Preliminary study on detection and cleaning of parasitic bunches

To establish a nuclear resonant scattering beamline at the High Energy Photon Source(HEPS),it is essential to develop tools for detection and cleaning of parasitic bunches,for meeting the stringent demands on bunch purity.To this end,a novel time-correlated single-photon counting system was implemented at the electron storage ring of the Beijing Electron–Positron Collider II(BEPCII).The purity deterioration process over a week-long operation was recorded by the system.In this study,the mechanism of impurity growth was analyzed by numerical methods and validated on measurements.The agreement between the experimental results and the cal-culation was fairly good.Two main sources of parasitic bunches,pre-accelerators and the Touschek scattering were confirmed.A bunch-cleaning technique,based on a sinu-soidal signal mixed with a pseudo-square wave,was also developed and implemented,and its capability to improve the bunch purity to the level of 10–7 was experimentally demonstrated.We present the experimental setup,princi-ple,and measurement results of a system for detection and cleaning of parasitic bunches.

Using a pre-kicker to ensure safe extractions from the HEPS storage ring

The High Energy Photon Source(HEPS)is a 6 GeV diffraction-limited storage ring light source under construction.The swap-out injection is adopted with the depleted bunch recycled via high-energy accumulation in the booster.The extremely high beam energy density of the bunches with an ultra-low emittance(about 30 pm horizontally and 3 pm vertically)and high bunch charges(from 1.33 to 14.4 nC)extracted from the storage ring could cause hazardous damage to the extraction Lambertson magnet in case of extraction kicker failure.To this end,we proposed the use of a pre-kicker to spoil the bunches prior to extraction,significantly reducing the maximum beam energy density down to within a safe region while still maintaining highly efficient extractions.The main parameters of the pre-kicker are simulated and discussed.

Development of the pulse bump magnet in HEPS

Purpose In the extraction process from booster to storage ring(BTS)for high energy photon source(HEPS),the implementation of four pulse bump magnets plays a crucial role in creating a localized bump.This serves to effectively reduce the upstream kicker strength and facilitate the extraction procedure.In this paper,the development of four pulse bump magnets is presented,which were meticulously designed and thoroughly discussed,taking into consideration dynamic characteristics of the pulse magnet such as magnetic field,eddy current,induced voltage,and vibration.Methods The magnetic field and eddy currents of the pulse bump magnet were calculated through simulation using OPERA/ELLEKTRA,based on the 3D model.The design of the magnet incorporated the utilization of eddy currents within the vacuum chamber to achieve improved field uniformity.Furthermore,the measurements were performed to validate the magnet's design.Results The central magnetic field,integral magnetic field,effective length,and field uniformity measured for the first magnet meet the design specifications.The temperature measurement of the first magnet indicates that the temperature in the magnet was within acceptable limits.The measurement results for the other three magnets are consistent with those of the first one.Conclusions The magnetic field performances of four pulse bump magnets meet the physical requirements for beam extraction in BTS of HEPS.Additionally,the magnets have demonstrated reliable operation during extended testing periods.

Electro-mechanical offset measurements of beam position monitors

Purpose The absolute beam position measurement in the booster and storage ring of the high energy photon source(HEPS)requires the offset between the electrical and mechanical centers of the beam position monitor(BPM).Method Traditionally,an RF signal is sent to an antenna or stretched wire aligned with the vacuum chamber,and the signal at each electrode is measured.Conversely,a replacement method using a vector network analyzer,which was proposed by Lambertson,does not involve mechanical alignment and can be used for electrical offset determination.Results and conclusions The electro-mechanical offsets of booster BPMs of the HEPS were measured using the Lambertson method.The result shows good agreement with the stretched wire method within a 30μm error.

Equilibrium electron beam parameters of the High Energy Photon Source

Purpose The physics design of the High Energy Photon Source(HEPS)was finished after many times of iteration.Hereby,the typical equilibrium electron beam parameters corresponding to the proposed two baseline operation modes in the baseline design of HEPS are presented.Methods To compute the equilibrium parameters of the electron beam,the lattice parameters,RF parameters,and the parameters of the insertion devices(IDs)were determined first.Furthermore,it is more precise to use the full-current electron beam parameters in the estimations of the performance of the synchrotron light.Therefore,not only the single-particle dynamics but also the current-dependent collective effects need to be considered in the computations of the full-current,equilibrium parameters of the electron beam.Both analytic computations and multi-particle tracking simulations were carried out.Results The full-current,equilibrium parameters of the electron beams in the HEPS storage ring are presented in this paper.Moreover,the main beam parameters in the injector(the booster and the LINAC),corresponding to the two baseline operation modes of the storage ring,are also presented.Conclusion The typical electron beam parameters corresponding to the two baseline operation modes are given in detail in this paper.

Design of the HEPS booster lattice

Purpose The high energy photon source(HEPS)is a diffraction-limited storage ring light source being built in China.Along with the deeper studies of booster and the evolution of the lattice design and injection scheme of the storage ring,four versions of the booster lattices have been proposed from the project proposal stage.Methods Unlike the design of the storage ring,in the booster design,more effort was made to realize stable and reliable operation rather than advanced performance.A FODO structure lattice and the"high-energy accumulation"scheme was adopted in the HEPS booster design.To find the ultimate performance of the lattice,a multi-objective genetic algorithm(MOGA)and particle swarm optimization(PSO)were used to optimize the emittance and the dynamic aperture.Results In the latest booster lattice design,the emittance was reduced to 16.3 nm rad.At the same time,the single-bunch charge limit was increased by minimizing the average vertical beta function and reducing the chromaticity.Conclusions Through multi iterations with the hardware system,the current lattice was basically frozen and can be used as a basis for related physics studies,hardware and engineering design of the booster.In the future,more detailed physical studies will be performed based on this lattice.

The design of HEPS global timing system

Purpose The high energy photon source(HEPS)is a 4th generation synchrotron light source under construction by the institute of high energy physics.The accelerator complex consists of a 500-MeV Linac,a full-energy synchrotron booster,a 6-GeV synchrotron storage ring(SR),and three e-beam transport lines for injection and extraction among accelerators.A global timing system(GTS)covers the timing needs for all accelerator,beamline,and experiment systems.The GTS is designed to coordinate the injection processes and various measurements and protections.Most systems require that the RMS jitter of the GTS signal is less than 30 ps,while the trigger jitters for the electron gun and SR injection and extraction kickers are less than 10 ps.Method The HEPS GTS is an event-based timing system based on MicroTCA.4 hardware architecture.The MicroTCA.4300 series products from the micro-research Finland Oy are implemented in the HEPS GTS system.Results and conclusions The RMS jitter,integrated from 1 Hz to 10 MHz,of the 166.6 MHz event clock is 5.489 ps.The RMS jitter of TTL outputs is less than 30 ps.This paper reports the design of the HEPS GTS,which satisfies all of the HEPS physics requirements for timing with preliminary test results shown.

Discovery of CECR2 Bromodomain Inhibitors with High Selectivities over BPTF Bromodomain

Cat's eye syndrome chromosome candidate 2 bromodomain(CECR2 BRD)and Bromodomain PHD transcription factor bromodomain(BPTF BRD)are the same subfamily proteins,both of which are highly conserved in sequence and binding pockets.Challenges remain in the development of small molecules to inhibit one of the two bromodomains(BRDs),in view of each subtype may possess unique physiological and pathological functions.There is still a lack of effective selective inhibitors of CECR2 BRD,which makes it difficult to fully understand the pathogenesis of CECR2-BRD in diseases,especially cancers.Herein,we report our efforts to discover a series of highly selective CECR2 BRD inhibitors over BPTF BRD based on TP-248.Structure-based molecular optimization led to the discovery of DC-CEi-26,whose IC_(50) for CECR2 BRD was 96.7±14.9 nmol/L and selectivity was up to 590×over BPTF BRD.DC-CEi-26 showed weak potencies for other classic BRDs in different subfamily,which may serve as a chemical probe for CECR2 BRD biological research.

Discovery of a subtype-selective, covalent inhibitor against palmitoylation pocket of TEAD3

The TEA domain(TEAD)family proteins(TEAD1-4)are essential transcription factors that control cell differentiation and organ size in the Hippo pathway.Although the sequences and structures of TEAD family proteins are highly conserved,each TEAD isoform has unique physiological and pathological functions.Therefore,the development and discovery of subtype selective inhibitors for TEAD protein will provide important chemical probes for the TEAD-related function studies in development and diseases.Here,we identified a novel TEAD 1/3 covalent inhibitor(DC-TEADin1072)with biochemical IC50 values of 0.61±0.02 and 0.58±0.12μmol/L against TEAD1 and TEAD3,respectively.Further chemical optimization based on DC-TEAD in 1072 yielded a selective TEAD3 inhibitor DCTEAD3 in03 with the IC_(50) value of 0.16±0.03μmol/L,which shows 100-fold selectivity over other TEAD isoforms in activity-based protein profiling(ABPP)assays.In cells,DC-TEAD3 in03 showed selective inhibitory effect on TEAD3 in GAL4-TEAD(1-4)reporter assays with the IC50 value of1.15μmol/L.When administered to zebrafish juveniles,experiments showed that DC-TEAD3 in03 reduced the growth rate of zebrafish caudal fins,indicating the importance of TEAD3 activity in controlling proportional growth of vertebrate appendages.

Investigation of spin rotators in CEPC at the Z-pole

Purpose Longitudinal polarization is an important design aspect of the future 100 km-scale Circular Electron Position Collider(CEPC).Spin rotators are needed in the CEPC collider rings to make the beam polarization along the longitudinal direction at the interaction points(IPs).This paper focuses on the design of spin rotators for CEPC at the Z-pole(45.6 GeV).Methods The design of spin rotators in the CEPC at the Z-pole is based on solenoidmagnets and horizontal bending magnets sections.The coupling of transverse motion introduced by solenoids is compensated with quadrupole lenses.Adjustments have been made to the layout to implement the spin rotators into the collider rings.Results Longitudinal polarized beam can be achieved at the IPs with the spin rotators.High degree of polarization is attainable,while the effect of spin rotators on orbital motion is acceptable.The detailed simulation results will be presented.Conclusion A solenoid-based spin rotator configuration is designed and integrated into the CEPC collider ring lattice.According to the simulation results,the polarization requirements can be satisfied.