1. Ion Backflow Studies at Cornell
Dan Peterson
Laboratory for Elementary-Particle Physics, Cornell University
LCTPC-Peterson

2. Upper traces show the anode signals.
Bottom traces, the field cage termination
(with expanded time scale).
Field cage termination signal is due to
the prompt inductive signal (on all wires)
and
(later) collection of the ion backflow.
on a single vertical wire.
In 2006, the Cornell small prototype
was configured to observe ion backflow
in the field cage termination.
(Gas amplification is 2-GEM in this photo,
wire gas-amplification was used.)
LCTPC-Peterson

3. The electron transmission was measured
by the relative strength of the anode signal.
The ion signal (lower trace) is measured
after ion transmission through the GEM.
The GEM bias was not pulsed.
( Shown, VGEM = 163V. )
Transmission was measured in a
standard GEM,
mounting in front of wire gas amplification
(used as a source of ions).
LCTPC-Peterson

4. The measured electron transmission (in red), as a function of VGEM ,
F. Sauli et al, IEEE Nucl. Sci Symp NS
Shown at Valencia and
Beijing
The measured electron transmission (in red), as a function of VGEM ,
does not agree with the results of Sauli’s group. The ion transmission does agree.
In the same paper, authors reported ~full transmission for the large hole GEM.
This was not observed in Asian group studies.
We are now considering designs for a wire gate.
LCTPC-Peterson

5. At Cornell, we are considering jumping back into the gating studies,
expanding on our earlier experience.
Cornell will build a new TPC for studying
wire gate designs adapted to the curved TPC module.
Accepts standard LP1 modules.
Other components fit in the rack:
cathode,
field shaping,
field cage termination,
ion detector.
Not a complete design,
but one should get the idea.
LCTPC-Peterson

6. Although the figure shows the 3GEM+Gate model from 2008,
the wire gate will probably be build above a stack of 10x10 CERN GEMs.
field cage termination
ion detection
Will also require
pad board
bias control for the gate,
bias control for the ion detector,
quieter amplifiers.
LCTPC-Peterson