MDI Study for CEPC Sha Bai, Hongbo Zhu On behalf of CEPC MDI sub-group The first IHEP-BINP CEPC Accelerator Collaboration Workshop Institute of High Energy Physics Chinese Academy of Sciences Budker Institute of Nuclear Physics

MDI study issues Illustrated design without realistic considerations To meet requirements from both accelerator and detector Beam background Collimator design SC magnet design Solenoid compensation Lumical ……..

Outline Establish the Uniform Computing Platform ---- MDIToolkit Background study Collimator design Superconducting magnet design Solenoid compensation Lumical Summary

Establish the Uniform Computing Platform Established the environment for MDI study on IHEP computing cluster Considered from the detector aspect by now Can be extended for accelerator study

Toolkit Structure In the pre-research of CEPC, the machine design and software have not been fixed. Many parameters need be optimized by doing simulations with specific values. Also some bugs of the software will be found and fixed. The MDIToolkit is aimed to make the accelerator and detector simulation more convenient Produce large data sample Quickly analysis the results ProjectTemplate Templates for detector simulation and accelerator simulation (AccTemplate, MDIProjectTemplate) Bin Bash tools to create projects and jobs BBSim Softwares to analysis the results setup.sh Setup environment variables for MDIToolkit

Design Philosophy of this Toolkit Create practical templates for common studies, which will eliminate most repetitive work and make the study process more clear. Use same code for similar processes but with different configurations. Most processes will be steered by configure files, which will make the software maintenance more easily. Produce standard data samples for all kinds of beam backgrounds and stored in a fixed location

General Workflow There are some modification in the machine/detector design and need to check the performance. Create a Project for this study Modify the configure files for this project according to the machine/detector design Submit jobs and extract useful information Check the results and compare the results with other projects

Background Synchrotron radiation background a).from the last bend magnet b).from the quadrupole in the IR Lost particles background a).radiative Bhabha scattering b).beamstrahlung Generator Geant4(Mokka) Analysis(Marlin) Accelerator Simulation

 CEPC IR Synchrotron radiation background: a) The High beam energy(120GeV)cause synchrotron radiation characteristic energy quite large(1MeV ）， make damage to detector （ LEP2~100KeV) ； b) In single ring symmetric design ， SR photons by electron and positron deposit in the same beam pipe, this effect should be doubled.  Source of IR SR ： a) Last quadrupole in IR ； b) Last bending magnet in IR Synchrotron radiation Synchrotron radiation by bending magnet and quadrupole in IR

For the SR by quad, depends on the bunch transverse distribution model, in general, we use Gaussian distribution. But Gaussian distribution is not fit the experimental result, so we use a double Gaussian distribution model. Algorithm of simulation on SR by bend Algorithm of simulation on SR by quad Synchrotron radiation

In simulation, consider two cases: all the magnets which have influence on IR and the last bend ； The statistic area according to the IR magnet element ； The radius of beam pipe is 2cm ， only consider single beam ； It can be seen from the upper figure ， SR of CEPC IR coming from last bend is the main source, put collimator to prevent from SR. Q2FFS (upstream) Q1FFS (upstream) Q1FFS (downstream) Q2FFS (downstream) （ -5 ， -4 ） 0000 （ -4 ， ） 0000 （ ， ） 0000 （ ， -1.5 ） 0000 （ -1.5 ， 0 ） 05.52E-200 （ 0 ， 1.5 ） 1.37E-11.56E000 （ 1.5 ， 2.75 ） 2.11E02.03E000 （ 2.75 ， 3.25 ） 1.03E01.05E19.81E10 （ 3.25 ， 4 ） 1.55E21.46E21.76E21.58E2 For SR, develop a monte carlo program to analyze the SR photons distribution by bend and quad, the energy deposit distribution and power distribution, and output coordinate and energy information of the photos, and put into the detector simulation software to do analysis. Synchrotron radiation

Preliminary design of SR collimation system, which can prevent from the most SR photons. Photon azimuth angle and energy statistic Synchrotron radiation

Loss mechanismsLifetimecomment Quantum effect ＞ 1000hours Touschek effect ＞ 1000hours Beam-gas scattering (Comlomb) ＞ 400hours P=1e-7 （ Pa ） Beam-gas scattering (beamstrahlung) ＞ 40hours Radiative BhabhaAbout 51 minsimulated beamstrahlungAbout 47 minsimulated Background study method From analysis, the main beam loss of CEPC should be Radiative Bhabha and beamstrahlung ， and also are the main consideration of beam loss particles background simulation. CEPC beam loss effect on beam lifetime Background from lost particles Generate lost particles coordinate Tracking in accelerator until lost in IR Simulate in detector

η(%)No cutoff(mb)Hard cutoffSoft cutoffLifetime(min) TLEPH CEPC Radiative Bhabha scattering process is: Generate photon which can take away some energy, so the spent particle will lose energy, cause energy spread, when out of energy acceptance, beam will loss. Radiative Bhabha scattering is one of the main process of beam loss during collision, by which the beam life time decided. It is the main source for small angle range during collision, can be used to measure luminosity.  Revise BBBREM to get Radiative Bhabha particles information, and do simulation.  Develop a monte-carlo program, generate Radiative Bhabha scattering events, results close to BBBREM. Radiative Bhabha scattering

Most event lost at downstream of IP after collision (large energy loss) Small part event will loss after one turn(small energy loss) Detector simulation results are, after one turn tracking, influence of Radiative Bhabha scattering event on detector is quite limit, but should be tracking in many turns to check the real case. Beam loss particles distribution from Radiative Bhabha scattering （ single turn ） Background generate sub- program ： BBBREM and monte-carlo program Accelerator simulation ： SAD Detector simulation ： GEANT4

Radiative Bhabha scattering background distribution statistic at IP1 and in turn Radiative Bhabha scattering background distribution statistic at IP3 and in turn Radiative Bhabha scattering

Beamstrahlung is synchrotron radiation from a particle being deflected by the collective electromagnetic field of the opposing bunch. This effect will increase the energy spread and limit the lifetime of the beams. Its importance increases considerably with energy, so beamstrahlung is an important effect in CEPC. Beamstrahlung is generated from the monte-carlo program from beam lifetime algorithm ， and get the energy spread distribution after that, then put in to accelerator and detector to do next tracking simulation. Beamstrahlung

Beamstrahlung background distribution statistic at IP1 and in turn Beamstrahlung background distribution statistic at IP3 and in turn Beamstrahlung

elementBeta functiondispersion position （ Km ） QFHFFS (H) QFHTM1.FFS (H) QDVFFS (V) QDVTM1FFS (V)  To prevent from the beamstrahlung, the effective method are putting collimators in upstream to shield the large amplitude particles.  Blue and green lines show the horizontal and vertical beta function in CEPC IR upstream a few hundred meters. Collimators should be put at large beta function and small dispersion region ， in order to shield the large amplitude particles. CEPC IR upstream beta function  Collimator aperture ~1cm could prevent almost all the Bhabha scattering and beamstrahlung, but have influence on beam.  Collimator aperture scan from 1cm to 5cm, initial decision ~2cm. Collimator design

Transverse Lost Position Aperture=3cmAperture=2cm

Momentum Direction hit density on VTX detector Energy of Lost Particles Lost Position in Z direction

Conceptual Design of CEPC Interaction Region Superconducting Magnets  Two types high gradient quadrupole magnets are needed in CEPC Interaction Region ： The magnetic field at the pole region exceeds 7T, and these two magnets are inside the detector solenoid magnet with a field of about 3.5T. These quadrupole magnets are iron-free magnets, and Nb 3 Sn technology must be used. The quadrupole coils have the same cross section, but with different lengths.  The coils are made of Rutherford Type Nb 3 Sn Cables, and are clamped by stainless steel collar.  The conceptual design is performed based on typical quadrupole block coil. The magnetic field calculation is performed by OPERA from Cobham Technical Services.

 Main design parameters of the quadrupole magnets are obtained. 2D flux linesMagnetic flux density distribution 3D model Quadrupoles

 To minimize the effect of the longitudinal detector solenoid field on the accelerator beam, anti-solenoid coils are introduced just outside the quadrupoles.  The total integral longitudinal field generated by the detector solenoid and anti-solenoid coils is nearly zero.  Coils of anti-solenoid are made of NbTi-Cu Conductor.  Magnetic field calculation is performed, and main design parameters are obtained. 2D flux lines of Anti-QD (half cross section) Longitudinal field distribution of Anti-QD Anti-solenoid coil

Main design parameters of CEPC interaction region Integral coil and Anti-QD Magnet nameIntegral coilAnti-QD Central field (T)73.3 Magnetic length (m)11.4 Conductor typeNbTi-Cu Conductor, 4×2mm Coil layers126 Coil turns12×2506×350 Excitation Current (kA)1.754 Target: The integral effect of the magnetic field is zero ( from 0 to 1.5m) The value of the magnetic field is zero in QD region.

The geometry of the MDI

The distribution of the magnetic field

Detector solenoid 3.5T 2.6T 3.5T 2.6T

Detector solenoid field of CEPC Rotate and focus beam on both planes Rsol=Rfoc.Rrot(  )  =  Bz*L/2B  =1 degree Solenoid field in superposition with anti-solenoid Solenoid field model: solenoid magnets sliced in pieces; QD0&QF1 magnets sliced in same pieces to insert solenoid pieces with longitudinal field; the QD0&QF1 magnets with hard edges; to make the ν x /ν y constant

Solenoid Slice – 0.01m βxβxβyβyHorizontal dispersion Vertical dispersion Horizontal and vertical unstable Real tune: u x =0 u y =0.5

Solenoid & anti-solenoid Slice – 0.01m βxβxβyβyHorizontal dispersion Vertical dispersion Horizontal and vertical unstable Real tune: u x =0 u y =0.5 Anti-solenoid design can not compensate the coupling, skew quads or rotation of quads are needed.

Luminosity Calorimeter Based on present MC sample, develop a program to select Bhabha events to measure the luminosity Learn simulation (partial sub-detector), reconstruction, analysis Learn to adjust LumiCal geometry and reconstruction events Adjust geometry and material and estimate their effects; generate MC sample with other generators Evaluate systematic uncertainties and optimize the detector design Beam effect with Guinea-Pig Global geometry and grid size Material etc Key parameters on design Detector performance Precision

Event display (only simulate and reconstruct LumiCal to speed up the process) 933 hits on LumiCal recorded 14 clusters reconstructed

Summary IR design and layout: overall optimization ongoing, DA optimization Develop MDIToolkit –uniform computing platform to established the environment for MDI study on IHEP computing cluster Background study: SR, Radiative Bhabha scattering, Beamstrahlung With 2cm aperture collimator, lost particles of radiative Bhabha and beamstrahlung in IR after several machine turns can be effectively prevented, but need to be optimized. SC magnets are designed preliminarily. Conceptual design and magnetic field calculation. Anti-solenoid design is optimizing, set up solenoid model in accelerator software. Luminosity calorimeter: luminosity measurement. Event display preliminary.

Many thanks to all members in CEPC MDI group