Multi-Wire Proportional Chamber detectors at FRS

Current status of detectors

mwpc status 2021

mwpc status 2021

Performance during previous beamtimes

FRS beamtime 2021

During the R3B exp. S455 (28.03 - 01.04) with 238U was found out:

Gas mixture prolem was revealed (end March):

The gas misture requred for correct MWPCs operation is a mix of Argon (80%) and CO2 (20%). The level of CO2 was discovered to be 0%, this was fixed with the help of det lab colleagues. This issue could be a source of such low efficiency of the detectors.

Later, during the next R3B run S515 (24.04 - 02. 05) with 136Xe the status was the following:

Before FRS beamtime 2021

mwpc status 2021

After engineering run 2019 (before FRS beamtime 2020)

mwpc status 2020

How to operate CFDs of MWPC

Important note: CFDs are controlled using Mesycontrol software. This software is installed under profi user and is also used to control other Mesytech modules e.g. MCFDs for ToF scintillators. Inside the software, one can open the setup file and choose which CFDs to control. However, the CFDs of MWPCs can be controlled only locally, meaning on the machine to which the remote control module (MRC) is physically connected to! This machine is lxg1267, it is located in the Messhuette ("go4" machine). Connection via ssh does not work, so please go locally.

1. Open mesytec control software for CFDs under profi user locally on lxg1267 machine

device tree

2. Select thresholds for anodes. The typed value is automatically sent.


3. Select thresholds for cathodes. The typed value is automatically sent.

cathodes cathodes

4. The setup file can be saved to or loaded from /u/profi/Documents/MWPC_control

MCFD-16 manual can be found here

How can detectors be tested

Cathodes are tested with generator. It is connected in FRS Messhuette. Generator produced bipolar analog signal, see Fig. 1. The signal is fed into the chain with cathodes. Output signal from cathode should look smth like this, see Fig.2.

If signal is missing, several things are possible:

generator signal
Fig.1 Signal from generator.
generator signal

Fig.2 Signal from cathode if generator is fed to it.

Anodes are tested only with voltage on (and detectors should be filled with gas!). All detectors except the ones at S8 are equipped with 90Sr beta source. MW81 and MW82 can only be tested on cosmics.

Starting from some value of voltage (from 2 kV and up, different for each detector), detectors begin to generate noise. This can be traced by looking at the anode current. During normal operation and with no beam the current is zero. For example, MW82 generates no noise up to 2 kV on anode (with 0.0 uA current), and starting from 2.1 kV (abrupt increase of current to 2 uA) one can see constant noise signals. If the voltage is too high, one can see also sparks. On the scope those look like huge saturated signals. If sparks start to appear, reduce the voltage immediately!

Where to find MWPC electronics in Messhuette

The patch panel of the MWPCs and all the corresponding electronic modules are located in the electronic room of the Messhuette, see the Figures below.

generator signal
Fig.3 Panel with output analog signals from MWPCs.
generator signal

Fig.4 NIM crate with three Mesytec CFDs (MCFD-16), one Remote Control module (MRC-1) and three delay modules* (DL8020). Flat cabels with logic signals from anodes and cathodes go to TDCs in one of the vme crates of FRS (called vme_user, the one with r4l-63 processor).
generator signal

Fig.5 Back side of the NIM crate. Make sure connection between MRC-1 and CFDs is there!

*Delay is introduced to the logic signals from all the anodes and 11, 21, 22, 31 cathodes. Those signals require to be delayed because the corresponding TDC (V775, geo 8) is configured for common start. Logic signals from 51, 71, 81, 82 cathodes are sent to the TDC (V775, geo 9) configured for common stop. The mapping of the TDCs can be found under profi in e.g. /lynx/Lynx/frs/usr/profi/mbsrun/sec_expfeb21/vme_user/mapping

Web page of MWPCs by Hemlut Weick

Can be found here, but it is partly not up-to-date.