ToF Measurement in Drift Chamber Detectors

The history of TDC's begins with experimental high energy physics. The search for elementary particles conquers the physicians to biggest experimental setups. In the analysis of the experimental data time-measurement takes an important part. Drift chambers are typical examples as they are used in the bid colliders like the CERN one. To learn something about the inner structure of atoms, particles are accelerated to enormous energies and then shot onto a target, where they burst into many smaller parts. The properties of these parts can be derived from their path in a magnetic field. This path is detected by drift chambers:

• Laser distance
• Ultrasonic flowmeter
• Ultrasonic density meter
• Ultrasonic thickness meter
• Magnetostrictive Positioning
• Drift chambers
• Frequency and Phaseshift

The detectors are arranged circular around the collision point. These consist of gas filled tubes in which a live wire is strung. If a reaction particle hits a gas molecule in one of these tubes, a cloud current is generated which drifts along the wire due to the electrical field (that's why it is called drift chamber). If the cloud current reaches the wire, an electrical pulse is triggered. The time from the collision of the particles to the hitting of the wire by the current cloud is measured by the TDC's.

Since some of these experiments require several hundred thousand of these gas filled tubes, reliable, precise, energy efficient and inexpensive TDCs are very important. The required resolution is around app. 500 ps - 1 ns and can be reached with todays multi-channel single chip TDCs without any problem.

See the advantages of TDC's in this application:

• Direct conversion from time to digital values in digitale Werte. No need for time-to-analog converters with followind analog-to-digital converter
• Multichannel - the GP1 offers 2 stop channels, the F1 will offer 8 channels in one IC.
• Multihit-Capability - the GP1 can sample up to 4 stop signals per channel. Queuing of the two channels leeds to 8-fold multihit capability
• High rates - as the ATMD-system demonstrates, it is possible to register up to 2.5 million measurements per second with the GP1

These properties make the TDC an ideal tool also for time-of-flight mass spectroscopy, fluorescence spectroscopy, analysis of photoelectrons an many more scientific applications.