Mass driver two: A status report

Mass Driver Two combines for the first time all the essential features of an operational mass driver, with the exception of bucket recirculation and payload handling. Its nominal design acceleration is 5000 m/s
²
, for a final velocity of 112 m/s. That velocity is to be obtained through a 1.25 m acceleration section of 59 drive coils, each of 13.1 cm caliber and 2.46 cm separation. It is followed by a decelerator section of identical design, to bring the bucket to rest with the return of energy to the power supply. Construction of Mass Driver Two (as well as portions of its extension for higher velocities) began in the spring of 1978. The accelerator section is now essentially complete. Testing began in July, 1979, with an ohmic bucket to simulate the superconducting bucket. The superconducting bucket, together with its cryogenic service station, is being built by a group at M.I.T. led by Dr. Henry H. Kolm. The ohmic bucket, capable of equalling the current density of the superconductor for a time of 0.2 second or less, allows our testing the accelerator in atmosphere rather than in vacuum, and without requiring liquid helium. Our major construction project in recent months has been the design and construction of the main recharging power supply, a large capacitor bank with SCR's and controls capable of supplying high-current pulses, for times of the order of 100 microseconds, to recharge the sector capacitor banks between the mass-driver's current pulses. That recharging supply is now complete and under test. We have written and run programs for simulating the operation of mass-drivers, and as a result have concluded that the accelerator model, when used with the M.I.T.-developed superconducting bucket, can achieve an acceleration at least as high as the design goal of 500 gravities. The calculations have also stimulated a new interest in more tightly coupled mass-drivers with novel methods for magnetic guidance. As a result, we are also building a tight-coupled ohmic bucket, which is calculated to achieve an acceleration of over 500 gravities.