Many detectors - including solid-state particle detectors, microchannel plates, and photodiodes - output small current signals that require amplification and conversion to a voltage. Current-to-voltage converters (I/Vs) are widely utilized in experimental and commercial applications for this task. Numerous detection systems require wide bandwidth, ultra-low noise, high gain, and linear amplification. Commercial I/Vs having this combination of features are surprisingly not readily available and many consumers resort to costly and time consuming in-house development. These factors, reflected presently within the heavy ion beam probe (HIBP) program supported by the U.S. Department of Energy, Office of Fusion Energy Sciences, motivate this effort. We propose to develop ultra-low noise, wide bandwidth, high gain, transimpedance amplifiers (TIA). They emanate from a design developed and used successfully by the HIBP program for over 25 years. Noteworthy characteristics will include linear amplification of current 1 nA, signal bandwidth 1 MHz (-3dB), equivalent input-noise ~ 1.5 nA (rms), and transimpedance (gain) 107 V/A. They will also be compact, vacuum grade (operable at 10-7 torr), and smartly-packaged. Contemporary methods, including computerized circuit modeling and surface-mount technology (SMT), will be used to achieve these state-of-the-art products. This significance of this effort is captured in the following; 1) It will advance heavy ion beam probe diagnostic capabilities, furthering fusion energy science; 2) It will result in novel TIA products suitable for communication, science, and service industries within government and private sector markets; and 3) It has broad inherent value likely to attract future development funding. This work is critical to realization of innovative Heavy Ion Beam Probe detectors and measurements under development within the O.F.E.S Diagnostic Program including: 1) Development of modern detector systems, enabling the HIBP to characterize /n and electrostatic fluctuation induced transport with greater than prevailing resolution; 2) Incorporation of more populous detector/aperture sets into energy analyzers, enabling the HIBP to achieve a better understanding of wavenumbers (k_nn, k_ and low-k fluctuations; 3) Development of a particle velocity detector, advancing the unique HIBP capability to measure the poloidal magnetic flux (t) and infer the evolution of the current density and q-profiles; 4) Development of wider bandwidth measurements, extending the frequency sensitivity of the HIBP to enable assessment of quantities not currently accessible; and 5) Advancement of HIBP detector technology toward a smaller and more economical alternative to an electrostatic analyzer (an option that may make the HIBP realizable on a larger number of devices). Near term benefits of this work will be realized in the U.S. fusion program domestically (with the HIBP operating on MST) and through an emerging international partnership with the Max-Plank Institute in Germany (and plans to operate HIBPs on ASDEX-U and W7-X). HIBPs having enhanced capabilities will access a wider range of quantities required for validation efforts and have broader impact within the fusion program. The new detection elements and measurements are central to these opportunities and Advanced-TIAs are vital to their success.
