DESIGN & CONSTRUCTION OF CRYOGENIC FTMS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The design and development of the Cryogenic FTMS, as a collaborative project with the Cardiovascular Proteomics Center, is a major project at the moment. The instrument is currently under construction and awaiting the magnet which should be delivered in the summer of 2005. Fourier Transform Mass Spectrometry is limited in its base performance characteristics (resolution, sensitivity, mass accuracy, et cetera) by three fundamental instrumental limitations, pressure, magnetic-field strength, and preamplifier noise. The need for low pressure implies need for a large bore for large conductance to the pumps, but the need for high field with high homogeneity implies the need for low bore diameter to simplify magnet design. Designing an FTMS for operation in the cold bore of a superconducting magnet eliminates this contradiction as the bore itself becomes a cryopump. Because the cold bore acts as a cryopump, the ion transfer vacuum chamber can be made substantially narrower than normal, allowing use of narrower bore magnets than are normally used in FTMS while still achieving the needed 60W at 50K. Due to the narrower 3? bore, the magnet has been designed as a 15 Tesla magnet which will achieve acceptance specifications at 14 Tesla. The bore is designed with two copper mounting brackets which will function as thermal anchors for the inner FTMS vacuum chamber. However, due to the large surface areas involved, the primary heat transfer will be due to direct radial radiative heat transfer, which will allow most of the heat flowing down the vacuum chamber walls to be transferred to the 50K shield before it reaches the 4K region. Thermal analysis shows that it is possible to build a vacuum chamber which can transmit less than 0.5W of heat from the source to the cell. The instrument is now under construction, and installation of the magnet id pending. The magnet has met field (14T) and homogeneity specifications (10 ppm over a 40 mm long by 40 mm diameter cylinder) and is currently being vacuum tested in the final dewar. The magnet was installed at BUSM and met field at 14T, and the ion source is assembled. The FTMS insert was assembled, and initial data is available and submitted for publication. Currently, the system is being upgraded with the low noise preamplifier and alignment, centering, and electrical connections at the ICR cell are being improved.