Train probe for beam diagnostics of the SC200 superconducting cyclotron

The SC200 proton therapy system commissioned by the Hefei CAS Ion Medical and Technical Devices Co.,Ltd.(HFCIM;Hefei,China)and the Joint Institute for Nuclear Research(JINR;Dubna,Russia)has made significant progress.A main radial beam diagnostic system(MRBDS)equipped with a new type of train probe was developed to satisfy the requirements of beam diagnosis.In this paper,the detailed design of the mechanical structure and electronics system of the MRBDS is presented.The electronics system,which includes hardware and software components,was tested and calibrated.The results show that measurement errors can be significantly reduced by the designed calibration procedures.The repeatability of the mechanical structure was also verified,and the experimental results indicate that the unidirectional repeatability of the positioning is better than 0.3 mm.Finally,the MRBDS was used to measure the phase lag of the particles in the beam,and the results showed a high degree of agreement with theoretical calculations,which proved the applicability and high efficiency of the MRBDS.

A normal-pressure MWPC for beam diagnostics at RIBLL2

A normal pressure MWPC for beam diagnostics at RIBLL2 has been developed, wmcn has a sensluve area of 80 mm×80 mm and consists of three-layer wire planes. The anode plane is designed with a wider frame to reduce the discharge and without using protection wires. The detector has been tested with a 55Fe X-ray source and a 200 MeV/u ^12C beam from CSRm. A position resdution better than 250 μm along the anode wires and a detection efficiency higher than 90% have been achieved.

On-line beam diagnostics based on single-shot beam splitting phase retrieval

We propose a novel on-line beam diagnostic method based on single-shot beam splitting phase retrieval. The incident beam to be measured is diffracted into many replicas by a Dammann grating and then propagates through a weakly scattering phase plate with a known structure; the exiting beams propagate along their original direction and form an array of diffraction patterns on the detector plane. By applying the intensity of diffraction patterns into an iterative algorithm and calculating between the grating plane, weakly scattering plane, and detector plane, the complex field of the incident beam can be reconstructed rapidly; the feasibility of this method is verified experimentally with wavelengths of 1053 and 632.8 nm.

Design of imaging system for CSNS near-target beam diagnostics

Introduction China Spallation Neutron Source(CSNS)is an accelerator-based pulsed neutron source which produces neutron with spallation reaction induced by proton bombarding tungsten target.With increasing beam powers and influences on target,near-target monitoring becomes extreme necessary.In this situation,an optical imaging system for proton beam diagnostics and monitoring near the target is being developed at CSNS,which can provide real-time images of the beam on target and beam distribution information.Target imaging system design and development In the design of CSNS target imaging system,coating of Cr^(3+):Al_(2)O_(3) is used to convert particle radiation into emission light.According to the geometry limits of CSNS target station,a special optical system was designed and fabricated to collect the emission light.When the proton beams strike on the target,the coating on the target will be excited,emitting luminescence at the same time.The mirrors and lenses of the optical system image the distribution of emission light into a radiation-hard imaging fiber,which transmits the images to the GigE camera located at low-dose area outside of the target station.Software was written on the LabView platform to control the camera and analyze the images on line.Mock-up of the imaging system was manufactured to test and evaluate the performances of the system.Some important characteristics of the system were obtained and studied.Conclusion Tests on the mock-up of the system present reliably expectation for beam diagnostics.The imaging system has been installed at CSNS recently.More work will be continued to improve the properties of the system.

Logical and Timing Control for Diagnostic Neutral Beam Injection on HT-7

The timing and master control logic （MCL） units are the most important function units of the diagnostic neutral beam （DNB） power supply control system. The units control the operation of nine power supply subsystems of the DNB system, and provide protection for the DNB system from faults such as beam source arc down. Based on the characteristics of the DNB power supply system, the timing and MCL units have been designed, fabricated and tested. Experiments prove that the timing unit is convenient, flexible and reliable, and the MCL is functional.

Charge Exchange Recombination Spectroscopy Based on Diagnostic Neutral Beam in HT-7 Tokamak

Charge exchange recombination spectroscopy （CXRS） based on a diagnostic neutral beam （DNB） installed in the HT-7 tokamak is introduced. DNB can provide a 6 A extracted current at 50 kV for 0.1 s in hydrogen. It can penetrate into the core plasma in HT-7. The CXRS system is designed to observe charge exchange （CX） transitions in the visible spectrum. CX light from the beam is focused onto 10 optical fibers, which view the plasma from -5 cm to 20 cm. The CXRS system can measure the ion temperature as low as 0.1 keV. With CXRS, the local ion temperature profile in HT-7 was obtained for the first time.

Performance of Diagnostic Neutral Beam for the HT-7 Tokamak

Diagnostic neutral beam （DNB）, combined with spectral diagnostics, is employed to measure the ion temperature in HT-7. The factors affecting the extracted beam are studied in the experiment for the high performance diagnostic neutral beam. A 6.5 A extracted hydrogen current at 43 keV of 100 ms was obtained after optimization. The extracted beam has a proton ratio as high as 40%, and can penetrate into the core plasma after neutralization to measure the ion temperature effectively.

Optimizing beam transport in rapidly compressing beams on the neutralized drift compression experiment-II

The Neutralized Drift Compression Experiment-II(NDCX-II)is an induction linac that generates intense pulses of 1.2 MeV helium ions for heating matter to extreme conditions.Here,we present recent results on optimizing beam transport.The NDCX-II beamline includes a 1-m-long drift section downstream of the last transport solenoid,which is filled with charge-neutralizing plasma that enables rapid longitudinal compression of an intense ion beam against space-charge forces.The transport section on NDCX-II consists of 28 solenoids.Finding optimal field settings for a group of solenoids requires knowledge of the envelope parameters of the beam.Imaging the beam on the scintillator gives the radius of the beam,but the envelope angle is not measured directly.We demonstrate how the parameters of the beam envelope(radius,envelop angle,and emittance)can be reconstructed from a series of images taken by varying the B-field strengths of a solenoid upstream of the scintillator.We use this technique to evaluate emittance at several points in the NDCX-II beamline and for optimizing the trajectory of the beam at the entry of the plasma-filled drift section.

Determining beam transverse absolute position by triangulation of multi-electrode signal phase differences

Accurate measurement of the transverse position of a beam is crucial in particle accelerators because it plays a key role in determining the beam parameters.Existing methods for beam-position measurement rely on the detection of image currents induced on electrodes or narrow-band wake field induced by a beam passing through a cavity-type structure.However,these methods have limitations.The indirect measurement of multiple parameters is computationally complex,requiring external calibration to determine the system parameters in advance.Furthermore,the utilization of the beam signal information is incomplete.Hence,this study proposes a novel method for measuring the absolute electron beam transverse position.By utilizing the geometric relationship between the center position of the measured electron beam and multiple detection electrodes and by analyzing the differences in the arrival times of the beam signals detected by these electrodes,the absolute transverse position of the electron beam crossing the electrode plane can be calculated.This method features absolute position measurement,a position sensitivity coefficient independent of vacuum chamber apertures,and no requirement for a symmetrical detector electrode layout.The feasibility of this method is validated through numerical simulations and beam experiments.

Electron Beam Spectrum Diagnostics with Optical Transition Radiation on the Beijing Free-Electron Laser

A measurement system was developed to measure the electron beam spectrum of the Beijing free-electron laser based on the optical transition radiation (OTR). This paper describes the system, which consists of a 32-channel high resolution of 0.02% OTR detector, especially the spectrometer. The OTR an-gular-distribution pattern at the focal plane has two apexes, but the two apexes are smoothed out due to the electron beam energy distribution. The energy spectrum can be measured if the magnet energy resolution is higher than 0.7% to distinguish the electron beam energy distribution.

Design and development of an ACCT for the Shanghai advanced proton therapy facility

The Shanghai advanced proton therapy facility is a proton cancer treatment device designed and built by the Shanghai Institute of applied physics at the Chinese academy of sciences.The accelerator part comprises a proton linear accelerator(linac)injector and a circular synchrotron.An alternating current current transformer(ACCT)is used for non-intercepting beam current measurement at the drift tube linac exit.According to the beam characteristics,the ACCT is required to complete real-time beam current and pulse width measurements at currents of3-30 mA,frequencies of 1-10 Hz,and pulse widths of40-400μs.In this paper,we report the design and development of an ACCT.The designed ACCT was simulated using CST Microwave Studio,and calibrated using an oscilloscope and signal generator.Variations in the output signal of the ACCT were investigated as a function of ceramic gap size,number of coil turns,and resistance.According to the simulation and experimental results,the optimal number of coil turns was found to be 30.In addition,a low-pass filter was adopted to filter the noise introduced during long-distance signal transmission using a coaxial cable with the length of 20 m.The calibration results show that the corresponding rise time of the ACCT is 800 ns with the sensitivity of 8.2 V/A and a droop of less than 1%,meeting the design requirements.

Measurement of electron beam transverse slice emittance using a focused beamline

A single-shot measurement of electron emittance was experimentally accomplished using a focused transfer line with a dipole.The betatron phase of electrons based on laser wakefield acceleration(LWFA)is energy dependent owing to the coupling of the longitudinal acceleration field and the transverse focusing(defocusing)field in the bubble.The phase space presents slice information after phase compensation relative to the center energy.Fitting the transverse size of the electron beam at different energy slices in the energy spectrum measured 0.27 mm mrad in the experiment.The diagnosis of slice emittance facilitates local electron quality manipulation,which is important for the development of LWFA-based free electron lasers.The quasi-3D particle-in-cell simulations matched the experimental results and analysis well.

Matched wavelength and incident angle for the diagnostic beam to achieve coherent grating tiling

Design and operation of a practical, accurate alignment diagnostic system is important for the grating tiling technology, which is supposed to be applied in a chirped-pulse amplification system to increase the output power. A diagnostic method is proposed and demonstrated for grating tiling. Provided that the wavelength and incident angle of the diagnostic beam are properly set, the far-field of the main laser beam and that of the diagnostic beam can vary in the same way with the tiling errors between the sub-aperture gratings. Therefore, rotational and translational errors can be controlled and compensated according to the far-field of the diagnostic beam. The real-time monitoring and alignment can be achieved without disturbing the main beam.

The beam-based calibration of an X-ray pinhole camera at SSRF

A pinhole camera for imaging X-ray synchrotron radiation from a dipole magnet is now in operation at the Shanghai Synchrotron Radiation Facility （SSRF） storage ring.The electron beam size is derived by unfolding the radiation image and the point spread function （PSF） with deconvolution techniques.The performance of the pinhole is determined by the accuracy of the PSF measurement.This article will focus on a beam-based calibration scheme to measure the PSF system by varying the beam images with different quadrupole settings and fitting them with the corresponding theoretical beam sizes.Applying this method at SSRF,the PSF value of the pinhole is revised from 37 to 44μm.The deviation in beam size between the theoretical value and the measured value isminimized to 4% after calibration.This optimization allows us to observe the horizontal disturbance due to injection down to as small as 0.5μm.

Measurements and characteristics of Al_(2)O_(3):Cr^(3+) coating for the proton beam imaging system

Introduction To set up an online proton beam diagnostic system near the neutron production target of China Spallation Neutron Source(CSNS),a luminescence coating sprayed on the target windowand a corresponding optic system were fabricated.In the work,the fabrication of Al_(2)O_(3):Cr^(3+) coating was explored.Measurements on the sprayed samples were performed to analyze the characteristics of the Al_(2)O_(3):Cr^(3+) coating.Fabrication and tests of coating samples Three kinds of powders with different Cr concentrations were used to fabricate the luminescence coating samples.The flame spraying,plasma spraying and D-gun spraying processes were explored.Photoluminescence(PL),X-ray diffraction(XRD),scanned electron mirror(SEM)and radioluminescence experiment by 300 MeV deuterium beam were carried out to analyze and characterize the samples.Results The emission spectrum excited by 532-nm laser has two obvious peaks at 692.9 nm and 694.3 nm.The samples by flame spraying process with the powders obtained from melting method show higher luminescence intensity than the samples by plasma spraying process.It is observed that the luminescence intensity has some relationships with the alpha phase in the samples,which is deduced from the XRD and photoluminescence tests results.A lower temperature during the flame spraying process will help to keep more alpha phase in the material.The selected four samples show successful fluoresced results in the radioluminescence experiment.Conclusions The luminescence intensity of the coating is improved greatly by the studies on the fabrication process and the characteristics of the samples.The luminescence coating used in beam diagnostics will be fabricated by the confirmed technical process.More works will be continued to improve the characteristics of the luminescence light by controlling Cr concentration and annealing in 1200∼2000℃ environment in the future.

Detector development at the Back-n white neutron source

Purpose Back-n is a white neutron beamline at China spallation neutron source,which was established in the year of 2018.It is a powerful facility for nuclear data measurement,neutron detector calibration,and radiation effect research.Method A series of detectors were built for different experiments,including beam monitoring,beam profile measurement,neutron induced secondaries(fission fragments,light charged particles and gamma)cross section measurement,and neutron resonance radiography,etc.A common digitization electronics and a cluster-based DAQ were developed for these detector systems.Most detectors have been employed at Back-n and serviced for experiments from the beginning of the beamline running.Results and conclusion As an overview of detectors of Back-n,the details of the detector design and the experiment performing are described in this paper.Some developing systems,e.g.,MTPC and B-MCP,are also included.

Time-resolved energy spectrum measurement of a linear induction accelerator with the magnetic analyzer

We recently set up a time-resolved optical beam diagnostic system. Using this system, we measured the high current electron beam energy in the accelerator under construction. This paper introduces the principle of the diagnostic system, describes the setup, and shows the results. A bending beam line was designed using an existing magnetic analyzer with a 300 mm-bending radius and a 60° bending angle at hard-edge approximation. Calculations show that the magnitude of the beam energy is about 18 MeV, and the energy spread is within 2%. Our results agree well with the initial estimates deduced from the diode voltage approach.

Electron bunch train excited higher-order modes in a superconducting RF cavity

Higher-order mode（HOM） based intra-cavity beam diagnostics has been proved effective and convenient in superconducting radio-frequency（SRF） accelerators.Our recent research shows that the beam harmonics in the bunch train excited HOM spectrum,which have much higher signal-to-noise ratio than the intrinsic HOM peaks,may also be useful for beam diagnostics.In this paper,we will present our study on bunch train excited HOMs,including a theoretical model and recent experiments carried out based on the DC-SRF photoinjector and SRF linac at Peking University.