Magnetic resonance imaging of magnetohydrodynamic flow field using modified echo-planar pulse sequences
The magnetic resonance imaging (MRI) is a technique that visualizes the distribution of nuclear magnetization based upon the resonance phenomena between the Larmor motion of nuclear magnetic dipole and applied RF magnetic field. With applying the so-called flow encoding pulse (FEP) additionally, the MRI can be adapted to map the velocity. In the conventional MRI which is widely used in the medical field the gradient echo imaging is used. Here, as the spatial resolution is of primary importance, a sufficient number of shots is used to acquire MR signals. Therefore, this is applicable to stationary or slowly moving objects. On the other hand the acquisition time can be drastically shortened by employing the so-called echo-planar imaging (EPI) developed by P. Mansfield. Therefore, the EPI has high potential of application to a wide variety of fluid motion. The works of Kose et al. successfully demonstrated this fact in the visualization of turbulent pipe flows. However, the velocity range ever treated is up to few meters per second and no attempt has been made to visualize flows of the sonic speed range. In this respect, the authors adapted the EPI to a magnetohydrodynamic (MHD) channel flow. However, even the EPI was not a high-speed enough to visualize flows of the sonic speed range. Therefore, they have shortened the measurement time of the EPI further by changing the pulse sequences. The total sampling time of several tens milliseconds in EPI could be shortened to several hundreds nanoseconds. The adaptability of ultra-high speed MRI using modified echo-planar pulse sequences (MEPS) to velocity mapping of MHD plasmas was investigated. An experiment was carried out to visualize the axial velocity distribution in a cross section of an MHD channel installed in a shock tunnel. The measured results agreed with simultaneously measured open circuit voltage and those predicted by 3D computer code for MHD plasma channel flows.
- Research Organization:
- Hokkaido Univ., Sappora (JP)
- OSTI ID:
- 20000337
- Resource Relation:
- Conference: 33rd Intersociety Energy Conversion Engineering Conference, Colorado Springs, CO (US), 08/02/1998--08/06/1998; Other Information: 1 CD-ROM. Operating system required: Windows 3.x; Windows95/NT; Macintosh; UNIX. All systems need 2X CD-ROM drive., PBD: 1998; Related Information: In: Proceedings of the 33. intersociety energy conversion engineering conference, by Anghaie, S. [ed.], [2800] pages.
- Country of Publication:
- United States
- Language:
- English
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