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Progress of the BEPCII- Linac Commissioning Shu-Hong Wang for the BEPCII - Linac Group

Progress of the BEPCII- Linac Commissioning Shu-Hong Wang for the BEPCII - Linac Group. BEPCII – IMAC, May 10-12, 2007. Contents. 1. What we have done after IMAC-2006 2. Beam performances 3. Orbit instability 4. Energy instability 5. Beam transmission

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Progress of the BEPCII- Linac Commissioning Shu-Hong Wang for the BEPCII - Linac Group

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  1. Progress of the BEPCII- Linac CommissioningShu-Hong Wangfor the BEPCII - Linac Group BEPCII – IMAC, May 10-12, 2007

  2. Contents 1. What we have done after IMAC-2006 2. Beam performances 3. Orbit instability 4.Energy instability 5. Beam transmission 6. Operation status 7. Next plan 8. Summary

  3. 1. What we have done after IMAC- 06

  4. ● March – July 2006 : Second Phase of the Linac Commissioning 1) Conditioned the last 3 RF unit for the design e+ energy； 2) Reached the design energy of 1.89 GeV both for e- and e+ ; 3) Commissioned the phase control system & put it into operation; 4) Measured the e- and e+ beam emittance at 1.89 GeV; 5) Improved the beam instability (orbit, energy and energy spread); 6) Past the Pre-Acceptance Test on the linac performances, done by a Test Group, organized by the BEPCII management.

  5. ●August – September 2006, Machine was shutdown for BT- line installation of BI. ● October 2006 – May 2007 (Now): The linac has been operated for 7 months, to deliver the e- and e+ beams for : 1) BEPCII new outer-ring commissioning & SR operation; 2) New e- ring and e+ ring commissioning separately; 3)e+ - e- collision commissioning.

  6. 2. Beam Performances

  7. Pre-Acceptance Test ( June - July, 2006 ) ● Purposes: ●to check each system performance of the Linac; ● to check the final beam performance, including energy, current, emittance, and beam instabilities. ● Test Group: Consists of 15 experts from Ring Group, headed by J.Q. Wang, ●Beam Physics: G. Xu, Q. Qin, N. Huang, J. Gao; ●RF system: W.M. Pan and J.G. Li; ●Modulator, e+ pulsed supply and e-Gun: Z.X. Xu and Q. Han; ●RF phase control: Z.X. Xu and Y.X. Luo; ●Beam Instrumentation: L. Ma; ●Vacuum system: H.Y. Dong and H. Song; ●Control system: J.J. Zhao and C. H. Wang.

  8. Test result: BEPCII-Linac Beam Performancemeasured by the Test Group, in June-July 2006 ** Energy spread were measured in early 2007.

  9. Test result:Beam instability measurement Dispersion = 0.63 m (△E/E)jitter≤±0.15% BPM Energy analyzer

  10. Conclusions by the Pre-Acceptance Test Group:●The linac beam energy, current , emittance and rep. rate are reached (or better than) the design goals;●The upgraded linac performance has gained a remarkable improvementcompared with the original BEPC-Linac.

  11. e- beam energy spread measurement Energy = 1.89 GeV Current= 600 mA 1.89 GeV

  12. Measured beam spread at PR downstream energy analyzer Dispersion: Dx = 0.63 m better than the design goal: (ΔP / P) = ± 0.50%

  13. e+ energy spread measurementDue to the low e+ beam intensity and weak light at PR, a beam collimator TP-BC2 in BT-line is used, where Dx = 1.85 m.TP-BCT3 + TP-BC2 We would measure the e+ beam current passing through the gap of BC2, within designed (△P/P) ≤ ±0.5%, hence we set its Gap = Dx×(△P/P) = 2×1.85m×0.5% = 18.5 mm, then we measured the beam current downstream of the BC-2, got the beam current of TP-BCT3 = 37 mA Design (△P/P) =±0.5%, 37 mA . 60 mA 58 mA Dx = 1.85 m ~37mA

  14. A long low energy tail in e+ beam The simulated energy spectrum downstream of target: 1 MeV ≤ E0 ≤30 MeV, most 1 MeV ≤ E0 ≤14 MeV. This tail still exists partly at high energy. e+ number Energy （MeV）

  15. 3. Beam orbit instability

  16. During April-June 2006, a periodic orbit oscillation appeared, seen by the BPMs. Properties of the oscillation: ● Periodical, with changed periods of2 s ~ 100 s; ● Amplitude changed between 0.5 mm ~ 3 mm。 BPM 03 @ upstream linac BPM 14 @ downstream linac

  17. Mini-workshop on the BEPCII-Linac at IHEP in July 17-19, 2006, KEK and IHEP colleagues attended (S. Ohsawa, K. Furukawa, T. Suwada) BPM 14 In the workshop, we found two phenomenon: ● The bunch distribution were oscillated with frequency of ~ 2 Hz at BPM 14 (oscilloscopeTDS-7254); ●Simultaneously, we found the bunch charge oscillation by BCM 2 @ downstream bunching system, with the same frequency of ~2 Hz. BPM14--TDS-7254 wake-effect It is expected that : Bunch charge oscillationbeam orbit oscillation Gun trigger jitter +non synchronization with 2856 MHz

  18. Simulated Beam distribution @ gun Exit Bunch distribution @ exit of bunching system for thegun pulse length 5 bunches downstream buncher 1.0ns (FWHM) and 1.6 ns(bottom)relative bunch charges: 0.17、0.83、1.0、0.65、0.06 So the gun trigger jitter + non synchronization with 2856 MHz may cause a bunch charge oscillation and leading to an orbit oscillation. For example: ● if the BPM sampling frequency is 2 Hz; ● if the bunch charge & the beam position oscillation freq. is 2.2 Hz, then their beat frequency is 2.2 Hz - 2.0 Hz = 0.2 Hz, so, the oscillation period displayed at BPM is 5 seconds.

  19. After making the synchronization of ring (499.8MHz) and linac frequency (2856 MHz),( i.e. by connecting two master oscillators of 2856MHz and 499.8MHz, and by reducing the gun trigger by factor of 4*7 =17.85MHz),we found that: ●At the 1st 6 BPMs, the orbit oscill. amplitude suppressed to be about 1/5, say ~ 0.2 mm ; ●At all other BPMs, the ampl. remained ~ 1 mm, and by orbit correction, these ampl. were suppressed to ~ 0.2 mm . BPM 14 non synchronization with synchronization

  20. 4. Beam energy stability

  21. Beam energy instability can be measured by the BPMs in BT line located at a large dispersion. TE-BPM1 At TE-BPM1, Dx = 2.0 m, the orbit oscillation seen by the BPM is △x ≤ 1.0 mm hence, e- beam energy jitter is (△P/P)e-≤0.05%； Same for the e+ beam: (△P/P)e+≤0.05%； TE-BPM 6, Dx = 0, near injection

  22. 5. Beam transmission

  23. Beam transmission table (1.89 GeV, e+) Bunching efficiency = BCM2 / BCM1 = 75%, e- beam current @ target = 7.9 A , e+ transm. in main-Linac = BCM11 / BCM4= 76%, TP-BCM1 / TC-BCM2 = 80%. TC-BCM2 TP-BCM1

  24. 6. Operation status

  25. ●Beam orbit stability: Last 2 BPMs in the Linac:jitter ≤ 0.1 mm (1σ) BPM 15 BPM 16

  26. ● Beam energy stability TE-BPM1 At the TE-BPM1, Dx = 2.0 m, the orbit oscillation seen by the BPM is △x ≤ 1.0 mm hence, e- beam energy jitter is (△P/P)e-≤0.05%； Same for the e+ beam: (△P/P)e+≤0.05%； TE-BPM 6, Dx = 0, near injection

  27. A stable beam energy is provided by: 1) Phase control system: to suppress the slow change of the beam energy due to the slow change of the RF phase; 2) Modulator’s voltage stability: to suppress the fast change of the beam energy due to the jitter effects of the RF voltage and phase.

  28. Phase control system works well K5 (off) Δφ ~ 4.50, in 6 hours K5 (on) Δφ ~ ± 1.50, in 6 hours K8 (off) Δφ ~ 6.50, in 6 hours K8 (on) Δφ ~ ± 1.00, in 6 hours

  29. Phase control panel Put phase control “on” for all RF units, except the stand-by ones.

  30. To have modulator’s high voltage stability of ≤±0.15% The following 3 measures are used: 1)by stabilizing the modulator DC voltage using Thyristor Voltage Regulator with feedback control function; 2) by using De-Qing circuit to stabilize the charging voltage; 3) by using high precision stabilizator to stabilize the klystron filament voltage and thyratron heater voltage. The measured voltage instability at modulator 7# & 10# :

  31. ●e+ / e- operation modes exchange 1）Integrated exchange mode: Just click one button “e+/e- Switch”torealize the following 6 items simultaneously in a few seconds : ● (e+ / e- ) optics and orbit ; ● (e+ / e- ) gun bias voltage (different gun current)； ● BCM’s amplifiers for e+ beam； ● e+ production target position; ● e+ pulsed focusing magnet timing moving; ● one more stand-by of RF unit for e- beam. 2）Exchange time is a few seconds only ( ≤ 10 seconds), and stable & repeatable usually. 3）The target positioning works not so stable some time, and have to be further improved. (to further improve the switch program).

  32. ●Operation reliability In principle, the linac works reliable, but with a few troubles some time. For example, in the last week ( Golden week, May 1—7 ), two faults: The operation reliability (with beam) is about 98.2%.

  33. 7. Next Step

  34. 1）To well operate the linac for the ring commissioning and operation ●Keep the facilities reliable and stable； ●Provide high quality beams from the linac for having a high injection rate; ●Integrate the Linac control & operation from Linac- Control Room to Central Control Room, to have a higher operation efficiency.

  35. 2) To install 4 new accelerating sections ●In the BEPCII project, 8 of the old accelerating sections (totally 56 sections) have been replaced by new ones, and the new structures can reach the high gradient of 25 MV/m by RF conditioning, and work well in operation. However, there are still 4 old accelerating sections fed by Klys. 5 # were damaged, the maximum RF power of only 16 MW can be fed into these structures (goal power 40 MW), otherwise high reflect power appeared. And hence only one klys. can be stand-by for e+ operation. ● The 4 new accelerating sections are being fabricated and will be RF conditioned and installed into the tunnel in the next machine shutdown.

  36. 56.02ns 17.85MHz 3)To construction the Sub-Harmonic Bunching System: Advantages of the SHB system： ●Higher bunching efficiency (70% →90%) & higher e+ yield; ●Only one bunch per pulse, more stable; ●Reduce the background in ring and detector； ● By using two-bunch operation scheme to upgrade the e+ injection rate by a factor of ~ 2. Gun SHB1 SHB2 Buncher Standard Acce. Section Linac BEPCII Ring 2856MHz 142.8MHz 571.2MHz 2856MHz 56.02ns SLED 499.8MH The SHBs are being fabricated, and is planed to start its commissioning by September 2008.

  37. 8. Summary ● The measured linac performance, including energy, current, energy spread, emittance both for e- and e+ beams have been reached and even better than the design goals; ●We need to continuously pay our efforts to keep the linac operation more reliable and stable, for having a high injection rate and a high integrated luminosity; ●As a next goal,a new SHB bunching system is being constructed. It is expected to further upgrade the e+ injection rate by a factor of ~ 2, by full 2008 or little later.

  38. Thank you very much for your attention !

  39. BEPCII – Linac Beam energy with Klystron Power Output If 2 of K5 – K16 be stand-by, then at linac-end E (e+) = 1.90 GeV； E(e-) = 2.30 GeV.

  40. Emittance measurement（e+, 1.89 GeV) ●The emittance changes may be due to the changes of the No. of stand-by RF power unit and related changes of beam optics and orbit. ● The beam matching between linac-end and BT-line is necessary when the change happen.

  41. ●Protection record(26/3 – 1/4 one week) 16 unitsWG 30L RF ref.ELOC M/K currentACCl. Vacc 20 24 0 4 0 3 Averaged protection times per unit per day ≤0.5

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