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

7 SLHiPP-4, May 15-16, 2014

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

8 SLHiPP-4, May 15-16, 2014

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

16 SLHiPP-4, May 15-16, 2014

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