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

6. Operation status

7. Next plan

8. Summary

1. What we have done after IMAC- 06

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.

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.

2. Beam Performances

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.

Test result: BEPCII-Linac Beam Performance

measured by the Test Group, in June-July 2006

** Energy spread were measured in early 2007.

DesignMeasuredBEPCEnergy (e+ / e-) ( GeV )1.891.891.30-1.55Current ( e+ ) ( mA )3761~ 5Current ( e- ) ( mA )500> 500 ~300Emittancee+( 1 , mm-mrad0.40 (37 mA)0.39~0.41 (40~46 mA)---- Emittance (e-) ( 1 , mm-mrad0.10(500 mA) 0.09~0.11 (600 mA)----Pulse Repe. Rate Hz505012.5Energy Spread ( e- ) %** 0.50(500 mA) 0.44 (600 mA) 0.80 Energy Spread ( e+ ) %** 0.50(37 mA) 0.50(37 mA) 0.80

Test result: Beam instability measurement

BPMEnergy analyzerDispersion = 0.63 m

(E/E)jitter0.15%

DesignMeasuredBeam orbit instability(BPMs @ Linac exit ) 0.20 mm 0.16 mm Beam energy instabilityBPM downstream energy analyzer) 1.0 mm 1.0 mm Gun trigger timing jitter35 ps

(1)39 ps (1) 27 ps (rms)*(* Checked on July 18)

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 improvement compared with the original BEPC-Linac.

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

Measured beam spread at PR downstream energy analyzerDispersion: Dx = 0.63 m better than the design goal:

(P / P) = 0.50%

e+ energy spread measurement

Due 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-BC2We 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)

= 21.85m0.5% = 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 mA58 mA Dx = 1.85 m~37mA

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

1

64

71

55

24

22

16

9

8

10

5

5

8

8

3

0

energy1

264

471

655

824

1022

1216

149

168

1810

205

225

248

268

283

300

energy1

64

71

55

24

22

16

9

8

10

5

5

8

8

3

0

Mev

3. Beam orbit instability

During April-June 2006, a periodic orbit oscillation appeared, seen by the BPMs. Properties of the oscillation: Periodical, with changed periods of 2 s ~ 100 s; Amplitude changed between 0.5 mm ~ 3 mm

BPM 03 @ upstream linac BPM 14 @ downstream linac

In the workshop, we found two phenomenon:

The bunch distribution were oscillated with frequency of ~ 2 Hz at BPM 14 (oscilloscope TDS-7254); Simultaneously, we found the bunch charge oscillation by BCM 2 @ downstreambunching system, with the same frequencyof ~2 Hz.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 14BPM14--TDS-7254It is expected that : Bunch charge oscillation beam orbit oscillation

Gun trigger jitter + non synchronization with 2856 MHz wake-effect

Simulated Beam distribution@ gun ExitBunch distribution @ exit of bunching system for the gun pulse length 5 bunches downstream buncher 1.0ns (FWHM) and 1.6 ns(bottom) relative bunch charges: 0.170.831.00.650.06 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.

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 .

non synchronization with synchronization BPM 14

4. Beam energy stability

Beam energy instability can be measured by the BPMs in BT line located at a large dispersion.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-BPM1 TE-BPM 6, Dx = 0, near injection

5. Beam transmission

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-BCM2TP-BCM1

PositionGun exit(BCM1)Bunching end(BCM2)on target(BCM3)e+ source(100MeV)(BCM4)Linac end(BCM11) Design 10 A 7.5 A 6.5 A 50 mA 37 mAReached11.8 A8.9 A7.9 A80 mA61mA

6. Operation status

Beam orbit stability: BPM 15 BPM 16 Last 2 BPMs in the Linac: jitter 0.1 mm (1)

Beam energy stabilityAt the TE-BPM1, Dx = 2.0 m, the orbitoscillation 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-BPM1 TE-BPM 6, Dx = 0, near injection

1) Phase control system:

to suppress the slow change of the beam energy due to the slow change of the RF phase;

2) Modulators voltage stability:

to suppress the fast change of the beam energy due to the jitter effects of the RF voltage and phase.

A stable beam energy is provided by:

K5 (off)

~ 4.50, in 6 hours K8 (off)

~ 6.50, in 6 hours K5 (on)

~ 1.50, in 6 hoursK8 (on)

~ 1.00, in 6 hoursPhase control system works well

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

The measured voltage instability at modulator 7# & 10# : To have modulators 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.

50 Hz 8 hours without De-Qing0.16% with De-Qing0.10%

e+ / e- operation modes exchange1Integrated exchange mode:

Just click one button e+/e- Switch to realize the following 6 items simultaneously in a few seconds :

(e+ / e- ) optics and orbit ; (e+ / e- ) gun bias voltage (different gun current) BCMs amplifiers for e+ beam e+ production target position; e+ pulsed focusing magnet timing moving; one more stand-by of RF unit for e- beam.

2Exchange time is a few seconds only ( 10 seconds), and stable & repeatable usually. 3The target positioning works not so stable some time, and have to be further improved. (to further improve the switch program).

Operation reliabilityIn principle, the linac works reliable, but with a few troubles some time.

For example, in the last week ( Golden week, May 17 ), two faults:

The operation reliability (with beam) is about 98.2%.

7. Next Step

1To 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.

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.

499.8MHGunSHB1SHB2BuncherStandard Acce. SectionLinacBEPCII Ring142.8MHz 571.2MHz 2856MHz2856MHz 56.02nsSLED 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. 3) To construction the Sub-Harmonic Bunching System:The SHBs are being fabricated, and is planed to start its

commissioning by September 2008.

8. Summary The measured linac performance, including energy, current, energy spread, emittance both for e- and e+ beamshave 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.

Thank you very much for your attention !

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.

# of Klystron# of acceler.sectionsMax. RF output MW Output in operation( MW )EnergygainEnergygain MeV NotesK114520-3040-50A few power for buncherK246545200e- beam energy @ target240 MeVK31451535 (e-)15 (e+)Decelerated in 1st 1 m, accelerated to 21 MeVK42453580e+ accelerated to 100 MeVK5-K1144535177K1246550 210K13-K1644535177

Emittance measuremente+, 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.

DateCurrent

(mA)(x) (1)

(mm-mrad)(x)

(m) (x)(y) (1)

(mm-mrad)(y)

(m) (y)

06-6-30410.3213.13-0.490.2419.98-0.8306-7-13400.4114.05-0.180.3914.37-0.2807-3-12460.3919.85-0.470.3328.26-0.92 Design 370.400.40

Protection record (26/3 1/4 one week)16 units WG 30L RF ref. ELOC M/K current ACCl. Vacc

20 24 0 4 0 3 Averaged protection times per unit per day 0.5

WG30L-IPEOLCM/KAccKout(MW)(MW)1K10000000036.90.32552K21020000050.80.93913K30000000117.80.43124K400000000471.25K50000000016.30.19226K60000100038.30.43137K70000000055.90.2858K80000300036.20.81679K92000000036.70.907510K105030000048.61.711K1100100000420.93112K121020000057.21.113K131000000150.10.307514K1440400000350.689315K1530120000042.60.669816K163000000145.90.3509