Plasma response to electron energy filter in large volume plasma device

The Large Volume Plasma device(LVPD), a cylindrically shaped, linear plasma device of dimension( m L m 3 , 2    ) have successfully demonstrated the excitation of Electron Temperature Gradient(ETG) turbulence[ Mattoo et al.,[1]]. The observed ETG turbulence shows significant power between ( ) ( ), corresponding to the wavenumber, ~ ( ) where, and ( ) ion cyclotron frequency and electron Larmor radius, respectively. The observed frequency and wave number matches well with theoretical estimates corresponding to Whistler-ETG mode. We investigated electromagnetic (EM) fluctuations induced plasma transport in high beta ( 2 2 /~0.01 0.4 oe nT B   ) ETG mode suitable plasma in LVPD. The radial electromagnetic (EM) electron (ion) flux () results primarily from the correlation between fluctuations of parallel electron current ( ) and radial magnetic field ( ). The electromagnetic particle flux is observed to be much smaller than the electrostatic particle flux, .The EM flux is small but finite contrary to the conventional slab ETG model. The electromagnetic flux is non-ambipolar. A theoretical model is obtained for the EM particle flux in straight homogeneous magnetic field geometry. The theoretical estimates are seen to compare well with the experimental observations. Sluggish parallel ion response is identified as the key mechanism for generation of small but finite electromagnetic flux.2

“…It divides LVPD plasma into three regions of source, EEF and target plasmas. ) regions [37]. The sandwiched EEF plasma region proposes a complex plasma scenario.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Observation of electromagnetic fluctuation induced particle transport in ETG dominated large laboratory plasma

Srivastav

Singh

Awasthi

et al. 2019

“…radially inward, will not supplement the generation of any particle drift in the EEF. However, a strong axial parametric gradient does exist within the EEF [23].…”

Section: Drift Directionsmentioning

confidence: 99%

Investigation of electromagnetic fluctuations in a magnetically screened high beta plasma

Adhikari,

Sanyasi,

Awasthi

et al. 2024

We report low-frequency electromagnetic turbulence in the large-volume plasma device in a region that is receiving magnetically screened plasma. The magnetic screen is produced by activating a large solenoid that generates a strong magnetic field (B_EEF) transverse to the background axial magnetic field (B_z). The magnetic field strength variation inB_EEF controls the plasma diffusion and is responsible for parametric profile modifications in LVPD. The turbulence is characterised by the observed features of an electromagnetic (EMHD) mode having frequency ordering in the lower hybrid range (f_ci < f <f_LH). The free energy source for the excited turbulence is believed to be the prevalent finite radial pressure gradient in the system. The excited electromagnetic mode shows typical scales for the wave number, k_⊥ ~ 0.13 cm-1 and frequency f ~ 6 kHz and propagates with a phase velocity comparable to ion acoustic velocity, Cs in electron diamagnetic drift direction. It is believed that the low-frequency pressure gradient-driven electromagnetic mode exhibits coupling with the lower hybrid or whistler wave.

“…The combined magnetic field of the EEF and the axial magnetic field substantially modifies plasma characteristics in the source and the target plasma regions. The subsequent use of subscript 'S' and 'T', represents the source and target plasma regions [22]. The averaged value of plasma density in the source and target regions are n s ∼ 3.5 × 10 17 m −3 and n T ∼ 4.5 × 10 16 m −3 and electron temperatures are T e,S ∼ 3.75 eV and T e,T ∼ 1.5 eV, respectively.…”

Section: An Overview: Lvpd Plasmamentioning

confidence: 99%

Investigations into growth of whistlers with energy of energetic electrons

Sanyasi¹,

Srivastav²,

Awasthi³

et al. 2021

Runaway electrons have great significance in fusion plasmas as they are considered to be responsible for the excitation of instabilities and for damage to the first wall components. The threshold for the generation of the runaway electron population in tokamaks strongly depends on the toroidal magnetic field and bulk electron temperature. The presence of these runaway electrons with a critical density and magnetic field value are correlated with the magnetosonic whistler activity. The Rosenbluth condition applies to the destabilization of upper hybrid modes, that remains mostly stable in large-scale tokamaks like Joint European Tokamakand International Thermonuclear Experimental reactor. On the other hand, whistlers with a frequency in the lower hybrid range are more likely to be destabilized in a lower magnetic field and temperature, along with the whistlers' excitation threshold. The process of destabilization of whistlers by energetic electrons thus has a finite overlap between fusion and basic plasma devices, and the outcome from the latter can be scalable to fusion machines. We report that in the linear large volume plasma device, the destabilization of quasi-longitudinal whistlers, driven by the reflected particles from the mirror, takes place in the bulk plasma region i.e. away from the mirror in the energetic belt region, and follows the frequency ordering of 40 kHz < ω r /2π < 80 kHz. Our explanation involves an alternate limit of quasi-linear analysis, commonly employed for recovering the instability threshold of runaways scattering off whistlers in fusion plasmas, and the growth rate due to the reflected particle is proportional to the inverse square root of electron temperature, where the reflected particle fraction is nr n0 > Kn0 4B0T 0.5 e (Sharma and Vlahos 1984 Astrophys. J. 280 405). The measurements required to obtain the energy scaling of runaway electrons with whistler instability are critical for large devices but remain scarce. We have emphasized the analytic correlation between the two regimes in these investigations.