ALICE CommissioningPart II : InjectorYuri Saveliev

Seminar on 14-15/07/2008

• Gun to Booster• Booster to FCUP-01• The rest of the Injector

GUN – to - BOOSTERsetting

Gun to Booster

BOO

STER

GU

N

SOL-01

H&V-01

H&V-06BPM-01

BUNCHERYAG-01

SOL-02

H&V-02 BPM-02SlitVertical

Aims:1. Setting Voltage, bunch charge, PRF,

Train Length2. Setting correct beam size: ~7-9mm FWHM

at YAG-013. Centre the beam at the entrance to booster with beam ~parallel to axis4. Buncher coarse setting - set zero-crossing phase (but we will not know yet if it is bunching or debunching phase) - set prescribed buncher RF power (but keep buncher OFF if the phase is not known)

Notes: a) we can and should use BPMs in the Injector !!!b) because of limited number of diagnostics, we must rely on gun beamline settings determined earlier during gun commissioning and the model (e.g. a new SOL-01 scan at nominal Q is required).

Setting SOL-01 and SOL-02

0

5

10

15

20

300 320 340 360 380 400

SQRT (XY)FWHM (Astra)

SQ

RT

(X

Y),

mm

B1, G

SOL-01 scanBeam size (FWHM) on YAG "A"Q = 54pC (#712)

•SOL-01 scan at “commissioning” Q (=80pC ?)note: the position of the waist is OK but notabsolute values

•Model: B1=330G (I=3.88A)on YAG-01: FWHM expected ~7-9mm (@ 80pC)

• “rule-of-thumb” : Find B1 at which the beam size onYAG -01 is minimal and subtract ~10%

Actual SOL-02 setting is very much open question• model: B2=220G (I=2.6A)• waist position is not a good model/reality match • SOL-02 optimisation is a subject for an injector fine tuning

0

1

2

3

4

5

6

7

200 220 240 260 280 300 320

SQRT (XY)FWHM (Astra)

SQ

RT

(X

Y),

mm

B2, G

SOL-02 scanBeam size (FWHM) on YAG "B"Q = 54pC (#712) B1 = -348G

Steering

1) Steer the beam to the centre of the BPM-01 use HVCOR-01 only (HVCOR-06 still set to zero)

2) Steer the beam to the centre of the YAG-01 using HVCOR-06 only 3) Steer the beam to the centre of BPM-02 (HVCOR-02 only)

4) Steer the beam to the centre of the SOL-02 (HVCOR-06 only)vary SOL-02 & observe no beam motion on BPM-02

5) Re-center the beam on BPM-02 using HVCOR-02 only

HVCOR-01 HVCOR-06 HVCOR-02Buncher

YAG-01BPM-01 BPM-02

SOL-01 SOL-02

Check steering & beam size at buncher position• vary buncher phase / gradient and observe no motion on YAG-01 and BPM-02• increase TrainLength to ~50-100us and vary SOL-01, HVCOR-01, HVCOR-06

and watch for pressure rise

If T=350keV, and ΔT=10keV,we may expect Δφ~10o that should be noticeable

L

buncher BPM

head

headt

EE

PROCEDURE: Setting zero-crossing phase in buncher

Beam acquires (or looses) energy if not at zero-crossing

• Compare BPM and reference 1.3GHz signals• Set phase such that BPM signal phase do not move with buncher RF ON or OFF

NOTE: we would not know (yet) if the phase is zero or 180o Hence leave it for later to set with the use of booster.

E ~ 60keV

Gun Beamline Setting : Summary

• Set the “commissioning” Q not straightforward (no current sensor in sight !!!) use QE scan results for estimates :

• SOL-01 scanrequired to set SOL-01 correctly for a given Q

• Cross -calibrate BPM-01 and YAG-01 (skip if Lifetime low)

• Set SOL-01 and SOL-02

• Steer the beam to the entrance of the booster

• Set the buncher zero-crossing phase but bunching or de-bunching ? – not known yet

LaserAttQEpCQ (%)50)(

BOO

STER

GU

N

SOL-01

H&V-01

H&V-06BPM-01

BUNCHERYAG-01

SOL-02

H&V-02 BPM-02

Booster – to – FCUP01

ERLP diagnostics: Booster to Linac

LINAC

BOO

STER

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-??

FCUP-01

BPM-04H&V-04

Q-06Q-07

Q-08Q-09

DIP-3

Q-10

YAG-04

Q-11 BPM-05H&V-05

Q-12

OTR-01BPM-01H&V-01

DIP-03

Twiss parametersEmittance

Slit here

Energy spread/spectrumAbsolute energy Buncher gradient / phase setting

Bunch charge

Setting achromaticcondition (Q01-Q05)

Twiss parametersEnergy spread

Setting achromaticcondition (Q10, Q12)

Q-01 Q-03Q-02 Q-04

YAG-02 YAG-03

ERLP Linac

Coarse cresting of the booster cavities

Based on the fact that the beam loading will affect the LLRF signalsExample: 10pC, 8MeV PRF ~ 6.5kW

Principle: the cavity is crested if RF power demand is maximal reflected power is minimal

Exact procedure to be developed by the RF group

Alternative Coarse cresting of the booster cavities

t

/2

At =0 and the beam shoulddisappear from the screen or the BPM downstream of the booster.The correct phase is in the middle between the two.

(A bit dodgy because of phase slippage etc, but worth trying)

Fine cresting of the booster cavities

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06 With the use of “DIP-01 / YAG-05” energy spectrometer

When the cavity is near on crest :

Δx is a minimal change in the beam image horizontal position that can be detected.

Assuming D~1m and Δx~0.5mm,the cavities could be crested with the accuracy of Δφ=±2°.

We need either a V-slit in YAG-03 or minimise at YAG-05 : ED Exx

Principle: vary cavity phases ; set those providing MAX beam energyalso, the image width should be minimal on YAG-05 (MIN energy spread)

Note: that is how ASTRA interprets “crest”

Booster cavities : setting correct phases

Cavity 1 = +10o

Cavity 2 = -10oCAVITY 1

Phaseshifter

CAVITY 2

Phaseshifter

~10keV~100keV ~ 20keV

Total bunch length (@ 10%) ~ 20ps ~ 10o E ~ 30keV

To set +10o : shift the phase such that the delay to cavity is DECREASED by 100

Energy spectrum may help to set Cavity 2 but not Cavity 1(any other ideas ?)

Hence: must know the way how the phase shifters change the delay time

Console phase shifters need calibration in terms of the signs of delays !!!

Setting beam on axis of the booster

Use RF focusing properties in the linac: beam centroid steers if not on axis of the cavity.

BPM-02

Q-01

YAG-02

H&V-03

Principle:

vary Cavity 1 and Cavity2 phases by +/- 30o

and observe no beam motion on YAG or BPM

(focusing / defocusing only !)

This method may not be that effective for Cavity 2 because f ~ 3

How ?

•vary HVCOR-02 and observe beam motion while varying phases•note x at a given - getting smaller ?•repeat until you get fed up with this

Buncher : correct zero-crossing phase

t

head

bunching debunching

After booster, the energy spread is dominated by a) bunch lengthb) booster phase

“Bunching” phase must be set.

cos65dt

dE[keV, ps]

(8 MeV, near on crest)

If we set the booster at 80o , we expect E~300keV with buncher OFFand E ~ 70keV with optimal buncher setting

Easy to find correct =0 phase and set “optimal” buncher gradient (“optimal” gradient should be set when booster cavities are set to nominal phases

Optimal buncher gradient = minimal energy spread after booster (i.e minimal bunch length)

Bunch charge - FCUP-01Emittance (Quad scan) - exact procedure to be developedEmittance (slit) - straightforward (slit in YAG-02 and YAG-03)Twiss parameters, beam size and profile - exact procedure to be developedEnergy spread and profile - DIP-01 / YAG-05Mean beam energy - DIP-01 / YAG-05(dispersion at YAG-05) - vary booster gradientBunch length - zero-crossing method

Measurements after setting booster straight

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06

Perhaps, we should forget the bunch length measurements until we achieve an energy recovery (time consuming task)

On beam energy measurements: effect of offsets and angles

Our E-measurement layout is quite similar to that at (old) TTF Manual

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06

X1X2

X1 X2 dE/E

0 5mm 0.7%-5mm 5mm 1.2%5mm 5mm 0.2%

Perhaps, even without trying too hard, we can get better than 0.5% accuracy inenergy measurements

The same applies to DIP-01 (ARC1) ….

Bunch length measurement: theory Use zero-crossing method.

Czxx 0

t

t

cavity 1 cavity 2

Czx

010

210

2

E

D

dz

dE

E

DECCC

E2

zx CC 10

zx CC 10

(wide image)

(narrow image)

02Cxx

z

02Cxx

z

(C1 >C0)

(C1 <C0)

E2 – cavity 2 is exactly on crest

Bunch length measurement

With existing design (i.e. model) – not trivial

Assume (from the model):After Cavity 1: 4z =7mm; E0 =4.0MeV; D=1m; (dE/dz)1 =25MeV/m; 4E = 160keV

Assume also quite modest E2 = 1.0MeV

C1 = 6.0 4x = 41mm (!!)C0 = 6.8 4x = 46mm (!!)x (wide image) =90mm (!!!!!!)x (narrow image) =5mm

YAG-05 : 30mm diameter

Reduction in Dx to ~0.25m needed (adjust quad Q-05)

New Injector design is expected to produce much lower total energy spread after the booster – hence we’ll be fine !

Injector setup : Summary

Booster-to-FCUP-01

•Thread the beam through booster (coarse)•Crest both cavities (coarse)

- using LLRF signals- use lower Q (10-20pC) initially

Optimise SOL-02 setting beam size and divergence (YAG-02)emittance

•Set the beam on axis of the booster•Thread the beam to FCUP-01 (coarse)•Set correct Q and buncher zero-crossing phase and gradient•Crest booster cavities (fine) and set correct phases•Check electron energy and adjust cavities gradients if needed

re-adjustment of everything starting with SOL-01 may be needed•Set Q-01 to Q-04•Measure baseline beam parameters

emittance, energy spread, but not bunch length at the moment•Calibrate BPM-01 and BPM-02 against Q (procedure to develop by RF group)

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06

The restof

the Injector

Q-01 Linac

Dispersion cancellation (Injector, DIP-01 / DIP-02)

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06Q-07

Q-08

ARC 2

ST4

Principle: vary booster gradient by 1-3% observe no beam motion on BPM-04if it moves – adjust Q-05

ensure beam centring in Q-05 (it is needed to ensure accuracy but …)

Note: Dx=0.01m x~0.3mm at E/E=3%

Q-01

YAG-02 Q-02

BPM-03

H&V-03 Q-03

Q-04

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06

FCUP-01

Q-06Q-07

Q-08Q-09

DIP-3

Q-10

YAG-04

Q-11 BPM-05H&V-05

Q-12

ST1

ARC 2

ST4

OTR-01Q-01 Q-02 Q-03 Q-04 Q-05

Dispersion cancellation (Injector, dog-leg)

Main points on setting the injector dog-leg

Make dispersion Dx = 0 at Q-11if Q-10 and Q-12 are identical and symmetric and of correct setting, this should be achieved automatically

If the beam is at an angle when emerging from DIP-03:this does not affect the quads settings

If the beam is offset after DIP-03:quads should be adjusted slightly, e.g. offset = 2mm ~0.3% in quads field adjustment

Setting the ERLP injector dog-leg needs a bit more elaborate procedure

Q-10 Q-11 Q-12BPM-05

BPM-01(ST1)

E0

E

Q-10: too strong

Setting Q-10 (to get Dx=0 at Q-11) and Q-12 (to cancel dispersion)

•Centre the beam at Q-11 (if not done, the beam will move even if D = 0)•Change the booster gradient by 1-3% and fix it there•Wobble Q-11 and observe BPM-05 and BPM-01 (ST1)

if beam moves – adjust Q-10 and try again

now set Q-12 in a regular way …

•Vary booster gradient 1-3% and observe BPM-01 (ST1)adjust Q-12 until beam does not move on BPM-01

Useful formulae: quads related

E

dE

f

xLxQ

0

E

dEDx xD

g

dg

f

xLxg

0

dr

dBg

klf

1

x0

L

fdx

Example: centring in quads

l=0.15m; k=8m-2; 35MeV; L=5m; dg/g=0.1

if dx=0.1mm (screen or BPM resolution) then:

minimal x0 to catch = 0.2mm

Injector: measurements

• Twiss parameters, beam size and profile at the entrance to linacexpected ~3-5m and ~0beam size ~ 3-5mm FWHM and round

Skip other measurements until energy recovery is achieved

•Emittance measurement at the entrance to linac•Energy spread and profile at the entrance to linac •Check R56 in the Injector line

use time-of-arrival detection system on BPM-01 (ST1)

Note : OTR-01 (ST1) has a hole of 15mm diameter at the centrehence you need to steer the beam off-centre to be able to see it !!

The rest of the Injector : Summary

•Set DIP-01 and DIP-2 (dispersion suppression)

•Thread beam through dog-leg section (coarse)

•Set dog-leg section (fine); dispersion suppression

•Match the beam to main linacperhaps beam size and position only

•Beam measurements probably, need none at the energy recovery stage

YAG-03

DIP-01

Q-05

DIP-02

YAG-05

FCUP-01

BPM-04H&V-04

Q-06Q-07

Q-08

ARC 2

ST4

FCUP-01

Q-06Q-07

Q-08Q-09

DIP-3

Q-10

YAG-04

Q-11 BPM-05H&V-05

Q-12

INJECTOR ST1

ARC 2

ST4

OTR-01Q-01 Q-02 Q-03 Q-04 Q-05