diagram ◽  
Front End ◽  
Collective Thomson Scattering ◽  
Diagram Analysis

scholarly journals Implementation of collective Thomson scattering on the TEXTOR tokamak for energetic ion measurements

2001 ◽  
Vol 72 (1) ◽  
pp. 1148-1150 ◽  
Author(s):  
L. Porte ◽  
H. Bindslev ◽  
F. Hoekzema ◽  
J. Machuzak ◽  
P. Woskov ◽  
...  
Keyword(s):  
Thomson Scattering ◽  
Collective Thomson Scattering
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