Experience of SNS Linac By Andrei Shishlo Spallation Neutron Source - - PowerPoint PPT Presentation

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Experience of SNS Linac By Andrei Shishlo Spallation Neutron Source - - PowerPoint PPT Presentation

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Commissioning Experience of SNS Linac By Andrei Shishlo Spallation Neutron Source Oak Ridge National Laboratory CSNS ICFA mini-Workshop on Beam Commissioning for High Intensity Accelerators June 8-10, 2015 Outline Introduction to SNS

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Commissioning Experience of SNS Linac

By Andrei Shishlo Spallation Neutron Source Oak Ridge National Laboratory CSNS ICFA mini-Workshop on Beam Commissioning for High Intensity Accelerators June 8-10, 2015

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2 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Outline

  • Introduction to SNS
  • How we commissioned the SNS linac
  • What we should have done differently
  • What worked well for us
  • Lessons learned
  • Present day tuning procedures
  • Ramp-up Timeline
  • Conclusions
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3 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

SNS Accelerator Complex

Front-End:

Produce a 1-msec long, chopped, H- beam

1 GeV LINAC Accumulator Ring:

Compress 1 msec long pulse to 700 nsec

7.5 kW beam dump

RTBT HEBT

Injection Extraction RF Collimators

Liquid Hg Target

7.5 kW beam dump 150 kW injection dump 1000 MeV Ion Source RFQ 2.5 MeV 87 MeV CCL SRF, b=0.61 SRF, b=0.81 186 MeV 387 MeV

DTL

MEBT

Design parameters Kinetic Energy [GeV] 1.0 Beam Power [MW] 1.4 Repetition Rate [Hz] 60 Peak Linac Current [mA] 38 Linac pulse length [msec] 1.0 SRF Cavities 81

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4 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Commissioning Timeline

2002 2003 2004 2005 2006

DTL Tanks 1-3 Front-End DTL Tank 1 DTL/CCL SCL Ring Target

5 stages of SNS linac commissioning

2005 Int. Particle Accelerator Conference, Knoxville, Tennessee LINAC 2006, Knoxville, Tennessee USA

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5 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

How long did it take (how much time did we spend)?

Section commissioned days actual* Front end 33 DTL 1 47 DTL 2-3 12 DTL 4-6 and CCL 1-3 135 (incl. ~40 days of planned shutdown) CCL 4 thru SCL 63 (incl. ~13 days of planned shutdown) *Some times could have been shorter. For example we spent a large amount of time studying the beam halo, and some of this work never bore fruit. On the other hand, this could be seen as time well spent gaining experience with the machine.

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6 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

How we did it

  • Staffed 24/7
  • Commissioned with beam in 7 stages (5 for linac, 2 for Ring and

target) over 3.5 years

  • Front End through CCL-3 “control room” was a few computer

stations in the Front End building, hard hats and safety shoes were required

  • Commissioned DTL-1 (7.5 MeV output energy) with a special

diagnostics beam line (D-plate) that had a high-power beam stop. We used it to demonstrate 1.0 MW equivalent power (26 mA pk, 650 us, 60 Hz) in 2003. After that did not return to 1 MW beam parameters until 2009.

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7 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

How we did it (cont.)

  • Most of used software was developed before particular stage of

commissioning

  • Today we’re still improving our linac tuning algorithms

– Utilize beam phase measurements inside the same warm linac cavity whose set points are being determined – New algorithms (DeltaT, PASTA, One BPM algorithm) – Tuning automation (Warm Linac 6-8 hours -> 50 min , SCL 8 h -> 32 min)

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8 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Beam Diagnostics for Commissioning

  • BPM – Beam Position Monitors. They measure transverse

coordinates of the center of the beam, the arrival time (as a phase), and a Fourier harmonic amplitude of the longitudinal density distribution.

  • Wire Scanners – transverse profiles
  • Slit-Harp Emittance Devices – transverse emittance
  • Faraday Cup with an energy degrader
  • BCM - Beam Current Monitors – beam peak current
  • BLM – beam loss monitors (Ionization chambers + neutron

detectors)

  • Sets of insertable apertures in MEBT to reduce peak current
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9 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

High Level Physics Applications

  • In the beginning: Combination of Matlab and XAL (Java) scripts
  • Later: XAL only
  • SCORE – save/restore all parameters relevant for tuning
  • 1D and 2D Scan Application (many purposes including MEBT

bunchers setup, DTL acceptance scan, and Detla-T)

  • Orbit Correction Application
  • PASTA – (Phase and Amplitude Scan and Tuning Application)

phase signature matching replacement of Delta-T

  • Orbit Difference Application – for optics control including cavities

setup

  • SLACS – SCL cavities tuning application
  • Loss Viewer – beam loss viewer along the whole accelerator
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10 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Present Day Warm Linac Tuning

  • Warm Linac Wizard – OpenXAL app for MEBT-DTL-CCL tuning
  • It is automated tuning – Operators are just watching the process (< 1h)
  • It uses generalized phase signature matching (sometimes even only one BPM is

needed) and the BPMs inside the same cavity BPM203 BPM209 BPM302 BPM308 DTL2 RF is On DTL3 RF is Off BPM209 Phase Red curve – Open XAL Model DTL2 Cavity Phase Scan The beam at BPM209 is always present We can get a good guess of the working phase and amplitude The 2nd Stage is a nonlinear phase scan matching 1st Stage of Automated Tuning

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11 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Delta-T, PASTA, and General Phase Matching Comparison

Algorithm Descriptions Delta-T

  • Developed at Los Alamos Lab
  • Uses 2 BPMs
  • Uses BPMs signals for RF On/Off
  • Linearized response from the model

PASTA (name inside XAL)

  • Method itself was developed at FNAL
  • Implemented in XAL by John Galambos (SNS)
  • Uses 2 BPMs
  • Can use BPMs signals for RF On with or w/o Off
  • Nonlinear phase matching

General Phase Scan Matching

  • Implemented in OpenXAL application
  • Can be used with one BPM only

Example: DTL3 Amp. and Phase tuning using only one BPM outside the cavity

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12 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Global RF Tune Control: RF Shaker

OpenXAL RF Phase Shaker Δφ BPMs Phases Diff OpenXAL DTL CCL MEBT z, m

  • OpenXAL Phase Shaker allows to test the RF phase set up for

several cavities or even the whole SNS linac

  • If we see increase in beam loss we can check if the cause is a

bad longitudinal tuning

Idea from Sasha Aleksandrov

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13 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

SCL commissioning

  • Initially commissioned at 4.2 and 2.1 deg. K, but cryo-plant at

2.1 K was not stable at the time

  • Cavity amplitudes set to maximum stable gradients – much

different than design gradients

  • Determining cavity phase set points was a lot easier than

expected, partly due to the large acceptance of the SCL

– Had two methods prepared: Beam Induced Signal (Drifting Beam method) and Phase Scan. Phase Scan method in combination with RF blanking and MEBT beam attenuation worked great, no need to further develop Drifting Beam method.

  • Operated at 4.2 K from 2005 to 2007 to give time for cryoplant

adjustments needed for stable 2.1 K operation, and also because 4.2 K met operations needs during that time

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14 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Improvements to phase scan method

  • When we first commissioned the SCL we turned off the RF to the

cavities downstream of the cavity whose phase was being

  • scanned. It took about 15 minutes to turn on the next cavity and

move on.

  • Now we just blank the RF at 1 Hz (59 RF pulses on, 1 pulse off)

and that can be turned on or off in about 1 second

  • We use low peak currents (~5 mA) and short pulses (~3 us) to

minimize the cavity excitations and beam loading

  • In the first years of routine operations the SCL phase scans took

about 12 hours. Today they are automated and take about 40 minutes.

beam

BPM 1 BPM 2

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15 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

What we should have done differently

  • During commissioning many system adjustments and

modifications were needed to get everything working together. The rapid pace did not accommodate careful reviews of the modifications.

– Modifications to the Machine Protection System should have been more carefully reviewed. Low pass filters were added to some MPS inputs to help with false trips due to noise. This ended up slowing down the response time of the MPS.

  • MEBT Chopper was burned and replaced with more robust one
  • later. Now we do not have it at all.
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16 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

What worked well for us

  • Thorough magnet measurement program allowed “dialing-in”

magnet currents and immediately transporting beam.

  • Physics apps were integrated with the on-line model and the

control system, and well developed before start of commissioning (by using Virtual Accelerators)

  • Physics apps written by commissioning team members
  • Commissioning the machine in stages
  • Good set of beam instrumentation (lots of beam position/phase

monitors, beam profile devices, and beam loss monitors)

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17 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Some lessons learned

  • Equipment checkout with beam takes a large fraction of the time

– Beam instrumentation – RF & LLRF – Control system – Machine Protection System

  • Initial commissioning at low beam power was easy once the

equipment was running properly

  • Be careful with modifications to critical systems (e.g. MPS system)
  • There could be surprises – SCL beam loss
  • Automated applications for long tasks are working better than human
  • The high power ramp up was and still is our biggest challenge
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18 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Power ramp up (the commissioning after the initial commissioning)

  • Two schools of thought here:

1) Keep the beam power low, get all the bugs worked out, don’t endanger beam availability, don’t activate beam line components until everything is working well 2) Aggressively push beam power to identify weak components and to solve high-power problems before the users expect/demand high availability

  • At SNS we choose the latter, and we are glad we did
  • At 1 MW we paused to focus on beam availability. Budget and

then target problems caused us to stay at 1 MW for longer than we had hoped.

  • We are now back on the trajectory to further increase the beam

power

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19 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Beam power vs time

  • Typical beam power today is 1.1 MW

1 MW Save $$$ Target supply issues

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20 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Conclusions

  • The commissioning and an initial power ramp-up of SNS was

performed according to the planed schedule (even slightly ahead)

  • Now our goal is 1.4 MW power at availability more than 90%
  • We still improving our knowledge of the machine
  • There still have puzzles that we are working on
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21 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Thank you for your attention!

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22 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Backup Slides

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23 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Design vs operation SCL gradients

5 10 15 20 25 1a 1c 2b 3a 3c 4b 5a 5c 6b 7a 7c 8b 9a 9c 10b 11a 11c 12b 12d 13b 13d 14b 14d 15b 15d 16b 16d 17b 17d 18b 18d 19b 19d 20b 20d 21b 21d 22b 22d 23b 23d Cavity number Eacc (MV/m)

December 05-February 06 (Ring Commissioning) May 06 (Production Run) HOM Conditioning HOM+Conditioning Turned on Tuner problem HOM Tuner (from R. Campisi, June 2006) Design gradient

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24 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Drifting beam method

  • This is the alternative method we developed to determine the

SCL set points

  • Not used since the phase scan method worked well
  • Requires longer beam pulses (~30 us) which can create much

more beam loss (compared to ~3 us for phase scan method) in downstream portion of SCL

  • 140
  • 130
  • 120
  • 110
  • 100

20 40 60 80 100

t (us) phase (deg)

Signal Pi mode

Simulation for 466 MeV, 38 mA, 50 s, rms size 3 deg

(Courtesy Y. Zhang)

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25 Managed by UT-Battelle for the U.S. Department of Energy A.Shishlo, ICFA Mini-Workshop, June 8-10, 2015

Linac Dump 7.5 KW Injection Dump 150kW Extraction Dump 7.5KW

End of Linac - HEBT Gate PPS 1.0, 1.2 DTL Tank 1 And DTL Tanks 1-3 PPS 0.4/0.5 HEBT -Ring Gate PPS 2.0

Ev Evolution of

  • lution of PPS Enc

PPS Enclosur losures es with Commis with Commissioning sioning

HEBT-RTBT- Target PPS 3.0