Physics issues of storage ring

1. Physics issues of storage ring  Gang XU IHEP, Apr. 26, 2006

2. contents • Beam-beam effects and luminosity • Impedance and instabilities • Optics issues • commissioning softwares • Summary

3. Tune survey with 11mrad crossing angle by Cai’s Code

4. Tune survey with 11mrad crossing angle (by Zhang’s Code)

5. Although there is some difference between Cai’s code and Zhang’s code, the higher luminosity means closer to the half integer • Even for Qx=0.51, L is just about 60% of L0 according to Cai’s code. According to the formula of L0, decreasing β*y and increasing kb can increase the L0

6. β*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

7. Impedance and instabilities • 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)

8. Fast valve near SC-cavity Loss factor 0.175V/pC. It can not be used in BEPCII Model in mafia

9. Impedance In-vacuum wiggler 4W2 the shielding chamber with 1mm gap Inducing part has been shielded But the HOM heating is serious The structure of shielding chamber must be modified

10. The simulation of the electron cloud in the magnetic fields 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.

11. For the quadrupole magnetic field, B 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.

12. 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 )

13. Electron cloud density in elliptic chamber and antechamber (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.

14. Comparing the length of solenoid region in KEKB and BEPCII 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.

15. Sorting for bending magnets 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

16. The dynamic aperture is less than 6.53/5.58 Dynamic aperture with/without aliagnment errors for 6.51/5.58

17. Using two bending magnets replace the SC-dipoles 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

18. backup IR scheme design

19. Related issues of Vacuum chamber deformation • 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

20. High level application(softwares) • 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)

21. RF phase adjustment panel for longitudinal separation during Injection and collision conditions tuning in the horizontal plane

22. Collision conditions tuning in the vertical plane and some simulation results during collision tuning in both horizontal and vertical plane

23. Detailed information during collision tuning in horizontal plane for the elimination of vertical crossing angle at the IP

24. Collision condition tuning monitored by 8-pole BPM in both horizontal and vertical plane

25. Control panel for Waist-y* scan

26. Control panel for the local coupling compensation in the IR. (Anti-solenoid system)

27. Control panel for the global coupling compensation. (Skew quadrupole system)

28. Orbit correction

29. 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.

30. Beam response-matrix(windows-epics)

31. Functions • 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

32. Summary • 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