TEMPUS, a Timepix4-based system for the event-based detection of X-rays

Abstract

TEMPUS is a new detector system being developed for photon science. It is based on the Timepix4 chip and, thus, it can be operated in two distinct modes: a photon-counting mode, which allows for conventional full-frame readout at rates up to 40 kfps; and an event-driven time-stamping mode, which allows excellent time resolution in the nanosecond regime in measurements with moderate X-ray flux. In this paper, the initial prototype, a single-chip device, is introduced, and the readout system described. Moreover, and in order to evaluate its capabilities, some tests were performed at PETRA III and ESRF for which results are also presented.

Keywords: Timepix4; X-ray detector; event-driven; photon science; sparse-readout.

Figure 1

Operation scheme of the TEMPUS single-chip prototype. Besides the readout and carrier boards, the different inputs (triggers, etc.) and also the control and data links are shown.

Figure 2

The TEMPUS single-chip prototype in its housing. The design of the carrier board allows for minimal dead area when a second system is placed on the top. Inputs to the system such as bias voltage, external trigger or digital pixels can be seen. Also, the optical cables connecting to the slow control and the high-speed data-links are visible.

Figure 3

(a) ToT versus ToA plot showing the phenomenon known as time-walk. Signals with lower amplitude are registered at a later ToA due to their later crossing of the threshold. (b) The ToT versus ToA correlation is shown after the time-walk correction is applied. Lower ToT hits are now registered at the same time as the higher ones.

Figure 4

ToT spectrum. After setting a threshold at 100 ns ToT, two contributions are visible: the first one at around 300 ns ToT, which we attribute mainly to the 6.4 keV K-α fluorescence energy of Fe, and a second one at around 1100 ns ToT, which we attribute to the scattered photons at 14.4 keV. We set an arbitrary cut-off energy at 650 ns ToT and split all events into these two distributions.

Figure 5

(a) Events binned by ToA obtained for several revolutions of PETRA III (initialized once per revolution). Hits corresponding to the 40 different electron bunches can be clearly distinguished due to the high time resolution of TEMPUS. (b) ToA binning of the two different TOT contributions divided by an arbitrary threshold placed at 650 ns ToT are shown. The obtained time resolution, defined as the FWHM of the distribution, corresponds to the expected values. The higher time resolution of the lower energy photons is due to the shorter absorption length in silicon. As mentioned in the text, time resolution was limited by the low biased silicon sensor: 23.3 and 9.7 ns, respectively.

Figure 6

(a) Events binned by ToA obtained for several revolutions of ESRF (initialized once per revolution). The 7/8 + 1 electron bunch structure is visible. (b) The low- and high-energy contributions are shown as a function of ToA. Due to the higher bias voltage, an improve time resolution was achieved: 12.1 ns and 8.5 ns, respectively.