... In this section, we explain the parametric Abel inversion technique to obtain the spectrum of... more ... In this section, we explain the parametric Abel inversion technique to obtain the spectrum of the local emission. ... for Rtop ≤ r<a and nα(r) = 0 (6c) for a ≤ r, where Rtop, Htop, Hin, Din and Dout are fitting parameters as shown in Fig. 5, and a is the radius of the plasma column. ...
Magnetic pickup (dB/dt) coils are used in MCX to study MHD activity in the edge of the plasma. Tw... more Magnetic pickup (dB/dt) coils are used in MCX to study MHD activity in the edge of the plasma. Two sets of three axis (r, Θ, z) coils are currently in use. When placed at a single z location this allows resolution of azimuthal mode numbers, and when placed at the same Θ location, information about axial mode structure is obtained. Analysis of azimuthal modes indicates that the edge region of the MCX plasma is moving at a velocity on the order of 40 km/s, consistent with spectroscopic measurements. In addition, we present evidence for the evolution of an M=1 mode into an M=2 mode over the course of the discharge.
The Maryland Centrifugal Experiment(MCX) studies enhanced confinement and stability produced by s... more The Maryland Centrifugal Experiment(MCX) studies enhanced confinement and stability produced by sheared supersonic rotation about a linear confining magnetic field. MCX has a mirror geometry of 2.5 m length, mirror ratio 2-20,maximum mirror field 1.9T, maximum midplane field 0.33T. Biasing of an inner electrode relative to the outer wall produces a radial electric field which drives azimuthal rotation. MCX has achieved high density (n>10 20 m -3) fully ionized plasmas rotating supersonically with velocities of ~100 km/sec for times exceeding 8 ms under a wide range of conditions. Ion temperatures are 30 eV and confinement times ~100 microseconds. Sonic Mach numbers are 1-2 and Alfven Mach numbers somewhat less than 0.5 for standard discharges. Plasmas remain grossly stable, or steady, for many milliseconds, much longer than MHD instability timescales for MCX, though significant magnetic fluctuations are clearly seen on magnetic probes. Recently MCX has demonstrated an enhanced mo...
Improvement in tokamak plasma confinement using biased electrodes observed in many tokamaks is a ... more Improvement in tokamak plasma confinement using biased electrodes observed in many tokamaks is a well-established phenomenon. In this paper we show that very use of the same biased electrode can mitigate the disruptions in tokamak plasmas through stabilization of magnetohydrodynamic (MHD) modes. Disruption induced in ADITYA tokamak by H 2 gas puffing is successfully mitigated by applying the positive bias voltage to the electrode placed inside the LCFS prior to the gas injection. Sheared B E r rotation of the plasma generated by biasing leads to substantial reduction in growth of MHD modes (m /n = 3/1, 2/1) and avoids disruptions through prevention of mode locking.
This paper summarizes the results of recent dedicated experiments on disruption control and runaw... more This paper summarizes the results of recent dedicated experiments on disruption control and runaway mitigation etc. carried out in ADITYA tokamak, which are of utmost importance for the successful operation of large size tokamaks, such as ITER. It is quite well known fact that the disruptions in tokamaks in which large fractions of the plasma thermal energy is lost in very short time and must be avoided for successful operation of a fusion reactor. Disruptions, induced by hydrogen gas puffing, are successfully mitigated by two innovative techniques in ADITYA tokamak using a bias electrode placed inside the LCFS and applying an ICRH pulse with power ~ 50 to 70 kW. These experiments led to better understanding of the disruption control mechanisms and also can be thought of as one of options for disruption control in ITER. In both the cases the physical mechanism seems to be the control of MHD modes due to increased poloidal rotation of edge plasma generated by induced radial electric ...
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts., 2004
Summary form only given. MCX studies supersonically rotating plasmas in a mirror-machine geometry... more Summary form only given. MCX studies supersonically rotating plasmas in a mirror-machine geometry. Theory predicts supersonic rotation in the azimuthal direction closes the loss cone and high velocity shear stabilizes MHD interchange modes. Construction began in September 2000 and the first rotating plasmas were formed in October 2002. The plasma is 2.6 m long between mirror throats and 28 cm
Normally, welded bellows are used to drive assembly inside the vacuum chamber for linear and rota... more Normally, welded bellows are used to drive assembly inside the vacuum chamber for linear and rotational motion. This system is costly. One of the cheaper option available is Wilson feed through, for linear as well as rotational motion of the probe assembly. But Wilson feed through has a drawback. During its linear/rotational motion, the vacuum of the system is disturbed, due to leak trough the O’ rings. To overcome this problem, one has applied differential pumping in between the space of two O’ rings, we have increased this interspaced volume, and by pumping of this interspaced volume we are able to use this probe assembly in UHV systems. This UHV compatible Wilson feed through, can provide easy linear as well as rotational motion with negligible disturbance to the vacuum of the system. The fabrication of this type of feed through is quite easy and can be utilized for driving any system, e.g. filament holder, sample holder etc. We have designed Langmuir probes using this UHV compat...
... In this section, we explain the parametric Abel inversion technique to obtain the spectrum of... more ... In this section, we explain the parametric Abel inversion technique to obtain the spectrum of the local emission. ... for Rtop ≤ r<a and nα(r) = 0 (6c) for a ≤ r, where Rtop, Htop, Hin, Din and Dout are fitting parameters as shown in Fig. 5, and a is the radius of the plasma column. ...
Magnetic pickup (dB/dt) coils are used in MCX to study MHD activity in the edge of the plasma. Tw... more Magnetic pickup (dB/dt) coils are used in MCX to study MHD activity in the edge of the plasma. Two sets of three axis (r, Θ, z) coils are currently in use. When placed at a single z location this allows resolution of azimuthal mode numbers, and when placed at the same Θ location, information about axial mode structure is obtained. Analysis of azimuthal modes indicates that the edge region of the MCX plasma is moving at a velocity on the order of 40 km/s, consistent with spectroscopic measurements. In addition, we present evidence for the evolution of an M=1 mode into an M=2 mode over the course of the discharge.
The Maryland Centrifugal Experiment(MCX) studies enhanced confinement and stability produced by s... more The Maryland Centrifugal Experiment(MCX) studies enhanced confinement and stability produced by sheared supersonic rotation about a linear confining magnetic field. MCX has a mirror geometry of 2.5 m length, mirror ratio 2-20,maximum mirror field 1.9T, maximum midplane field 0.33T. Biasing of an inner electrode relative to the outer wall produces a radial electric field which drives azimuthal rotation. MCX has achieved high density (n>10 20 m -3) fully ionized plasmas rotating supersonically with velocities of ~100 km/sec for times exceeding 8 ms under a wide range of conditions. Ion temperatures are 30 eV and confinement times ~100 microseconds. Sonic Mach numbers are 1-2 and Alfven Mach numbers somewhat less than 0.5 for standard discharges. Plasmas remain grossly stable, or steady, for many milliseconds, much longer than MHD instability timescales for MCX, though significant magnetic fluctuations are clearly seen on magnetic probes. Recently MCX has demonstrated an enhanced mo...
Improvement in tokamak plasma confinement using biased electrodes observed in many tokamaks is a ... more Improvement in tokamak plasma confinement using biased electrodes observed in many tokamaks is a well-established phenomenon. In this paper we show that very use of the same biased electrode can mitigate the disruptions in tokamak plasmas through stabilization of magnetohydrodynamic (MHD) modes. Disruption induced in ADITYA tokamak by H 2 gas puffing is successfully mitigated by applying the positive bias voltage to the electrode placed inside the LCFS prior to the gas injection. Sheared B E r rotation of the plasma generated by biasing leads to substantial reduction in growth of MHD modes (m /n = 3/1, 2/1) and avoids disruptions through prevention of mode locking.
This paper summarizes the results of recent dedicated experiments on disruption control and runaw... more This paper summarizes the results of recent dedicated experiments on disruption control and runaway mitigation etc. carried out in ADITYA tokamak, which are of utmost importance for the successful operation of large size tokamaks, such as ITER. It is quite well known fact that the disruptions in tokamaks in which large fractions of the plasma thermal energy is lost in very short time and must be avoided for successful operation of a fusion reactor. Disruptions, induced by hydrogen gas puffing, are successfully mitigated by two innovative techniques in ADITYA tokamak using a bias electrode placed inside the LCFS and applying an ICRH pulse with power ~ 50 to 70 kW. These experiments led to better understanding of the disruption control mechanisms and also can be thought of as one of options for disruption control in ITER. In both the cases the physical mechanism seems to be the control of MHD modes due to increased poloidal rotation of edge plasma generated by induced radial electric ...
The 31st IEEE International Conference on Plasma Science, 2004. ICOPS 2004. IEEE Conference Record - Abstracts., 2004
Summary form only given. MCX studies supersonically rotating plasmas in a mirror-machine geometry... more Summary form only given. MCX studies supersonically rotating plasmas in a mirror-machine geometry. Theory predicts supersonic rotation in the azimuthal direction closes the loss cone and high velocity shear stabilizes MHD interchange modes. Construction began in September 2000 and the first rotating plasmas were formed in October 2002. The plasma is 2.6 m long between mirror throats and 28 cm
Normally, welded bellows are used to drive assembly inside the vacuum chamber for linear and rota... more Normally, welded bellows are used to drive assembly inside the vacuum chamber for linear and rotational motion. This system is costly. One of the cheaper option available is Wilson feed through, for linear as well as rotational motion of the probe assembly. But Wilson feed through has a drawback. During its linear/rotational motion, the vacuum of the system is disturbed, due to leak trough the O’ rings. To overcome this problem, one has applied differential pumping in between the space of two O’ rings, we have increased this interspaced volume, and by pumping of this interspaced volume we are able to use this probe assembly in UHV systems. This UHV compatible Wilson feed through, can provide easy linear as well as rotational motion with negligible disturbance to the vacuum of the system. The fabrication of this type of feed through is quite easy and can be utilized for driving any system, e.g. filament holder, sample holder etc. We have designed Langmuir probes using this UHV compat...
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