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MOCO02 |
Broadband Microwave Emission Spectrum Associated With Kinetic Instabilities in ECR Plasmas | |
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ECRISs are susceptible to kinetic instabilities due to resonance heating mechanism forming an anisotropic electron velocity distribution function. Well-known and frequently observed extracted ion beam current oscillations in case of high heating power and/or low magnetic field gradient are proven to be caused by the instabilities of cyclotron type leading to a notable reduction of highly-charged ion beam intensities. It has been shown recently that heating power level and magnetic field gradient affect the spectrum of microwave emission of plasma related to cyclotron instabilities, being in the frequency range of 8-14 Ghz. More detailed study of microwave emission spectrum of ECR plasma conducted with an improved setup is presented in this work. It was found that frequencies of microwaves emitted by the plasma can be far beyond the primary heating frequency (14 GHz) and up to 25 GHz. Moreover, a threshold transition from periodic pulsed emission to a CW emission has been observed in the experiment for the first time, as was predicted theoretically*. The transition occurs at certain threshold levels of heating microwave power and magnetic field gradient.
*A.G. Shalashov et all, JETP Letters, 2006, Vol. 84, No. 6, pp. 314-319 (2006) |
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Slides MOCO02 [48.375 MB] | |
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| MOCO03 | Cavity Tuning Experiments with the JYFL 14 GHz ECRIS | 18 |
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| Experimental results showing the effect of cavity tuning on oxygen beam currents extracted from the AECR-type JYFL 14 GHz ECRIS are reported. The microwave-plasma coupling properties of the ion source were adjusted by inserting a conducting tuner stub through the injection plug, thus changing the dimensions of the plasma chamber and affecting the cavity properties of the system. The beam currents of high charge state ions were observed to vary up to some tens of percent depending on the tuner position and the microwave frequency. | ||
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Slides MOCO03 [5.745 MB] | |
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-ECRIS2016-MOCO03 | |
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| WEPP41 | Measurement of Microwave Frequencies Emitted by Instabilities of ECRIS Plasma with Waveguide Filters and Microwave Sensitive Diodes | 134 |
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| Periodic emission of strong microwave bursts at certain frequencies is a characteristic feature of kinetic instabilities in ECRIS plasmas. Precise measurement of the temporally evolving microwave frequency spectra requires a high bandwidth oscilloscope, which can make the experiments prohibitively expensive to conduct. An alternative low-cost method to study the microwave emission in narrow frequency bands is to apply band-pass waveguide filters and microwave sensitive diodes. The microwave emission from the plasma of the JYFL 14 GHz ECRIS has been studied with both methods. The results of the experiments are compared and their interpretation is discussed. It is demonstrated that the method based on filters and diodes can provide useful information about the microwave emission spectra induced by electron cyclotron instabilities. | ||
| DOI • | reference for this paper ※ https://doi.org/10.18429/JACoW-ECRIS2016-WEPP41 | |
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