Gas puff Z-pinch implosions with external Bz field on COBRA

Abstract

Abstract. We present preliminary experimental results on mitigating Magneto-Rayleigh-Taylor (MRT) instabilities by applying an external Bz field. The experiments were conducted on the 1-MA, 200-ns COBRA generator at Cornell University. In the experiments, a triple-nozzle was used to produce z-pinch loads from concentric outer and inner annular gas puffs and a center gas puff column. A single coil was used to produce a Bz field in the pinch region. We have used two 4-frame 2-ns gated EUV cameras to obtain images of the imploding plasmas, in which the MRT instabilities were observed. The MRT instabilities can grow when the plasma accelerates toward the axis. With a triple gas puff (outer, inner and center puff), reduced acceleration or de-acceleration of the imploding plasma occurred when the outer puff plasma imploded onto the inner annular puff plasma resulting a relatively stable implosion. In the absent of the inner annular gas puff, the imploding outer annular plasma continued to accelerate toward the axis. Large turbulent flares at the edge of the implosion or pinch plasma were observed. The implosion was not stable. To stabilize the implosion without the inner gas puff, a Bz field was applied. This external Bz field was compressed by the outer imploding plasma shell. A relatively stable implosion was observed. Increasing the Bz field to 2-kG resulted in a relatively fatter pinch plasma.

Effects of a Preembedded Axial Magnetic Field on the Current Distribution in a Z -Pinch Implosion

“…(iii) A relative very small B z0 = 0.1−0.2 T significantly stabilizes the implosion and stagnation in our experiment [19], and in the experiments on the 0.9-MA COBRA [35] and 1-MA ZEBRA facilities [37].…”

Effect of a dynamic axial magnetic field on a preconditioned single-wire Z-pinch

“…Furthermore, utilizing an external axial magnetic field is an effective technique for suppressing plasma instability in Zpinch experiments [20,21]. The compressed axial and azimuthal magnetic field outside the plasma generates a magnetic shear, which can suppress MRTI [22].…”

Self-generated plasma rotation in a Z-pinch implosion with preembedded axial magnetic field

“…Z-pinch implosions with preembedded axial magnetic fields (B z0 ) have been intensively studied during the last decade [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] due to their importance both for inertial confinement fusion [1,2,8,9] and for the study of fundamental plasma physics [18,19]. A primary difference from standard Z-pinches (without B z0 ) is that during the implosion not only the plasma is compressed, but also the axial magnetic field, leading to a profound effect on the implosion dynamics.…”

“…Additionally, the rotation might affect the plasma dynamics by the mitigation of MRT and MHD instabilities, either by affecting the effective acceleration direction of the Z-pinch [26][27][28][29], or by phase mixing of an instability perturbation due to the non-uniform angular velocity (ω = v θ /r) distribution [52,53]. Indeed, in almost all Z-pinch experiments with preembedded B z , significant instability mitigation was observed during the implosion and stagnation [3,4,6,7,12,13,16,54,55]. It is a common assumption that the observed stabilization is solely due to the radial bending of the B z -field lines [56].…”