Cups of Cold Water Another important factor when dealing with klystrons is heat. Not all of the developed in the cathode becomes radiated output. Much of the energy is dissipated as heat. If the tube gets too hot, it can become a hazard to itself. Temperature sensors are placed in various places to shut down the tube in the event of overheating. Also, the means by which the tube is cooled can vary. At low power levels, air cooling (fans) is sufficient. As the heat increases, however, it is necessary to find alternate methods of cooling. Water cooling, much like in automobiles is an option, but there are some precautions to be made. Recall the old saying "electricity and water don't mix"? Well it's not quite true. You see, water, if it is perfectly pure H2O is a very good resistor. It is only when contaminants are added to the water that it becomes conductive. The problem is, how do you get pure water? If you have pure water, and put your hand into it, the natural body oils enter the water, and it is no longer pure. Many materials can make water unpure, so it must be constantly monitored and controlled. Water can be made pure by distillation or by filtering. Water can either be distilled, or run through oxygen scavenging and mixed bed resins to pull out the ions. The water must be reduced to as low as .05 ppm (parts per million) by weight of some elements. Even then there are problems. Many filter cartridges and resins will break down at elevated temperatures (some as low as 50o C). The cooling process is accomplished via "Heat Exchangers" - basically big radiators, much like the one in your car. The water is run through the heat exchanger to cool down. The heat exchanger can either have cooled air, or some other coolant (say, liquid nitrogen or amonium glycol) run across the fins in order to further cool the pure water. In systems using two coolants (pure water and glycol for instance), care must be taken to insure that they do not mix. A leak in a heat exchanger is a bad thing. Glycol doesn't work well inside some klystrons. It can heat up to a point where it turns to burned sugar on the cooling fins of the klystron, causing it not to cool at all. Another problem is that certain chemicals can "leach" into the pure water. Even in a perfectly sealed system, water doesn't like to remain pure. It likes to pull ions of other chemicals from the very containers it is in. Think not? Check the water that comes out of your tap. Just look at the rust and other debris that it picks up. All metallic components within the pure water system, to include the heat exchanger, pipes, pump, etc., must be made of copper, or stainless steel. If bronze or unleaded brass is used, zinc or other chemicals may wind up leaching out of the metal into the system. Other metals such as lead iron, or cold rolled steal will REALLY mess up the water. Even if the water is perfectly distilled, and the pipes and such are stainless and copper, it is possible for metals, oxygen, and carbon dioxide to contaminate the water. Also, it may be necessary to flush the coolant system with sodium hypochlorate (bleach) to prevent bacteria and algae growth. For these reasons, as continuous filtering loop should be inserted in the cooling system. Constant monitoring of the conductance (in microseimans) of the pure water is also suggested.

This Course was written by Ray Dall © All Rights Reserved.
This page and all it's content Copyright, Trademarks, Intellectual Properties
and other legal issues 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Ray Dall.
All Rights Reserved.
And for what it's worth... this page was last updated HexDate 01-11--7D1

VISITORS: