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This article describes a process for generating a cold ion beam using a helium pulse cluster source and a graphite target rod coated with C60. The fullerenes react with carbon vapor, undergo supersonic expansion, and then enter the ion optics for accumulation and transfer to the ICR cell. The process involves the use of a Nd:YAG laser pulse to vaporize the target rod and a stepper motor for continuous translation and rotation of the rod.
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C60-coated graphite rod Cluster Source Valve emits a helium pulse Fullerenes react with C, C2 etc exit and undergo supersonic expansion to create a cold beam Nd:YAG laser pulse vaporises the target rod The rod is continuously translated and rotated by a stepper motor
stepper motor target rod accumulation octopole transfer octopole pulsed valve ICR cell skimmer pulsed valve source 10-7 torr diffusion pump 10-7 turbo pump 10-8 turbo pump 10-10 turbo pump
after 3-10 laser shot accumulations, the ions are transferred to the ICR cell C60 reacts with C species then exits supersonic expansion and skimmed ions accumulate in the octopole trap
fullerene-coated graphite target rod Cluster Source Block Valve emits a helium pulse Fullerenes react with carbon vapor (C, C2) in the “clustering zone”. Then, the gas exits the channel and undergoes a supersonic expansion to create a cooled, molecular beam Nd:YAG laser (532 nm, 3-5 ns, 5mj/pulse) vaporises the target rod by a single pulse/shot The rod is continuously translated and rotated by a stepper motor
After 3-10 single laser shot accumulations, the ions are transferred to the ICR cell, which is located within in the bore of a 9.4 tesla superconducting magnet. Under the influence of the high magnetic field, the ions exhibit cyclotron motion. The ions induce a current on electrodes, which is detected as an “image current” in the time domain, and then the signal is converted to the frequency domain by an FT. Thus, the mass of the ion is detected as a frequency. the ions which enter the ion optics, where they are acuumulated in the central octopole segment Fullerenes react with carbon species in the vapourisation zone, then exit reaction channel …undergo supersonic expansion and are skimmed into beam
Answer to questions from email. Q: How do you stop the pulse of ions in the accumulation trap A: The ions are confined radially by an oscilating radiofrequency within in octopole, and axially by voltages at the ends of the “accumulation octopole:.
Answer to questions from email. Q: How many pulses do you need to accumulate? A: A single laser shot is used vaporize the target during a single Helium pulse. Ten singe laser shot + He pulse are used to accumulate ions. Q:How do you decide when to transfer them. A: After the final laser shot, a voltage at the “back” of the accumulation octopole switched, and the ions are transferred to the ICR cell. The switching of the voltage is controlled by the computer program interface. Q: How many runs do you need in general for an average result? A: 3 time-domain aquisitions are averaged for when “growing” a preformed fullerene…….the signal is extremely strong. And 10 time-domain acquisitions are averaged when form endohedrals from a graphite-metal target. Thus, up to 10 time-domain acquisitions are averaged.
Fullerenes react with carbon vapor in the “clustering zone”, then the gas exits the channel and undergoes a supersonic expansion. As the clusters move from a region of high pressure through a small orifice into a high vacuum, they undergo a supersonic expansion. The random thermal energy of the clusters is converted into a directed motion (creating a cooled, molecular beam in which very few collisions occur) toward the skimmer and the ions subsequently enter the ion optics where they are accumulated and then transferred to the ICR cell for detection.
