The strength of the EMP is dependent upon strength and orientation (dip-angle) of the geomagnetic field. The Earth’s magnetic field varies across the globe and also varies with time at a given location. Since Kazakhstan’s latitude and magnetic field (magnitude and orientation) are similar to that over the continental US, we would expect very similar EMP fields from a large (300-kiloton) two-stage device exploded about 290 kilometers over the continental US. Of course, such devices are not available to new nuclear proliferator states.
Effects upon power-delivery systems
It has been argued that the lack of damage to both the power and communications systems in Hawaii from the 1.4-megaton Starfish test counters the prevalent view that EMP is devastating to such systems [17]. However, it should be noted that the line-runs in Hawaii were considerable shorter than on the continental United States, so one cannot dismiss the vulnerability altogether based only the empirical data collected in Hawaii.
While high E1 fields may not couple to the long-lines in a power delivery system, the E1 pulse could disrupt/destroy the IC-based controllers for power-delivery systems, leading to at least temporary failure, and possibly more serious effects in the hardware. As the EMP commission reports:
[T]he local switching, controls, and critical equipment have become largely electronic with concomitant vulnerability to [E1] EMP… The continuing evolution of electronic devices into systems that once were exclusively electromechanical, enabling computer control instead of direct human intervention and use of broad networks like the Internet, results in ever greater reliance on microelectronics and thus the present and sharply growing vulnerability of the power system to [E1] EMP attack… The E1 pulse can upset the protection and control system, including damaging control and protective system components, and cause the plant to trip or trigger emergency controlled shut down… Given the range of potential E1 levels, analysis and test results provide a basis to expect sufficient upset to cause a plant’s system to shut down improperly in many cases. Proper shutdown depends on synchronized operation of multiple controllers and switches. For example: coal intake and exhaust turbines must operate together or else explosion or implosion of the furnace may occur. Cooling systems must respond properly to temperature changes during shut down or thermal gradients can cause boiler deformation or rupture. Orderly spin-down of the turbine is required to avoid shaft sagging and blades impacting the casings.
Electronic control systems are effectively, according to the EMP commission, the Achilles’ heel of our power delivery network. While it is uncertain what the exact implications of losing such control systems would be on the major hardware (e.g. transformers, turbines, etc.), it is best to be prudent and assume substantial damage may result, at least in the peak E1 field region, for a large nuclear device. (The spatial extent of this peak-field region, for the types of the threats most feared by the EMP commission, see Fig 1.) Outside the region exposed to a substantial E1 pulse cascading grid failure may well occur, but since the associated hardware damage would not be expected there, it would reasonable to assume that that portion of the grid could be resuscitated after a short outage.
Specifically regarding nuclear power plants, in the early 1980s a Sandia Laboratories analyzed the “worst case” scenario and concluded that EMP poses no substantial threat to such plants based upon both analysis and simulated EMP tests. [18]
For the reasons outlined above, one cannot simply use the peak E1 field numbers to calculate the effects on long-lines. It is the weaker, but longer lasting and lower-frequency E3 pulse that causes the greatest direct damage to power delivery systems, as it is this component that couples to the long-lines [17].
EMP effects upon IC-based devices
The effects of EMP on ICs include malfunctions and loss of data, thermal runaway, gate-insulator breakdown, avalanche breakdown, tunnel breakdown, and metalization burnout. The energy required may be provided by the surge itself and/or by other sources (such as the power supply or storage capacitors). As successive generations of electronics pack ever more components into smaller spaces, this increasingly inhibits the ability of the circuit to conduct away the heat that results from the typically intense, short voltage and current flows generated by an EMP.
Tests with EMP simulators have shown that a very short pulse of about 10-7 Joule is sufficient to damage a microwave semiconductor diode, and roughly .05 J will damage an audio transistor, whereas 1 J would be required for vacuum tube damage [ref. 5, pp. 522–4]. More precisely, the limit is defined in terms of the instantaneous (few nanoseconds risetime) power delivered to the IC [19]. A few watts to a few hundred watts of power are sufficient to destroy most ICs, when delivered in a few nanoseconds (e.g. 10-7 J /10-8 sec = 10 W).
Thus, how quickly the EMP E1 pulse is delivered affects the consequent IC damage. Note that the pulse length increases as one goes further from the peak field region [6], and this is another reason (besides the natural decrease of the E1 field strength) to expect somewhat less damage towards the periphery of the exposed region, especially for a small (~1 kiloton) device.
The effects of prompt, E1 EMP on ICs cannot be calculated directly without knowledge of the details of the particular electronic system set-up. An E1 pulse acts on an electronic system by inducing surges in the interconnections (cables, wires, inductors, etc.), which arrive at input, output, and power-supply terminals of solid-state components to cause transient and/or permanent failures. When applied to solid-state parts, a nuclear EMP can be considered a quasi-static field because most of the EMP energy is carried by the spectral components below 108 Hz, which corresponds to a wavelength of about 3 m. Investigations have shown that the
direct effects of such a field are negligible for most purposes if its electric and magnetic components are less than 100 kV/m and 600 A/m, respectively [20].
The bottom line is that, indeed, our infrastructure is vulnerable to significant E1 and E3 pulses. While significant E3 would not be expected from a low yield weapon, it would be expected from a solar storm. |
Thus, EMP hardness assurance of ICs is concerned with EMP-
induced voltage surges rather than the actual EMP field intensity, per se. To be able to properly asses the induced voltage surges one must be able to characterize EMP voltage surges that may arise in wires and at the terminals of solid-state components and then determine the response of a particular solid-state component to the voltage surges. It is important to note that an EMP can induce powerful voltage surges even when the electromagnetic field itself is moderate in strength. This occurs in electronic systems with suboptimal layouts, such as those with long connecting cables that act as antennas. EMP-induced surges are also strongly dependent on the orientation of the parts relative to the electric and magnetic fields, the precise parameters of the solid-state components, the amount of shielding provided, and the method of grounding.
In recent tests, three types of failure were observed: upset, temporary failure due to latchup, and permanent damage caused by secondary effects [20]. Upsets occurred from 1- or 10-microsecond pulses. While a 0.1-microsecond pulse was found to be too short to change the charge state of parasitic capacitances and corrupt the data, its steep (~few nanosecond rise-time) leading edge activated latchup of the components. Even a few hundred volts of
induced voltage was found to be sufficient to cause permanent IC damage.
Comparisons with lightning
Lightning shares many of characteristics of E2, but contrary to what is often quoted, its magnitude can exceed even the peak E1 fields in the discharge region [17]. Research on lightning indicates that a stroke may contain significant components with rise-time of less than 10-7 sec and electric fields greater than 106 V/m—more than a order of magnitude greater than even the highest peak E1 fields, from the biggest nuclear devices. [21]. Although the aforementioned Russian study [20] indicates that it is the sharp leading edge of the pulse, with components from 10-9 to 10-8 sec that are of most concern to IC latchup, the implications of lightning research for EMP vulnerability is a critical topic to include in any future peer-reviewed study of the EMP threat.