# Commissioning and first measurements of the initial X-ray and $\gamma$-ray
detectors at FACET-II
††thanks: The work at LOA was supported by the ANR (UnRIP project, Grant No.
ANR-20-CE30-0030). The work at LOA was also supported by the European Research
Council (ERC) under the European Union’s Horizon 2020 Research and Innovation
Program (M-PAC project, Grant Agreement No. 715807). Work supported in part by
the U.S. Department of Energy under contract number DE-AC02-76SF00515. The
work of EG and DAR were supported by the U.S. Department of Energy, Office of
Science, Fusion Energy Sciences under Award DE-SC0020076. The work of HE was
supported by the Knut and Alice Wallenberg Foundation (KAW 2018.0450). The
work of MV and TG is supported by the Portuguese Science Foundation grant FCT
No. CEECIND/01906/2018, CEECIND/04050/2021 and PTDC/FIS- PLA/3800/2021. The
UCLA contribution was made possible by DOE grant DE-SC0010064:0011

P. San Miguel Claveria1,2,1, D. Storey3, G. J. Cao4, A. Di Piazza5, H.
Ekerfelt3, S. Gessner3, E. Gerstmayr6
T. Grismayer2, M. Hogan3, C. Joshi7, C. H. Keitel5, A. Knetsch1, M. Litos8, A.
Matheron1, K. Marsh7, S. Meuren3
B. O’Shea3, D. A. Reis6, M. Tamburini5, M. Vranic2, J. Wang9, V. Zakharova1,
C. Zhang7, S. Corde1 1ORCID-IDs: 0000-0001-9342-1573  1Laboratoire d’Optique
Appliquée, ENSTA Paris, CNRS, Ecole Polytechnique, Institut Polytechnique de
Paris, Palaiseau, France  2GoLP/Instituto de Plasmas e Fusão Nuclear,
Instituto Superior Técnico, Lisboa, Portugal  3SLAC National Accelerator
Laboratory, Menlo Park, CA 94025, USA  4Department of Physics, University of
Oslo, Oslo, Norway  5Max-Planck-Institut für Kernphysik, Heidelberg, Germany
6Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park,
CA 94025, USA  7University of California Los Angeles, Los Angeles, CA 90095,
USA  8Department of Physics, Center for Integrated Plasma Studies, University
of Colorado Boulder, Boulder, Colorado 80309, USA  9Department of Physics and
Astronomy, University of Nebraska–Lincoln, Lincoln, NE 68588, USA

###### Abstract

The upgraded Facility for Advanced Accelerator Experimental Tests (FACET-II)
at SLAC National Accelerator Laboratory has been designed to deliver ultra-
relativistic electron and positron beams with unprecedented parameters,
especially in terms of high peak current and low emittance. For most of the
foreseen experimental campaigns hosted at this facility, the high energy
radiation produced by these beams at the Interaction Point will be a valuable
diagnostic to assess the different physical processes under study. This
article describes the X-ray and $\gamma$-ray detectors installed for the
initial phase of FACET-II. Furthermore, experimental measurements obtained
with these detectors during the first commissioning and user runs are
presented and discussed, illustrating the working principles and potential
applications of these detectors.

###### Index Terms:

X-ray detectors, $\gamma$-ray detectors, beam-plasma interaction, Strong-Field
QED

##  I Introduction

The detection and measurement of high energy photons (X-rays and
$\gamma$-rays) produced in laboratory remains an important challenge in
several experimental contexts, largely due to the low probability of
interaction of these photons with matter. Furthermore, since the cross-section
of the photon-matter interactions have a strong dependence on the incoming
photon energy, these detectors are typically designed for a defined energy
range, outside of which their sensitivity significantly drops. At the new
Facility for Advanced Accelerator Experimental Tests (FACET-II), which
accelerates electron - and ultimately positron - bunches to maximum delivered
beam energy of 13 GeV using the middle kilometer of Linear Accelerator (LINAC)
of the SLAC National Accelerator Laboratory, several experimental campaigns
rely on the X-ray and $\gamma$-ray photons produced by these particle beams to
retrieve valuable information of the key physical processes under study. Yet,
depending on the experiment, the relevant spectral range of these photons can
span from several to hundreds of keV all the way up to the beam energy.

At FACET-II, the X-ray and $\gamma$-ray photons are produced at the
Interaction Point (IP) where the relativistic electrons interact with matter
and/or with an Ultra-High-Intensity (UHI) laser pulse. After the interaction,
these high energy photons co-propagate in vacuum with the relativistic
particle bunch until the electrons are deflected down by the imaging
spectrometer dipole magnet placed $\approx 13$ m downstream of the IP. Both
the photons and electrons exit the vacuum pipe through a 5 mm thick Al window
placed $\approx 20$ m downstream of the IP, after which they are detected at
the so-called Dump Table, an optical table immediately prior to the beam dump
where the detector hardware is mounted (see Fig. 1). At the location of the
dump table, the photon axis is vertically separated by $\approx 60$ mm from
the dispersed electron axis for the nominal deflection of the spectrometer
dipole magnet. This article starts with a brief introduction of the working
principles of these high energy radiation detectors together with a
description of the installed hardware. Afterwards, the article shows how
different experiments at FACET-II benefit from these detectors, presenting the
first X-ray and $\gamma$-ray measurements obtained during the initial user-
assisted commissioning runs.

Figure 1: Sketch of the relevant beam line elements for the high energy
radiation measurement at FACET-II.

##  II Design of GAMMA detectors at FACET-II

Prior to the initial runs of FACET-II, a collaborative effort involving users
from different experiments was carried out with the goal of developing a
unified set of diagnostics that would meet the measurement requirements of the
initially planned experiments. Based on the outcomes of several simulation
tools described in the next paragraphs, the first set of two scintillation-
based detectors were developed and installed. Referred to as GAMMA1 and
GAMMA2, they are designed to acquire X-ray/gamma-ray angular and spectral
information.

When a high energy photon propagates through the scintillator, some of its
energy is deposited in the bulk of the material, some of which is then
transformed to visible light. The amount of deposited energy depends on the
choice of the scintillation material, but also on the incoming photon energy.
For instance, a photon with energy $\lesssim$ 1 keV will deposit, on average,
almost its entire energy in most commercially available scintillators, i.e. it
will be absorbed. In contrast, a 1 GeV photon will deposit a much smaller
fraction of its energy in the passage through the scintillator screen. In this
article we will refer to the spectral response of the detector as the average
fraction of the incoming photon energy $\hbar\omega$ that is deposited in the
scintillator $\Gamma_{\rm dep}(\hbar\omega)$. Given the wide photon spectra
produced during different experimental campaigns at FACET-II, understanding
the spectral response of these X-ray and $\gamma$-ray detectors over the
relevant photon energies is of key importance to understand the sensitivity of
these detectors.

The spectral responses have been calculated using the GEANT4 simulation
toolkit [1]. The main advantage of using GEANT4 with respect to tabulated data
of X-ray absorption is to account for the photon-matter interactions that
happen prior to the interaction of the incoming photons with the scintillation
screens. Namely, these simulations account for the secondary particle
production that can ultimately contribute to the total energy deposited in the
scintillator. For this purpose, the angular distributions of these secondary
particles as well as the spatial distribution of the detectors need to be
accounted for in the simulations. In the GEANT4 simulations used here, this
was achieved by tracking both the primary and secondary particles through a
simplified version of the FACET-II geometrical set-up. In these simulations
all the scintillating screens, as well as other elements on the photon axis,
had a transverse spatial extent of $10\times 10\;\rm cm^{2}$, corresponding to
the acceptance angle of the different vacuum components from the IP to the
GAMMA1 and GAMMA2 detectors. Furthermore, all these elements were placed with
the same longitudinal spacing as in the experimental set-up.

Figure 2(a) shows an example of the spectral response of two GAMMA1
scintillators as computed using GEANT4, with and without the effect of the Al
exit window. For each photon energy, $10^{6}$ photons were used to compute the
averaged energy deposited in the scintillation screen. We observe that at low
energies ($10$-$20\;\rm keV$) the Al window absorbs the photons and therefore
no energy is deposited in the scintillator, meaning that those photons cannot
be detected. For high energy photons ($\gtrsim 2\;\rm MeV$) the Al window has
the opposite effect on the amount of energy deposited in the scintillator: the
secondary particles produced during the passage through the Al exit window
reach the detectors and increase the amount of energy deposited in the
scintillator.

Figure 2: Spectral response of GAMMA1 scintillation screens (a) and of the
GAMMA2 scintillation screen (DRZ-fine) with different conversion filters (b),
as computed using GEANT4. See text for details regarding the filter and
scintillator layout.

###  II-A GAMMA1

The GAMMA1 detector at FACET-II is a scintillation-based X-ray and
$\gamma$-ray detector designed to measure the integrated radiation yield and
its angular distribution. This detector has two scintillation screens that can
be individually inserted into the photon-axis: a DRZ-FINETM screen
(manufactured by Mitsubishi Chemical Group) and a pixelated CsI array
(manufactured by Epic-Crystal). The CsI array, formed by $165\times 165$
crystals of $0.5\times 0.5\times 3\;\rm mm^{3}$ size, offers better
sensitivity than the DRZ-FINE, both in terms of the spectral response (see
Fig. 2a) and light output (number of scintillation photons emitted for a given
amount of deposited energy). This better sensitivity comes at the cost of a
worse spatial resolution, given by the transverse size of an individual CsI
crystal (0.5 mm). The visible light emitted by the scinitillator is imaged via
a Nikon NIKKOR 50mm f/1.2 objective on an Allied Vision Manta G-125 GigE
camera.

Similarly to the effect of the Al window on the spectral responses discussed
above, a foil of high-Z material, such as 0.1 mm tungsten, can be installed on
the upstream face of the DRZ-FINE scintillator in order to increase the
sensitivity of the DRZ-fine to high photon energies ($\gtrsim 2$ MeV).

###  II-B GAMMA2

The GAMMA2 detector at FACET-II is a scintillation-based X-ray and
$\gamma$-ray detector designed to assess the spectral distribution of the
incoming high-energy photons. It consists of a set of filters placed
immediately prior to a second DRZ-FINE scintillating screen centered on the
photon axis at $\sim 70$ cm distance downstream of the GAMMA1 scintillator
(see Fig. 1). The set of filters, distributed as in an axis-symmetric pie
chart around the photon axis (see Fig. 5(a)), are glued onto the upstream face
of the GAMMA2 scintillating screen. The rear face of the GAMMA2 scintillating
screen is imaged via a Nikon NIKKOR 50 mm f/1.2 objective on a Manta G-125
GigE camera.

The working principle of this detector relies on the modification of the
spectral response by the different filter materials. For X-ray photons with
energies below 100 keV, a pair of Ross filters [17] can be used to accurately
measure the amount of radiation at a given spectral range. For higher photon
energies, step filters of different materials and thicknesses have been used
to reconstruct the incoming spectra from the transmission rates [13]. However,
as explained earlier, for photon energies above 1 MeV these filters act as
converters, and thus both the absorption and the secondary particle production
need to be taken into account. The conversion phenomenon occurring at these
high photon energies actually plays a central role to extend the GAMMA2
detector sensitivity up to the 10’s of MeV energy range, where the
absorption/transmission detectors are very insensitive.

For the first set of user-assisted commissioning runs at FACET-II, a set of Cu
and W step filters were mounted on the GAMMA2 detector. One of the filter
placements, referred as ”Gap” in Fig. 5(a), was left empty for normalisation
purposes. The associated spectral responses are shown on Fig. 2(b). It should
be noted that the Al window as well the GAMMA1 scintillation are included in
the simulations performed to compute these spectral responses, which allowed
for an accounting of their absorption and production of secondary particles.
These curves show the trend explained above: for low incident photon energies
($\lesssim 1\;\rm MeV$) the thicker filters lead to a lower deposited energy
in the scintillator, and thus lower signal (transmission mode), whereas for
high incident photon energies ($\gtrsim 1\;\rm MeV$) the thicker filters lead
to a stronger signal (conversion mode). As will be shown in the following
sections, comparing the relative signals on the GAMMA2 scintillator behind
each filter can be used, with the help of simulations, to assess the spectral
distribution of the incoming X-ray and $\gamma$-ray photons.

It should be noted that the choice of an axis-symmetric pie distribution of
the GAMMA2 filters is optimised for cylindrically symmetric radiation
profiles. Yet, deviations from this ideal distribution can be corrected during
the data analysis by weighting the signals after each of the GAMMA2 filters
using the corresponding GAMMA1 angular distribution recorded upstream.

##  III Commissioning results

The first set of consistent measurements of high-energy photons at FACET-II
was carried out by inserting Al foils into the electron beam axis at the IP to
produce bremsstrahlung photons. These Al foils of thicknesses ranging from 0.1
mm to 2 mm have been installed at the IP of FACET-II for the “Near-field-CTR-
based self-focusing in beam-multifoil collisions” E332 experiment [18]. This
experiment aims to measure a significant production of $\gamma$-ray photons
when the Near-Field-CTR effect dominates the beam-solid interaction over
multiple scattering, leading to a strong focusing effect on the beam and a
high transfer efficiency from the electron beam energy to the $\gamma$-ray
radiation.

During the initial commissioning runs the beam parameters were such that the
photons produced in the beam-solid interactions were originated predominantly
via bremsstrahlung. By inserting Al foils of different thicknesses, the
linearity of the detectors was assessed. The result of this test for GAMMA1
with the CsI scintillating screen is shown in Fig. 3(a), indicating an
acceptable linear relation between the GAMMA1 signal and the thickness of the
Al foil used to produce bremsstrahlung radiation.

Figure 3: (a) Integrated GAMMA1 signal of Bremsstrahlung photons for different
Al foil thicknesses (blue dots) and linear fit (red line) (b) Experimental and
theoretical GAMMA2 signals of Bremsstrahlung photons produced with a W target
of 1 mm thickness inserted at the IP.

The GAMMA2 signal produced by these photons behind each filter was also
recorded and compared with the theoretical predictions. For this analysis, a 1
mm thick W foil was inserted at the IP to maximize the flux of bremsstrahlung
photons. The result of this analysis is shown in Fig. 3(b). In this plot, both
the simulated signals and the experimental signals are normalised by the
corresponding GAMMA1 signals as explained in Sec. II-B, but also by the no-
filter signal. For the theoretical values, the spectral responses shown in
Fig. 2(b) are applied to the analytical bremsstrahlung spectrum [11] produced
by 10 GeV electrons propagating through a W foil. A fair agreement is observed
between the experimental measurement and the theoretical values, benchmarking
the modelling of the GAMMA2 detector described above. For this Bremsstrahlung
measurements the GAMMA2 detector works in conversion mode, i.e. the thickest
filters have the highest signals.

##  IV Probing Strong-field QED at FACET-II

Similarly to the seminal E144 experiment at the FFTB facility [5], FACET-II
hosts an experimental campaign to study the Strong-Field regime of QED in the
collision of a 10-TW class laser pulse with the 10-13 GeV electrons.

The main goal of this campaign is to observe the transition from perturbative
to non-perturbative electron laser interaction as well as to observe electron-
positron pair production in the tunneling regime [15, 14]. In these
collisions, the beam electrons that are scattered by the electromagnetic field
of the laser pulse emit high energy photons via (non)linear Compton scattering
[7, 4]. If detected, these photons can be used to retrieve information about
the collision. For instance, theoretical calculations predict that when
$a_{0}>1$ ($a_{0}$ being the normalised laser vector potential) the divergence
of the inverse-Compton photons is proportional to $a_{0}$ [21]. Therefore
measuring the divergence of the emitted photons can be used to track energy
jitters of the laser and the true $a_{0}$ experienced by the colliding
electrons on a shot-to-shot basis [9]. It should nevertheless be noted that
for the cases of few-cycle pulses or pulses significantly deviating from a
Gaussian shape a more detailed analysis is needed, requiring a good
experimental characterisation of the laser parameters. In order to test if the
GAMMA1 detector is sensitive to this variation of $\gamma$-ray divergence for
the FACET-II experimental configuration, GEANT4 simulations were performed to
compute the spatially resolved energy deposition on the pixelised CsI crystal.
In this simulation, the incoming photons were initialised using a Monte-Carlo
algorithm that produced the angular and spatial distributions dictated by
numerical QED simulations [20, 16]. Figure 4(a) shows the horizontal (over the
laser-polarisation direction) lineout of the simulated GAMMA1 signals for
three different values of $a_{0}$. The root-mean-square values of this
distribution confirms the linear relation between the measured $\gamma$-ray
divergence and $a_{0}$.

Figure 4: (a) Simulated horizontal distribution of the GAMMA1 signal of the
high energy radiation produced during laser-beam collisions for three
different values of laser normalised vector potential $a_{0}$. (b) Correlation
between horizontal angle of laser-scattered electrons and $\gamma$-ray
pointing of a temporal synchronisation scan of laser-beam collisions.

During the commissioning runs on August 2022, first laser-electron collisions
were achieved at the IP of FACET-II. Scattered electrons, with up to 2.5 GeV
energy loss as well as the associated $\gamma$ photons were recorded by the
different detectors of the experimental area. In this initial configuration, a
laser pulse of $a_{0}\lesssim 1$ collided with the 10 GeV electron beam at a
horizontal angle of $\approx 30^{\circ}$. At the collision point the electron-
beam waist was much larger than the $\approx 2\;\rm\mu m$ laser focal spot,
and the electron beam waist was not set at the laser-IP. Preliminary analysis
of these collisions suggests that linear Compton scattering was dominant in
the measured $\gamma$-ray signal. Yet, scans of the spatial and temporal
laser-beam overlap were performed and allowed for characterisation of the
collision parameters. In these scans, the GAMMA1 detector provided a clean
signature of the collision.

Figure 4(b) shows data from a temporal overlap scan that manifests the
correlation between the measured $\gamma$-ray horizontal pointing and the
pointing (angle) of the scattered electrons as measured from the FACET-II
electron spectrometer. It should be noted that, due to the $30^{\circ}$ angle
of incidence, the temporal scan also encodes information on the horizontal
spatial electron distribution. Both the $\gamma$-ray pointing and the
scattered electron angle are measured in the non-dispersive plane of the
electron spectrometer, which is along the laser polarisation direction. The
scattered electron pointing was measured at around $9\;\rm GeV$, the
spectrometer being set to image the $8\;\rm GeV$ electrons from the IP to the
screen. The clear correlation observed in Fig. 4(b) between the $\gamma$-ray
pointing and the angle of the scattered electrons corresponds to a converging
electron beam with negative transverse position-momentum correlation. As the
laser delay $\Delta T$ is scanned, the collision happens at different
transverse positions of the converging electron beam, resulting in the
observed time-dependent electron and $\gamma$ angles. This data shows, in a
similar way to a laser-wire scanner [3], how the detection of the high-energy
inverse-Compton photon produced in laser-electron collisions can provide a
valuable signature of the interaction that can complement and improve the
measurements of the scattered electrons, the latter suffering from high
background levels of non-scattered electrons.

##  V Beam-driven Plasma Wakefield Accelerator

The E300 experiment, “Energy Doubling of Narrow Energy Spread Witness Bunch
while Preserving Emittance with a High Pump-to-Witness Energy Transfer
Efficiency in a Plasma Wakefield Accelerator”, is the main beam-driven plasma
wakefield accelerator experiment that will explore the current experimental
challenges of this accelerator technology at the FACET-II facility [12]. Among
these challenges, the preservation of the transverse quality of the
accelerated beam, i.e. of the normalised emittance, is one of next milestones
for the application of plasma acceleration technologies to high-energy
particle colliders. To achieve this goal, controlling the matching of the beam
betatron oscillations in and out of the plasma [2] as well as mitigating the
transverse Hosing instability [10] is needed. Recently, simulations have shown
that the betatron radiation produced by the accelerated beam can be used to
diagnose the presence and mitigation of these two sources of emittance growth
(mismatch propagation and Hosing instability) [6]. The non-destructive nature
of this novel diagnostic could help optimising the beam-plasma interaction and
to preserve the emittance of the accelerated beam.

During the initial commissioning runs of this experiment, the region of the IP
was filled with $\rm H_{2}$ gas with static pressures $P$ ranging from 0.05 to
5 Torr. Similarly to what was done at FACET-I [8], the beam was able to field-
ionise the $\rm H_{2}$ molecules over $\approx 3$ meters and drive strong
plasma waves. Despite the large shot-to-shot fluctuations of the beam’s
longitudinal parameters due to the development of microbunching instabilities
along the LINAC, significant energy loss and betatron radiation was
consistently observed at every $\rm H_{2}$ pressure. Furthermore, multi-GeV
particle acceleration was measured and is currently under study.

From the GAMMA2 measurement of these betatron photons it was possible to
retrieve a fitted critical frequency $\omega_{c}$ of a synchrotron-like
spectrum. Results of this study are shown in Fig 5. Figure 5(a) shows a GAMMA2
image of the scintillation signal behind each filter. The observed hierarchy
of these signals, i.e. higher signal after the thinner filters, indicates that
photon absorption dominates over secondary particle production in the GAMMA2
filters. Therefore the detector works in transmission mode, in contrast to the
conversion mode of the bremsstrahlung measurements [Fig. 3(b)], and thus most
of the betatron radiation photons are below the $\sim 1\;\rm MeV$ limit
mentioned in Sec. II-B.

After averaging the signal behind each GAMMA2 filter over a selection of
events (the 20 events with the highest $\gamma$-ray yield at each $\rm H_{2}$
pressure), the normalised signals - see Sec. III for details of the
normalisation procedure - are plotted in Fig. 5(b) for $P=0.08$ Torr and
$P=1.5$ Torr. Despite the large errorbars originating from the aforementioned
shot-to-shot fluctuations, the comparison of the GAMMA2 signals for the two
different pressures shows that, as pressure is increased, a much larger
relative increase of the GAMMA2 signal behind the thicker filters (a factor of
$\approx 4$ for W 3 mm) than after the thinner filters (a factor of $\approx
1.2$ for W 0.1mm) is observed. Qualitatively, this feature is explained by the
shift of the betatron spectrum towards higher energies due to higher plasma
densities at higher $\rm H_{2}$ pressure, which in turn results in more
transmission of the higher energy photons and a more significant secondary
particle production on the thicker filters.

Figure 5: (a) GAMMA2 image of betatron radiation produced in a beam ionised
$\rm H_{2}$ plasma of static pressure $P=1.5\;\rm Torr$, together with labels
of the material and thickness of each filter. (b) Averaged GAMMA2 signals
behind each filter at $P=0.08\;\rm Torr$ (blue dots) and $P=1.5\;\rm Torr$
(purple dots). The errorbars represent the standard deviations. The fitted
values (see text) are plotted in dashed lines.

A more quantitative analysis of this data is carried out by fitting a
synchrotron spectrum, defined by a critical frequency $\omega_{c}$, to the
experimental data [19, 13]. For each pressure, two fits are performed, one
using the Cu filters and the other one using the W filters. For $P=0.08\;\rm
Torr$ ($n_{p}\approx 2.5\times 10^{15}\;\rm cm^{-3}$ assuming single $\rm
H_{2}$ ionisation), the fitted critical frequencies are $7\;\rm keV$ and
$29\;\rm keV$ for the Cu filter and for the W filters respectively. The
corresponding fitted signals are plotted with the blue dashed lines on Figure
5(b). For $P=1.5\;\rm Torr$ ($n_{p}\approx 5\times 10^{16}\;\rm cm^{-3}$
assuming single $\rm H_{2}$ ionisation) the fitted critical frequencies are
$24\;\rm keV$ and $123\;\rm keV$ respectively. It should be noted that at this
plasma density, significant energy losses of more than 5 GeV were observed,
which can substantially modify the shape of the emitted spectra and is not
taken into account in this fitting analysis. Moreover, a discrepancy between
in the absolute values of the retrieved critical frequencies from the Cu and W
filters is observed and is currently under study.

This preliminary analysis shows a first study of the sensitivity of the GAMMA2
detector for the reconstruction of the betatron spectra produced at FACET-II.
With the future optimisation of the beam performance at FACET-II, mainly in
terms of shot-to-shot stability thanks to the mitigation of longitudinal
instabilities, as well as foreseen improvements in the data analysis, the
reconstruction of the betatron spectrum should constrain the beam parameter
space and associated beam dynamics in the plasma.

##  VI Conclusions

In this article, we have reported on the design, commissioning and first
measurements of X-ray and $\gamma$-ray detectors for the initial phase of the
new accelerator facility FACET-II. As a results of a collaborative simulation
campaign, two scintillation-based detectors, named GAMMA1 and GAMMA2, have
been manufactured and installed to measure the broadband high-energy radiation
produced at the Interaction Point of different experimental campaigns hosted
at the facility. During the first user-assisted commissioning runs of FACET-
II, bremsstrahlung, linear Compton scattering, and betatron high energy
photons have been produced and measured using the GAMMA1 and GAMMA2 detectors,
allowing several commissioning tests and experimental studies of their working
principles. The results of the studies presented here show the potential uses
of these detectors in the context of several experimental campaigns, from
Strong-Field QED to beam-driven plasma wakefield acceleration experiments.

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