In the intricate realm of cosmic-ray detection, precision timing is akin to the heartbeat of the AMS experiment. Enter the Time-of-Flight system (ToF), AMS’s stalwart stopwatch, boasting an impressive accuracy of 1.5×10⁻¹⁰ s in measuring particle transit times.

Unraveling ToF’s Mechanism

Much like a stopwatch, the ToF system employs a Time-to-Digital Converter (TDC) as its timer. As a particle traverses through the ToF planes, the TDC commences its countdown. Upon exiting the opposite end of the magnet barrel, the TDC halts, marking the particle’s transit time.

With a timing precision of 150 picoseconds and a distance span of approximately 1.2 meters between Upper and Lower ToF planes, the ToF becomes a speedometer, capable of discerning particle velocities nearing 98% of the speed of light!

The Significance of ToF

A particle traversing both Upper and Lower ToF planes falls within the AMS acceptance, triggering a cascade of events. The ToF serves as a sentinel, alerting all AMS sub-detectors to commence data collection and processing. Moreover, it plays a pivotal role in antimatter detection, discerning particle directionality and charge sign with remarkable accuracy. The ToF’s discerning power extends to evaluating absolute particle charge, bolstering AMS’s chemical distinction prowess.

Constructing the ToF

The AMS-02 ToF system comprises four planes of scintillation counters—two above and two below the magnet. Each plane houses a series of scintillator paddles, aligned along x and y coordinates. These paddles, crafted from polyvinyltoluene scintillator, are coupled to Photo-Multipliers (PMTs) via plexiglass light guides, ensuring efficient light collection and conversion.

Delving Deeper: The Science Behind Scintillation

As a charged particle traverses a scintillator, it induces molecular excitations, triggering fluorescence light emission. This light, efficiently converted into electrons by PMTs via the photoelectric effect, undergoes amplification through a dynode cascade, magnifying the initial signal by up to 10⁸ times. Fine-mesh PMTs, tailored to AMS’s needs, mitigate magnetic field interference, ensuring precise measurements amidst cosmic chaos.

In the saga of cosmic-ray detection, the AMS-02 Time-of-Flight system emerges as a beacon of precision, unfurling the mysteries of particle kinetics with unparalleled accuracy.