ORNL is managed by UT-Battelle

for the US Department of Energy

1.4 MW Power

Ramp-up and

Reliable Operation

J. Galambos

SNS AAC Review

March 24-25, 2015

2 1.4 MW

SNS: Designed for 1.4 MW

…

The SNS Project Parameter List

3 1.4 MW

Early Power Ramp-up Expectations

• Mason / Holtkamp White Paper, 2002

1.4 MW: mid 2009

4 1.4 MW

1.4 MW Beam Power at SNS: The Reality

• First neutron production at 1.4 MW: June 27, 2014

– Sustained power increase during the 2014 run, increasing power from ~ 1. MW to 1.4 MW

1 hour demo, Sept. 2013

1 day operation June 2014

Unable to run 1.4 MW

Target Limited Beam Power

5 1.4 MW

1.4 MW Operation: The Final Assault

FY 14a Run

– Power ramp-up approach:

• Adiabatic

• Most effective use of what works

– Plan is to operate at 1.3-1.4 MW from now on

Target paranoia

850 kW

1.4Spare target deliveries

1.2

1.0

0.8

1.4

0.6

0.4

Beam

Pow

er

(MW

)

0.2

0.

Oct. 2013

June2014

Jan. 2014

6 1.4 MW

Stable 1.4 MW Operation

• 1.4 MW operation ~24 hr. scale existence proof

– Foil works

– No instability

– RF supports full beam loading

0

200

400

600

800

1000

1200

1400

1600

6/25/1

40:00

6/25/1

412:0

0

6/26/1

40:00

6/26/1

412:0

0

6/27/1

40:00

6/27/1

412:0

0

Beam

Power(kW)

24 hrs

1.38 MW1.41 MW

Water pump outage

7 1.4 MW

Macro-pulse

Structure

(made by the

High power RF

– 60 Hz)

Mini-pulse

Structure

(made by the

choppers ,

1 MHz)

645 ns 300 ns

945 ns

1ms

16.7ms

~1000 mini-pulses per macro-pulse

Some Background: Accelerator Time

Structure

chopped fraction

unchoppedfraction

Chopped gap is to provide an extraction gap in the ring

8 1.4 MW

Proton Beam Power

• Not many knobs:

– Beam energy (Ebeam)

– Rep-rate

– Beam current (Imacro-pulse)

– Macro-pulse length (tmacro-pulse)

– Chopping fraction (fun-chopped)

Pbeam = Ebeam ´Qpulse ´ rep-rate

Qpulse =tmacro-pulse ´ Imacro-pulse ´ fun-chopped

, where

9 1.4 MW

Beam Energy History

• Never run 1 GeV production

• Beam energy constant for last 1.5 years

• Plan to increase to 1 GeV in 1-2 years: plasma processing

800

820

840

860

880

900

920

940

960

980

1000

9/5/05

10/10/0611/14/0712/18/081/22/10

2/26/11

4/1/12

5/6/13

6/10/14

Beam

Energy(M

eV)

Fix cryo-components

Errant beam degradation

Errant beam control, spare cryo-module

10 1.4 MW

Duty Factor History

• Duty factor (=rep-rate x pulse length) is a driver on equipment stress

– Slow increase in pulse length since initial operations

– Final push in 2014

0

10

20

30

40

50

60

70

0

200

400

600

800

1000

1200

10/10/06

6/17/07

2/22/08

10/29/08

7/6/09

3/13/10

11/18/10

7/26/11

4/1/12

12/7/12

8/14/13

4/21/14

RepRate(Hz)

Beam

PulseLength(

ms)

PulseLength

RepRate

RF at full duty factor

11 1.4 MW

Ion Source History: RFQ Output

(Courtesy M. Stockli)

• RFQ output current fairly constant last 2 years

0

5

10

15

20

25

30

35

40

45

50

6/2/06

10/15/07

2/26/09

7/11/10

11/23/11

4/6/13

8/19/14

Beam

Current(m

A)

Source 3

Source 2

Source 4

Degraded RFQ

12 1.4 MW

RFQ Transmission is Low

(Courtesy M. Stockli)

• Reduced RFQ transmission 2012-present

– 60-75%

• Input current 45-55 mA

RFQ operated at higher power

13 1.4 MW

Historical RFQ Performance

• Nominal: operate with ~ 600 kW, 90% transmission

Courtesy of Sasha Aleksandrov 690 kW

620 kW

760 kW

Tra

nsm

issio

n (

%)

Historical power scan

RFQ RF Power

575 kW

90% transmission

14 1.4 MW

Getting the most out of a wounded RFQ

(Courtesy A. Shishlo)

• Running at higher RFQ power gives more current…– But we are significantly below the expected transmission

– Running at 600+ kW is not always possible (Champion)

– New RFQ is a key step in path to reliable 1.4 MW operation

old set-

point

Set-point for 1.4

MW operation, not

always attainableRF

Q O

utp

ut

Curr

ent

(a.u

.)

Normal output should be near saturation and close to

90% transmission

Transmission typically 65-75% (Stockli)

15 1.4 MW

Keys for Reduced Chopping Fraction

(courtesy R. Saethre)

• Fast, reliable clean single stage chopping (LEBT)

• Clean up Ring extraction kicker jitter

Beam chopping circa 2009

slower

slow

After thermal isolation of trigger

electronics

Building

temperature2 days

Extraction-kicker timing drift

16 1.4 MW

Beam Current: Better Chopping

~20 % gap

< 100 ns rise time

Time (us)

Curr

ent

(AU

)

• Chopping quality for 1.4 MW operation

– Smaller gaps than previously used

– High quality LEBT chopping

Ion source waveform

1 ms

17 1.4 MW

1.4 MW: The Final Assault

• Improved chopping covered up other deficiencies

• We need to provide margin in beam energy, current and pulse length to permit reliable, steady 1.4 MW operation

1.4 MW

Design

1.08 MW

Operation

(March 2014)

1.4 MW

Operation

(June 2014)

Energy (GeV) 1.0 0.94 0.94

Rep rate (Hz) 60 60 60

Macro-pulse length (ms) 1.0 0.87 0.97

RFQ output beam current

(mA)

38 32 35

“un-chopped” fraction 0.68 0.72 0.78

18 1.4 MW

2013 AAC Recommendations

• 30. Establish an accelerator operations and development strategy based on beam tests that can be safely performed during the restrictions on operational power, followed by exploration of high power limits as soon as a sufficient spares queue is established.

• 31. Retain flexibility to respond to development outcomes by adjusting to new points in (E, I, L) space if the primary plan does not pan out.

• 32. Socialize the above strategy with the neutron user community.

– Have explored 1.4 MW operation space

– Power increases / decreases were communicated to users

19 1.4 MW

We Need Margin for Reliable 1.4 MW

Operation

• We can run 1.4 MW “when the stars are aligned”

• Areas that will provide “power margin”

– Spare RFQ needs testing with beam: 15-20% increase in transmission (Champion, Aleksandrov)

– Smart Chopping: 5-10% (Plum)

– Beam energy: plasma processing: 7% increase in beam energy (Kim/Doleans)

– HVCM (modulator) development: ~5% from pulse flattening (Anderson)

• Some additional areas for attention

– Injection area: Foil changer, foil holders, electron catcher (Plum)

– Targets (Abercrombie, Galambos)

20 1.4 MW

Smart Chopping

• Implementing chopper controller changes this summer

– 10% increase in “average un-chopped” fraction may be possible

1 turn

Relatively large un-chopped flattop most of injection

Longitudinal “tricks” to recover big gap at extraction time

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 200 400 600 800 1000 1200

ChoppingFrac

on

Time(ms)

GeneralizedRampedChoppingPa ern

Ramp-

up

Flat-top

Ramp-down

Spin-cycle

New features

21 1.4 MW

Beam Loss / Machine Activation at ~1.4 MW

• Linac beam loss

– Compare beam loss along the SCL for different powers

– Track historical activation trend

• Average residual activation along the SCL at 30 cm

• Ring beam loss

– Compare beam loss at injection (dominate loss) for different powers

– Track historical activation of injection region

• Hottest spot down-stream of foil, at 30cm

22 1.4 MW

Superconducting Linac Beam Loss History

• Big drop in losses with focusing strength reduction in early 2009

• Modest benefit since

BLMs along the SCL

23 1.4 MW

SC Linac Activation: Not Horrible

(Courtesy C. Peters)

• Fairly steady activation level since 2010

24 1.4 MW

0

10

20

30

40

50

60

70

80

90

100

Ring_Diag:BLM_A11c

Ring_Diag:BLM_A13b

Ring_Diag:BLM_B04

Ring_Diag:BLM_B07

Ring_Diag:BLM_B09c

Ring_Diag:BLM_BMov02

Ring_Diag:BLM_C01

Ring_Diag:BLM_C05

Ring_Diag:BLM_C08

Ring_Diag:BLM_C11b

Ring_Diag:BLM_D02

Ring_Diag:BLM_DMov01

Ring_Diag:BLM_D09

Ring_Diag:BLM_D11d

Ring_Diag:BLM_D13

Ring_Diag:BLM_A03

Ring_Diag:BLM_A06

Ring_Diag:BLM_A11a

RingB

eam

Loss(Rad

/C)

Dec.2008,650kW

Sept.2009,1MW

June2014,1.4MW

Ring Beam Loss History

• Ring loss not getting worse – a bit of improvement

injection area

BLMs along the Ring

collimation

extraction

25 1.4 MW

Ring Injection Activation (Peak)

(Courtesy C. Peters)

• No obvious jump in activation downstream from the foil

26 1.4 MW

Summary

• SNS was designed to operate at 1.4 MW

– 1.4 MW was achieved, albeit not as designed

– Minimal operational margin though

• Margin is possible with

– Proper RFQ behavior (new RFQ)

– Smart chopping

– Plasma processing

– Modulator flattop