Former Research Facilities: Electromagnetic Pulse facilities (1970 – 1993)
Electromagnetic Pulse Facilities (1970 – 1993)
Background
An electromagnetic 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. EMP caused the defects and failures that occurred. The effects were comparable to that 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 causing transistors in the radio to be ‘fried’. Electrical systems and installations with long wires and cables will likely be disrupted or destroyed, such as electrical power stations, refineries with process controls, communication centres, computers, etc. The treacherous aspect is that EMP effects may occur in an area with a radius of more than 1,000 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.
Therefore, since 1970, TNO Waalsdorp has used EMP simulators and computer programs to investigate exactly what the effects of EMP are on electronic systems. 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 “Piggybank”. Its internal size was about 0.8 x 0.8 x 1 meter; the external cube size was 2 * 2* 2 metres. 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 the 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 that was installed at the military airfield Ypenburg in 1982. EMIS-3 allowed the 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 used to test the 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 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 mentioning that the EMIS-2 antenna was completely destroyed by an anti-aircraft tank, the Armored Caterpillar Against Air Targets (PRTL), when it underwent EMP tests. The PRTL unit commander mailed us his account to us in 2024:
“As a conscription soldier, I was enlisted with the 43rd Armoured Anti-aircraft Artillery. I was stationed in Havelte. Sometime in 1983, TNO asked the battalion commander to assist in performing EMP tests on the detection and guidance systems of the PRTL. As PRTL unit commander, I was assigned to that task together with two soldiers. That was nice; all three of us lived in The Hague. In this way we could work on the Waalsdorpervlakte for a week or two, I think, and just be at home in the evenings.
The PRTL was transported with a LoLo (DAF YT-616 with Notoboom semi-trailer) and delivered to the Frederikkazerne. The next day, we drove the tank along the road to the Waalsdorpervlakte with a military motorcycle escort. A short ride, but quite an experience in itself of course. The PRTL was a ‘beast of a tank’. I think we had to drive up and down every day because the PRTL was not allowed to remain on TNO’s EMIS-2 installation for the night. We also did some maintenance work at the barracks according to the maintenance schedule.
At TNO’s EMIS-2 location, the PRTL was placed under the installation’s antenna wires. After a general explanation of what we were going to do, we were instructed each time to configure the PRTL equipment in a certain way: radar on or off, tracking radar activated or not, turret hatch open or closed, gun barrels high or low, a whole series of configurations passed.
We always set the PRTL in the desired configuration and then had to leave the test installation before the pulse was issued. After each pulse, a series of tests were performed. External equipment was connected to the PRTL and the TNO technicians performed a test program. Sometimes we were needed for assistance, sometimes not. A nice activity for us as conscript soldiers: not too busy work and a nice and quiet environment.
The PRTL crew took turns. The driver had his tasks, but my fellow soldier and I took turns configuring the PRTL for the next test.
One night it had rained. The next morning it was my turn to prepare the PRTL for the tests. The tracking radar would be activated that morning. However, next to the EMIS-2 installation lay a large roll of mesh. The meshes of the mesh roll contained rainwater, making the entire roll radar-reflective. The tracking radar responded, immediately followed by the guns. However, the roll of mesh was well within the minimum distance to track an aircraft. The PRTL tower couldn’t turn that close given the angular velocities.
The PRTL’s systems then automatically started a vertical search. During that search, the tracking radar found the EMP antenna wires strung above the PRTL. Since they were also wet and reflective, the barrels automatically assumed an almost vertical position. However, the antenna wires were much closer than the minimum tracking distance. With the barrels raised, the ends of the barrels stuck between the antenna wires and the thick wooden beams that kept those wires separated. The PRTL tower then automatically made a 360-degree search.
With the circular search, the antenna wires and beams rotated around the barrels like a coil. Both the antenna wires and the beams broke. I was slightly injured because part of one of the beams landed on my head. Of course, the crash also made a lot of noise. My reflex was to return the PRTL to its resting position: tracking radar retracted, barrels horizontal and the turret at zero degrees of rotation. To do that, I pushed one button. To that resting position the tower rotated almost 180 degrees and that movement, together with the downward moving barrels, caused the entire EMIS-2 antenna installation pulled downwards. Remember, all these actions happened in a few seconds.
Chaos everywhere on the test site. I stepped out of PRTL with a bloody head. It was not immediately clear that I was only slightly injured. I suffered a cut and a bump on my head. In a short time, the EMIS-2 test site was overrun by many people from TNO and the military. Later, two military police officers arrived to record my statement. ‘Was I to blame?’ I refused to answer questions by the military police without an officer present with knowledge of radar systems in general and the PRTL in particular. After a while, a Colonel from the nearby Frederikkazerne arrived. He knew all about the system. In the meantime, a medic was able to treat my head wounds. In the presence of the Colonel, I told the story above to the military police. The Colonel confirmed the PRTL’s automatic actions. It was concluded that I had not made any mistakes with the PRTL operation. The PRTL system automatically responded as programmed and was supposed to work. The problem was the wet roll of mesh next to the EMP installation. I never heard anything about the incident again.
There was a chance that the PRTL barrels had twisted and were no longer straight. That is why we painted two red rings on each barrel of the PRTL cannons at the Frederikkazerne to mark them disabled for shooting. With that, unfortunately, our stay in The Hague ended. When we returned to Havelte with red markings on the barrels of the PRTL, we attracted a lot of attention. Word had preceded us. Together with colleagues we dismantled the cannons. Those were sent back to the factory. We then drove a PRTL without guns for some time. That was a bit weird.“
