The Columbia Linear Machine (CLM) is a quiescent, steady-state linear machine designed for fundamental plasma studies. It has been devoted to the production and study of instabilities believed to be principal candidates responsible for the degraded confinement in tokamaks and the observed anomalous transport of particles and heat and the exploration of feedback control techniquest to stabilize the instabilities. The principal investigator is Prof. Amiya K. Sen. The students who run the machine are: Johannes S. Chiu.

Here are some of the current features of CLM:

• Differential pumping produces collisionless hydrogen plasma in the experimental region.
• A movable magnetic coil in the experimental region can be energized and used to form a magnetic field. The current in the magnet control the fraction of the trapped particles, while the axial location determines the mirror length.
• An ICRF mesh in the transistion region ensures heating of ions in the radial center of the plasma, hence producing an ion temperature gradient, facilitating the studies of the Ion Temperature Gradient (ITG) instabilities.
• A small ion beam source (IBS) is located at the end of the experimental region. This ion beam (also configurable as an electron beam) is used as a remote suppressor for feedback control studies.

If you want to see the Columbia Linear Machine in more detail, here is a cross-sectional view of the machine (122K Jpeg).

These are the modes that have been or are being studied in CLM:

• Curvature driven trapped ion/particle instability(TPI)
• Ion temperature gradient Instability (ITG)
• ExB rotational flute mode

Several means of diagnosis are available in CLM:

• Langmuir probes are used to measure the density, electron temperature and various anomalous fluctuations.
• Gridded ion energy analyzers are used to measure ion temperature.
• Emissive probes are used to measure plasma potential.

Here are some of the students that have graduated from this group:

• John T. Slough, PhD. thesis titled "Production and experimental study of the dissipative trapped ion instability", 1981.
• Alan B. Plaut, PhD. thesis titled " Growth rate, saturation and radial transport for the trapped ion instability", 1986.
• Robert Scarmozzino, PhD. thesis titled "Production and study of a collisionless trapped particle instability", 1987.
• Akihisa Sekiguchi, PhD. thesis titled " Stabilization of plasma instabilities using halo feedback and ion beam suppressor", 1991.
• Jiong Chen, PhD. thesis titled "Production and study of the ion temperature gradient instabilities", 1992.
• Philip Tham, PhD. thesis titled "Feedback control of plasma instabilties with charged particle beams and study of plasma turbulence", 1994.

If you want to know more about CLM, the best place is to look up the following published papers:

• G.A. Navratil, J. Slough and A.K. Sen, Phys. Rev. Lett., 47 , 1057, (1981).
• R. Scarmozzino, A.K. Sen, and G.A. Navratil, Phys. Rev. Lett., 57 , 1729 , (1986).
• A. Sekguchi, A.K. Sen, and G.A. Navratil, Halo feedback control of trapped particle instabilities , IEEE trans. Plama Sci., PS-18 , 695 (1990).
• R.G. Greaves, J. Chen, and A.K. Sen, Experimental studies of an ion temperature gradient driven instability in a linear machine , Plasma Phys. Controlled Fusion, 34 , 1253 (1992).
• P. Tham and A.K. Sen, Feedback stabilization of plasma instabilities using a modulated ion beam , Phys. of Fluids B, 4 , 3058 (1992).
• P. Tham and A.K. Sen, Remote multimode feedback stabilization of plasma instabilities , Phys. Rev. A, 46 , 8, R4520 (1992).