Electromagnetic Pulse Facilities (1970 – 1993)
Electro-Magnetic Pulse or EMP is a very intense impulse of electromagnetic energy that can occur during a nuclear explosion. In 1962, EMP was discovered after a nuclear test at 400 km altitude, about 800 km from Hawaii. The effects on July 9, 1962, in Honolulu were described in a magazine: “The quiet predawn in Honolulu in 1961 was shattered by the simultaneous pealing of hundreds of burglar alarms. At the same instant, circuit breakers on the power lines started blowing like popcorn“.
Only sometime later, when no cause was found, a correlation was made with the nuclear test at a large distance. The defects and failures that occurred were caused by EMP and were comparable effects of a short-range lightning strike. EMP is, therefore, a phenomenon in which the strengths of the electric and magnetic fields increase to very high values in less than one hundred-millionths of a second. As a result, for example, a peak voltage of 25,000 V occurs in a rod antenna of a portable radio, as a result of which transistors in the radio are fried. It is likely that electrical systems and installations with long wires and cables will be disrupted or are destroyed, such as electrical power stations, refineries with process controls, communication centres, computers and the like. The treacherous aspect is that EMP effects may occur in an area with a radius of more than 1000 km when a nuclear weapon explodes high in or just outside the atmosphere. Even when this happens far outside the Dutch territory, it still can be dangerous.
Since 1970, TNO Waalsdorp has therefore been using EMP simulators and computer programs to investigate exactly what the effects of EMP are on electronic systems and what countermeasures can be taken. In summary, an EMP simulator requires a high electrical voltage, very short rise times and very high frequencies. Therefore, such a simulator consists of a high-voltage pulse generator connected to a so-called flat-plate transmission line, which is terminated at the end with an ohmic load R = Z0 where Z0 is the characteristic impedance of the transmission line.
EMIS-1, EMIS-2 and EMIS-3
At first, a small EMP-simulator was built called EMIS-l with the nickname “Piggy bank”. It size was about 0.8 x 0.8 x 1 meter. Only small devices up to 50 x 50 x 50 cm could be tested in EMIS-1 for their EMP sensitivity up to 50 kV/m.
Later, a large 60-meter simulator was built behind the laboratory at Waalsdorp: EMIS-2. EMIS-2 allowed testing of entire systems with dimensions up to 3 x 8 x 25 meters. To simulate an EMP in EMIS-2, a capacitor battery was charged up to 500,000 V and then discharged into the transmission line using a very fast switch (spark gap). In less than 5 nanoseconds, a current of about 5,000 Ampères would flow into the transmission line. Between the “plates” of the transmission line, the generated impulse-shaped electromagnetic field then corresponds to a nuclear EMP. The strength of the generated field could be set because it was necessary to know at which EMP level system defects would occur. The highest field strength that could be generated in the test volume of EMIS-2 was 80 kV/m.
At the start of an EMP test, the power flows in cables, antennas and circuits were first measured using special measuring equipment. The possibly vulnerable parts could then be identified from the measurements and from studying the schematics of the equipment. If the EMP-test showed that defects occurred, TNO investigated what kind of protection measures could be taken.
EMIS-3 was an even larger, mobile EMP simulator which was installed at the military airfield Ypenburg in 1982. EMIS-3 allowed testing of aircraft, ships, and complete communication centres for their sensitivity to EMP. In 1983, a horizontal emitter for EMIS-3 was installed and a transmission line that could be used to test accommodations and aircraft at threat level was completed. In the next years, the system was continuously in use to test equipment of the Armed Forces. In 1987 experiments started with the current induction generator with which, at EMP threat level, currents could be induced in cables of communication systems.
In July 1992, a completely renewed pulse generator for the EMIS-3 was transported to the EMIS installation at Ypenburg. This simulator met the newest, 1990, NATO test requirements. On 14 October 1992, all acceptance tests were successfully completed and the installation became operational. Aside from EMIS-3 at Ypenburg, only an EMP test installation existed in the USA that was capable of generating a comparable pulse, albeit with some limitations.
It is worth noting that the EMIS-2 antenna became inoperative when all systems of an Anti-Aircraft tank, type CA-1 (CAESAR), were undergoing an EMP test. When the Royal Netherlands Navy flew along the coast with a Breguet Atlantique, the AA-system automatically tracked that aircraft as a target. The gun barrels followed the Navy plane and ruptured the EMIS-2 antenna system.