index

0916 TNT: ultra-low-q operation of an iron-cored tokamak achieved by a high-resistance primary circuit

Finally, ultra-low q operation. find attached one of old papers where we did this on CLEO (with and without using the old stellarator coils to assist the low-q operation) but a quick read does not indicate what we did on the primary circuit, which I remind you was to add a significant series resistance so the the primary current was mainly dictated by the bank voltage divided by that resistance. CLEO was an iron-cored machine like GOLEM and the Russian machines that did similar experiments, so the secondary current (i.e. the plasma current) has to be minus one times the primary current amp-turns (apart from any offset due to core bias), irrespective of any q-limits or MHD activity - until the MHD is so strong that the loop resistance (multiplied by the transformer ratio) becomes larger than the primary series resistance.

I recall that Derek Robinson told us that if the Magnetic Reynolds number (S) was smaller than a few hundred, the very cold plasma (~10eV?) would have insufficient free energy to drive any MHD and the plasma would be extremely resistive but very quiescent. This may be an outcome if one tries to achieve q a little below unity, but as we said when we discussed this, reversed field pinches necessarily go rapidly through q=1, towards q~0.2 or lower, every time they are initiated so q=1 is not a hard limit, whatever Kruskal and Shafranov said!

Here’s a more complete version of the important reference [2] as copied from a more modern document, so you can copy and paste parts of it into the web - I tried for some time but could not find this article on line: Leonov, V. M., Merezhkin, V. G., Mukhovatov, V. S., Sannikov, V. V. and Tilinin, G. N., “A Study of Plasma Confinement under Conditions of Ohmic and Neutral Injection Heating in the T-11 Tokamak,” in 8th International Conference of Plasma Physics and Controlled Nuclear Fusion Research, Paper IAEA-CN-38/N-2, IAEA/ Brussels, 1980.