Energy StabilityUpdate

Tim Maxwell on behalf of the Stability Performance Program:F.-J. Decker, Andy Benwell, William Colocho, Anatoly Krasnykh, Jeff de Lamare, Jim Lewandowski,Minh Nguyen, Phil Seward, John Sheppard, Mike Stanek, Tao Tang, Jim Turner, Lanfa Wang, …

January 22nd, 2015

MD Physics Meeting

2

Outline

• Jitter evolution• Theory• Application to LCLS (L1S sensitivity & L2/L3 setup)

• Recent stabilization activities• L1S AIP upgrade recovery• Soft x-ray jitter reduction (BC2 E)• Impact on (H/S)XRSS

• In development• Auto-ranging of thyratrons• Auto-diagnosis of known station issues• Auto-suggest linac complement• Improved RF loads

3

Jitter Evolution

We know the phase space ellipse• Each point is an electron in one bunch

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Jitter Evolution

But also note the centroid (or jitter) ellipse• The same matrix math describes evolution of the time-

energy distribution of the centroids of many shots• Each offset point is the centroid of a different bunch*

* Not the same asdist. of each bunch

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Coordinates

• Do math using covariance matrix

• Easy to relate to (measurable) rms RF jitters σt , σE andtheir correlation | ρ | < 1

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Jitter Evolution

• We know linear transformations M

• For some coordinates X / Y (e.g.: z / δ), if

• …then new ellipse σ' around new mean vector μ' :

• Abs. E coordinate is calculated, can normalize to μ

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Linear Operators

• RF accelerating structure:

- R65 (elsewhere “h”) is the rf chirp- Shear phase space in E direction, add energy offset to mean E

• Magnetic chicane:

- Shears phase space in time

( )rfrfE fsin-µ

• Linac sections each have an intrinsic phase-amp. jitter ellipse σrf

• Seen by centroids of (frozen) beam, locally adds purely uncorrelatedenergy jitter at station:

• Phase jitter factors in if station is chirping (R65)• Increases irreducible total t-E jitter (“centroid emittance”) as• Consecutive RF stations chirp and add their jitter independently

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Primary Nonlinear Contribution: RF Jitter

66,5522

rfssee ¢+=¢

2rf,

265rf,rf,rf65

2rf,

2beam,66rf, gg

2 ttEEE RR sssrsss ++==¢

Chirp of incoming jitter + Increase of uncorr. E jitter due to station instability

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L1S jitter: critical station

• If all other sources negligible (zero), L1S contribution transforms as:

• If φL3 = 0, final jitter is:

• R56,BC1 (-0.691 ps/MeV), L2 @ 5 GeV & -32º, R65,L2 (67.2 MeV/ps)

L1XBC1L2BC2L3T MMMMMMMMσ =÷÷

ø

öççè

æ= ,

000

2L1Sbeam,,E

final s

L1Sbeam,,final

L1SBC1,56L2,65finalbeam,,L1Sbeam,,BC1,56L2,65finalbeam,, 1or1 dd ssss

EERRRR EE +=+=

L1Sbeam,,final

finalbeam,,L1Sbeam,,finalbeam,,GeV28.11or48~ dd ssss

EEE ==

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L1S jitter: critical station

• SXR: 4.7 GeV and < 0.05% jitter at the end, 235 MeV @ L1S:

• HXR: 13.6 GeV and < 0.025% jitter at the end, 235 MeV @ L1S:

%021.0

%05.07.428.11

L1Sbeam,,

finalbeam,,

L1Sbeam,,finalbeam,,

<Þ

<

=

d

d

dd

s

s

ss

%030.0

%025.06.1328.11

L1Sbeam,,

finalbeam,,

L1Sbeam,,finalbeam,,

<Þ

<

=

d

d

dd

s

s

ss

Was 0.0196% summer 2014

Not quite… need more jitter overheadfor HXR to allow for > L3 abs. jit. growth

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L1S jitter: critical station

Compute L1S jit. limits*:

* w/ L1S SLEDed, ρ = -0.35 typ.

2L1S,

265L1S,L1S,L1S65

2L1S,L1S, gg

2 ttEEE RR sssrss ++=

Goal

L1S SLEDed requires:σA,L1S < 0.04%σφ,L1S < 0.04º

Today

Run 10start

July 2014

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Low Energy Jitter Reduction

• EBC2 historically maintained at 5 GeV, regardless of EL3

• Reconfig time and collective effects primary concerns

• Compare RF phasors for EBC2 = (5 or 3) GeV, EL3 = 3.4 GeV:

220 MeV 3 GeV 3.4 GeV

5 GeV

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Low Energy Jitter Reduction

• Each station contributes uncorrelated absolute E jitter in quadrature• +Higher abs. t jit. after BC2 makes L3 jit/station larger

• Higher abs. E jit., same final abs E → Higher rel. E jit.• Quasi-linear model predicts ~40% jitter reduction

220 MeV 3 GeV 3.4 GeV

5 GeV

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L3 HXR “Decker Phasing” – Jitter ellipse evolution

2) After BC2R56 = -24.7 mm

3) L3 linear transformw/ φL3 = 0º (same)

4) L3 uncor.0.38 MeV growth*

* Competition: chirp can remove incomingcorr. E-jitter, but also increases uncor.jitter from L3

From LiTrack, φL3 = -15º should yield < 1%relative increase of proj. e-spread

1) After L2(5 GeV, ~3.5 kA)

t (ps)

ΔE(M

eV)

t (ps)

ΔE(M

eV)

t (ps)

ΔE(M

eV)

3) L3 linear transformw/ φL3 = -14.6º

(positive R65 fightsnegative BC2 chirp)

t (ps)

ΔE(M

eV)

4) L3 uncor.1.72 MeV growth*

t (ps)

ΔE(M

eV)

t (ps)

ΔE(M

eV)

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Outline

• Jitter evolution• Theory• Application to LCLS (L1S sensitivity & L2/L3 setup)

• Recent stabilization activities• L1S AIP upgrade recovery• Soft x-ray jitter reduction (BC2 E)• Impact on (H/S)XRSS

• In development• Auto-ranging of thyratrons• Auto-diagnosis of known station issues• Auto-suggest linac complement• Improved RF loads

L1S AIP Upgrade Recovery

• L1S Modulator (AIP upgrade) and Tube changed over fall ’14 down,recovered with phase jit. out of tol (> 0.04º)

• History of L1S work maintained in CATER and athttps://portal.slac.stanford.edu/sites/lclscore_public/Pages/Performance_Stability.aspx

• Restored after efforts from A. Benwell, T. Tang, M. Nguyen, …

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June 18th SXR Jitter Reduction Study

Constants: 1.5 kA, L3 Energy 4 GeV1. 32 L2 Klys., BC2 E = 5 GeV, R56 = -24.7 mm2. 22 L2 Klys., BC2 E = 3 GeV, R56 = -24.7 mm3. 22 L2 Klys., BC2 E = 3 GeV, R56 = -27.2 mm

o Calc.+ Meas.

Exp’t proposed by Lanfa from LiTrack MOGA

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SXR jitter reduction

• BC2 energy change for Efinal < 6 GeV used so far in Run 11• 16 redundant stations removed @ 540 eV (3.4 GeV)• Consistently 40% less jitter, ex: 0.12% → 0.072% @ 540 eV• No (apparent) FEL loss…

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SXR jitter reduction – beam impact

Slice energy spread by XTCAV (lasing off)

May 9, 2014 Jan 12, 2014

RMS SES = ~2.4 MeV RMS SES = ~2.4 MeV(horns cut @ BC1)

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SXR jitter reduction – beam impact

LTU EmittanceDec. 5, 2014 Jan 12, 2014

εx = 1.26 μm / εy = 1.13 μm εx = 1.74 μm / εy = 1.23 μm

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SXRSS on Jan. 12 @ 540 eV (3.4 GeV)

• Had 0.12% jitter in Dec 2014 test, now 0.078%• “Jitter reduction factor”

• F = <U>seeded,δ-cut / <U>seeded,all

• How much higher avg. brightness is w/o jitter• F = 1.66 w/i 2x FWHM seed bw

Avg. spec. in small δ window U within 2x FWHM bw

<U>seeded,δ-cut

<U>seeded,all

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SXRSS @ 540 eV

May 2014σδ = 0.11%

F = 2.02

Jan 2015σδ = 0.071%

F = 1.66

“Moving the goal post”: Impact of jitter was reduced despite tuning up a narrower “mustache” in Jan ’15

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HXRSS

• Delivering 0.025% jit. @ 8.3 keV in Run 9 w/ “L3 Decker phasing”• F ~ 1!

May 2012 @ 8.3 keV June 2014 @ 8.3 keV

σδ> 5x10-4 = σSASE σδ= 2.6x10-4 ≈ σSASE / 2

<U> = 0.15 mJ <U> = 0.33 mJ

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HXRSS

HXRSS on Jan. 14 2015 @ 5.5 keV• Noted L3 phase trick was less effective• Still some “meh” L2/L3 stations and injector still being squeezed• Avg. 0.47 mJ and 26% fluctuations in 1.2 (x2) eV BW• F = 1.17

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Outline

• Jitter evolution• Theory• Application to LCLS (L1S sensitivity & L2/L3 setup)

• Recent stabilization activities• L1S AIP upgrade recovery• Soft x-ray jitter reduction (BC2 E)• Impact on (H/S)XRSS

• In development• Auto-ranging of thyratrons• Auto-diagnosis of known station issues• Auto-suggest linac complement• Improved RF loads

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Auto-diagnosis for modulators

William created/logging PVs monitoring BV stability at timesindicating various known issues:

1

2

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1. [station]:MKBVTRIGJITT, detectBV jitt due to trigger

2. [station]:MKBVTOPJITT, beam-time BV jitter

3. [station]:MKBVTHYBACKSWING,known to multi-state if thyratronrecovery is unstable

4. [station]:[tbd], well after pulse,monitor station BV recovery

5. [station]:MKBVTSREDUCED,beam-time jitter after removingtime slot jitter

Ops Klystron Display -> Jitter Report -> TS Jitter

Thyratron instability

Tao Tang on Thyratron instability:• Self breakdown

- High gas pressure / reservoir voltage- Impact next a few pulses, much lower BV (beam drop out)- Can not start modulator

• Random recovery- Low gas pressure / reservoir voltage- Impact almost every pulse- High PFN instability

* Stations require periodic thyratron ranging to stay in “sweet spot”

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Auto-ranging thyratrons

AIP Modulators include EPICS-controllable thyratron tuning

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Auto-ranging thyratrons

William, Tao, Andy, et al, testing new control + jitter PVs to devise anauto-ranging scheme1. Short term: One-click remote ranging for PEM

2. Long term: Monitor and automate RF maintenance from MCC

Thy. res.V

Backswing jitter

Beam-time BV jitter

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Auto-suggest compliment

Read all station data, find best compliment for requested config

1. Choose the best stations2. Tune the worst a.s.a.p.

Devising clearer at-a-glancecompliment summary GUIincluding jitter & drop outs

Link directly to jitter prediction& diagnosis tools

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Improved RF Load

• One of two potential new loads in development to handleincreased RF power

• Modified all-metal SLAC design w/ fins & new coating toimprove attenuation

• Goal: Mitigate multipactoring, stabilize refl. power from load

* Image courtesy Anatoly Krasnykh

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Improved RF Load

• Sufficient performance of one test unit demonstrated• Working to improve consistency

• Anatoly looking into more local vendor, provide more control over processing

• Stress test of new load(s) under high power forthcoming

* Image courtesy Anatoly Krasnykh

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Run 11 Stability Program Goals

• Attain/maintain ρ/2 jitter (0.05% SXR, 0.25% HXR)• Demonstrate reduced E-jit impact to SS expt’s to users• Continue rollout of AIP modulators• Develop tools for automation of linac maintenance

• Auto-diagnosis, -ranging, -compliment• RoboDecker™

• Demonstration of performance enhancement from newSLAC RF loads

• Improve ESA pulse stealing transverse stability

The Stability Program meets semi-regularly at 2pm on Fridays. Contact Tim Maxwell to be notified.