Time-resolved observation of discrete and continuous MHD dynamo in the reversed-field pinch edge

Ji, H.; Almagri, A. F.; Prager, S. C.; Sarff, J. S.

doi:10.2172/10119073

Cited by 2 publications

(5 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…where B rec is the reconnecting eld, which i s t ypically the radial eld B r in the RFP. The typical drift parameter can be estimated to be on the order of 0.2-0.3 based on the observation of current carrying fast electrons [Stoneking et al, 1994] or the measured j k , n, and T e [Ji et al, 1994]. Using typical parameters [Ji, Prager, and Sar, 1995] in MST (Madison Symmetrical Torus) plasmas as we shall mention in the next section, i.e., B T = 2kG, n = 1 10 19 =m 3 , T e = 100eV, and the plasma radius a = 0 : 5m, we h a v e =a(1:5-2:5) 10 3 .…”

Section: Relative Rate Of Change In Helicity and Energy A Quantitatimentioning

confidence: 99%

“…In the case of a laboratory plasma (the MST RFP), direct measurements indicated that the turbulence is predominantly electrostatic, thus causing helicity transport in the mean eld with no eects on the turbulent eld. Figure 9 shows such an example of measured helicity ux caused by the electrostatic turbulence [Ji, Prager, and Sar, 1995] together with the measured -eect [Ji et al, 1994].…”

Section: Helicity In Mean and Turbulent Fieldsmentioning

confidence: 99%

See 1 more Smart Citation

Helicity, Reconnection, and Dynamo Effects

Ji¹

1998

View full text Add to dashboard Cite

The interrelationships between magnetic helicity, magnetic reconnection, and dynamo eects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly aects the reconnection rate as well as the shape of the diusion region. Conversely, magnetic reconnection events also strongly aect the global helicity, resulting in ecient helicity cancellation (but not dissipation) during counter-helicity reconnection and a nite helicity increase or decrease (but less eciently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo eects. The turbulent electromotive force along the mean magnetic eld (-eect), due to either electrostatic turbulence or the electron diamagnetic eect, transports mean-eld helicity across space without dissipation. This has been supported by direct measurements of helicity ux in a laboratory plasma. When the dynamo eect is driven by electromagnetic turbulence, helicity in the turbulent eld is converted to mean-eld helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery eect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

show abstract

Section: Relative Rate Of Change In Helicity and Energy A Quantitatimentioning

confidence: 99%

Section: Helicity In Mean and Turbulent Fieldsmentioning

confidence: 99%

Helicity, Reconnection, and Dynamo Effects

Ji¹

1998

View full text Add to dashboard Cite

show abstract

“…The resistive slow dynamo term, appearing as the second term of Eq. (20), changes the mean helicity also in the resistive time scale. The electrostatic MHD dynamo and diamagnetic dynamo, both appearing in the surface integral, transport the mean helicity across space while the inductive part of the MHD dynamo − (∂ A/∂t) · B , appearing in the volume integral in the both equations but with opposite signs, converts helicity from the fluctuations to the mean field [46].…”

Section: Magnetic Helicity and Dynamo Effectsmentioning

confidence: 95%

“…The first successful detection [20] of the MHD dynamo in the RFP plasmas was made in the well-controlled Madison Symmetric Torus (MST) plasmas. As discussed in Sec.…”

Section: Measurements Of Dynamo Effectsmentioning

confidence: 99%

See 1 more Smart Citation

The Alpha Dynamo Effects in Laboratory Plasmas

Ji¹,

Prager²

2001

View full text Add to dashboard Cite

A concise review of observations of the α dynamo effect in laboratory plasmas is given. Unlike many astrophysical systems, the laboratory pinch plasmas are driven magnetically. When the system is overdriven, the resultant instabilities cause magnetic and flow fields to fluctuate, and their correlation induces electromotive forces along the mean magnetic field. This α-effect drives mean parallel electric current, which, in turn, modifies the initial background mean magnetic structure towards the stable regime. This drive-andrelax cycle, or the so-called self-organization process, happens in magnetized plasmas in a time scale much shorter than resistive diffusion time, thus it is a fast and unquenched dynamo process. The observed α-effect redistributes magnetic helicity (a measure of twistedness and knottedness of magnetic field lines) but conserves its total value. It can be shown that fast and unquenched dynamos are natural consequences of a driven system where fluctuations are statistically either not stationary in time or not homogeneous in space, or both. Implications to astrophysical phenomena will be discussed.

show abstract

Time-resolved observation of discrete and continuous MHD dynamo in the reversed-field pinch edge

Cited by 2 publications

References 5 publications

Helicity, Reconnection, and Dynamo Effects

Helicity, Reconnection, and Dynamo Effects

The Alpha Dynamo Effects in Laboratory Plasmas

Contact Info

Product

Resources

About