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Heavy Ions
Heavy ions used at the BASE Facility are accelerated in the form of “cocktails,” named because of the fact that several heavy ions with the same mass-to-charge ratio are sent into the Cyclotron, which accelerates the ions while acting as a precision mass separator. The Control Room Operator then uses Cyclotron frequency to select only the desired ion, a process that takes about 2 minutes. We provide three standard cocktails: 4.5, 10, and 16 MeV/nucleon. Our 4.5 MeV/nucleon cocktail provides LETs from 1 to 100 MeV/mg-cm2 with flux levels of up to 1E7 ions/cm2-sec, while our 16 MeV/nucleon cocktail allows testing in air with a reduced LET range. A 32.5 MeV/nucleon cocktail, with a reduced LET range, is also available for use in our adjacent proton facility.
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Parts are tested in our vacuum chamber, and can be remotely positioned horizontally, vertically, or rotationally (y and z axes) with the motion table. An alignment laser is available to ensure the part is in the center of the beam. Mounting hardware is readily available. 12xBNC (F-F), 2x25-pin D (F-M or M-F), 4x40-pin flat ribbon (M-M), 4x50-pin flat ribbon (M-M), 12xSMA (F-F), and 2xEthernet vacuum feedthroughs are mounted upon request. Holes are provided through the cave shielding blocks for connecting additional test equipment, with a distance of approximately 10 feet from vacuum feedthrough to the top of the shielding block.
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To tune the beam in to the cave, the beam is first spread out (4-inch diameter) evenly on the cave phosphor and viewed with a digital camera by the Control Room Operator. Once the visual spread is satisfactory, the beam is attenuated and five Hamamatsu R647 photomultiplier tubes (PMTs) are inserted. Four PMTs are placed around the edge of the beam, and one is placed in the middle. These PMTs are then calibrated by Cyclotron operations staff, after which the center PMT is removed to permit exposure of the target. All PMTs currently use YAP:Ce crystals that have proven to show minimal, if any, degradation in performance after extended periods of time in high-flux, high-LET beams. The PMT signal is routed through (CAMAC) scaler and discriminator modules before being sent up to the computer.
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The final processing and indication is performed with LabView software. The beam may be stopped manually, or by setting run time, fluence, or effective fluence limits. A run log is automatically created and maintained on the PC desktop that provides a detailed history of the run, and can be downloaded to a memory stick or similar device via USB ports on the front of the computer upon completion of testing.
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