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Physics issues of storage ring . Gang XU IHEP, Apr. 26, 2006. contents. Beam-beam effects and luminosity Impedance and instabilities Optics issues commissioning softwares Summary. Tune survey with 11mrad crossing angle by Cai’s Code. Tune survey with 11mrad crossing angle

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Physics issues of storage ring

Physics issues of storage ring 

Gang XU

IHEP, Apr. 26, 2006


Contents
contents

  • Beam-beam effects and luminosity

  • Impedance and instabilities

  • Optics issues

  • commissioning softwares

  • Summary




According to the formula of L0, decreasing β*y

and increasing kb can increase the L0


β Zhang’s code, the higher luminosity means closer to the half integer*y is by decreasing αp from 0.0235 to 0.0188,

σz=1.08cm, β*y=1.2cm

The microwave instability threshold will decrease, HOM heating increase

Kb increase from 93 to 120 even 130

bunch spacing 6ns, e-cloud acceptable, parasitic beam-beam effect acceptable, RF power increase 30%, HOM heating increase

So L0 will increase by factor (1.5/1.2)*(120/93)=1.6

Lmax=1.6*0.6*L0~L0---1×1033 could be reached


Impedance and instabilities
Impedance and instabilities Zhang’s code, the higher luminosity means closer to the half integer

  • impedance of pumping screen in IR

    Width 4mm,depth 2mm,step 6mm,number 27

Loss factor 2.25×10-4V/pC(1.78V/pC).

Z0||=2.4×10-4Ω(0.23Ω)


Loss factor 0.175V/pC.

It can not be used in BEPCII

Model in mafia


Inducing part has been shielded

But the HOM heating is serious

The structure of shielding chamber must

be modified


The simulation of the electron cloud in the magnetic fields Zhang’s code, the higher luminosity means closer to the half integer

Because of the short circumference of the BEPC storage ring, most of the arc regions are occupied by magnets. So it is necessary to study the distribution and the motion of electron cloud in different magnetic fields. A two- dimensional code evoluted from the ECIC was used to simulate the motion, formation, distribution of the electron cloud in drift, dipole, quadrupole, sextupole and solenoid field regions.

In dipole magnetic field region without considering the fringe field, the magnetic field is only in vertical direction.

B=By

the electrons in the cloud are confined to move in tight vertical helices whose radius is typically a few microns, and whose cyclotron frequency is f=eB/2m, B=8000Gs, f=22.3GHz. The main consequence of the cyclotron motion of the electrons is the severe suppression of the horizontal component of the velocity of the electrons in the cloud.


For the quadrupole magnetic field, Zhang’s code, the higher luminosity means closer to the half integerB can be expressed by

For the sextupole magnetic field, B can be expressed by

In a uniform solenoid field, the magnetic field is only in longitudinal direction, i.e., B=Bz.


Distribution of electron cloud in various kinds of magnetic field

(left: antechamber chamber; right: elliptic chamber)

(a: field free region; b: dipole field; c: quadrupole field; d: sextupole field; e: solenoid field with Bz=10Gs )


Electron cloud density in elliptic chamber and antechamber field

(left: antechamber; right: elliptic chamber)

The uniform solenoid field is the most effective way to confine the photoelectrons. All of the photoelectrons are confined to the vicinity of the vacuum chamber wall. So in the design of the BEPCII, solenoids will be wound on the vacuum chamber of the straight sections with the magnetic field of 30Gs, which is enough to clear the electron cloud in the central region.


Comparing the length of solenoid region in KEKB and BEPCII field

The drift length in BEPCII is much shorter than that in KEKB.

The occupation of all the drift region in BEPCII will profit to increase the luminosity.


  • Sorting for bending magnets field

    before sorting 3~5mm COD

    after sorting 0.3~0.5mm COD

  • Sorting Quadrupole --- select quadrupoles with better quality for positron ring

  • 6.51/5.58 working point

  • αp=0.0188

  • Spare IR scheme design

  • Related issues of Vacuum chamber deformation


The dynamic aperture is less than 6.53/5.58 field

Dynamic aperture with/without aliagnment errors for 6.51/5.58


Using two bending magnets replace the SC-dipoles field

Changing the polarity of the two magnets to connect SR ring, e+/e- ring

Orbit of the backup IR scheme

dot-dash: SR mode solid: e- ring dotline: e+ ring



Related issues of vacuum chamber deformation
Related issues of Vacuum chamber deformation field

  • Physical aperture ok

  • Impedance ok

  • E-cloud acceptable

  • Heating from SR light serious

    Acceptable mini-gap : 11mm(15mm designed)

    Potential issues: damage by heating, need more attentions


High level application softwares
High level application(softwares) field

  • Optics(done)

    calculation (beta, tune, dispersion, emittance, bunch length, RF bucket-height)

    match (beta, tune, dispersion)

    chromaticity correction

    dynamic aperture and Poincare phase-plot

    main magnets (main bending, (de)focusing quadrupoles) setting

    optics record

  • Collision adjusting(done)

    IR orbit feedback(in preparation)

  • Orbit correction(nearly done)

  • Beam response-matrix based on windows-epics

  • Others in preparation (transport line optics calculation and match,orbit adjusting at injection point, injection adjusting(repetition,kicker/suptum setting, filling pattern), orbit bump in ring)


RF phase adjustment panel for longitudinal separation during

Injection and collision conditions tuning in the horizontal plane


Collision conditions tuning in the vertical plane and some simulation results

during collision tuning in both horizontal and vertical plane


Detailed information during collision tuning in horizontal plane

for the elimination of vertical crossing angle at the IP


Collision condition tuning monitored by 8-pole BPM plane

in both horizontal and vertical plane


Control panel for Waist- plane y* scan




Orbit correction quadrupole system)


  • Measure orbit of ring with good BPMs or with all “not good” BPMs.

  • Display the measured, calculated, golden, reference, statistical COD, and the differences between measured and calculated, measured and reference, and statistical and reference COD at each BPM along the ring.

  • Display the above CODs or differences of COD’s in different regions (IR/ARCs/RF/INJ) around the ring and any assigned BPM nearby regions.

  • Display the max. and rms values of COD around the ring.

  • Display all the Twiss parameters at every element around the ring.

  • Calculate the COD with different methods (SVD, MICADO), and different beam conditions.

  • Compare the calculated COD with the measured one.

  • Set the strengths of correctors according to the calculated COD.

  • Continuous COD correction (CCC) has the orbit corrected every 20 seconds during routine operation.

  • Save the measured orbit, reference orbit, golden orbit, and the difference between measured and reference orbits.

  • List the IR related info.



Functions good” BPMs.

  • Fit quadruple gradient changes that best correct both beta and dispersion functions

  • Fit BPM gains and coupling

  • Fit horizontal and vertical corrector magnet kicks and coupling

  • Fit energy change at correctors

  • Fit skew gradients

  • Save the results of every iteration to the designated file

  • The number of iteration and from which to start can be selected


Summary
Summary good” BPMs.

  • By decreasing β*y and increasing bunch number, the luminosity could reach 1×1033

  • The lattice with β*y=1.2cm, αp=0.0188 and Qx=6.51 still need research

  • The 70% physics part of commissioning software has been finished


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