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PS-RF for LHC beams and what is new (protons/ions). H. Damerau, S. Hancock Acknowledgments: G. Metral. 53. BE/OP Shutdown Courses 2012. 25 January 2012. Outline. Introduction LHC multi-bunch beams in the PS Proton beams

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slide2

PS-RF for LHC beams and

what is new (protons/ions)

H. Damerau, S. Hancock

Acknowledgments:

G. Metral

53

BE/OP Shutdown Courses 2012

25 January 2012

slide3

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide5

Proton and ion beams for LHC

For protons: M. Benedikt, LHC-OP-ES-0002 rev. 1.0, edms.cern.ch/document/487892/

p+ beam

# bunches

el [eVs]

Intensity per bunch

LHC25ns

12 to 72

0.35

2 · 1010 to 1.3 · 1011 ppb

LHC50ns

12 to 36

2 · 1010 to 1.7 · 1011 ppb

0.35

  • LHC50ns
    • Main physics beam in 2011, most probably also in 2012
  • LHC25ns
    • Injected into LHC in 2011, extensive tests and scrubbing (?) in 2012
  • LHC100ns  new production scheme in 2012
    • Low intensity proton beam for proton-ion collisions in LHC

Pb54+

# bunches/spacing

el [eVs]

Intensity per bunch

Early

1

  • 10.4

6.5 · 109 charges/bunch

Intermediate

2/200 ns

Up to 1.3 · 1010 charges/b.

10.4

Nominal

4/100 ns

6.5 · 109 charges/bunch

10.4

slide6

The LHC25ns cycle in the PS

gtr

Eject 72 bunches

Inject 4+2 bunches

(sketched)

Low-energy BUs

h = 21

h = 7

High-energy BU

h = 84

Triple splitting after 2nd injection

Split in four at flat top energy

2nd injection

inj2allb.dat

foursplitb12.dat

1.4 GeV

26 GeV/c

→ Each bunch from the Booster divided by 12 → 6 × 3 × 2 × 2 = 72

slide7

The LHC50ns cycle in the PS

Eject 36 bunches

Inject 4+2 bunches

gtr

Low-energy BUs

h = 21

h = 7

h = 84

Triple splitting after 1st injection

Split in two at flat top energy

2ndinjection

inj2allb.dat

twosplitb12.dat

1.4 GeV

26 GeV/c

→ Each bunch from the Booster divided by 6 → 6 × 3 × 2 = 36

slide8

Problems? Need tools

Proton Synchrotrons

C P S

http://cdsweb.cern.ch/record/1398557/files/ATS%20104%20perf.pdf

  • OASIS, Tomoscope, Bunch shape measurement (BSM)...
  • Use Tomoscope or OASIS reference files whenever possible!
slide9

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide10

The first bunch from the booster must arrive 250 ns after the common rising edge of the RF trains

First bunch in the PS: protons and ions

Local video display

With ions, only the RF trains are visible

2. Receive bunch correctly phased, 250 ns after

1. Send RF trains (h = 1, 4, 8) to PSB for phase positioning

Convention for PSB → PS transfer: ‘250 ns rule’

  • Adjust BA3.PSYNCOFFSET such that this rule is respected
  • Bucket must then be at the correct phase with respect to the bunch (local)
slide11

Injection oscillations

  • To minimize the glitch when switching to beam signals, check injection oscillations with loops closing after 2 ms

1st injection

1st injection

2nd inj.

3

4

2

1

3

4

2

1

3

4

inj2osc.dat

inj1osc.dat

  • Ring 3 of 1st injection: no or only small correction should be required
  • Correct oscillations with PSB synchronization offset BAn.PSYNCOFFSET
slide12

Second injection

Adjust DR

EXTFREQPSB/7

→ Make frev (closed loop, 2nd inj.) the same as frev at first inj.

slide13

After transfer

Observe bunches after injection into the PS with the BSM:

  • Bunches must have equal intensity as seen by the wall-current monitor in the PS
  • Transfer losses should be negligible at the same time
slide14

Longitudinal emittance control

Why bother about longitudinal emittance?

  • 1.3 eVs is required for triple splitting (LHC50/LHC25)
  • During acceleration el/Nbunch > 1.4 eVs/5.2 · 1011 ppb for stability
  • Stringent specification at PS extraction of el = 0.35 eVs/bunch

Prepare splitting flat bottom

Stability gtr or final el/bunch

Stability and final el/bunch

(LHC25 only)

slide15

Emittance budget of the LHC beam variants

Tomoscope: Cxxxbn.dat

LHC25ns LHC50nsLHC75 LHC100 LHC150

Injection, h = 7 1.1 eVs 1.0 eVs

After 1st blow-up 1.3 eVs 1.3 eVs

Splitting on flat bottom triple triple

After splitting 0.45 eVs0.45 eVs

After 2nd blow-up 0.65 eVs0.65 eVs

Acceleration h = 21 h= 21

After 3rd blow-up 1.3 eVsno blow-up

Splitting on flat top quadruple double

Final emittance per bunch 0.35 eVs0.35 eVs

Total emittance increase +280 % +100 %

Obsolete

  • Most of the long. emittance increase is applied via blow-ups
  • Small contribution by each splitting (only few percent)
slide16

Longitudinal emittance along the cycle

el per bunch

LHC25

gtr

Arrival flat-top

High-energy BU

Triple split

Quad split

Low-energy BUs

el per bunch at extraction

C1395b4.dat

C1515b12.dat

C2205b12.dat

Triple split

Transition

Stability, final el

→ Wrong el may cause all kind of funny effects later in the cycle!

slide17

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide18

Triple bunch-splitting (LHC25, LHC50)

  • Split bunches in three similar parts (h7 → h21)
  • Three RF harmonics at the same time
    • Control two relative phases to level of ~ 2º
    • Control one relative RF amplitude to level of better than ~ 5%
slide19

Phase control for triple splitting

PA.GSRPB

PA.GSRPC

CERN-ATS-Note-2011-104 PERF

…or just use the amplitude knobs

  • Tuning Group A (C36, C46):
    • h7 → h21, phase reference,PA.GSRPA zero everywhere
  • Tuning Group B (C51, C56, C66, C76, C81, C91):
    • h21 only, relative forward phase h7/h21, PA.GSRPB
  • Tuning Group C (C86, C96):
    • h14 → h21 only, relative forward phase h7/h14, PA.GSRPC
slide20

Effect of phase errors during triple split

trisplitb1.dat

trisplitb1.dat

h21 phase 15º too low

h14 phase 10º too high

  • Relative phases must be controlled to well below 5°
  • Slightly intensity dependent adjustment
slide21

Centre to outer bunch symmetry

trisplitb1.dat

h14 RF voltage 10% too low

  • RF voltage on h14 defines intensity ratio in inner/outer bunches after splitting
  • Relative control and stability to the level of few percent
slide22

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide23

RF

Slow signal

Digital signal

What is a beam control?

Loop corrections

Reference magnet

B+

h·frev

B

Df

frev

B-

RF-Gen.

→ Calculate frev, open loop from bending field and multiply by h

→ Correct with beam measurements to obtain frev, closed loop

slide24

RF

Slow signal

Digital signal

Df

Df

  • Phase loop adjusts the RF phase to where the beam would like it
  • • Suppress phase transients and RF phase noise to avoid blow-up

Beam phase loop

Phase pick-up

RF cavity

Cavity phase

Beam phase

frev, closed loop

Loop correction

Synchronous phase, fs

-

Move the wave!

frev, open loop

slide25

Df

Adjustment of phase measurement

Phase pick-up

RF cavity

Cavity phase

Beam phase

Df (frev) = Dfoffset + 2phfrev·Dt

  • Every phase measurement is a phase comparison between two signal
  • Cable lengths of beam and cavity return signals influence measurement

How to reference phase, Dfoffsetmeasurement and avoid cable delay, Dt?

  • Button to compensate offset
  • Beam reference: Df = 0 on flat-bottom and flat-top
  • Adjust absolute cable length
  • Not very sensitive, checked once during start-up
slide26

How to measure beam phase?

...independent from RF voltage and beam intensity

Crystal

filter

AVC

Df,Dt

Beam/ cavity ret.

To phase detector

Various harmonic components, amplitude not constant

hfrev appears at fIF

fIF is only component

PA.DPC10PA.DPC10ACCPA.DDC20RETPA.DDC40RET

LO:hfrev+fIF

  • Absolute length equalization normally only after hardware changes
  • BUT: Detection electronics slightly dependent upon beam intensity
  • Remove remaining offset on flat-bottom and -top with offset knob
slide27

Phase loop offset during acceleration

What is the phase reference for the phase loop?

→ Remote button to adjust the offset of the phase measurement!

OASIS global ‘LHC50ns RF adjustments’

  • One button for each phase loop or harmonic number
    • PA.DPC10: h7 phase loops offset
    • PA.DPC10ACC: h21 (LHC50, LHC25)
slide28

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide29

Synchronization: in two steps

1. Coarse synchronization, h1: Move the whole batch

Reference given by frev SPS

  • Batch at the correct position

2. Fine synchronization, h84: Put bunch to bucket centre

  • Improve precision
  • Phase error of 1º at h = 1
  • corresponds to 84º at h = 84 (40 MHz)
  • corresponds to 420º at h = 420 (200 MHz)

More than one SPS bucket

slide30

Coarse synchronization

  • Coarse synchronization before RF manipulations on flat-top
  • Set radial steering to adjust beam frequency  Smooth lock!

OASIS global ‘LHC25ns RF adjustments’

tbeat

  • • Time constraint:
    • Synchronization loop must lock before voltage program of 13.3/20 MHz cavity starts

• Fine synchronization later, before extraction

slide31

RF

Slow signal

Digital signal

Df

How to change frev? Radial loop

Beam

Hybrid

D

S

D/S

frev, closed loop

  • Normally: Keep beam in the centre of the radial loop pick-ups
  • Move beam radially by adding perturbation function PA.GSRPOS
  • Change revolution frequency
  • Change beating between closed loop frev and fRF,SPS/420

Loop correction

-

frev, open loop

Steering: PA.GSRPOS

slide32

LHC50ns bunch splitting at flat-top energy

  • Long. emittance: ~ 0.65 eVs
  • Bucket area (h21): ~ 3.2 eVs
  • Synchrotron freq.: 120 Hz
  • Splitting duration: 118 ms

twosplitb12.dat

  • RF harmonics (h21 → h42) the same as for a 25 ns beam, but half longitudinal emittance
  • Sensitive to RF phases → prone to drift → PA.DPC20
slide33

Rebucketingor splitting?

  • LHC25 and LHC50 (ns) seem to be very similar at first sight: Just turn the last bunch splitting (h42 → h84) into a rebucketing

h = 84

h = 84

LHC25

LHC50

h = 42

h = 42

  • Splitting and rebucketingvery similar manipulations
  • Relative RF phase determines what happens (180º)
  • Rebucketingis much more robust to phase errors
slide34

Adjustment of rebucketing

1. Change PA.DPC40 by ~ 180º and search phase where bunches jump from one side to the other

rebucketing.dat

rebucketing.dat

2. Change PA.DPC40 by exactly 180º to go back to stable phase

slide35

Well adjusted rebucketing

Switching of RF trains

PAX.SSWTDISTSPS disabled

rebucketing.dat

rebucketing.dat

  • Rebucketingis a very robust process
  • No problem even with a forward phase error of 20º on PA.DPC40
  • There should be not much to see…
slide36

Fine synchronization

h84LOC

Delay

Df

fRF SPS, 200 MHz (h = 420)

Multi- plier × 4

h84REF

Divider by 5

Internal h = 21, syn- chronous to cavity RF

Fine sync. phase

PA.DDCSYNCF

Reset

PA.DCNBEJ

Df

Reset

Divider by 21 (MHS)

Divider by 84

h1LOC

h1REF

Coarse sync. phase

• Coarse (PA.PSYNCDISC-LHCC) and fine (PA.PSYNCDISC-LHCF) synchronisation phase discriminators compare the same signals, but:

• Fine synchronisation 84 times more sensitive (h = 84/h = 1)

  • New after start-up 2011: Remote delay PA.DDCSYNCF to align synchros
slide37

Phase discriminators on the flat top

  • The harmonic number for the phase loop must follow the harmonics of the cavities active

Zero at switch-over

DPC10ACC

DDC20RET

OASIS global ‘LHC50ns RF adjustments’

DDC40RET

DDCSYNCF

  • The offset of each phase loop harmonic must be compensated:
    • PA.DPC10ACC: h21 phase loop
    • PA.DDC20RET: h42 phase loop
    • PA.DDC40RET: h84 phase loop (only LHC25)

→ No h = 84 phase loop with LHC50ns

→ Rebucketing directly to fRF,SPS divided by 5

slide38

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide39

Bunch rotation in two steps:

1. 290 ms before extraction:

h = 84 (40 Mhz): 100 → 300 kV

2. 90 ms before extraction:

h = 168 (80 Mhz): 0 → 600 kV

For the second step: Bunches must be shorter than 12.5 ns (full length)!

R. Garoby, CERN PS/RF/Note 93-17

Bunch rotation for LHC-type beams

h = 168

h = 84

80 MHz phase controlled by PA. DPC80

slide40

The first bunch from the must be aligned within ± 2.5 ns with respect to the rising edge of the frev marker from the SPS

Synchronization check and ejection bucket

frev marker

PS ejection video

pulse switch

  • from SPS
  • RF simulation

Beam signal from wall current monitor

Move beam with PA.DCNBEJ

  • The bucket number PA.DCNBEJ is integer by definition
  • 2012: New fine delay to correct extracted bunch position -2.5...2.5 ns
slide41

What is finally delivered

  • 36 bunches with up to 1.7 · 1011 ppb →6.1 · 1012ppp
  • Separate PPM users to switch between 12/36 bunches
  • 50 ns beam already well above nominal intensity
slide42

2012: Study alternative production schemes

h2+1PSB → h9PS and h = 9 → 10 → 20 → 21

Pure h = 21

Voltage programs:

C. Carli, Chamonix 2011

h = 21

h = 9

h = 20

h = 10

Pure h = 9

OR

Becoming operational in 2012 for LHC100ns for p-Pb collisions and CNGS, small emittance LHC beam

R. Garoby, 2011

h = 7→ 8 → 9 → 10 → 11 → 12 → 13 → 14 → 7 → 21

 Initial MDs in 2012

slide43

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide44

Injecting and accelerating lead ions

  • PS with ions is like TGV at 10 km/h:
  • You don’t feel that it moves
  • The PS RF does not feel the beam
  • RF wise a textbook accelerator!

 Only few remote adjustments needed for the ion beam control

slide45

Lead ion Pb54+ beam variants for LHC

MSWG 04/12/2009

VLEIR=2.8kV, VPS=15kV

VLEIR=2.8kV, VPS=25kV

  • New in 2011: Intermediate beam
  • Turn bunch splitting of nominal beam into rebucketing
  • Twice more intensity per bunch
  • No margin for long. emittance in PS

→ Luminosity production beam in LHC of 2011 run. Also in 2012?

slide46

The early ion cycle in the PS

Eject 2 bunches spaced 200 ns

Inject 1 bunch

h = 169

h = 16

gtr

h = 16

Intermediate flat-top

No manipulation

Rebucket

Single bunch injected from LEIR

Accelerate from flat-bottom to flat-top on h = 16 (2.8  7.6 MHz)

Synchronized (h = 1/ h = 9)

Rebucketed to h = 169 for adia-batic bunch shortening to < 4 ns

Extraction

rebucketing.dat

1.4 GeV

26 GeV/c

→Single bunch from LEIR results in one bunch at ejection

slide47

The nominal ion cycle in the PS

Eject 4 bunches spaced 100 ns

Inject 2 bunches

h = 169

h = 21

gtr

h = 16

Intermediate flat-top

Batch expansion

Rebucket

rebucketing.dat

bexpand.dat

0.38 GeV/u

5.9 GeV/u

→ Each bunch from LEIR divided by 2 → 2× 2 = 4

slide48

The intermediate ion cycle in the PS

Eject 2 bunches spaced 200 ns

Inject 2 bunches

h = 169

h = 21

gtr

h = 16

Intermediate flat-top

Batch expansion

Rebucket

rebucketing.dat

bexpand.dat

0.38 GeV/u

5.9 GeV/u

→ Each bunch from LEIR results in one bunch at ejection

slide49

199.81

Main challenges with Pb54+ beam

  • Low signals from due to low beam intensity, especially on the flat bottom
    • Mechanical relay to switch wall-current monitor to beam control
    • Sensitive beam phase detection
  • Huge and fast frequency swing frev,ej/frev,inj = 2.7 (1.09 for protons)
    • Signal path length of beam and (simulated) cavity return well equilibrated
    • Compensate frequency dependent delay t(fRF) of power amplifiers
  • Sophisticated RF manipulation for “Intermediate” and “Nominal” beams
    • Inverse batch compression (cf., AD beam)
    • Bunch splitting (cf., proton LHC beams)
    • Four different phase loop harmonics: hPL = 16, 12, 21, 169
    • Delicate rebucketing from h = 16 or 21 to h = 169
slide50

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide51

Manipulations on intermediate flat-top

  • Batch expansion + splitting + batch expansion
  • Harmonic number h = 16  14 12 24 21

bexpand.dat

h24

h21

h16

h14

h12

MSWG 04/12/2009

h = 12 & h = 24 in counter-phase  “nominal” beam, 100 ns spacing

slide52

Adjustment of ion batch expansion/splitting

  • RF phases programmed via GFAS PA.GSRPA/B/C

h = 21

h = 21

h = 21

h = 16

h = 16

h = 14

h = 12

Split phase

h = 24

h = 16

→Batch expansion steps h = 16  14  12: ideal phase settings

slide53

Manipulations on intermediate flat-top

  • Batch expansion + rebucketing + batch expansion
  • Harmonic number h = 16  14 12 24 21

Not PPM compatible with “nominal”

bexpand.dat

h24

h21

h16

h14

h12

h = 12 & h = 24 in phase  “intermediate” beam, 200 ns spacing

slide54

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide55

Rebucketingh = 16/21  h = 169

  • Bunch centres h = 21 and h =169 not aligned as 169/21 = 8.0476
  • Change PA.DPC80 by ~ 180
  • Adjust PA.DPC80 to observe two bunches split mirror-image asymmetric
  • Flip PA.DPC80 back by 180
  • Check extraction bucket and adjust PA.DCNBEJ

rebucketing.dat

MSWG 04/12/2009

slide56

Coarse and fine synchronization

Df

Synchr. h = 9 DDS (MHS)

fRF SPS, 200 MHz (h = 423)

h9LOC

h9REF

Divider by 47

Internal h = 16 or 21, syn- chronous to cavity RF

Fine sync.

Reset

Align delay

PA.DCNBEJ

Df

Reset

Divider by 16 or 21 (MHS)

Divider by 9

h1LOC

h1REF

Same set-up as for protons

Coarse sync.

Only parameters to adjust:

  • Radial placing for coarse beating  PA.GSRPOS
  • Ejection bucket number  with PA.DCNBEJ
slide57

Phase and synchro loop signals on flat-top

DR

Dfh=169

Dfh=16/21

coarse sync.

fine sync.

  • All loop offsets must be well compensated:
  • Rebucketing sensitive due to large harmonic ratio up to 169/16 = 10.56
  • Fine synchronization must lock simultaneously

MSWG 06/12/2010

slide58

Outline

  • Introduction
    • LHC multi-bunch beams in the PS
  • Proton beams
    • Flat-bottom and acceleration: injection, longitudinal emittance control, triple splitting
    • Flat-top: synchronization, splitting and bunch rotation
  • Lead ion beams
    • Acceleration + manipulations on intermediate flat-top
    • Rebucketing, synchronization, extraction
  • Summary
slide59

What is finally delivered

“Early”

In front of 1st bunch:

Reflection from PU!

  • One bunch, 4s < 4 ns
  • Satellites may occur during re-bucketing + synchronization
  • No remote control to adjust (yet)

2-3%

slide60

What is finally delivered

“Intermediate”

“Nominal”

200 ns

100 ns

→Intermediate beam has almost twice the intensity per bunch

→ Caveat: No longitudinal emittance margin  4s slightly > 4 ns

slide61

Summary

  • Proton beams
    • Tuning of LHC proton beams 25 and 50 ns has become routine operation
    • Few changes to beam control with respect to 2010
    • New beam generation schemes to be tested in 2012
  • Lead ion beams
    • Beam control operationally delivering “early”, “intermediate” and “nominal beams”
    • Only few remote adjustments needed thanks to low beam intensity
slide63

Adapt for intensity change in two minutes…

1. Check phase loops up to arrival on flat-top (DPC10, DPC10ACC)

DPC10

DPC10ACC

2. Check splitting symmetries DPC20/40 and phase loop offsets

Zero at switch-over

DPC10ACC

Sensitive!

DDC20RET

DDC40RET

DDCSYNCF

Smooth lock

→ Fine synchronization discriminator is an extremely sensitive indicator if all loops on the flat-top are happy

slide64

What is going wrong?

DPC20: -3º

DPC40: -3º

  • The intensity FFT is an extremely sensitive tool to detect and correct small asymmetries of injection and splittings