CHAPTER 3 OHMIC BUCKET 3.1 Ohmic Bucket Requirements The ohmic bucket originated from the desire to be able to test mass driver two before the superconducting bucket was ready from M.I.T. This permitted routine testing of mass driver two without the need for vacuum and liquid helium. The ohmic bucket consists of two aluminum wire coils mounted on a G-10 tube as shown in Fig. 3.1. The capacitor bank that powered the ohmic bucket through a tether is shown in Fig. 3.2. To obtain current densities comparable to the of a superconductor it was necessary to cool the ohmic bucket to liquid nitrogen temperature. This reduced its resistance by a factor of more than nine. Cooling the ohmic bucket with liquid nitrogen is shown in Fig. 3.3. A hose with warm air is positioned near the resistor-diode network at the back of the ohmic bucket to prevent frost buildup. During a test firing the ohmic bucket is removed from the liquid nitrogen and placed into the injector. Within 15 seconds (to prevent it from warming up too much and increasing its resistance) the ohmic bucket is fired. It was caught with a backstop consisting of a box of styrofoam backed with lead bricks as shown in Fig. 3.4. Based on energy transfer calculations for different buckets (mass and coupling) currents of 24,000 to 45,300 amp turns are required to obtain 500 g's of acceleration. Previous design details of the ohmic bucket and its associated injector can be found in APPENDIX I.
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