Electron Power Systems, Inc. of Acton, Massachusetts, United States, claims to have developed a technology for maintaining small stable plasma toroids called electron spiral toroids (ESTs) which remain stable in Earth's atmosphere without the use of any special magnetic fields. They claim to have created these toroids in the laboratory, and to have developed a mathematical model for them that is similar to some explanations for ball lightning. An EST may be a special case of a spheromak.