pith. sign in

arxiv: 1906.09406 · v1 · pith:GLXYK3VJnew · submitted 2019-06-22 · ⚛️ physics.ins-det

Studies on ion back-flow of Time Projection Chamber based on GEM and anode wire grid

Shuai Wang , Fuwang Shen , Xiao Zhao , Zhihang Zhu , Fangang Kong , Changyu Li , Qinghua Xu , Zhangbu Xu
show 2 more authors
Chi Yang Chengguang Zhu
This is my paper

Pith reviewed 2026-05-25 18:14 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords ion back-flowGEM foilTPC readoutanode wire gridion suppressionenergy resolutionGarfield simulation
0
0 comments X

The pith

A TPC prototype using two staggered GEM foils at low voltage plus anode wires suppresses ion back-flow to 0.58 percent at gain 2500 with 10 percent energy resolution.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper builds and tests a hybrid readout chamber that combines two layers of GEM foils with an anode wire grid to reduce ion back-flow while providing stable amplification. Simulations with Garfield++ and finite element analysis identify low GEM voltages and staggered alignment as the way to absorb most ions before they reach the drift volume. Measurements on the prototype confirm the simulated performance under the chosen operating point. A sympathetic reader would care because the approach removes the dead time of traditional gated grids and could therefore support continuous, higher-rate data taking in future detectors.

Core claim

With both GEM foils operated at 255 V and the anode wire grid supplying most of the gain, double-layer staggered GEMs reduce the ion back-flow ratio to approximately 0.58 percent at an effective gain of about 2500 while delivering an energy resolution of about 10 percent, as verified by direct measurement in the prototype after parameter optimization from simulation.

What carries the argument

The hybrid GEM-plus-anode-wire readout, where the GEM foils at low voltage absorb ions and the wire grid provides the bulk of electron multiplication.

If this is right

  • Continuous TPC readout becomes feasible without the dead time introduced by switching a gated grid.
  • Ion back-flow can be held below one percent while most of the gain comes from a stable, long-lifetime wire grid.
  • Energy resolution around 10 percent is maintained at the tested gain with the chosen low GEM voltages.
  • The combination exploits the ion-blocking property of GEMs together with the high-voltage stability of anode wires.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • If the geometry scales without increasing ion transmission, the same hybrid layout could be applied to larger TPCs.
  • Similar low-voltage GEM plus wire combinations might reduce ion feedback in other gas-based detectors that currently rely on gating.
  • Further tests at different gas mixtures or higher overall gains would show whether the 0.58 percent level holds beyond the reported conditions.

Load-bearing premise

The Garfield++ and finite-element simulations correctly predict the real ion and electron transmission through the actual geometry and voltage settings of the prototype.

What would settle it

A measurement in the same prototype that finds an ion back-flow ratio well above 0.58 percent at 255 V GEM settings, staggered alignment, and effective gain near 2500 would falsify the reported suppression.

Figures

Figures reproduced from arXiv: 1906.09406 by Changyu Li, Chengguang Zhu, Chi Yang, Fangang Kong, Fuwang Shen, Qinghua Xu, Shuai Wang, Xiao Zhao, Zhangbu Xu, Zhihang Zhu.

Figure 2
Figure 2. Figure 2: The layout of the chamber and the test system based on [PITH_FULL_IMAGE:figures/full_fig_p002_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: (a) Structure of GEM foil. (b) Double-layer GEMs with [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Visualizing the model of double-layer GEMs by ANSYS [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Simulation results of electron collection e [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Simulation results of IBF ratio versus Edrift for several fixed values of Etransfer (2.0, 4.0, 6.0, 8.0kV/cm). Here Vanode wires=1120V, ∆VGEMupper=∆VGEMlower=255V. ∆VGEM=255V for both GEM foils, Etransfer=4.0kV/cm and Edrift=0.1kV/cm are set as default values. 4.1. 55Fe spectrum and gain measurements The 55Fe source has been used for the testing, which mainly emits 5.9keV X-rays. In P10 gas, it will pro￾du… view at source ↗
Figure 8
Figure 8. Figure 8: (a) shows the distribution of Qsignal for ∼50000 events under the same voltage set up as in [PITH_FULL_IMAGE:figures/full_fig_p006_8.png] view at source ↗
Figure 9
Figure 9. Figure 9: Effective gain scan over anode high voltage Vanode wires. and its energy resolution reaches 10.8% [PITH_FULL_IMAGE:figures/full_fig_p007_9.png] view at source ↗
Figure 11
Figure 11. Figure 11: Comparison of measurement and simulation results for [PITH_FULL_IMAGE:figures/full_fig_p008_11.png] view at source ↗
read the original abstract

Gated wires are widely used in Time Projection Chamber (TPC) to avoid ion back-flow (IBF) in the drift volume. The anode wires can provide stable gain at high voltage with a long lifetime. However, switching on and off the gated grid (GG) leads to a dead time and also limit the readout efficiency of the TPC. Gas Electron Multiplier (GEM) foil provides a possibility of continuous readout for TPC, which can suppress IBF efficiently while keeping stable gain. A prototype chamber including two layers of GEM foils and anode wires has been built to combine both advantages from GEM and anode wire. Using Garfield++ and the finite element analysis (FEA) method, simulations of the transmission processes of electrons and ions are performed and results on absorption ratio of ions, gain and IBF ratio are obtained. The optimized parameters from simulation are then applied to the prototype chamber to test the IBF and other performances. Both GEM foils are run at low voltage (255V), while most of the gain is provided by the anode wire. The measurement shows that the IBF ratio can be suppressed to ~0.58% with double-layer GEM foils (staggered) at an effective gain about 2500 with an energy resolution about 10%.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports on a hybrid TPC readout using double-layer GEM foils (staggered alignment) plus an anode wire grid. Garfield++ and FEA simulations are used to optimize GEM voltages (255 V) and geometry so that most of the gain occurs at the wires; these parameters are then applied to a physical prototype. The central experimental result is an IBF ratio of ~0.58 % at effective gain ~2500 with ~10 % energy resolution.

Significance. If the measured IBF suppression holds, the design offers a route to continuous TPC readout without the dead-time penalty of a gated grid, which is relevant for high-rate experiments. The work supplies a concrete, simulation-guided prototype benchmark that can be compared with other GEM or Micromegas solutions.

major comments (2)
  1. [Abstract] Abstract and results: the headline IBF value of ~0.58 % is given without reported uncertainties, raw counting statistics, or a description of the ion-current measurement technique (e.g., how the back-flowing ions are collected and normalized to the primary ionization). This directly affects the reliability of the central experimental claim.
  2. [Prototype measurements] Prototype section: no table or figure presents the measured IBF ratio together with its uncertainty or the corresponding effective-gain and energy-resolution values; the absence of these data makes it impossible to judge whether the quoted 0.58 % is statistically distinguishable from other operating points.
minor comments (2)
  1. The text should state the precise definition of “effective gain” used for the wire-grid stage and how it was extracted from the prototype data.
  2. Clarify whether the staggered alignment of the two GEM foils was verified optically or by X-ray imaging after assembly, and report the achieved alignment tolerance.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments. We address the two major points below and will revise the manuscript to improve the presentation of the experimental results.

read point-by-point responses

  1. Referee: [Abstract] Abstract and results: the headline IBF value of ~0.58 % is given without reported uncertainties, raw counting statistics, or a description of the ion-current measurement technique (e.g., how the back-flowing ions are collected and normalized to the primary ionization). This directly affects the reliability of the central experimental claim.

    Authors: We agree that the abstract and results section would benefit from these details. In the revised manuscript we will add a concise description of the ion-current measurement (back-flowing ions collected on the cathode and read out with a picoammeter, normalized to the primary ionization current measured in the absence of amplification) together with the statistical uncertainty derived from repeated measurements. The headline IBF value will be updated to include the uncertainty. revision: yes

  2. Referee: [Prototype measurements] Prototype section: no table or figure presents the measured IBF ratio together with its uncertainty or the corresponding effective-gain and energy-resolution values; the absence of these data makes it impossible to judge whether the quoted 0.58 % is statistically distinguishable from other operating points.

    Authors: We acknowledge the omission. The revised manuscript will contain a new table (and, if space permits, an accompanying figure) that tabulates the measured IBF ratio, effective gain, and energy resolution at the optimized point, each with its associated uncertainty. This will allow direct assessment of statistical significance and comparison with other operating conditions. revision: yes

Circularity Check

0 steps flagged

No significant circularity: experimental measurement after simulation-guided setup

full rationale

The paper's central claim is a direct experimental measurement of IBF ratio (~0.58%) on a physical prototype chamber after applying simulation-selected parameters (255 V GEM bias, staggered alignment). Simulations (Garfield++ and FEA) are used only to choose operating points and are not invoked to compute or fit the reported IBF value; the headline result is obtained from prototype data, not from any equation or parameter that reduces to the same dataset by construction. No self-definitional steps, fitted-input predictions, or load-bearing self-citations appear in the derivation chain.

Axiom & Free-Parameter Ledger

2 free parameters · 1 axioms · 0 invented entities

The work rests on standard assumptions about gas ionization and transport plus the validity of the Garfield++ simulation package; the main empirical addition is the measured IBF ratio in the hybrid geometry.

free parameters (2)
  • GEM operating voltage = 255 V
    Set to 255 V on both foils to keep them at low voltage while anode wires supply most gain.
  • target effective gain = 2500
    Chosen as operating point for the IBF and resolution measurements.
axioms (1)
  • domain assumption Garfield++ and finite-element analysis accurately model electron and ion transmission through the GEM-wire geometry.
    Used to select voltages and geometry before building the prototype.

pith-pipeline@v0.9.0 · 5790 in / 1345 out tokens · 27371 ms · 2026-05-25T18:14:31.943945+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

24 extracted references · 24 canonical work pages

  1. [1]

    Marx and D.R

    J.N. Marx and D.R. Nygren, The time projection chamber, Phys. Today 31 (10) (1978), 46-53

    work page 1978

  2. [2]

    Sauli, GEM: a new concept for electron amplification in gas detectors, Nucl

    F. Sauli, GEM: a new concept for electron amplification in gas detectors, Nucl. Instr. Meth. A 386 (1997), 531-534

    work page 1997

  3. [3]

    Bouclier, et al., New observations with the gas electron mul- tiplier (GEM), Nucl

    R. Bouclier, et al., New observations with the gas electron mul- tiplier (GEM), Nucl. Instr. Meth. A 396 (1997), 50-56

    work page 1997

  4. [4]

    Lippmann, A continuous read-out TPC for the ALICE up- grade, Nucl

    C. Lippmann, A continuous read-out TPC for the ALICE up- grade, Nucl. Instr. Meth. A 824 (2016), 543-547

    work page 2016

  5. [5]

    Gasik, et al., Building a large-area GEM-based readout cham- ber for the upgrade of the ALICE TPC, Nucl

    P. Gasik, et al., Building a large-area GEM-based readout cham- ber for the upgrade of the ALICE TPC, Nucl. Instr. Meth. A 845 (2017), 222-225

    work page 2017

  6. [6]

    Aiola, et al

    S. Aiola, et al. , Combination of two Gas Electron Multipliers and a Micromegas as gain elements for a time projection cham- ber, Nucl. Instr. Meth. A, 834 (2016), 149-157

    work page 2016

  7. [7]

    Shen, et al., MWPC prototyping and performance test for the STAR inner TPC upgrade, Nucl

    F. Shen, et al., MWPC prototyping and performance test for the STAR inner TPC upgrade, Nucl. Instr. Meth. A 896 (2018), 90- 95

    work page 2018

  8. [8]

    , Design and implementation of wire tension measurement system for MWPCs used in the STAR iTPC up- grade, Nucl

    Xu Wang, et al. , Design and implementation of wire tension measurement system for MWPCs used in the STAR iTPC up- grade, Nucl. Instr. Meth. A 59 (2017), 90-94

    work page 2017

  9. [9]

    Yang, et al

    S. Yang, et al. , Cosmic Ray Test of Mini-drift Thick Gas Electron Multiplier Chamber for Transition Radiation Detector, Nucl. Instr. Meth. A 785 (2015), 33-39

    work page 2015

  10. [10]

    Berger, et al., A large ungated TPC with GEM amplification, Nucl

    M. Berger, et al., A large ungated TPC with GEM amplification, Nucl. Instr. Meth. A 869 (2017), 180-204

    work page 2017

  11. [11]

    Natal da Luz, et al., Ion backflow studies with a triple-GEM stack with increasing hole pitch, JINST 13 (2018), P07025

    H. Natal da Luz, et al., Ion backflow studies with a triple-GEM stack with increasing hole pitch, JINST 13 (2018), P07025

    work page 2018

  12. [12]

    Bouianov, et al

    O. Bouianov, et al. , Progress in GEM simulation, Nucl. Instr. Meth. A 450 (2000), 277-287

    work page 2000

  13. [13]

    Gasik, et al., Charge density as a driving factor of discharge formation in GEM-based detectors, Nucl

    P. Gasik, et al., Charge density as a driving factor of discharge formation in GEM-based detectors, Nucl. Instr. Meth. A 870 (2017), 116-122

    work page 2017

  14. [14]

    S.Bachmann, et al., Charge amplification and transfer processes in the gas electron multiplier, Nucl. Instr. Meth. A 438 (1999), 376-408

    work page 1999

  15. [15]

    Sauli, The gas electron multiplier (GEM): Operating princi- ples and applications, Nucl

    F. Sauli, The gas electron multiplier (GEM): Operating princi- ples and applications, Nucl. Instr. Meth. A 805 (2016), 2-24

    work page 2016

  16. [16]

    M ¨ormann, et al., Evaluation and reduction of ion back-flow in multi-GEM detectors, Nucl

    D. M ¨ormann, et al., Evaluation and reduction of ion back-flow in multi-GEM detectors, Nucl. Instr. Meth. A 516 (2004), 315- 326

    work page 2004

  17. [17]

    Betts, et al., Studies of several wire and pad configurations for the STAR TPC, STAR Note 0263

    W. Betts, et al., Studies of several wire and pad configurations for the STAR TPC, STAR Note 0263

    work page

  18. [18]

    Technical Design Report for the Upgrade of the ALICE Time Projection Chamber, CERN-LHCC-2013-020, ALICE-TDR- 016

    work page 2013

  19. [19]

    Jeanneau, et al., Ion back-flow gating in a micromegas device, Nucl

    F. Jeanneau, et al., Ion back-flow gating in a micromegas device, Nucl. Instr. Meth. A 623 (2010), 94-96

    work page 2010

  20. [20]

    Zhangbu Xu, et al., GEM based TRD for Identifying electrons at EIC, R&D proposal for an Endcap TOF and TRD for Identifying electrons at EIC, 2014

    work page 2014

  21. [21]

    B¨ohmer, et al., Simulation of space-charge effects in an un- gated GEM-based TPC, Nucl

    F.V . B¨ohmer, et al., Simulation of space-charge effects in an un- gated GEM-based TPC, Nucl. Instr. Meth. A 719 (2013), 101- 108

    work page 2013

  22. [22]

    Rossegger and J

    S. Rossegger and J. Thomas, Space-charge e ffects in the ALICE TPC: a comparison between expected ALICE performance and current results from the STAR TPC, ALICE Internal Note, 2011, ALICE-INT-2010-017

    work page 2011

  23. [23]

    Thomas, M

    J. Thomas, M. Mager and S. Rossegger, The Langevin equa- tion expanded to 2nd order and comments on using the equation to correct for space point distortions in a TPC, ALICE Internal Note, 2010, ALICE-INT-2010-016

    work page 2010

  24. [24]

    S.Rossegger, B.Schnizer and W.Riegler, Analytical solutions for space charge fields in TPC drift volumes, Nucl. Instr. Meth. A 632 (2011), 52-58. 9

    work page 2011