sns operating modes and reliability studies presented at the 4 th open collaboration meeting on...
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SNS Operating Modes and Reliability Studies
Presented at the 4th Open Collaboration Meeting on Superconducting Linacs for High Power Proton Beams (SLHiPP-4), CERNMay 15-16, 2014
Sang-ho KimSpallation Neutron SourceResearch Accelerator Division, ORNL
2 SLHiPP-4, May 15-16, 2014
FY14 Operation ScheduleNP delivery committed: 5064 h*90%~4500 h
Special in FY14 to replace target
Long maintenance:2328 hMachine start up: 464 hTransition to NP: 129 hAP study: 528 hMaintenance during NP: 516 h
3 SLHiPP-4, May 15-16, 2014
65
70
75
80
85
90
95
0
1000
2000
3000
4000
5000
6000
FY07 FY08 FY09 FY10 FY11 FY12 FY13 FY14 YTD
NP Hrs. delivered
MWh delivered to target
NP Downtime
NP Availability
NP Availability w/o Target Failures
Availability commitment
Till May 4, 2014• FY12 downtime includes ~150 hours target premature failure
• FY13 downtime includes ~1030 hours target premature failure and ~70 hours PPS
SNS Operational StatisticsN
P h
ours
, M
Wh
Ava
ilabi
lity
4 SLHiPP-4, May 15-16, 2014
SNS operational history
Ion Source,LEBT
TargetCMS leak
HVCM
Stripperfoil
1 MW beam power on target achieved in routine operation
High reliability?Management decision
Target premature Failure – QA/QC/Spares
1.4MW demo
5 SLHiPP-4, May 15-16, 2014
Current run (93.5% availability)Optional maintenance day
6 SLHiPP-4, May 15-16, 2014
Downtime by Fiscal Year (07-13) comparison
Targ
etE
-HV
CM RF
Ion
Sou
rce
E-M
agP
SE
-cho
pper
Con
trol
sV
acuu
m
E-o
ther
Coo
ling
Cry
o
AP
Pro
t. S
ys.
Mis
c./M
ag/R
S/E
SH BI
Fac.
/Mec
h. S
ys.
Ops
CM
/SR
FN
eut.
Inst
.
0
50
100
150
200
250
300
350
400
450FY07-FY13 Downtime by group
FY07
FY08
FY09
FY10
FY11
FY12
FY13
System
Ho
urs
of
do
wn
tim
e
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SNS SCL systems downtime statistics
0
5
10
15
20
25
30
35
40
45
FY13
FY12
FY11
NP scheduled hours
: 5802
: 5248
: 5436
Cav
ity T
rip
Con
trol
/BI
HV
CM
Pow
er d
ip
Vac
uum
CH
L
HP
RF
T
rans
mitt
er
Oth
ers
elec
tric
&
wat
er
• FY13 other electric: Large transformer switchgear failure
• FY13 HPRF: a filament power supply spare problem for klystron
• CHL: 2K trip due to VFD glitch, loose wire, power glitch
• HVCM: one or two bad actors every run
• FY12 NP hours includes ~150 hours target premature failure
• FY13 NP hours includes ~1030 hours target premature failure and ~70 hours PPS
Dow
ntim
e (h
our)
Next page
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Downtime statistics from cavity/CM
0
2
4
6
8
10
12
FY13
FY12
Cou
pler
Tem
p.
Err
ant
beam
or
its
con
sequ
ence
Hal
o at
ups
trea
m o
r its
con
sequ
ence
Arc
det
ecto
r
Bad
inst
rum
ent/
im
prop
er s
ettin
g
Tru
ncat
ion
by H
PR
F
Con
ditio
ning
per
iod
at m
achi
ne s
tart
up
• Large reduction from errant beam/halo or their consequences in FY13 (FY14 is not as good as FY13)
• FY13 cavity trips due to conditioning: during preparation of full duty factor and 1.4 MW run
• 95 % of cavity trip due to Arc detector: during arc detector test (every mid-night to check the functionality of arc detector)
• FY13 bad instrument: Pressure transducer failure in CM19
• Trips due to coupler temperature: flow is well-balanced or enough
Dow
ntim
e (h
our)
9 SLHiPP-4, May 15-16, 2014
Current operational strategy for 1.4 MW
• Beam current– Ion source current is providing the design current or higher– RFQ field is running lower than design (transmission is lower)– Added capability to run at shorter gap in LEBT chopper
• Pulse width– HVCM has been running at full duty factor (975us for beam)
• Beam energy– 940 MeV (+13 MeV energy margin) mainly due to lower operating
gradients of high beta cavities – R&D, spare CMs, rework, etc.
10 SLHiPP-4, May 15-16, 2014
SNS Cavity Operating Regime
Time
Measurements of Radiation during RF Pulse
Rad
iatio
n (a
rb.
Uni
t)
Rad
iatio
n (in
log,
arb
. U
nit)
Eacc
FE onset
Radiation onset
MP Surface condition
Operating setpoints: Basically running in the field emission regime.
Majority of cavities
11 SLHiPP-4, May 15-16, 2014
Current SCL operating gradients• Average Eacc of medium and high beta cavities:12 MV/m,
13 MV/m respectively
0
2
4
6
8
10
12
14
16
18
0 20 40 60 80Cavity Number
Ea
cc (
MV
/m)
Spare CM developed in house Operation since summer 2012
12 SLHiPP-4, May 15-16, 2014
Performance improvement
• Rework of cryomodules: only option for unrecoverable damage
• Spare cryomodules– High beta spare was developed and in service now– Medium beta spare is waiting for funding
• In-situ processing?– Investigated possible method for the SNS CMs
• Helium processing: did not work due to severe MP in the end group/HOM• Plasma processing: just attempted. Promising result.
13 SLHiPP-4, May 15-16, 2014
High beta spare cryomodule was developed by in-house SNS resources and is the first to be ASME pressure-vessel code compliant
• Allows removal of operating high beta cryomodule for repair– Rework is the only option for the unrecoverable damages of cavity surface/parts– Maintain same beam energy while conducting complex repairs
• High beta spare cryomodule serves as prototype for upgrades– Fabrication techniques were developed (the first ASME Boiler and Pressure Vessel code
stamped cryomodule addressing10CFR851 requirement)– Commissioning was successfully performed at the SNS test facility
• Sets the baseline design for a medium beta spare cryomodule
Spare has been in service since the summer of 2012 and all four cavities are operating at 16 MV/m (RF power limited)
14 SLHiPP-4, May 15-16, 2014
The spare cryomodule
15 SLHiPP-4, May 15-16, 2014
Motivation for in-situ processing in the tunnel• Medium term
– Recover from cavity performance degradations– Reach 1GeV + energy reserve (Increase high beta cavity
gradients by about 2 MV/m in average)
• Long term– STS: 2 beam (50 Hz 33.3mA for FTS, 10 Hz 38mA for STS)– 38-mA beam loading with 2nd target station: Need narrower
performance scattering Efficient utilization of RF power (ideally constant RF power/cavity is preferred)
• Develop a cost effective processing method with minimal impact on machine operation
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0
100
200
300
400
500
600
700
1 21 41 61 81 101
RF p
ower
requ
irem
ent (
incl
udin
g 15
%
mar
gin)
, kW
Cavity number
Eacc and RF power requirement for STS
For new cavitiesBlue Qex, ref -20 %Red Qext, ref =7e5Green Qex, ref +20 %
RF Power requirement
0
2
4
6
8
10
12
14
16
18
1 51 101
Eacc
(MV/
m)
Cavity Number
STS
Present
Existing klystrons
Klystrons for STS: 700kW7 additional high beta CMs1.3 GeV + energy margin
17 SLHiPP-4, May 15-16, 2014
Cavity D 12 MV/mCamera exposure; 30 ms
Cavity A 9.3MV/mCamera exposure; 30 ms
Phosphor screen images before processing
0.01
0.10
1.00
10.00
100.00
0 2 4 6 8 10 12
Eacc (MV/m)
Do
se
Ra
te (
BL
M7
)
baseline before processing
after processing
Processed at cold and warm upRGA analysis some C-H-(O)-(N)
Statistically optimized?Coupler damage?Solid byproduct?
Need R&D
18 SLHiPP-4, May 15-16, 2014
• Develop in-situ plasma processing technique for superconducting RF cavities– In-situ processing means a processing in the tunnel for the cost saving
with minimal impact on the machine operation– Preliminary test in 2009 gave a promising result
• Plasma processing aims at removing residual surface contaminants to increase cavity accelerating gradients by 10-15 % in average – This technique could be a alternative or additional cleaning method for
any SRF cavities during production or in operation if successful
• R&D started in 2012 to develop a reliable technique for in-situ plasma processing at SNS
R&D for performance improvement
19 SLHiPP-4, May 15-16, 2014
SRF facilities are being developed to meet the immediate reliability goals and to provide for the long term stewardship of the accelerator• Mission Statement
The SCL Systems Facility will enable laboratory staff to develop and test improvement plans for the SNS SCL, advance material science for SRF, cultivate collaborations with other laboratories, and contribute to future machines and projects.
• With this facility in place, SNS can be responsive to customer needs!
• Conduct our own repairs• R&D focused on improving our application• Support Second Target Station (STS) with increased capability
• System is not intended to be production scale
• Reduces capital investment• Ensures priorities of facility are in line with SNS objectives
20 SLHiPP-4, May 15-16, 2014
SNS SRF Facilities
Fixed Rail
60 m
Test caveControl room
VTA
CTF
KinneyFor CTF
HTA
CM development
CM development
5MW klystron &Coupler conditioning
HPRCMrework
String Assem.
Clean room
Barrel PolishingFurnace
Cavity R&D
21 SLHiPP-4, May 15-16, 2014
Summary
• The current reliability and availability of the SCL is high but there are key issues that must be addressed
• Cryomodule rework and development is an active program– High beta spare cryomodule commissioned and operating in LINAC– Medium beta spare cryomodule design initiated– CM6, CM20 repaired
• Research and development is ongoing to improve the current performance of the accelerator and prepare for the STS– Plasma R&D focused on achieving 1.4 MW – Cavity and coupler development in preparation for STS
• An investment in facility development is already supporting the operation and has ensured priorities are aligned with SNS goals including STS