E. Berdermann

The use of CVD-diamond for heavy-ion detection

Abstract The suitability of CVD-diamond detectors is investigated for applications in heavy-ion accelerator facilities with high intensity beams. Various diamond films of ‘optical’ and ‘electronic grade’ used and unpolished (as grown) are tested with different ions from α-particles (241Am-source) up to the heaviest ions like 208Pb and 238U. The diamond signals are processed in a single-particle mode with current sensitive low-noise broadband electronics. An intrinsic time resolution of σi(ΔT)=29 ps is achieved using detectors of ‘optical grade’ with a thickness of 100 μm. The time resolution improves for thicker samples and for higher electric field applied to the detector. Determined by the strip capacitance and the electronics used, a single-particle counting rate capability >108 ions/s is obtained. The charge collected from different particles increases linearly with the energy loss of the particle and non-linearly with the detector thickness. The pulse-height resolution depends strongly on the material texture and on the irradiation state of the sample and weakly on the ionisation density produced by the particle. ‘Priming’ is observed up to a fluence of 1010 ions/cm2. The homogeneity over the detector area increases significantly. The charge-collection efficiency improves by a factor of 2 and the pulse-height resolution significantly by a factor of 5. The bandwidth of available electronics limits the results obtained at present. Nevertheless, the selection of data presented demonstrates an excellent suitability of CVD diamond for a variety of heavy-ion applications.

Review of the development of diamond radiation sensors

Abstract Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

Radiation hardness of diamond and silicon sensors compared

The radiation hardness of silicon charged particle sensors is compared with single crystal and polycrystalline diamond sensors, both experimentally and theoretically. It is shown that for Si- and C-sensors, the NIEL hypothesis, which states that the signal loss is proportional to the Non-Ionizing Energy Loss, is a good approximation to the present data. At incident proton and neutron energies well above 0.1 GeV the radiation damage is dominated by the inelastic cross section, while at non-relativistic energies the elastic cross section prevails. The smaller inelastic nucleon-carbon cross section and the light nuclear fragments imply that at high energies diamond is an order of magnitude more radiation hard than silicon, while at energies below 0.1 GeV the difference becomes significantly smaller.

Broadband electronics for CVD-diamond detectors

The application of CVD-diamond detectors for particle detection has created a demand for the development of very fast, low-noise electronics operated at high dc bias voltages. To take advantage of the high charge-carrier mobility of the new detector material the signal processing is performed using microwave layout techniques as well as picosecond pulse shapers and GHz-frequency dividers. The particle detection limits of CVD-diamond detectors processed with low impedance broadband electronics are described. The properties of the developed electronics are discussed in conjunction with results from beam diagnostics operation in the broad energy range of 120 keV/amu up to 2 GeV/amu for GSIs heavy ion accelerators.

Efficiency of dislocation density reduction during heteroepitaxial growth of diamond for detector applications

The development of dislocation density and micro-strain in heteroepitaxial diamond films on iridium was measured over more than two decades of thickness up to d ≈ 1 mm. Simple mathematical scaling laws were derived for the decrease of dislocation density with increasing film thickness and for its correlation with micro-strain. The Raman line width as a measure of micro-strain showed a huge decrease to 1.86 cm−1, close to the value of perfect single crystals. The charge collection properties of particle detectors built from this material yield efficiencies higher than 90% in the hole-drift mode, approaching the performance of homoepitaxial films.

In-Beam Diamond Start Detectors

This paper describes operation principles and the in-beam performance of Start Detector (SD) assemblies consisting of Diamond Detectors (DDs) grown by Chemical Vapour Deposition (CVD) and Front End Electronics (FEE) which have been designed for and used in various nuclear physics experiments at GSI Helmholtz Center for Heavy Ion Research in Darmstadt. In parallel to the FEE design we have performed extensive calculations to model the dependence of the signal-to-noise ratio (S/N) and the time resolution σt on various quantities such as the collected charge Qcol, the detector capacitance CD, the temperature T, and finally the noise contribution and bandwidth of the amplifier. In combination with the new FEEs (including an application-specific integrated circuit, ASIC) we have tested both polycrystalline and single-crystal diamonds of various sizes and thicknesses with relativisticion beams ranging from protons to heaviest ions. For heavy ions all setups deliver time resolutions σt <; 60 ps. In case of protons the small primary detector signals require single crystals as material and more elaborated designs like segmentation of the detector area and the increase of the amplifier input impedance. The best time resolution obtained for relativistic pro tons was σt = 117 ps.

Status of the R&D activity on diamond particle detectors

Chemical Vapor Deposited (CVD) polycrystalline diamond has been proposed as a radiation-hard alternative to silicon in the extreme radiation levels occurring close to the interaction region of the Large Hadron Collider. Due to an intense research effort, reliable high-quality polycrystalline CVD diamond detectors, with up to 270μm charge collection distance and good spatial uniformity, are now available. The most recent progress on the diamond quality, on the development of diamond trackers and on radiation hardness studies are presented and discussed.

Tracking with CVD diamond radiation sensors at high luminosity colliders

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

CVD diamond sensors for charged particle detection

Abstract CVD diamond material was used to build position-sensitive detectors for single-charged particles to be employed in high-intensity physics experiments. To obtain position information, metal contacts shaped as strips or pixels are applied to the detector surface for one- or two-dimensional coordinate measurement. Strip detectors 2×4 cm2 in size with a strip distance of 50 μm were tested. Pixel detectors of various pixel sizes were bump bonded to electronics chips and investigated. A key issue for the use of these sensors in high intensity experiments is the radiation hardness. Several irradiation experiments were carried out with pions, protons and neutrons exceeding a fluence of 1015 particles/cm2. The paper presents an overview of the results obtained with strip and pixel detectors in high-energy test beams and summarises the irradiation studies.

Performance of irradiated CVD diamond micro-strip sensors

Abstract CVD diamond detectors are of interest for charged particle detection and tracking due to their high radiation tolerance. In this article, we present, for the first time, beam test results from recently manufactured CVD diamond strip detectors and their behavior under low doses of electrons from a β-source and the performance before and after intense (>10 15 /cm 2 ) proton- and pion-irradiations. We find that low dose irradiation increase the signal-to-noise ratio (pumping of the signal) and slightly deteriorate the spatial resolution. Intense irradiation with protons 2.2×10 15 p / cm 2 lowers the signal-to-noise ratio slightly. Intense irradiation with pions 2.9×10 15 π / cm 2 lowers the signal-to-noise ratio more. The spatial resolution of the diamond sensors improves after irradiations.