Three-dimensional effects for radio frequency antenna modeling

Abstract

Electromagneticfield calc_ationsforradio frequency(rf)antennas in two dimensions(2-D) neglectfinite antenna lengtheffects as wellas thefeedersleadingto the main current .strap.Comparisons with experimentsindicate that these 2-D calculations can overestimate the loadingof the antenna and fail to givethe correctreactive behavior.The 2-D calculationsalsopredictthat the returncurrentsin the sidewalls of the antenna structuredepend stronglyon plasma parameters,but thisprediction isalsosuspectbecause of experimental evidence.To study the validity of the 2-D approximation,the MultipleAntenna Implementation System (MAntIS) has been used to perform 3-D modeling of the power spectrum, plasma loading,and inductancefora relevant loop antenna design.Effects on antenna performance caused by feedersto the main currentstrap,conductingsidewalls, and finite phase velocity are considered.The plasma impedance matrix for the loadingcalculation is generatedby use of the ORION-ID code. The 3-D model isbenchmarked with the 2-D model in the 2-D limit.For finite-length antennas,inductance calculations are found to be in much more reasonable agreement with experiments for 3-D modeling than for the 2-D estimates. The modeling shows that the feeders affect the launchedpower spectrum in an indirect way by forcingthe drivenrf currentto returnin the antenna sidewalls ratherthan in the plasma as in the 2-D model. Thus, the feedershave much more influence than the plasma on the currentsthatreturnin the sidewall. It has alsobeen found thatpoloidaldependenciesin the : plasma impedance matrix can reducethe loadingfrom that predictedin the 2-D model. For some plasma parameters,the combined 3-D effects can lead to a reductionin the predicted loading by as much as a factorof 2 from that given by the 2-D model.

Three dimensional modelling of ICRF launchers for fusion devices

“…Thus, resources need not be wasted during the preliminary design phase but can be brought to bear on the design as required. The method relies upon two newly developed 3-D modelling tools, the RANT3D and PLASMAIMP computer codes [18]. Accurate benchmarking with experiment is possible because of a high resolution measurement of the density profile in TFTR taken with a two-frequency differential phase reflectometer system [19] located near the RF antenna and combined with multichannel infrared interferometer data [20].…”

“…The process is completed by the recently developed RANT3D code, which is briefly described in Section 3. Reference [18] gives a more detailed description of the methods used in RANT3D. In Section 4, the model used in RANT3D for the TFTR Bay-M antenna is given.…”

“…The treatment of multiple nested recesses in the RANT3D code requires that every recess be treated in a generic manner, as discussed in Ref. [18]. This treatment requires a complicated indexing scheme that is beyond the scope of this article to keep track of the different Fourier coefficients and basis sets.…”