Tech Level: 11
The word compulsator is an amalgam of the term Compensated Pulsed Alternator. They were originally conceived in the 1970s at the University of Texas Center for Electromechanics (UT-CEM) to power laser flash-lamps for nuclear fusion research. Prototypes were built at UT-CEM in the early 1980s, and they have since found applications in a number of other fields, most significantly at the US Department of Defense and NASA in powering experimental electromagnetic launchers.

A closely related technology to flywheel batteries, compulsators are an advanced form of alternator that stores potential energy in the form of rapidly spinning rotors. (Technically these rotors can also be called flywheels, but they are referred to here as “rotors” to avoid confusion with flywheel batteries.) The main difference between the two technologies seem to be that compulsators are designed for short-term use as an alternative to high-voltage capacitors, while flywheel batteries are designed for long-term energy storage. The rotors in a compulsator tend to be lightweight to allow for super-high spin, while the flywheels in flywheel batteries tend to be heavy and dense to store more energy with less extreme spin rates.

An external power source typically spins up the rotors in a compulsator, allowing it to store the energy potential in the form of inertia from its spin. A compensating shield or winding in the alternator is used to lower the rotors’ internal impedance, i.e., it allows it to spin up to speed with only minimal interference from the surrounding electromagnetic fields.

Like with flywheel batteries, the amount of energy a compulsator can store depends on its size and its maximum rate of spin. One rate of spin on test rotors in military compulsators was quoted at over 18,000 rpm’s. Unlike flywheels in flywheel batteries, however, their rotors depend much more on high velocity spin than on the mass and density to retain their imparted energy.

Compulsators store energy from large but relatively low-current generators and motors for use in the short term as quick-access high-current sources. In this way, they act like capacitors, but are capable of storing and releasing greater amounts of energy per unit of weight and volume.

Similarly to their flywheel battery cousins, material technology is one of the great limiting factors in exactly how much energy the unit can store. If the rotors in a compulsator are spun too fast, centrifugal force will literally rip them apart. Typically being lighter and spun much faster than a flywheel disc, compulsator rotors are much more vulnerable to this kind of damage.

Also, even though theirs rotors are designed to be relatively lightweight, compulsator units themselves tend to be massive and bulky, needing to handle heavy-duty torque and magnetic forces. Efforts to make them more lightweight and compact are ongoing.

Because of the anticipated need for frequent large pulses of power on a moment’s notice in a number of applications, including high-performance electric vehicles and high-energy weapons like railguns, compulsators are a technology that is likely to enjoy more wide-spread use in the near-term. Much research is going into constructing them of much tougher composite materials that can better withstand ultra high rates of spin and thus allowing them to store more and impart energy.

Currently the most advanced compulsators, built by UT-CEM for the US Marine Corps’ Cannon Caliber Electromagnetic Gun System (CCEMG) program, could store up to 40 megajoules of energy and was capable of delivering the energy for 15 shots for the prototype weapon before needing to be recharged. Compulsators are also to be an integral component of the US Army Research Laboratory’s Future Main Battle Tank program, scheduled for deployment by 2015, which would feature an armored fighting vehicle with an electrically-powered main armament.