Alex Bogacz

Operated by JSA for the U.S. Department of Energy

Thomas Jefferson National Accelerator Facility 1

Alex Bogacz

EIC14 Workshop, Jefferson Lab, March 20, 2014

Lattice Design Choices for LHeC ERL

Jefferson Lab March 17-20, 2014



Linac-Ring Option - LHeC ERL Recirculator

LHC p

1.0 km

2.0 km

10-GeV linac

10-GeV linac injector

dump

IP

comp. RF

e- final focus

tune-up dump

0.26 km

0.17 km

0.03 km

0.12 kmcomp. RF

10, 30, 50 GeV

20, 40, 60 GeV

total circumference ~ 8.9 km

The baseline 60 GeV ERL option proposed can give an e-p luminosity of 1033 cm-2s-1 (extensions to 1034 cm-2s-1 and beyond are being considered)


F. Zimmermann



Why Energy Recovering RLA?

High energy (60 GeV), high current (6.4 mA) beams: (384 MW beam power) would require sub GW (0.8 GW)-class RF systems in conventional linacs .

Invoking Energy Recovery alleviates extreme RF power demand (power reduced by factor (1 - hERL) ⇨ Required RF power becomes nearly independent of beam current.

Energy Recovering Linacs promise efficiencies of storage rings, while maintaining beam quality of linacs: superior emittance and energy spread and short bunches (sub-pico sec.).

GeV scale Energy Recovery demonstration with high ER ratio (hERL = 0.98) was carried out in a large scale SRF Recirculating Linac (CEBAF ER Exp. in 2003)

No adverse effects of ER on beam quality or RF performance: gradients, Q, cryo-load observed – mature and reliable technology (next generation light sources)




0.5 GeV

0.5 GeV

LHeC Recirculator with ER

10 GeV/pass

Linac 1

Arc1, 3, 5 Arc 2, 4, 6 + l/2

10 GeV/pass

LHC

IP

Linac 2

injector

dump

60 GeV




0.5 GeV

0.5 GeV

10 GeV/pass

Linac 1

Arc1, 3, 5 Arc 2, 4, 6 + l/2

10 GeV/pass

LHC

IP

Linac 2

injector

dump

60 GeV





0.5 GeV

0.5 GeV

10 GeV/pass

Linac 1

Arc1, 3, 5 Arc 2, 4, 6 + l/2

10 GeV/pass

LHC

IP

Linac 2

injector

dump

60 GeV





ERL–Ring: Dimensions/Layout

IP


J. Osborne



Beam Dynamics Challenges/Mitigations

Incoherent and coherent synchrotron radiation related effects on the electron beam

energy losses Size/Layout

longitudinal emittance increase Size/Layout

transverse emittance increase Lattice

Beam Breakup Instability (BBU)

single beam Lattice

multi-pass Lattice

Depolarization effects Lattice




Cryo Unit Layout/Optics - Half-Cell 1300 FODO

802 MHz RF, 5-cell cavity:l = 37.38 cmLc = 5l/2 = 93.45 cm Grad = 18 MeV/m (16.8 MeV per cavity)DE= 269.14 MV per Cryo Unit

29.60

160

0

50

BET

A_X

&Y[

m]

BETA_X BETA_Y DISP_X DISP_Y

Cavity Cryo: 8 RF cavities

Lc

×38

quad

Cavity Cryo: 8 RF cavities

D. Schulte




10 GeV Linac - Focusing profile

19 FODO cells (19 × 2 × 16 = 608 RF cavities)

E = 0.5 - 10.5 GeV

10080

200

0

50

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


quad gradient

min

1 dsE L E =




Linac 1 - Multi-pass ER Optics




Linac 1 and 2 - Multi-pass ER Optics




Natural momentum spread due to quantum excitations:

Emittance dilution due to quantum excitations:

Momentum Compaction – synchronous acceleration in the linacs:

Arc Optics – Beam Dynamics Issues

10

L D dsI

=




52.35990

150

0

1.5

-1.5

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


1350 FODO Cell

602 2

5548 3

N r c Hmc

D

=

2 2.2 10H m-=

82N micron radD =

50.5at GeV




52.35990

150

0

0.3

-0.3

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


Flexible Momentum Compaction (FMC) Cell

Emittance dispersion〈 H〉 avereged over

bends

2 22 ' 'H D DD D =

Momentum compaction

56 bendDM ds D

=- =-

356 1.16 10 mM -=

factor of 27 smaller than 1350

FODO

factor of 2.5 smaller than 1350 FODO

3 8.8 10 H m-=




52.35990

500

0

0.5

-0.5

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y52.35990

500

0

0.5

-0.5

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y52.35990

500

0

0.5

-0.5

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


Arc Optics – Emittance preserving FMC cell

total emittance increase in Arc 5: DxN =

4.268 mm rad

Arc 1 , Arc2

TME-like Optics DBA-like Optics Imaginary t Optics

Arc 3, Arc 4

Arc5, Arc 6

3 1.2 10 H m-= 3 8.8 10 H m-= 3 2.2 10 H m-= factor of 18 smaller than FODO

602 2

5548 3

N r c Hmc

D

=




Energy Loss and Emittance Dilution in Arcs

A. Valloni




Vertical Separation of Arcs

-50

0

50

100

150

0 1000 2000 3000 4000 5000 6000 7000 8000

y [cm]

z [cm]

Spreader 1, 3 and 5

Arc 1 (10 GeV)

Arc 3 (30 GeV)

Arc 5 (50 GeV)




Vertical Spreaders - Optics

Spr. 1

Spr. 3

Spr. 5

760

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


760

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


760

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


vertical step I

path-length adjustment ‘doglegs’

path-length adjustment ‘doglegs’

path-length adjustment ‘doglegs’vertical step

II

vertical step I

vertical step II

vertical chicane




Vertical Separation of Arcs

Arc 1 (10 GeV)

Arc 3 (30 GeV)

Arc 5 (50 GeV)




Arc 1 Optics (10 GeV)

doglegs 58 FMC cellsdis. sup.

cell180 deg. Arc

2300

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]BETA_X BETA_Y DISP_X DISP_Y 3292.613060

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


dis. sup. cell

vert. 2-step spreader

vert. 2-step recombiner

doglegs

Arc dipoles:$Lb=400 cm$B=0.47 kGauss




Arc 3 Optics (30 GeV)

doglegs 58 FMC cellsdis. sup.

cell180 deg. Arc

dis. sup. cell

vert. 2-step spreader

vert. 2-step recombiner

doglegs

2300

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]BETA_X BETA_Y DISP_X DISP_Y 3292.583060

600

0

0.6

-0.6

BET

A_X

&Y[

m]

DIS

P_X&

Y[m

]


Arc dipoles:$Lb=400 cm$B=1.37 kGauss




Vertical Stack - Combined Aperture Arc Dipole


×

0.264 T

60 GeV

0.176 T

40 GeV

0.088 T

20 GeV

××

×

∙

∙

∙∙

A. Milanese



SummaryHigh luminosity Linac-Ring option - ERL

RF power nearly independent of beam current.

Multi-pass linac Optics in ER modeChoice of linac RF and Optics - 802 MHz SRF and 1300 FODOLinear lattice: 3-pass ‘up’ + 3-pass ‘down’

Arc Optics Choice - Emittance preserving latticesQuasi-isochronous latticesFlexible Momentum Compaction OpticsBalanced emittance dilution & momentum compaction

Complete Arc ArchitectureVertical switchyardMatching sections & path-length correcting ‘doglegs’

Alternative ERL Topology - ‘Dogbone’ Option?




Frank ZimmermannDaniel Schulte

Erk JensenOliver Brüning

andMax Klein


Special Thanks to:



‘Racetrack’ vs ‘Dogbone’ RLA

DE/2

DE/2

1.5 DE

DE3 DE

Twice the acceleration efficiency for the ‘Dogbone’ topology

Challenge: traversing linac in both directions while accelerating




‘Dogbone’ vs ‘Racetrack’ – Arc-length

9×DE/29×DE/2

= 2npR

2n×

Net arc-length break even: if = p/4

n× = n(p 4)R




Project XStage I

Project XStage II

Project XStage III

Linac + RLA to 4 GeV

NF Decay Ring RLA to 63 GeV

n to Homestake

Higgs Factory

Fermilab

Future Muon Facilities - Muon Acceleration

Neutrino FactoryLBNE

J.-P. Delahaye, MASS (Muon Accelerator Staging

Studies)




Droplet Arcs - Layouttop view

side view

2.4 GeV1.2 GeV

1.2 GeV

2.4 GeV

1 m




‘Racetrack’ vs ‘Dogbone’ ERL for LHeC

12 GeV linac0.5 GeV

0.5 GeV24GeV

48 GeV

IP60 GeV

12 GeV 36 GeV60 GeV

Baseline

‘Dogbone’

10 GeV linac

10 GeV linac

IP60 GeV

0.5 GeV

0.5 GeV

10 GeV30 GeV50 GeV

20 GeV40 GeV60 GeV

3-pass RLA

5-pass RLA


5 3003 180

/ 6 p = =



‘Dogbone’ RLA - Multi-pass Linac Optics

Acceleration Deceleration




Pros and Cons of a ‘Dogbone’ RLA

High acceleration efficiency (≤2) –

traversing the linac in both directions

while accelerating

Better orbit separation at linac’s end

~ energy difference between

consecutive passes (2DE) vs (DE) in

case of the ‘Racetrack’

Suppression of depolarization effects

Beam trajectory can be made to follow

a Figure-8 path (by reversing field

directions in opposing droplet arcs)

Beams of different energies moving

in the opposite direction through

the linac – orbit separation needed

to avoid parasitic collisions.

As linac length and number of

passes are increased, the BBU threshold can be a problem.

Travelling ‘clearing gaps’ to

alleviate ion trapping - No practical

solution found


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Alex Bogacz

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