**5. Conclusion**

To conclude, we have briefly discussed different plasma diagnostic techniques and specifically investigated the novel features of interaction potentials caused by a test charge moving with constant velocity **v***<sup>T</sup>* along the z-axis in a collisionless unmagnetized Lorentzian dusty plasma. For this purpose, the linearized coupled Vlasov-Poisson equations are employed to model suprathermal electrons and ions with Kappa-df, as well as negatively charged dust grains with Maxwell-df, respectively. After applying the space-time Fourier transformations, an electrostatic potential is obtained with a modified dielectric constant. For taking the test charge speed much smaller than the dust thermal speed in a Lorentzian dusty plasma, we then express the total potential distribution in terms of short-range Debye-Hückel (DH) and long-range far-field potentials. The DH potential exponentially decays with distance, whereas FF potential decreases as the inverse cube of the distance. Both the potentials are substantially influenced by the plasma and superthermality parameters. However, a resonating test charge with DA oscillations introduces the long-range WF potential excitations behind the test charge in Lorentzian dusty plasmas. A Coulomb potential is obtained when the test charge is moving very fast compared to plasma species, and there is no shielding around it in the Lorentzian dusty plasma.

Vladimirov and Nambu [40] have already utilized the idea of WF potential for making new materials by attracting the same polarity dust grains in dusty plasmas. The physics of attractive forces between the negatively charged dust grains is completely analogous to that of Cooper pairing of electrons in superconductors [59]. The dust particle physically polarizes the plasma medium and creates attractive potential regions, where positive ions from collective interaction of DA waves can be focused. This may in turn lead to the possibility for dust crystallization and dust coagulation in both laboratory and space dusty plasmas.

### **Acknowledgements**

Dr. S. Ali dedicates this document to Late Prof. P.K. Shukla and Dr. B. Eliasson (University of Strathclyde, UK) who were very kind to him at many occasions

*Plasma Diagnostic Methods: Test Charge Response in Lorentzian Dusty Plasmas DOI: http://dx.doi.org/10.5772/intechopen.92460*

during discussions on dusty plasmas, and acknowledges the partial financial assistance from USTC, Hefei, China, and ICTP, Trieste, Italy, for making his visits feasible in 2018 and 2019, respectively. Professor Y. Al-Hadeethi also acknowledges the technical support of the Deanship of Scientific Research (DSR), King Abdulaziz University, Saudi Arabia.
