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

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Progress of the BEPCII- Linac
Commissioning Shu-Hong Wang
for the BEPCII - Linac Group
BEPCII IMAC, May 10-12, 2007
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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

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1. What we have done after IMAC- 06
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• ? 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.

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• ? 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.

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2. Beam Performances
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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.

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Test result BEPCII-Linac Beam Performance
measured by
the Test Group, in June-July 2006
Design Measured BEPC
Energy (e / e-) ( GeV ) 1.89 1.89 1.30-1.55
Current ( e ) ( mA ) 37 61 5
Current ( e- ) ( mA ) 500 gt 500 300
Emittance(e)( 1 s, mm-mrad) 0.40 (37 mA) 0.390.41 (4046 mA) ----
Emittance (e-) ( 1 s, mm-mrad) 0.10 (500 mA) 0.090.11 (600 mA) ----
Pulse Repe. Rate (Hz) 50 50 12.5
Energy 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
Energy spread were measured in early 2007.
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Test result Beam instability measurement
Design Measured
Beam orbit instability (BPMs _at_ Linac exit ) ? 0.20 mm ? 0.16 mm
Beam energy instability (BPM downstream energy analyzer) ? 1.0 mm ? 1.0 mm
Gun trigger timing jitter 35 ps (1s) 39 ps (1s) 27 ps (rms) ( Checked on July 18)
Dispersion 0.63 m (?E/E)jitter0.15
BPM
Energy analyzer
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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.
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e- beam energy spread measurement

Energy 1.89 GeV Current 600 mA
1.89 GeV
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Measured beam spread at PR downstream energy
analyzer
Dispersion Dx 0.63 m
better than the design goal (?P / P)
0.50
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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-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) 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 mA
58 mA
Dx 1.85 m
37mA
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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)
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3. Beam orbit instability
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• 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 _at_ upstream linac BPM 14 _at_
downstream linac
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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 (oscilloscope
TDS-7254) ? Simultaneously, we found the
bunch charge oscillation by BCM 2 _at_
downstream bunching system, with the same
frequency of 2 Hz.
BPM14--TDS-7254
wake-effect
It is expected that Bunch charge oscillation
beam orbit oscillation Gun trigger
jitter non synchronization with 2856 MHz
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Simulated Beam distribution _at_ gun Exit
Bunch distribution _at_ exit of bunching system
for the gun pulse length
5 bunches downstream buncher 1.0ns
(FWHM) and 1.6 ns(bottom)
relative bunch charges

0.17?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.
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• 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 47 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
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4. Beam energy stability
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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
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• 5. Beam transmission

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Beam transmission table (1.89 GeV, e)
Position Gun 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 mA
Reached 11.8 A 8.9 A 7.9 A 80 mA 61mA
Bunching efficiency BCM2 / BCM1 75, e-
beam current _at_ target 7.9 A , e transm. in
main-Linac BCM11 / BCM4 76, TP-BCM1 /
TC-BCM2 80.
TC-BCM2
TP-BCM1
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• 6. Operation status

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? Beam orbit stability
Last 2 BPMs in the Linac jitter 0.1 mm
(1s)
BPM 15 BPM 16
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? 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
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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) Modulators voltage stability
• to suppress the fast change of the beam
  energy
• due to the jitter effects of the RF voltage and
  phase.

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Phase control system works well
K5 (off) ?f 4.50, in 6 hours
K5 (on) ?f 1.50, in 6 hours
K8 (off) ?f 6.50, in 6 hours
K8 (on) ?f 1.00, in 6 hours
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Phase control panel
Put phase control on for all RF units,
except the stand-by ones.
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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.
The measured voltage instability at modulator
7 10
50 Hz 8 hours
without De-Qing 0.16
with De-Qing 0.10
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? e / e- operation modes exchange

• 1)Integrated 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.
• 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).

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? Operation reliability

• In principle, the linac works reliable, but with
  a few troubles some time.
• For example, in the last week ( Golden week, May
  17 ), two faults

Date Time Fault Trouble duration
May 6. 1340 1500 Gun high voltage charging power supply Problem. 80 min.
May 6 7 2320 100 One electricity distributed cabinet problem, no electricity (380 V) for RF units of 13 14, induced by trigger problem of 13 unit. 100 min
Total 180 min
The operation reliability (with beam) is
about 98.2.
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7. Next Step
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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.

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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.

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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.
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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.

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• Thank you very much
• for your attention !

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BEPCII Linac Beam energy with Klystron Power
Output
of Klystron of acceler.sections Max. RF output ( MW ) Output in operation ( MW ) Energy gain Energy gain ( MeV ) Notes
K1 1 45 20-30 40-50 A few power for buncher
K2 4 65 45 200 e- beam energy _at_ target 240 MeV
K3 1 45 15 35 (e-) 15 (e) Decelerated in 1st 1 m, accelerated to 21 MeV
K4 2 45 35 80 e accelerated to 100 MeV
K5-K11 4 45 35 177
K12 4 65 50 210
K13-K16 4 45 35 177
If 2 of K5 K16 be stand-by, then at linac-end
E (e) 1.90 GeV

E(e-) 2.30 GeV.
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Emittance measurement(e, 1.89 GeV)
Date Current (mA) e(x) (1s) (mm-mrad) ß(x) (m) a (x) e(y) (1s) (mm-mrad) ß(y) (m) a (y)
06-6-30 41 0.32 13.13 -0.49 0.24 19.98 -0.83
06-7-13 40 0.41 14.05 -0.18 0.39 14.37 -0.28
07-3-12 46 0.39 19.85 -0.47 0.33 28.26 -0.92
Design 37 0.40 0.40
? 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.
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?? ?? WG?? ?? 30L-IP ?? EOLC ??? M/K?? Acc?? Kout(MW) ??(MW)
1 1 K1 0 0 0 0 0 0 0 0 36.9 0.3255
2 2 K2 1 0 2 0 0 0 0 0 50.8 0.9391
3 3 K3 0 0 0 0 0 0 0 1 17.8 0.4312
4 4 K4 0 0 0 0 0 0 0 0 47 1.2
5 5 K5 0 0 0 0 0 0 0 0 16.3 0.1922
6 6 K6 0 0 0 0 1 0 0 0 38.3 0.4313
7 7 K7 0 0 0 0 0 0 0 0 55.9 0.285
8 8 K8 0 0 0 0 3 0 0 0 36.2 0.8167
9 9 K9 2 0 0 0 0 0 0 0 36.7 0.9075
10 10 K10 5 0 3 0 0 0 0 0 48.6 1.7
11 11 K11 0 0 1 0 0 0 0 0 42 0.931
12 12 K12 1 0 2 0 0 0 0 0 57.2 1.1
13 13 K13 1 0 0 0 0 0 0 1 50.1 0.3075
14 14 K14 4 0 4 0 0 0 0 0 35 0.6893
15 15 K15 3 0 12 0 0 0 0 0 42.6 0.6698
16 16 K16 3 0 0 0 0 0 0 1 45.9 0.3509

? 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