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Internal Transport Barrier: Difference between revisions
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ITBs can be actively produced by modifying the current profile using external means. | ITBs can be actively produced by modifying the current profile using external means. | ||
<ref> | <ref>R.C. Wolf, ''Internal transport barriers in tokamak plasmas'', [[doi:10.1088/0741-3335/45/1/201|Plasma Phys. Control. Fusion '''45''' (2003) R1-R91]]</ref> | ||
They are used to improve plasma confinement and stability properties, and to drive additional [[Bootstrap current|bootstrap current]]. Therefore, they are included in some alternative operational scenarios for [[ITER]]. | They are used to improve plasma confinement and stability properties, and to drive additional [[Bootstrap current|bootstrap current]]. Therefore, they are included in some alternative operational scenarios for [[ITER]]. | ||
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The mechanism for the formation of Internal Transport Barriers in magnetically confined plasmas is complex and not fully understood. | The mechanism for the formation of Internal Transport Barriers in magnetically confined plasmas is complex and not fully understood. | ||
The general consensus is that ITBs are the consequence of turbulence suppression due to sheared (''E'' × ''B'') flows. | The general consensus is that ITBs are the consequence of turbulence suppression due to sheared (''E'' × ''B'') flows. | ||
<ref> | <ref>K.H. Burrell, ''Effects of E × B velocity shear and magnetic shear on turbulence and transport in magnetic confinement devices'', [[doi:10.1063/1.872367|Phys. Plasmas '''4''' (1997) 1499]]</ref> | ||
Such sheared flows can be generated by the turbulence itself via the [[Reynolds stress]] mechanism. | Such sheared flows can be generated by the turbulence itself via the [[Reynolds stress]] mechanism. | ||
This process is related to the formation of the [[H-mode]] barrier. | This process is related to the formation of the [[H-mode]] barrier. | ||
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Factors contributing to the formation of ITBs include: | Factors contributing to the formation of ITBs include: | ||
<ref> | <ref>J.W. Connor et al, ''A review of internal transport barrier physics for steady-state operation of tokamaks'', [[doi:10.1088/0029-5515/44/4/R01|Nucl. Fusion '''44''' (2004) R1-R49]]</ref> | ||
* The power deposited inside the [[Flux surface|magnetic surface]], and/or local pressure gradients | * The power deposited inside the [[Flux surface|magnetic surface]], and/or local pressure gradients | ||
* [[Magnetic shear]] and the shape of the [[Rotational transform|rotational transform]] profile (e.g., reversed shear) | * [[Magnetic shear]] and the shape of the [[Rotational transform|rotational transform]] profile (e.g., reversed shear) | ||
* MHD activity | * MHD activity | ||
* Momentum torques (poloidal or toroidal) | * Momentum torques (poloidal or toroidal) | ||
* Enhanced collisionless losses of trapped particles, generating a radial electric field <ref> | * Enhanced collisionless losses of trapped particles, generating a radial electric field <ref>U. Stroth et al, ''Internal Transport Barrier Triggered by Neoclassical Transport in W7-AS'', [[doi:10.1103/PhysRevLett.86.5910|Phys. Rev. Lett. '''86''' (2001) 5910 - 5913]]</ref> | ||
* Reduced collisional damping, allowing the growth of zonal flows <ref> | * Reduced collisional damping, allowing the growth of zonal flows <ref>K. Itoh et al, ''Physics of internal transport barrier of toroidal helical plasmas'', [[doi:10.1063/1.2435310|Phys. Plasmas '''14''' (2007) 020702]]</ref> | ||
The relation between some of these factors can be understood from the steady state ion force balance for the radial electric field: | The relation between some of these factors can be understood from the steady state ion force balance for the radial electric field: | ||