Top-Up Experience at SPEAR3

Jeff Corbett Stanford Linear Accelerator Center (SLAC)

National Accelerator Laboratory

Presented at University of Melbourne

9 October, 2009

• SPEAR 3 and the injector

• Top-up requirements

• Hardware systems and modifications

• Safety systems & injected beam tracking

• Interlocks & Diagnostics

---------------------------------------• Beam lifetime rate equation • PEP-X

Contents

3GeV Injector

BTS5W, 1.6nA

E

W

N S

3GeV10nm-rad 500 mA

Booster (White Circuit)

LINAC/RF Gun

10Hz

SPEAR3 Accelerator Complex

PXPD/XAS

SAXS/PX

XAFSNEXAFS

PX

PX

XAS/TXM

ARPES

EnvironmentXAS

CoherentSingle bunch/pulse

o Rebuild SPEAR into SPEAR3 (1999-2003)

o Operated at 100mA for ~6 years (beam line optics)

o Recently increased to 200mA

o Chamber components get hot at 500ma (450kW SR, impedance)

o 500mA program suspended because of

power load transient on beam line optics

o Instead worked to top-off mode (beam decay mode, fill-on-fill)

Top ‘off’ at SPEAR3

RF system and vacuum chamber rated for 500ma

o 13 exit ports taking SR (9 Insertion Device, 4 Dipole)

o 7 ID ports presently in ‘fill-on-fill’ open shutter mode

o 4 dipole beam lines open shutter injection by end of October 2009

o Last two ID shutters fill-on-fill by June 2010

o Trickle charge 2011

Present Status

SPEAR 3 100 vs. 500 mA Fill Scenarioslifetime = 14 h @ 500 mA = 60 h @ 100 mA

0

50

100

150

200

250

300

350

400

450

500

0 4 8 12 16 20 24

time (hrs)

curr

ent

(mA

)

100mA and 500mA Operation

=12ma

=180ma

100ma

500ma

~6.5 Amp-hr

delivery time = 8 hrtfill = ~6-7 min

delivery time = 2 hrtfill = ~1.5-2 min

0

50

100

150

200

250

300

350

400

450

500

0 6 12 18 24

time (hrs)

cu

rren

t (m

A)

delivery time = 0.5 hrtfill = ~17 sec

0

50

100

150

200

250

300

350

400

450

500

0 6 12 18 24

time (hrs)

cu

rren

t (m

A)

delivery time = 1 mintfill = ~0.5 sec(or 10ms single shot)

500mA Injection Scenarios

RFB132-102

B116-101

B117control roomB118power

suppliesSLM room

B132-101

B120

B131

B130

3 GeVBooster

120 MeV linac

B140

LTB

BTS

RF HVP

S

• Guno higher currento stablize emission rateo “laser-assisted” emission

• Linaco restore 2nd klystron

(higher energy, feedback)o phase-lock linac and booster rf

• Boostero improve capture with modified latticeo improve orbit and tune monitorso develop fast turn-on mode

• BTSo eliminate vacuum windows (done)o diagnostics

• SPEARo add shielding, interlockso improve kicker responseo transverse feedback

• Beamlineso add shielding, interlockso timing

Hardware Upgrades

• Vertical Lambertson septum (booster outside ring) - operates DC, skew quadrupole added

• Three magnet bump• ~15 mm amplitude, ~12mm separation• Injection across three cells (sextupoles)• Slotted stripline kickers (DELTA, low impedance)• Transverse field dependence in K2

SPEAR3 Injection Notes

Elevation viewPlan view

Injected beam

Stored beam

Se

ptu

m w

all

Se

ptu

m w

all

With windows: ~20% beam loss No windows: ~no loss

Hardware Upgrade: BTS Windows

Huang & Safranek

Injected beam profile measurements

Turn number

Movies…

Visible diagnostic beam line

• Synchrotron oscillations measured with turn-by-turn BPMs:

• Kickers set to dump injected beam each cycle• Injection energy stable• Injection time varies over hours

– RF cable temperature

• Develop method to measure timing with stored beam

Before correction After correction

Hardware upgrade: Injection Timing and Energy

Huang, Safranek & Sebek

V

H

mS

V

H

mS

Single shot

injection kicker transient = ~10 ms

(~0.1 ms with feedback)

• Kickers can interrupt data acquisitiono What is interruption sequence?

• depends on current ripple, beam lifetime and charge/shot

• bunch train filling needs new booster RF system

o Gated data acquisition

o Tests with beam lines no complaints

o Lots of work to match kicker waveforms

Hardware upgrade: Injection Bump Closure

Huang & Safranek

downconverter schematic

Hardware Upgrade: PEP-II Bunch Current Monitor

bunch-by-bunch processor chassis

- visible APD (ASP)- x-ray APD (CLS)

downconverter chassis

A.S.Fisher

► S-band RF gun with thermionic cathode, alpha magnet, and chopper

► Most charge during the 2 μs RF pulse stopped at the chopper ► 5-6 S-band buckets pass into the linac, single booster bucket

► SPEAR3 single bunch injection, 10Hz presently ~50pC/shot

2.856 GHz (2s)

e- beam Tungstendispenser-cathode (1000 C)

1.5 cell RF gun

Hardware Upgrade: Thermionic Cathode as a Photo-Emitter

Nominal configuration

► high singe-bunch charge for top-off - reduce beam loading in linac - eliminate cathode back bombardment - eliminate chopper

2.856 GHz (~2s)

e- beam (~500ps) cold-cathode

UV or green laser

UV Green

1.5W heating

Sara Thorin/MAXLab, EPAC'08'Turning the thermionic gun into a photo injector has been very successful '

1.5 cell RF gun

Photo-emission cathode (cont’d)

Laser-driven configuration

Cu

S.Gierman

• Radiation Safety: the first hurdleo AP studies to demonstrate injected beam can not escape shielding

o Many clever scenarios (dreams and zebras)

o BL shielding sufficient? (higher average current, more bremsstrahlung)

o PPS/BCS interlock modifications

o Do users wear badges?

• Efficient injection into main ringo Injection time, charge/shot, repetition rate

The Injected Beam Safety Dilemma

Safety is complicated!

18

SPEAR3 DBA cell

Synchrotron Radiation Exit Ports

V4 MASK

V1, V2 MASKS

BPMs

H2 ABSORBER

TSPs

EDDY CURRENTBREAK

BM-2BM-2

QFCQFCBM-1BM-1

220 L/SION PUMP

150 L/S ION PUMP

TSP

V3 MASK

BELLOWS

BELLOWS

H1 ABSORBER H3 ABSORBER

TSP

BPM

BPM

BPM

ID BPM

ADDITIONAL BPM SET

220 L/S ION PUMP

84 mm

44.2 mm

34 mm

24 mm13 mm18.8 mm

ID BPM

BPM

Vacuum Chamber Construction

e- beam

photon beam

outside absorber

inside absorber

Photon Beam Exit Channel

A Closer Look…

22

Stored Beam

X-RaysInjected BeamX-Rays

Stored Beam

Injected Beam

NORMAL

X-RaysInjected BeamX-Rays

Stored Beam

Injected Beam

ACCIDENT

Stored Beam

X-RaysInjected BeamX-Rays

Injected Beam

Ratchet Wall

Fixed Mask

Top-Up with Safety Shutters Open

SAFE

23

X-Rays

Injected BeamX-Rays

Stored Beam

Injected BeamACCIDENT

•Bad steering, energy

Experimental

FloorStored Beam

Simulation is necessary!

Is this a real possibility?

•Bad magnet fields

Shield

Wall

QF QD BEND SDINSERTION DEVICE

A1 A2

Stored Beam on design orbit

Ratchet Wall

Fixed Mask I

Fixed Mask II

Comb Mask 9.1

CM

SPEAR3 Magnets BeamlineIncoming Beam

•No assumptions about initial steering

•All physical positions and angles possible

•Energy errors!

•No magnetic field

•Straight trajectories

Beamline Apertures Vacuum Chamber Radiation Masks

Safe Endpoint

Start Point

Field simulation region

SSRL Approach to Calculations

• Wide fringe fields

A.Terebilo

25

A1 Aperture

A2 Aperture

Fixed Mask

Stored Beam

Injected Beam

Ratchet Wall (2-ft Concrete)

Photon Beam Line

Forward Propagation Only

Chamber boundary

26

-3 -2.5 -2 -1.5 -1 -0.5 0-0.24

-0.22

-0.2

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08

X [m]

X' [

rad]

Phase Space at Z = Fixed Mask

Phase Space at Z = Ratchet Wall

Fixed Mask Opening

Ratchet Wall Opening

Horizontal Position (m)

Hor

izon

tal A

ngle

(ra

d)

vacuum chamber acceptance fixed mask

10 bendo

spread in angles

(far fringe field)

Trajectories in Phase Space

27

-0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

X [m]

X' [

rad]

Initial: A1 and BPM7

After BPM1

-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 0.12-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

X [m]

X' [

rad]

BPM1

After QFA2

Dipole Entrance

-0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

X [m]

X' [

rad]

Dipole Entrance

Dipole Exit

SD Exit

-3 -2.5 -2 -1.5 -1 -0.5 0-0.24

-0.22

-0.2

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08Allowed Phase Space in BL coordinates

X [m]

X' [

rad]

Z = SD exit

Z = Fixed Mask

Z = Ratchet Wall

QF QD BEND SDInsertion Device HCOR

A1 A2

Stored Beam on design orbit

X-Rays to Beamline

Ratchet Wall

Fixed Mask I

BPM 7 BPM 1

Evolution of allowed phase space

28

-3 -2.5 -2 -1.5 -1 -0.5 0-0.24

-0.22

-0.2

-0.18

-0.16

-0.14

-0.12

-0.1

-0.08

X [m]

X' [

rad]

Phase Space at Z = Fixed Mask

Phase Space at Z = Ratchet Wall

Fixed Mask Opening

Ratchet Wall Opening

The Metric: Separation in Phase Space to Apertures

29

A1

QF QD BEND SD

ID A2BPM 7 BPM 1

Stored Beam on design orbit

Beamline Axis

Extreme Ray

4 6 8 10 12 14 16-1.4

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

Z [m]

BL

aper

ture

s an

d E

xtre

me

Ray

pos

ition

[m

]

Beamline apertures and the most severely mis-steered beam

BL4

BL5BL6

BL7

BL9

BL10BL11

mis-steered beam

Extreme Ray

All other Trajectories

The Extreme Ray

Position along beam line [m]

rise/run ~ -0.1 rad

ratchet wall

Off

set

[m

]

Separation at Fixed Mask

beam pipe w/apertures

30

Large SPEAR3 magnet field error

- and/or -

Large injected beam energy error

- AND -

“extensive intentional steering”

Condition for ‘Abnormal’ Scenario

special SLAC interpretation

4 6 8 10 12 14 16-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

Z[m] from ID center

BL

aper

ture

and

Ext

rem

e R

ay p

ositi

on [

m]

BL5BL6

BL7

BL9

BL10BL11

NominalB/B = -10%B/B = -50%B/B = -60%

Parameter To Pass Beyond Fixed Mask

To Pass Beyond Ratchet Wall

Target Value for Interlock Limit

EINJ/ESPEAR +59% +100% +10%

B/B -48% -60% -1% (-10%)

QF -100% Only with polarity reversed

-25%

QD +300% 55% (PS Limit)

HCOR 22 mrad 30 mrad 3mrad (2 x PS Limit)

Parameter Sensitivity

QF QD BEND SDInsertion Device HCOR

A1 A2 A3

Stored Beam on design orbit

X-Rays to Beamline

Ratchet Wall

PM

+60 / -43 mm +50 / -43 mm BL9: +112 / -101 mm

SPEAR Apertures

Beamline-Specific Aperture

Alignment of Apertures is Critical

33

FixedMask

ID sourceRingAperture

Experimental Floor

xxx

Mechanical Drawings & Tolerances

Documentation

Periodic checks

More documentation

Dose Calculations & Testing

Bauer & Liu

mis-steer and measure…

35

Passive Systems-Limiting apertures in transport line (BTS)

-Limiting apertures in SPEAR3 and beam lines

- Permanent magnets for dipole beam lines

Active Systems (Redundant Interlocks)

- Injection energy interlock - BTS dipole supply

- SPEAR3 magnet supplies

- Stored beam interlock

- Radiation detectors at each beam line

‘Hazard Mitigation’

Hardware Interlock Envelope

Software Alarm Envelope

A

B

* *

path 1

path 2

Software Monitor Envelope

Interlock Hierarchy

(reportable incident)

A Rastafarian Logic Table

Corbett & Schmerge

Accident Event Probability Analysis – Dipole Short

27333333 1010102

10102

102

10

SCIRadMon

DipoleShort

OrbitIntl’k

ConfigControlVolt

Intl’k

r=100m grain of sand: V=10-12 m3

How much sand?

1027 * 10-12 = 1015 m3 = 106 km3

1. Load operational lattice - software check of PS readbacks

2. Inject to <20 mA (orbit interlock)

3. Start orbit feedback (few microns)

4. Inject to 50 mA – top-off permit

5. Open beam line injection stoppers

6. Fill 500 mA maximum (FOFB runs continuous)

7. Fill-on-fill or trickle charge

SPEAR3 Operating Sequence

Thank you for hosting the Australian Synchrotron TopUp Workshop…

/0)( teNtN

CoulombungBremstrhalTouschek 1111

Classically, for short times t,

Electron Beam Lifetime - Analytic Calculations

where ~100

1

50

1

20

11

/NvNNN scatter

CoulGasBremsGasTousbunchbunch

iiscatteri

vPNvPNvM

N

M

NvNNN )( ,

More technically, use a rate equation

Touschek

bremsstrahlung

Coulomb

(units)

CoulGasBremsGasTousbunchbunch

iiscatteri

vPNvPNvM

N

M

NvNNN )( ,

Big rate equation from before…

The gas pressure has two terms: static and dynamic

NPPP DGBGGas ,,

CoulDGBGBremsDGBGTousbunch

vNPPNvNPPNvM

NN

)( ,,,,

2

)()( ,,,,22

CoulBGBremsBGCoulDGBremsDGbunch

Tous vPvPNvPvPM

vNN

Then

Collecting terms

or bNaNN 2

where a=a(Mbunch,VRF, yscraper)

b=b(VRF, yscraper)

NOTE: keep it simple – no coupling, dynamic aperture or bunch lengthening

first-order, non-linear rate equation

Touschek

bremsstrahlung

Coulomb

b

ae

eNtN

bt

bt

)1(1)( 0

bNaNN 2

Finally integrating the rate equation

yields tbaeNtN )(0)( ~

What's the point of all this?

a. want to know the relative Toushek, bremsstrahlung & Coulomb contributions b. plan for top-off shot/charge, fill pattern, duty cycle c. plan for future coupling (high brightness operation) d. ID collimators e. shielding, etc

Excellent, tractable student projectDelves deep into particle beam and accelerator physics, NN application

Very low emittance with on-axis injection: bunch replacement

• Assume ~30-40 pm natural emittance (15-20 pm/plane, fully coupled), very small dynamic aperture

• Lifetime (not yet calculated) < 1 h

• Injection options:

1. Accumulator ring used to replace all bunches in ring

2. Bunch train replacement (~20 bunches per train, trains separated by gaps (~10-20 ns, 5-10 buckets) to accommodate rise- and fall-times of injection kicker

• ~0.5 nC/bunch (68 A/bunch x 20)

• 116-140 trains (~160-190 mA total)

• inject every 1-10 sec, depending on desired current stability

R. Hettel

single-bunch injection limit

multi-bunch injection limit

PEP-X:

h = 3492 nb = 3400 Trev = 7.336 ms t(0) = 1800 sec

itot = 1.5 A qtot = 11010 nC ibavg = 0.441 mA qbavg = 3.235 nC

R. Hettel