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Description
Diamond detectors are increasingly adopted for fast-neutron measurements owing to their
excellent timing, radiation hardness, and low noise. In a campaign at the ISIS spallation source, a
single-crystal diamond detector was coupled to a fully digital acquisition chain based on a CAEN
DT5751 digitizer (10-bit, 1 GS/s), recording waveforms synchronized to the accelerator trigger for
time-of-flight (ToF) analysis [1].
Combining ToF and pulse-integral information, the biparametric ToF–energy spectra resolved
the distinct neutron interaction channels on carbon and the dual-bunch time structure of the beam,
while discriminating prompt γ-ray flashes — all without analog shaping or external timing modules.
A compact, fully digital front-end can thus characterize fast-neutron beams with high accuracy.
This approach is enabled by the CAEN Digitizer 2.0 platform, whose open FPGA architecture
runs real-time digital pulse-processing algorithms (timing, charge integration, pulse-shape
discrimination) on board, with high channel density and on-board waveform memory. The family
spans the x2740/x2745 (64-channel, 16-bit, 125 MS/s), the x2730 (32-channel, 14-bit, 500 MS/s),
and the x2751 (16-channel, 14-bit, 1 GS/s), from high-density acquisition to the nanosecond
sampling required for ToF.
The same platform already underpins plasma diagnostics in fusion devices. In the Materials
Plasma Exposure eXperiment (MPEX), a linear plasma–material interaction device, the VX2745B
handles high-density multichannel acquisition [2]. In the VEST spherical tokamak, the V2740
digitizes the soft X-ray (SXR) diagnostic — two 20-channel AXUV photodiode arrays — whose
signals reconstruct the magnetic-island structure and m-mode numbers of resistive MHD
instabilities [3], with waveform processing tailored to the detector as for the diamond data.
A single digital front-end thus serves both neutron and plasma fusion diagnostics, enabled by
the flexibility of the platform and by the ability to run timing and energy analysis directly on the
FPGA.
[1] M. Rebai, L. Giacomelli, C. Andreani et al. (2012) Diamond detectors for fast neutron measurements at
pulsed spallation sources. JINST, 7, C05015.
[2] J. Rapp, C. Lau, T.M. Biewer et al. (2023) Physical and technical basis of the Materials Plasma Exposure
eXperiment from modeling and Proto-MPEX results. Nucl. Fusion, 63. doi:10.1088/1741-4326/acc2d1.
[3] S. Lim (2024) Development of Soft X-ray Diagnostic System for MHD Instability Measurement in
VEST. Ph.D. thesis, Seoul National University (Q-BEAM Solution).