CsI Photocathode Research Articles

Absolute calibration of the spectral sensitivity of an x-ray streak camera over the 0.1-10keV spectral range equipped with CsI photocathode.

In this paper, we report the absolute measurement of the spectral sensitivity of a bilamellar tube x-ray streak camera (XRSC) over the 0.1-10keV range equipped with a CsI photocathode for Laser MégaJoule (LMJ) fusion experiments. This calibration of the XRSC is performed in static mode by using two multi-anode x-ray generators. Two silicon drift detectors (SDDs) previously calibrated at the Physikalisch-Technische-Bundesanstalt radiometric laboratory are used as secondary standards. Both x-ray generators work with a specific monochromator for radiometric measurements. In the sub-keV region, a 1 m-grazing incidence Rowland geometry monochromator specifically developed to handle LMJ's x-ray camera is used, whereas for higher energies (>2keV), a double-crystal monochromator is employed. The absolute spectral sensitivity of the XRSC is obtained by comparing the CCD counts of the XRSC output with the output counts in x-ray lines recorded by the SDD. The results obtained below 1.2keV are, to our knowledge, the first measurements of the spectral sensitivity of an XRSC in the soft x-ray range with a CsI photocathode. Comparison with a model describing the spectral dependence of the sensitivity of the XRSC revealed that measurements obtained in the sub-keV region are greater than expected, whereas they agree with the model above 4.5keV. There may be several contributors to this behavior, including the grain morphology of the CsI layer and exposure to air.

Long-term stability and perspectives of the ALICE-HMPID detector at LHC during run 3

The ALICE High Momentum Particle IDentification (HMPID) is a Ring Imaging Cherenkov detector that identifies π, k and p in the transverse momentum interval 1 < pT < 5 GeV/c. The HMPID consists of seven proximity focusing RICH modules, 1.3 × 1.3 m2 each. They are based on liquid C6F14 as Cherenkov radiator, and on MWPCs equipped with CsI pad segmented photocathodes as photon detector. During the LHC Long Shutdown 2 (LS2, 2019–2021) the HMPID underwent upgrading activities that increased the event read out rate up to ∼20 kHz, 10 times faster than in Run 2. The performance of the read-out electronics and the MWPCs status after a stop of 4 years, using the first Run 3 data (2022), are presented. The HMPID will also constraint the measurement of the inelastic (anti-)deuteron inelastic cross section in the momentum interval 0.2–2 GeV/c. For such aim during LS2 two aluminium absorbers 1.3 × 1.3 m2, one with a thickness of 8 cm, half interaction length, and the other with a thickness of 4 cm, were installed in front of two RICH modules. Preliminary Monte Carlo results on the expected uncertainties on the cross section measurement are given. Finally, the projection of the CsI photocathodes stability at the end of Run 3 after the absorption of a charge dose ten times higher than in Run 2, is discussed.

Study of hybrid micropattern gaseous detector with CsI photocathode for Super Tau-Charm facility RICH

Super τ-Charm facility (STCF) is a future electron-positron collider operating in the τ-Charm energy region with the aim of studying hadron structure and spectroscopy. The baseline design of the STCF barrel particle identification (PID) detector, which covers momentum up to 2 GeV/c, is provided by a Ring Imaging Cherenkov Counter (RICH). The RICH features an approximately focusing design with liquid perfluorohexane sealed in a quartz container as the radiator and a hybrid combination of CsI-coated THGEMs and Micromegas as the photo-electron detector. A 16×16 cm2 prototype with a quartz radiator has been built and tested at DESY and stably operated with an effective gain of 105. In this paper, the design, performance, and reconstruction algorithm of RICH detectors are discussed.

Theoretical calculation of response sensitivity of CsI photocathode of soft X-ray streak camera

The response sensitivity of CsI photocathode is an important parameter for the quantitative diagnosis of X-ray spectroscopy by soft X-ray streak camera, and its theoretical calculation has important guiding significance. The current theoretical analytical models are based on the one-dimensional random walking model of secondary electrons generated by thin film photocathodes, including the Henke model under the condition of normal incidence of X-rays and energy greater than 1 keV, and the Fraser model under variable angle incidence and photocathode thickness greater than 100 nm, which have certain limitations. In this paper, the basic expression of the probability of secondary electron transmission is introduced, and the general expression of the response sensitivity of CsI photocathode is deduced, which varies with X-ray energy &lt;i&gt;E&lt;/i&gt;, photocathode thickness &lt;i&gt;t&lt;/i&gt;, and angle &lt;i&gt;θ&lt;/i&gt; between X-ray and cathode surface in a larger parameter range (X-ray energy 0.1–10 keV, photocathode thickness 10–200 nm). Finally, the theoretical calculation results of this paper are discussed by comparing it with those from the Henke model, Fraser model, literature data and experimental data on Beijing synchrotron radiation facility, which verifies the accuracy and universality of the computational model, and a theoretical reference is provided for optimally designing the CsI photocathode in high-time-resolution spectrometric quantitative measurement.

Sub-25 ps timing measurements with 10 × 10 cm[formula omitted] PICOSEC Micromegas detectors

The PICOSEC Micromegas detector is a precise timing gaseous detector based on a Cherenkov radiator coupled to a semi-transparent photocathode and a Micromegas amplifying structure. First single-pad prototypes demonstrated a time resolution below σ= 25 ps, however, to make the concept appropriate to physics applications, several developments are required. The objective of this work was to achieve an equivalent time resolution for a 10 × 10 cm2 area PICOSEC Micromegas detector. The prototype was designed, produced and tested in the laboratory and successfully operated with a 80 GeV/c muon beam. Preliminary results for this device equipped with a CsI photocathode demonstrated a time resolution below σ= 25 ps for all measured pads. The time resolution was reduced to be below σ= 18 ps by decreasing the drift gap to 180 μm and using dedicated RF amplifier cards as new electronics. The excellent timing performance of the single-channel proof of concept was not only transferred to the 100-channel prototype, but even improved, making the PICOSEC Micromegas detector more suitable for large-area experiments in need of detectors with high time resolutions.

A new experimental system for electron transverse diffusion measurements

The knowledge of the electron transverse diffusion in detection media is mandatory to assess the accuracy in systems that require precise event tracking. A new experimental system was developed to measure the transverse diffusion of electrons in gases. Electrons are generated in a transmissive CsI photocathode by Xe VUV light from a pulsed Xe lamp, and drift a fixed distance that can be varied from 4 to 60 mm. The charge is then multiplied in a GEM and collected in a multistrip target. The results were obtained for Xe and CH4 at two different E/N values, at 800 Torr, for drift distances between 4 and 12 mm. The characteristic energy associated with the transverse diffusion obtained were (5.75±0.45) eV and (7.15±0.63) eV for Xe, and (0.065±0.005) eV and (0.097±0.008) eV for CH4, respectively for 0.92 and 1.53 Td. All values are in good agreement with results from the literature.

A sealed X-ray microchannel plate imager with CsI photocathode to improve quantitative precision of framing camera

In this paper, we propose a hermetically sealed X-ray microchannel plate imager as a more effective and stable alternative to the traditional open-structured imager. With two microstrip photocathodes of 100 nm Au and 100 nm CsI, respectively, the proposed imager has a measured exposure time of 65 ps when applied with a 200 ps width gate pulse. The static response test shows that the image intensity of the CsI microstrip photocathode is 3.4 times that of the Au microstrip photocathode when illuminated by a non-monochromatic portable X-ray source with high energy photons. The sealed imager not only enhances the sensitivity and stability of the framing camera, but also has the potential to reduce crosstalks and artifacts, thus further improves the precision of measurement in practice.

Bubble-assisted Liquid Hole Multipliers in LXe and LAr: towards “local dual-phase TPCs”

The bubble-assisted Liquid Hole Multiplier (LHM) is a novel concept for the combined detection of ionization electrons and scintillation photons in noble-liquid time projection chambers. It consists of a perforated electrode immersed in the noble liquid, with heating wires generating a stable vapor bubble underneath. Radiation-induced ionization electrons in the liquid drift into the electrode's holes and cross the liquid-vapor interface into the bubble where they induce electroluminescence (EL). The top surface of the electrode is optionally coated with a CsI photocathode; radiation-induced UV-scintillation photons extract photoelectrons that induce EL in a similar way. EL-photons recorded with an array of photo-sensors, e.g. SiPMs, provide event localization. We present the basic principles of the LHM concept and summarize the results obtained in LXe and LAr.

Gaseous counters with CsI photocathodes: The COMPASS RICH

COMPASS RICH is a wide acceptance Cherenkov imaging counter with gas radiator, where single photon detection is performed by gaseous detectors and multianode photomultiplier tubes. It accomplishes high-momentum hadron identification in the COMPASS spectrometer at CERN SPS, which is dedicated to hadron physics studies. The counter, designed and built in the last years of the twentieth century, has been in operation since 2001. It has been upgraded several times over the 20 years of operation and, in particular, the photon detection system has been renewed twice, in 2005/06 and in 2015/16, to improve matching the demanding goals of the COMPASS physics programme and the continuously increasing trigger rate.The RICH has adopted the state-of-the-art technologies enriched with original complements for radiator gas handling, the ultraviolet mirror wall, the multiwire proportional chambers equipped with CsI photocathodes, the multianode photomultiplier tubes coupled to telescopes of fused silica lenses and the read-out electronics. It is the first RICH counter where, in a recent upgrade, part of the original gaseous photon detectors have been replaced with single photon detection by micropattern gaseous detectors, thanks to an original development.The RICH design principle, construction, upgrades and performance are reported.

Ageing results of N,N′-Bis (3-methylphenyl) -N,N′-diphenylbenzidine (TPD) and 8-Hydroxyquinoline (Alq3).

Ageing results of N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and 8-Hydroxyquinoline (Alq3) are presented in this work. Photocathodes were investigated under accumulated photon and ion bombardment. QE of degraded photocathodes were compared with QE results of freshly prepared photocathodes. Negligible change in QE of photocathodes was observed as compared to the results of CSI photocathodes under similar experimental conditions.

First results of Resistive-Plate Well (RPWELL) detector operation at 163 K

We present for the first time, discharge-free operation at cryogenic conditions of a Resistive-Plate WELL (RPWELL) detector. It is a single-sided Thick Gaseous Electron Multiplier (THGEM) coupled to a readout anode via a plate of high bulk resistivity. The results of single- and double-stage RPWELL detectors operated in stable conditions in Ne/5%CH4 at 163 K are summarized. The RPWELL comprised a ferric-based (Fe3+) ceramic composite (“Fe-ceramic”) as the resistive plate, of volume resistivity ∼ 1011 Ω ⋅cm at this temperature. Gains of ∼ 104 and ∼ 105 were reached with the single-stage RPWELL, with 6 keV X-rays and single UV-photons, respectively. The double-stage detector, a THGEM followed by the RPWELL, reached gains ∼ 105 and ∼ 106 with X-rays and single UV-photons, respectively. The results were obtained with and without a CsI photocathode on the first multiplying element. Potential applications at these cryogenic conditions are discussed.

Results From a Prototype Combination TPC Cherenkov Detector With GEM Readout

A combination Time Projection Chamber-Cherenkov prototype detector has been developed as part of the Detector R&D Program for a future Electron Ion Collider. The prototype was tested at the Fermilab test beam facility to provide a proof of principle to demonstrate that the detector is able to measure particle tracks and provide particle identification information within a common detector volume. The TPC portion consists of a 10x10x10cm3 field cage, which delivers charge from tracks to a 10x10cm2 quadruple GEM readout. Tracks are reconstructed by interpolating the hit position of clusters on an array of 2x10mm2 zigzag pads The Cherenkov component consists of a 10x10cm2 readout plane segmented into 3x3 square pads, also coupled to a quadruple GEM. As tracks pass though the drift volume of the TPC, the generated Cherenkov light is able to escape through sparsely arranged wires making up one side of the field cage, facing the CsI photocathode of the Cherenkov detector. The Cherenkov detector is thus operated in a windowless, proximity focused configuration for high efficiency. Pure CF4 is used as the working gas for both detector components, mainly due to its transparency into the deep UV, as well as its high N0. Results from the beam test, as well as results on its particle id capabilities will be discussed.

Recent advances in bubble-assisted Liquid Hole-Multipliers in liquid xenon

We report on recent advances in the operation of bubble-assisted Liquid Hole-Multipliers (LHM). By confining a vapor bubble under or adjacent to a perforated electrode immersed in liquid xenon, we could record both radiation-induced ionization electrons and primary scintillation photons in the noble liquid. Four types of LHM electrodes were investigated: a THGEM, standard double-conical GEM, 50 μm-thick single-conical GEM (SC-GEM) and 125 μm-thick SC-GEM—all coated with CsI photocathodes. The 125 μm-thick SC-GEM provided the highest electroluminescence (EL) yields, up to ∼ 400 photons per electron over 4π , with an RMS pulse-height resolution reaching 5.5% for events comprising ∼ 7000 primary electrons. Applying a high transfer field across the bubble, the EL yield was further increased by a factor of ∼ 5. The feasibility of a vertical-mode LHM, with the bubble confined between two vertical electrodes, and the operation of a two-stage LHM configuration were demonstrated for the first time. We combine electrostatic simulations with observed signals to draw conclusions regarding the location of the liquid-gas interface and suggest an explanation for the observed differences in EL yield between the investigated electrodes.

Optimized MPGD-based Photon Detectors for high momentum particle identification at the Electron-Ion Collider

Particle IDentification (PID) is a central requirement of the experiments at the future EIC. Hadron PID at high momenta by RICH techniques requires the use of low density gaseous radiators, where the challenge is the limited length of the radiator region available at a collider experiment. By selecting a photon wavelength range in the far UV domain, around 120 nm, the number of detectable photons can be increased. Ideal sensors are gaseous Photon Detectors (PD) with CsI photocathode, where the status of the art is represented by the MPGD-based PDs at COMPASS RICH. Detector optimization is required for the application at EIC. Here we report about a dedicated prototype where the sensor pad-size has been reduced to preserve the angular resolution. A new DAQ system based on the SRS readout electronics has been developed for the laboratory and test beam studies of the prototype.

Photoelectron extraction efficiency into Ar-CF4 and Xe-CF4 gas mixtures

Experimental measurements of the extraction efficiency f of the photoelectrons emitted from a reflective CsI photocathode into Ar-CF4 and Xe-CF4 gaseous mixtures are presented, as a function of reduced electric field E/p in the range 0.1 to 3 V cm−1 Torr−1 and as a function of CF4 concentration. The experimental data is compared to Monte Carlo simulation results. The investigation confirms that backdiffusion of low-energy photoelectrons emitted from a photocathode into a gas medium depends strongly on the nature of the gas. The effect is especially significant in pure noble gases, but it can be considerably reduced by the admixture of certain molecular gases, like CF4.

Design and construction of a new ultraviolet sensor using CsI deposition in the ionization chamber

Abstract In this article, a UV sensor that is an appropriate tool for fire detection has been designed and constructed. The structure of this UV sensor is an air-filled single-wire detector that is able to operate under normal air condition. A reflective CsI photocathode is installed at the end of the sensor chamber to generate photoelectrons in the ion chamber. An electric current is produced by accelerating photoelectrons to the anode in the electric field. The detector is able to measure the intensity of the incident UV rays whenever the current is sufficiently high. Therefore, the sensitivity coefficient of this sensor is found to be 7.67 × 10−6 V/photons/sec.

Calculation of CsI photocathode spectral response in 10-100 keV X-ray energy region

CsI photocathode is widely applied to high energy X-ray detection. And the spectral response is an important character of CsI photocathode. In this paper, the interaction process of high energy X-ray with CsI is analyzed and the spectral response of CsI photocathode is calculated in a 10-100 keV range. The influences of Compton scattering, X-ray fluorescence radiation and Auger emission on the spectral response are analyzed in accordance with the physical process of high energy X-ray interaction with CsI photocathode. These influences prove to be negligible in comparison with photo-ionization influence. Thus only the photoelectric transition is taken into account in calculation. According to the analyses of the processes of the photoelectron creation, transition and escaping, the formula for CsI spectral response is deduced as a function of secondary electron mean escape depth and photocathode thickness. The formula of secondary electron mean escape depth is then deduced as a function of X-ray energy. These formulae indicate that the mean escape depth of the secondary electrons increases markedly with the rise of X-ray energy and has a remarkable influence on the CsI spectral response. The spectral responses for different CsI thickness values are then calculated in a range of 10-100 keV. The results show that 1000 nm CsI has the best response under 20 keV, while 10000 nm CsI has a higher response over 60 keV. Then the calculation data are compared with experimental data of Hara's and Khan's hard X-ray streak camera measurements. These data agree well with each other and prove that our calculation of CsI spectral response for high energy X-ray is reliable. The spectral responses to CsI thickness for 17.5 keV and 60 keV are also calculated and shown in figures. These calculation data match experimental data of Frumkin and Monte-Carlo simulation data of Gibrekhterman. The measurement error of Frumkin's experiment and the uncertainty of the secondary electron mean escape depth are considered to be the reasons for the deviations of calculation and experimental data. The figures of spectral responses to CsI thickness also reveal the optimal thickness values of CsI for different X-ray photon energies. It is shown that 1 m is the optimal thickness for 17.5 keV X-ray detection, and 10 m is optimal for 60 keV. Finally the spectral response of CsI photocathode in a 10-100 keV range is calculated and the formulae prove to be reliable. According to these formulae and calculations, the optimal thickness of CsI photocathode can thus be given for designing and optimizing the high energy X-ray imaging detectors.

A Prototype Combination TPC Cherenkov Detector with GEM Readout for Tracking and Particle Identification and its Potential Use at an Electron Ion Collider

A prototype detector is being developed which combines the functions of a Time Projection Chamber for charged particle tracking and a Cherenkov detector for particle identification. The TPC consists of a 10×10×10 cm3 drift volume where the charge is drifted to a 10×10 cm2 triple GEM detector. The charge is measured on a readout plane consisting of 2×10 mm2 chevron pads which provide a spatial resolution ∼ 100 μm per point in the chevron direction along with dE/dx information. The Cherenkov portion of the detector consists of a second 10×10 cm2 triple GEM with a photosensitive CsI photocathode on the top layer. This detector measures Cherenkov light produced in the drift gas of the TPC by high velocity particles which are above threshold. CF4 or CF4 mixtures will be used as the drift gas which are highly transparent to UV light and can provide excellent efficiency for detecting Cherenkov photons. The drift gas is also used as the operating gas for both GEM detectors. The prototype detector has been constructed and is currently being tested in the lab with sources and cosmic rays, and additional tests are planned in the future to study the detector in a test beam.

Study of semi-transparent conductive layers for the realization of high quantum efficiency transmission mode CsI photocathodes for vacuum photodetectors

We worked on the R&D of an innovative photodetector, the Vacuum Silicon Photomultiplier Tube (VSiPMT). The VSiPMT is composed by a photocathode and a solid state amplification stage. A semi-transparent conductive layer is necessary to supply voltage and to obtain a highly efficient CsI photocathode. Since the literature is poor on this topic we performed a systematic and detailed study of a set of semi-transparent conductive layers, made by different material and thickness. A CsI photocathode was evaporated on each sample. The impact of the semi-transparent conductive layer on the quantum efficiency of the photocathode is discussed.

Laboratory reflectometer for the investigation of optical elements in a wavelength range of 5–50 nm: description and testing results

We describe a laboratory reflectometer developed at the IPM RAS for precision measurements of spectral and angular dependences of the reflection and transmission coefficients of optical elements in a wavelength range of 5–50 nm. The radiation is monochromatised using a high-resolution Czerny–Turner spectrometer with a plane diffraction grating and two spherical collimating mirrors. A toroidal mirror focuses the probe monochromatic beam on a sample. The X-ray source is a highly ionised plasma produced in the interaction of a high-power laser beam with a solid target at an intensity of 1011–1012 W cm–2. To stabilise the emission characteristics, the target executes translatory and rotary motions in such a way that every pulse irradiates a new spot. The short-focus lens is protected from contamination by erosion products with the use of a specially designed electromagnetic system. The samples under study are mounted on a goniometer is accommodated in a dedicated chamber, which provides five degrees of freedom for samples up to 500 mm in diameter and two degrees of freedom for a detector. The sample mass may range up to 10 kg. The X-ray radiation is recorded with a detector composed of a CsI photocathode and two microchannel plates. A similar detector monitors the probe beam intensity. The spectral reflectometer resolution is equal to 0.030 nm with the use of ruled gratings with a density of 900 lines mm–1 (spectral range: 5–20 nm) and to 0.067 nm for holographic gratings with a density of 400 lines mm–1 (spectral range: 10–50 nm). We analyse the contribution of higher diffraction orders to the probe signal intensity and the ways of taking it into account in the measurements. Examples are given which serve to illustrate the reflectometer application to the study of multilayer mirrors and filters.