Engineering is as much a part of the scientist and science is a part of the engineer. The difference is just in what your job discription and pay is.
A formal engineer is a guy who designs and makes stuff
A formal scientist is someone who does experiments, collects data and arrives at conclusions.
There is not much room in today's world for the pure versions of either the engineer or the scientist. All tend to get their hands dirty and experiment with ideas within the limits of both science and engineering. Each occasionally pushes the limits of one or the other or both of the disciplines.
Employers often push hires in either discipline to be both. I have a friend who is a physicist with NRL and she is doing 90% engineering work only.
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As for Steven's question.........What is differential pumping............
Virtually all ion gunned systems are differentially pumped.
The ion gun may be considered or viewed as a slow leak in a very high vacuum system.
Ion guns have a flow of gas constantly added to them which is regulated. All ion guns have an extractor port where the ion stream pass freely through a focused hole into the reaction or vacuum chamber. Thus, a gas leak is a permenant load on the master pumps on the high vacuum chamber.
While the conductance of the ion gun or guns is extremely low, it is quite real, nonetheless, (leaks).
Thus, the pump on the main vacuum chamber has to have enough pumping capacity to evacuate the main reactor vessel or chamber to the its ultimate pressure against these real leaks. There are complex but very doable calcs extant that can compute the exact pump capacity needed to achieve the final bottom pressure desired in the main chamber against the gas leak load of the ion gun or guns. Most avoid the calcs and massively over pump a system and use a pinch off valve to set the final pressure to any desired level.
An example would be that the ion guns must be kept at 25-50 microns to allow for high current glow discharge while the main chamber is kept at 10e-5 torr to assure an MFP large enough so that the bulk of the ions produced will arrive on target in the vessel without gas collisons inducing major loses in the ion beam.
Some complex systems (rare) vaccum pump both the guns and the chamber.
The term differential is obvious from the above explanation. There are pressure differentials in the devices within the vacuum system.
Carl's extractor opening is huge by most standards. Thus his smaller pump can't handle the load. Traditionally, extractor openings are measured in the mm to sub mm range. As such extractors get very hot and their openings errode rapidly due to the velocity of ionic fluid flowing through them. Most ion guns are serviced regularly and must be designed for rapid component replacement.
Note: I am not saying Carl made his extractor hole too big. Large extractor holes usuall mean very bright ion sources and concomitant heroic differential pumping efforts. 1-2 ma ion sources would be considered fairly bright, especially for simple amateur efforts.
Carl, do you need or have access to an electrometer for faraday cup measurements?
Richard Hull |
2008-14-09 04:09 RF ion source sees first light 
(Carl Willis) [Latest: 2010-03-05 09:23]
2008-15-09 11:10 Re: RF ion source sees first light (Richard Hull)