Beam Monitoring Devices Research Articles

Dosimetric characterization of a novel UHDR megavoltage X-ray source for FLASH radiobiological experiments

A first irradiation platform capable of delivering 10 MV X-ray beams at ultra-high dose rates (UHDR) has been developed and characterized for FLASH radiobiological research at TRIUMF. Delivery of both UHDR (FLASH mode) and low dose-rate conventional (CONV mode) irradiations was demonstrated using a common source and experimental setup. Dose rates were calculated using film dosimetry and a non-intercepting beam monitoring device; mean values for a 100 μA pulse (peak) current were nominally 82.6 and 4.40 × 10−2 Gy/s for UHDR and CONV modes, respectively. The field size for which > 40 Gy/s could be achieved exceeded 1 cm down to a depth of 4.1 cm, suitable for total lung irradiations in mouse models. The calculated delivery metrics were used to inform subsequent pre-clinical treatments. Four groups of 6 healthy male C57Bl/6J mice were treated using thoracic irradiations to target doses of either 15 or 30 Gy using both FLASH and CONV modes. Administration of UHDR X-ray irradiation to healthy mouse models was demonstrated for the first time at the clinically-relevant beam energy of 10 MV.

First evaluation of a novel ionisation chamber for thermal neutron beam monitoring

The European Spallation Source ERIC (ESS), currently under construction in Lund, Sweden is a facility established to deliver the highest integrated neutron flux originating from a pulsed source with the aim of supporting an initial fifteen neutron instruments for cutting edge science experiments. This in turn requires reliable monitoring at complex neutron beam lines: in particular, linearity, timing capability, adaptability of the design for various flux ranges (dynamic range) and sensitivity to neutrons within the range of 0.6-10Å are expected from the neutron beam monitors to be installed at the ESS beam lines. Additionally, operational stability and low attenuation are also desirable characteristics for such neutron beam monitoring. A prototype neutron beam monitor based on the ionisation chamber principle and a boron converter, designed by CDT CASCADE Detector Technologies GmbH and ESS, has been investigated at the BER-II research reactor of Helmholtz Zentrum Berlin (HZB). The effort to design and investigate a thermal neutron ionisation beam monitor was initiated by adapting the concept of ionisation chambers previously known elsewhere. So far all the characterised neutron beam monitors discriminate neutron hits on a discrete event basis (pulse mode), whereas the beam monitor prototype introduced in this paper estimates the total flux as a function of current (current mode). While most other neutron beam monitoring devices and detectors rely upon a signal amplifying gain stage, the ionisation chamber operates without any gain and is consequently robust against typical detector ageing effects that compromise the sensitivity over time. The initial tests were performed at the ESS V20 test beam line under realistic conditions resembling those of the future pulses of ESS. The linearity is demonstrated for 3Å pulses in the flux range of 2-3 × 105 n/s/cm2 and for white pulses (0.6-10Å) in the range of 1-5 × 106 n/s/cm2. The timing behaviour resembles the data previously recorded at the V20 beam lines. This novel implementation of a neutron sensitive ionisation chamber shows great promise for beam monitoring and diagnostics at ESS. As the ionisation beam monitor itself is an entirely passive device, it is adequately robust to be employed in areas of high irradiation where no regular servicing or maintenance can be provided.

Remote sensing array (RSA) for linac beam monitoring

The purpose of the present work is to evaluate the feasibility of a novel real-time beam monitoring device for medical linacs which remotely senses charge carriers produced in air by the beam without intersecting and attenuating the beamline. The primary goal is to elaborate a theoretical concept of a possible detector geometry and underlying physical model that allows for determination of clinically relevant beam data in real time, namely MLC leaf positions and dose rate. The detector consists of two opposing electrode arrays arranged in two possible orientations around the beamline. Detection of charge carriers is governed by electromagnetic principles described by Shockley–Ramo theorem. Ions produced by ionization of the air column upstream of patient move laterally in an external electric field. According to the method of images, mirror charges and mirror currents are formed in the strip electrodes. Determination of MU rate and MLC positions using the measured signal requires solution of an inverse problem. In the present work we adopted a Least-Square approach and characterized detector response and sensitivity to detection of beam properties for different electrode geometries and MLC shapes. Results were dependent on MLC field shape and the leaf position within the active volume. The accuracy of determination of leaf positions were in the sub-mm range (up to 0.25–1 mm). Additionally, detector sensitivity was quantified by simulating ions/pulse delivered with a radiation transport deterministic computation in 1D in CEPXS/ONEDANT. For a 6 MV linac pulse, signal amplitude per pulse was estimated to be in the lower pA to fA range. We computationally demonstrated feasibility of the remote sensing detector capable of measuring beam parameters such as MLC leaf positions and dose range for each pulse. Future work should focus on optimizing the electrode geometry to increase sensitivity and better reconstruction algorithms to provide more accurate solutions of the inverse problem.

The challenges of beam polarization and keV-scale centre-of-mass energy calibration at the FCC-ee

The capability to determine the FCC-ee centre-of-mass energies (ECM) at the ppm level using resonant depolarization of the beams is essential for the Z line shape measurements, the W mass and the possible observation of the Higgs boson s-channel production. A first analysis (Blondel A et al Polarization and centre-of-mass energy calibration at FCC-ee. arXiv:1909.12245) demonstrated the feasibility of this programme, conditional to careful preparation and a number of further developments. The existing simulation codes must be unified; the analysis and design of the instrumentation must be developed; and a detailed planning must be developed for the simultaneous and coordinated operation of the accelerator, of the continuous polarization and depolarization measurements, and of the beam monitoring devices, ensuring a precise extrapolation from beam energies to centre-of-mass energy and energy spread.

Beamline characterization of a dielectric-filled reentrant cavity resonator as beam current monitor for a medical cyclotron facility.

At PSI (Paul Scherrer Institute), Switzerland, a superconducting cyclotron called "COMET" delivers proton beam of 250MeV pulsed at 72.85MHz for proton radiation therapy. Measuring proton beam currents (0.1-10nA) is of crucial importance for the treatment safety and is usually performed with invasive monitors such as ionisation chambers (ICs) which degrade the beam quality. A new non-invasive beam current monitor working on the principle of electromagnetic resonance is built to replace ICs in order to preserve the beam quality delivered. The fundamental resonance frequency of the resonator is tuned to 145.7MHz, which is the second harmonic of the pulse rate, so it provides signals proportional to beam current. The cavity resonator installed in the beamline of the COMET is designed to measure beam currents for the energy range 238-70MeV. Good agreement is reached between expected and measured resonator response over the energy range of interest. The resonator can deliver beam current information down to 0.15nA for a measurement integration time of 1s. The cavity resonator might be applied serving as a safety monitor to trigger interlocks within the existing domain of proton radiation therapy. Low beam currents limit the abilities to detect sufficiently, however, with the potential implementation of FLASH proton therapy, the application of cavity resonator as an online beam-monitoring device is feasible.

First measurement and online monitoring of the stripper foil thinning and pinhole formation to achieve a longer foil lifetime in high-intensity accelerators

We have established and also implemented a nondestructive online monitoring system for measuring the stripper foil degradation, such as foil thinning and pinhole outbreak, for the first time during beam operation in a high-intensity proton accelerator. We aimed to achieve a realistic and longer lifetime of a stripper foil by ensuring proper uses and determining its end of usefulness without any failure. A stripper foil is used for negative hydrogen (${\mathrm{H}}^{\ensuremath{-}}$) stripping to proton (p) for multiturn charge-exchange injection in high-intensity proton accelerators. A longer foil lifetime is expected, while foil failure during operation should be avoided, as it reduces the accelerator availability and also has serious issues for regular accelerator maintenance. A proper use of the foil should also be ensured to minimize the replacement of the foil magazine, as it involves unhealthy radiation exposure to the workers. We have measured the partially stripped ${\mathrm{H}}^{0}$ and unstripped ${\mathrm{H}}^{\ensuremath{-}}$ charge fractions of the injection ${\mathrm{H}}^{\ensuremath{-}}$ beam out of the stripper foil to understand details of foil degradation, such as foil thinning and pinhole formation due to high-intensity beam irradiation, which are believed to be foil breaking signals. We used two independent beam monitoring devices and precisely measured both ${\mathrm{H}}^{0}$ and unstripped ${\mathrm{H}}^{\ensuremath{-}}$ charge fractions by each monitor. As a result, we obtained a detail of foil degradation during operation to determine a realistic end of its usefulness by successfully achieving a record of nearly 2 yr of operation with a single foil without any failures. The detailed measurement result of the foil degradation also gives strong feedback for producing stronger and durable stripper foils. The present research was done by using simple and ordinary beam diagnostic devices including a nondestructive one, which can be easily applied to overcome the stripper foil issues in any similar existing and next-generation further higher-intensity accelerators.

Description of Radiation Damage in Diamond Sensors Using an Effective Defect Model

The Beam Condition Monitoring Leakage (BCML) system is a beam monitoring device in the CMS experiment at the LHC consisting of 32 poly‐crystalline (pCVD) diamond sensors. The BCML sensors, located in rings around the beam, are exposed to high particle rates originating from the colliding beams. These particles cause lattice defects, which act as traps for the ionized charge carrier leading to a reduced charge collection efficiency (CCE). The radiation induced CCE degradation was, however, much more severe than expected from low rate laboratory measurements. Measurement and simulations presented in this paper show that this discrepancy is related to the rate of incident particles. At high particle rates, the trapping rate of the ionization is strongly increased compared to the detrapping rate leading to an increased build‐up of space charge. This space charge locally reduces the internal electric field increasing the trapping rate and hence reducing the CCE even further. In order to connect these macroscopic measurements with the microscopic defects acting as traps for the ionization charge, the TCAD simulation program SILVACO was used. It allows to introduce the defects as effective donor and acceptor levels, and can calculate the electric field from Transient Current Technique (TCT) signals and CCE as a function of the effective trap properties, like density, energy level, and trapping cross section. After each irradiation step, these properties were fitted to the data on the electric field from the TCT signals and CCE. Two effective acceptor and donor levels were needed to fit the data after each step. It turned out that the energy levels and cross sections could be kept constant and the trap density was proportional to the cumulative fluence of the irradiation steps. The highly non‐linear rate dependent diamond polarization and the resulting signal loss can be simulated using this effective defect model and is in agreement with the measurement results.

Severe signal loss in diamond beam loss monitors in high particle rate environments by charge trapping in radiation‐induced defects

The beam condition monitoring leakage (BCML) system is a beam monitoring device in the compact muon solenoid (CMS) experiment at the large hadron collider (LHC). As detectors 32 poly‐crystalline (pCVD) diamond sensors are positioned in rings around the beam pipe. Here, high particle rates occur from the colliding beams scattering particles outside the beam pipe. These particles cause defects, which act as traps for the ionization, thus reducing the charge collection efficiency (CCE). However, the loss in CCE was much more severe than expected from low rate laboratory measurements and simulations, especially in single‐crystalline (sCVD) diamonds, which have a low initial concentration of defects. After an integrated luminosity of a few corresponding to a few weeks of LHC operation, the CCE of the sCVD diamonds dropped by a factor of five or more and quickly approached the poor CCE of pCVD diamonds. The reason why in real experiments the CCE is much worse than in laboratory experiments is related to the ionization rate. At high particle rates the trapping rate of the ionization is so high compared with the detrapping rate, that space charge builds up. This space charge reduces locally the internal electric field, which in turn increases the trapping rate and recombination and hence reduces the CCE in a strongly non‐linear way. A diamond irradiation campaign was started to investigate the rate‐dependent electrical field deformation with respect to the radiation damage. Besides the electrical field measurements via the transient current technique (TCT), the CCE was measured. The experimental results were used to create an effective deep trap model that takes the radiation damage into account. Using this trap model, the rate‐dependent electrical field deformation and the CCE were simulated with the software SILVACO TCAD. The simulation, tuned to rate‐dependent measurements from a strong radioactive source, was able to predict the non‐linear decrease of the CCE in the harsh environment of the LHC, where the particle rate was a factor 30 higher.

Intelligent low-level RF system by non-destructive beam monitoring device for cyclotrons

The project of a 10 MeV PET cyclotron accelerator for medical diagnosis and treatment was started at Amirkabir University of Technology in 2012. The low-level RF system of the cyclotron accelerator is designed to stabilize acceleration voltage and control the resonance frequency of the cavity. In this work an Intelligent Low Level Radio Frequency Circuit or ILLRF, suitable for most AVF cyclotron accelerators, is designed using a beam monitoring device and narrow band tunable band-pass filter. In this design, the RF phase detection does not need signal processing by a microcontroller.

Characterization and performances of a monitoring ionization chamber dedicated to IBA-universal irradiation head for Pencil Beam Scanning

Every radiotherapy center has to be equipped with real-time beam monitoring devices. In 2008, we developed an ionization chamber in collaboration with the IBA (Ion Beam Applications) company. This monitoring device called IC2/3 was developed to be used in IBA universal irradiation head for Pencil Beam Scanning (PBS). Here we present the characterization of the IC2/3 monitor in the energy and flux ranges used in protontherapy. The equipment has been tested with an IBA cyclotron able to deliver proton beams from 70 to 230MeV. This beam monitoring device has been validated and is now installed at the Westdeutsches Protonentherapiezentrum Essen protontherapy center (WPE, Germany). The results obtained in both terms of spatial resolution and dose measurements are at least equal to the initial specifications needed for PBS purposes. The detector measures the dose with a relative uncertainty lower than 1% in the range from 0.5Gy/min to 8Gy/min while the spatial resolution is better than 250μm. The technology has been patented and five IC2/3 chambers were delivered to IBA. Nowadays, IBA produces the IC2/3 beam monitoring device as a part of its Proteus 235 product.

The VANILLA sensor as a beam monitoring device for X-ray radiation therapy

Cancer treatments such as intensity-modulated radiotherapy (IMRT) require increasingly complex methods to verify the accuracy and precision of the treatment delivery. In vivo dosimetry based on measurements made in an electronic portal imaging device (EPID) has been demonstrated. The distorting effect of the patient anatomy on the beam intensity means it is difficult to separate changes in patient anatomy from changes in the beam intensity profile. Alternatively, upstream detectors scatter and attenuate the beam, changing the energy spectrum of the beam, and generate contaminant radiation such as electrons. We used the VANILLA device, a Monolithic Active Pixel Sensor (MAPS), to measure the 2D beam profile of a 6MV X-ray beam at Bristol Hospital in real-time in an upstream position to the patient without clinically significant disturbance of the beam (0.1% attenuation). MAPSs can be made very thin (~20μm) with still a very good signal-to-noise performance. The VANILLA can reconstruct the collimated beam edge with approximately 64μm precision.

The Miniball spectrometer

The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the \(\gamma\)-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities.

Therapeutic techniques applied in the heavy-ion therapy at IMP

Superficially-placed tumors have been treated with carbon ions at the Institute of Modern Physics (IMP), Chinese Academy of Sciences (CAS), since November 2006. Up to now, 103 patients have been irradiated in the therapy terminal of the heavy ion research facility in Lanzhou (HIRFL) at IMP, where carbon-ion beams with energies up to 100 MeV/u can be supplied and a passive beam delivery system has been developed and commissioned. A number of therapeutic and clinical experiences concerning heavy-ion therapy have been acquired at IMP. To extend the heavy-ion therapy project to deep-seated tumor treatment, a horizontal beam line dedicated to this has been constructed in the cooling storage ring (CSR), which is a synchrotron connected to the HIRFL as an injector, and is now in operation. Therapeutic high-energy carbon-ion beams, extracted from the HIRFL-CSR through slow extraction techniques, have been supplied in the deep-seated tumor therapy terminal. After the beam delivery, shaping and monitoring devices installed in the therapy terminal at HIRFL-CSR were validated through therapeutic beam tests, deep-seated tumor treatment with high-energy carbon ions started in March 2009. The therapeutic techniques in terms of beam delivery system, conformal irradiation method and treatment planning used at IMP are introduced in this paper.

The ATLAS Beam Conditions Monitor

Beam conditions and the potential detector damage resulting from their anomalieshave pushed the LHC experiments to build their own beam monitoring devices. The ATLASBeam Conditions Monitor (BCM) consists of two stations (forward and backward) of detectorseach with four modules. The sensors are required to tolerate doses up to 500 kGy and in excessof 1015 charged particles per cm2 over the lifetime of the experiment. Each module includes twodiamond sensors read out in parallel. The stations are located symmetrically around theinteraction point, positioning the diamond sensors at z = ±184 cm and r = 55 mm (a pseudo-rapidity of about 4.2). Equipped with fast electronics (2 ns rise time) these stations measuretime-of-flight and pulse height to distinguish events resulting from lost beam particles fromthose normally occurring in proton-proton interactions. The BCM also provides a measurementof bunch-by-bunch luminosities in ATLAS by counting in-time and out-of-time collisions.Eleven detector modules have been fully assembled and tested. Tests performed range fromcharacterisation of diamond sensors to full module tests with electron sources and in protontestbeams. Testbeam results from the CERN SPS show a module median-signal to noise of 11:1for minimum ionising particles incident at a 45-degree angle. The best eight modules wereinstalled on the ATLAS pixel support frame that was inserted into ATLAS in the summer of2007. This paper describes the full BCM detector system along with simulation studies beingused to develop the logic in the back-end FPGA coincidence hardware.

Diamond thin film detectors for beam monitoring devices

AbstractDiamonds offer radiation hard sensors, which can be used directly in primary beams. Here we report on the use of a polycrystalline CVD diamond strip sensor as beam monitor of heavy ion beams with up to ∼109 lead ions per bunch. The strips allow for a determination of the transverse beam profile to a fraction of the pitch of the strips, while the timing information yields the longitudinal bunch length with a resolution of the order of a few mm. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

RF acceleration system at cooler-synchrotron TARN II

An ion cooler-synchrotron TARN II has been constructed at INS. The RF acceleration system in this ring has a specification of wide frequency range, from 0.62 to 7.50 MHz, and of high sensitivity of beam monitoring devices for RF frequency control. With use of this RF acceleration system, beam acceleration has been successfully achieved for the light ion beams. In the present paper, the designed RF parameters including the beam feedback system, and the details of hardware for the RF system, are described as well as the experimental results of beam acceleration.

A high pressure 4He polarimeter for double scattering experiments

We describe the performance of a high pressure (up to 50 bar) 4He polarimeter designed as the second scatterer in nuclear double-scattering experiments for protons and deuterons at energies up to 12 MeV. The main characteristics are an efficiency of ∼3 × 10 −5 and an effective analyzing power of 0.7–0.8 for protons (measured at a pressure of 20 bar). For deuterons the efficiency is estimated to be of the same order of magnitude whereas the effective analyzing power is about half the magnitude. The polarimeter is equipped with several beam monitoring devices and can be moved along its symmetry axis as well as rotated around it.

Beam Transport System for Heavy-Ion Storage Ring -TARN-

Beam transport system from the INS-SF cyclotron to the TARN was designed and constructed. The system is composed of optical matching elements, beam monitoring devices and vacuum system. In the present paper, design conception and details of components in the system are described as well as the experimental results of the performance.

Dosimetry and instrumentation for helium and heavy ions

The use of large particle accelerators for biological experiments and medical procedures requires a very reliable and accurate beam-monitoring system. The instrumentation at the 184-in. cyclotron medical facility and the Bevalac biomedical facility includes beam-monitoring devices and instruments used in their calibration. The variables involved in hellum- and heavy-ion dosimetry will be discussed.

Master Timing System for CEA Colliding Beam Project

The CEA colliding beam project requires trigger signals relative to the e- and e+ circumferential beam positions in the accelerator. These triggers are required for proper timing of multicycle injection, steering of the beam into the bypass, triggering of beam monitoring and excitation devices. The synchronizer was built to provide these triggers.