Data was taken in the test lab without a magnetic field 20080710-2008005.
Data was taken using the CLEO magnet 20080808-20080818.
Gas is Ar-CF4-Isobutane (95:3:2).
MPGD tested were triple-GEM(CERN) (figure 1) and bulk-Micromegas(Saclay)(figure 2).
Figure 3 shows the TPC mounted in the CLEO magnet.
Figure 4 shows geometry of the TPC and trigger counters.
Figure 5 shows the diffusion for 3-GEM and Micromegas with B=0. The average diffusion constant is 0.298 mm/(cm^.5).
Figure 6 shows the diffusion for 3-GEM and Micromegas with B=1T and B=1.45T. The average diffusion constant is 0.71 mm/(cm^.5) for B=1T and 0.052 mm/(cm^.5) for B=1.45T. All are in agreement with Magboltz.
The offset observed in measured diffusion for the 3-GEM, in 1T and 1.45T magnet field provides a measurement of the diffusion constant in the GEM transfer field. This is 0.55 mm/(cm^.5) at 1500V/cm, about 1.4 x that predicted by Magboltz.
The pad distribution function, as a function of charge center position, is calculated from the abserved charge widths (figure 7).
In Figure 8, The point resolution, extrapolated to zero drift distance, is 158 microns for the 3-GEM and 209 microns for the Micromegas. The track angle is typically 5 degrees.
Measurements of GEM transmission are relevant to the use of a GEM as a gating grid.
A single wire plane is used for the gas amplification. It provides a healthy source of ions for the ion transmission measurement.
The GEM is placed over the wire plane. One surface of the GEM serves as the cathode of the gas-amplification field cage.
The GEM voltage will be varied while measuring the trasmission. The electron transmission measurement is based on the observed anode pad signal.
Positive ions are collected on the field cage termination (FCT) plane. The ion transmission measurement is based on the observed FCT plane signal, normalized to the anode pad signal.
Correlation of horizontal position measurements of the electron signal (from the anaode pads) and the ion signal (from the FCT plane) indicates that the FCT signal is due to ions.
The measured electron transmission is less than expected.
We have reinstalled the Purdue Micomegas.
These are CERN GEMs mounted by Purdue. (This is the November 2006 pad board: 5 rows with 5mm pads, 4 rows with 2mmpads, contact to surround, bare copper.) The 1st photo shows the triple GEM mounted on the module. The 2nd photo shows the module mounted in the TPC. The event is with ArCO2(90:10) 330V/GEM.
A Bulk Micromegas has been prepared by the Orsay group on the Cornell/Purdue pad board. (This is the November 2006 pad board: 5 rows with 5mm pads, 4 rows with 2mmpads, contact to surround, bare copper.) The 1st photo shows the Micromegas mounted on the module. The 2nd photo shows the Micromegas mounted in the TPC. The Micromegas stand-offs are visible. Event is with ArCO2(90:10) 420volts. Resolution plot is with Ar-isoButane(93:7) 410volts; adjacent 2mm layers are instrumented.
Struck operation notes (notes made at Cornell)