Post on 16-Jan-2016
description
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CESR-c Vacuum PerformanceCESR-c Vacuum PerformanceYulin Li, Yun He and Nari Mistry
Laboratory for Elementary-Particle PhysicsCornell University, Ithaca, New York, USA
The 13th ICFA Beam Dynamics Mini-Workshop
Beam Induced Pressure Rise in RingsBrookhaven National Laboratory, Upton, NY
December 9 – 12, 2003
CESR-c Vacuum
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OutlineOutline
• CESR Layout• CESR-c Conversion
► Motivation and Objective ► Hardware Modifications ► Status and Performance
• CESR-c Vacuum System and Requirements
• Beam Conditioning and Wall-Pumping
CESR-c Vacuum
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CESR LayoutCESR Layout
CESR-c Vacuum
Principal Parameters:
768 m Circumference 1.5-6 GeV beam energy Y > 0.06 @(4S)
Ibeam > 350 mA
L > 1.2 x 1033 cm-2sec-1 @(4S)
45 bunches each e+, e-
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CESR-c Conversion – ObjectivesCESR-c Conversion – Objectives
CESR-c Vacuum
We propose to modify CESR to provide high luminosity colliding beams over the (beam) energy range from 1.5 to 5.6 GeV.
Energies (Ebeam) of interest and Luminosity goals:
J/: 1.55 GeV – 1.5 x 1032
Charm threshold (’’): 1.885 GeV – 3.0 x 1032
Above DD threshold: 2.1-2.5 GeV – 5.0 x 1032
states: 4.7-5.6 GeV – 10 x 1032
CESRc is designed to deliver 20-200x the world data sample in the 1.5-2.5 GeV (Ebeam) range during it’s proposed 3 year operation.CESR will be continuing to provide beams for SR BLs to CHESS
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CESR-c ModificationsCESR-c Modifications1. Extend energy range, reduce spot size at IP.
Replace PM IR quads with S.C. quads for full energy range, lower *, p.c. separation, and better solenoid compensation.
2. Reduce bunch length in proportion to spot sizeUpgrade RF system to shorten bunch length in order to take
advantage of smaller *.
3. Recover radiation damping lost at low energyInstall ~18 m of 2.1 T wigglers to control emittance and damping times.
CESR-c Vacuum
Items 1 and 2 have been previously planned and implemented as an upgrade to CESR performance.
The wigglers are the only major change specific to low energy operation.
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Status and PlanStatus and Plan
CESR-c Vacuum
► Completed CLEO-c Detector Upgrade this summer
► Six SC wigglers were installed this summer
► Six more to be installed next spring, that completes CERS-c conversion
Performance Achieved (Goal)
@1.88 GeV Beam Current (mA) – 135 (360)Lpeak (1032 cm-2s-1) – 0.4 (3.0)Int. Lum. /day – 1.6 pb-1
Accum. Lum. Exceeded BESII
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Vacuum Pumping in CESR-cVacuum Pumping in CESR-c
• SR induced desorption is much smaller in the most part of CESR
• Pumping in the Interaction Region (IP ±15 m ) are dominated by TiSP
• Distributed ion pumps (DIPs) in the arcs rely on dipole magnetic field and stop pumping @<700 Gauss (1.9 GeV)
• Fortunately, well-conditioned chamber walls function as effective getters (more later)
CESR-c Vacuum
1.0
0.8
0.6
0.4
0.2
0.0
Rela
tive
DIP P
um
pin
g S
peed
2000150010005000
Dipole Field (Gauss)
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Beam-Gas Loss LifetimeBeam-Gas Loss Lifetime
CESR-c Vacuum
Average pressure of ≤1 x 10-9 torr required
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““Wall Pumping” ExperimentWall Pumping” Experiment
CESR-c Vacuum
► Tests were made by turning off/on DIPs in a well instrumented sector of CESR while operating at 5.3 GeV.
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““Wall Pumping” ExperimentWall Pumping” Experiment
CESR-c Vacuum
► Measured pressure profiles are compared with one-dimensional calculations
► A ‘wall-pumping’ speed of ~110 l/s/m gives the best fits to the measured profiles
► DIPs were left off for several weeks
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SR Power ComparisonSR Power Comparison5.2 GeV 5.2 GeV vs.vs. 1.9 GeV 1.9 GeV
CESR-c Vacuum
1, ,Totalphoton Se Rb am SP F
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Beam ConditioningBeam Conditioning
CESR-c Vacuum
1, ,Totalphoton Se Rb am SP F
Two-Stage Beam Conditioning :
• Primary (direct) ‘beam-scrubbing” – Reducing on SR main-strip ( )SR
vheight
• “Activate” wall-pumping via scattered photons
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CESR-c Commissioning & CESR-c Commissioning & OperationOperation
• Starting commissioning in July 10, 2003• Alternating SR and CESR-c runs• Two CESR-c / CLEO-c ‘engineering runs’• Started 2.5-month CESR-c - CLEO-c ‘production’ run
CESR-c Vacuum
Init
al C
omm
issi
onin
g
SR Run
SR Run SR Run
CE
SR
-c M
S
CE
SR
-c M
SC
LEO
-c E
ngin
eeri
ngCESR-c MS
CLEO-c HEP Run
250
200
150
100
50
0Am
p•H
r pe
r B
eam
340320300280260240220200
500
400
300
200
100
0
Total A
mp•H
r
7/19 8/09 10/27 12/68/29 10/79/18 11/16
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Beam Conditioning – IR Beam Conditioning – IR
CESR-c Vacuum
0.1
1
10
100
1000
dP/d
I p (
ntor
r/Am
p)
0.1 1 10 100
Positron Beam Dose (Amp·hr)
East I R
1
2
4
68
10
2
4
68
100
2
4
68
1000
dP/d
I tot
al (
ntor
r/Am
p)
0.1 1 10 100 1000
Total Beam Dose (Amp·hr)
Hardbends
P=230•D-0.99
0.1 1 10 100 1000
Total Beam Dose (Amp·hr)
P=22.29•D-1
Sof tbends
0 – 8 m from 0 – 8 m from I.P.I.P.
8 – 15 m from I.P.8 – 15 m from I.P. 15 – 35 m from 15 – 35 m from I.P.I.P.
TiSP Pumped, Independent of Ebeam
Reduced Pumping @ L.E.
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Beam Conditioning – Arc Beam Conditioning – Arc
CESR-c Vacuum
1
2
4
6
810
2
4
6
8100
2
4
6
81000
dP/
dI to
tal (
ntor
r/A
mp)
0.1 1 10 100 1000
Total Beam Dose (Amp·hr)
“Main” ConditioningReduction of ph
Establishing the “wall-pumping”
35
30
25
20
15
10
5
0
dP/
dI to
tal (
ntor
r/A
mp)
500400300200100
Total Beam Dose (Amp·hr)
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Sustainable “Wall Pumping” Sustainable “Wall Pumping”
CESR-c Vacuum
6
81
2
4
6
810
dP/
dI
(nto
rr/A
mp)
0.1 1 10 100
Total Beam Dose (Amp·hr)
Well-conditioned sector In sectors where VCs have been fully conditioned, we do not see difference between the H.E. and L.E. operations
In sectors where VCs only been partially conditioned, NO deterioration over the current long L.E. run
20
15
10
5
0dP/
dI
(nto
rr/A
mp)
330325320315310305300295
J ulian Day, 2003
SC Wiggler Sector
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SummarySummary• With installation of six SC wigglers in CESR
and upgrade of CLEO-c detectors, CESR-c / CLEO-c program is performing well and on schedule
• The operation mode of alternating between the SR Run and L.E. HEP Run worked well (where H.E. SR Run acts as VCs conditioning)
• Vacuum ‘wall-pumping’ from conditioned VCs proved to be effective and lasting for the planned HEP program
CESR-c Vacuum