Re: EMP VS. LED
Actually a lot of things attached power lines are not likely to be bothered much at all. Anything with an transformer on the input side is probably safe. At the frequencies involved with EMP, the transformer is huge brick wall. This is demonstrated almost every day everywhere in the world. EMP is very much like induced voltages from a lightening strike. The instantanous power is huge, but the total energy is very small. A direct lightning strike is another matter, there the instataneous power is huge, and the energy is huge. Direct strikes do a lot of damage, induced voltages tend not to do much damage, even though the induced voltages in a power transmission line my be as much as 100Kv...
EMP tends to be a problem only with high density devices. You get very high instantaneous power, but relatively little energy. This is why for example, Vacuum tube devices are pretty much immune to EMP damage, they have large energy dissipation areas. My gut feel is that devices such as 1 watt + led's are not likely to be damaged. Just not enough energy delivered.
The bind is you take something like a transitor on an IC, which is a 1 micron feature for example. You hit it with an induced voltage of 50 volts, and the characterisitic line impedance which determines the EMP current is probably in the 50-70 ohm range, so you deliver say 50 volts at 1 amp for 1 micro second. Total delivered energey is 50 microjoules. Not much until you realize it was delivered to a device an area of about 1 billonth of a square inch. Energy density= 50,000 joules per square inch. Instant toast. Apply that same energy to MOSFET device, and the 50V part will simply punch a hole in the gate, also toast. Apply to a high power bipolar device, or for example a 1 watt LED, and it is still 50 microwatts, but say the feature size is now .1 inches, that is 50 microjoules spead of .01 square inches,
of that is 5 millijoules per square inch. You can raise that 50 volts to even 5000 volts (.5 joules, 1/2 watt for 1 second), and It isn't even going to get very warm. EMP is deadly against low power, and MOS devices, it just isn't a big hazard for higher power devices, it is more of a nuisance.
There is practical experience to back this up. In the early 1960's several tests were carried out in space, the largest was roughly 1.5 Megatons. It caused considerable havoc in the telphone system in Hawaii, and it caused power outages. the power outages were a result of the induced currents in the transmission network being sufficient to trip circuit breakers. (although it took a while for any to realize that the telephone and power network problems in the Hawaiian islands were EMP effects). There was damage to the telephone solid state gear, but at the time, much of it was still electromechanical, and that stuff, plus the older telephone (rotary dial), the older stuff escapced undamaged.
A similar induced current lead to one of the major blackouts in the 1970's in the eastern United States when a breaker in Canada tripped because of an geo magnetic storm(auroral) induced current added to the AC current in the transmission circuits.
The bottom line is that for the most part only low power, small feature devices, and insulated gate devices such as MOS technology, tend to be damaged by EMP. The larger featured, high power devices can usually dissipate the energy. The instantaneous power is very high, but the actualy energy delivered is very modest. So things like computer memories, 5mm LED's, CPU's etc are toast, your CRT is likely to escape damage.
Oh yes, the skin depth is pretty shallow. The formula for skin depth in copper is 6.6/f^.5 in cm. So at 60Hz it is .85 cm (hence copper wires up to about 1.7cm in diamter work well. Bigger then that, and you should use stranded conductors. at 1Kz it is .21 cm (about 1/100 th of an inch),
at 10 Mhz, 21 microns (about 1/10,000 th of an inch). Now you know why silver plating of high power vacuum tubes, and copper braid for a ground conductor is so attractive.
In short, an ammo box will provide more than adequate EMP protection. EMP sources are in the Mhz range, not Hz, not Khz. The accelerator issue is the wrong problem. The magnets in accelerators provide a uniform field, they are assential DC devices, so skin depth isn't meaningful, it is essentially a DC field.
