1. Construction and Test of a Modular GEM for EIC
Matthew Bomberger, Jacob Chesslo
Dr. Marcus Hohlmann, Dept. of Aerospace, Physics and Space Sciences
Florida Institute of Technology
Abstract
Florida Tech GEM Design
ions
The construction and test of a prototype gas-electron multiplier (GEM) is presented, with reduced mass to decrease multiple Coulomb scattering. This design is proposed to be implemented at a future electron-ion collider (EIC). Capacitance of and between the GEM foils is compared when stack frames and pull-outs are either 3D printed acrylonitrile-butadiene-styrene (ABS) or polyether-ether-ketone (PEEK). This study suggests that the introduction of PEEK parts in the stack support structure improves the stack geometry.
The Florida Tech team has implemented a mechanical stretching method to maintain taut foil surfaces and foil spacing for large-area GEMs in a future EIC (Fig. 2). An interesting design element is that the total mass of the active region is reduced by introducing two foils to act as drift and read-out boards.
3D printers at Florida Tech and Fermilab were used to make ABS inner frames as a first order test of this stretching method. A second order test was performed using two layers of PEEK inner frames machined using a waterjet. The distinction between the two can easily be seen in Figure 3.
electrons
9 m
Background
Fig. 1: Simulated view of BeAST [2]; GEM positions circled
A new particle accelerator is proposed to be constructed at either Brookhaven National Laboratory (BNL) or Jefferson accelerator Laboratory (JLab). In this accelerator, called the EIC, electrons and ions will be accelerated and the ensuing collisions will be studied [1]. This will shed light on the interactions that occur within protons and neutrons.
In particle physics experiments, detector complexes are required for identifying particles originating from interaction points. One such assembly, proposed by the Brookhaven-led endeavor, is called the Brookhaven eA Solenoid Tracker (BeAST, Fig. 1). Various particle detectors are required to track different species of particles. Our detector is a GEM, with proposed positions circled in Figure 1.
GEMs are made of stacks of foils. These foils are composed of two thin conducting surfaces sandwiching an insulating layer with small holes etched across the surface, spaced apart at specific distances using inner frames, and stretched with pull-out parts. The detector is flushed with ionizable gas, producing a measurable signal via electron avalanche when a charged particle traverses through it [3].
Results
The capacitance of and between the GEM foils was compared to theoretical predictions of the capacitance between two parallel plates. Measurements were performed for the configurations with (1) all ABS parts, (2) ABS inner frames and PEEK pull-outs, and (3) two layers of PEEK inner frames and PEEK pull-outs (Tab. 1). Spacing for the first order test was mm and for the second mm.
These results suggest that the introduction of more PEEK in the stack construction results in better detector performance, since a uniform geometry results in uniform electric fields.
Fig. 2: Open GEM chamber showing stack; PEEK inner frames and pull-outs
Fig. 3: Inner frames, ABS (white) and PEEK (brown)
Tab. 1: Capacitance results for drift gap, first GEM foil, first transfer gap, second GEM foil, second transfer gap, third GEM foil (top to bottom); theoretical capacitances are discriminated by foil spacing (first order test, second order test)
References
[1] “Electron Ion Collider: The Next QCD Frontier.” BNL and JLab. arXiv:
[2] Alexander Kiselev. “BeAST Detector.” Argonne EIC User Group Meeting
[3] F. Sauli. “GEM: A new concept for electron amplification in gas detectors.” Nuclear Instruments and Methods in Physics Research A