LHeC Recirculator with Energy Recovery – Beam Optics Choices

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

Thomas Jefferson National Accelerator Facility

Alex Bogacz 1

LHeC Recirculator with Energy

Recovery – Beam Optics Choices

Alex Bogacz

in collaboration with

Frank Zimmermann and Daniel Schulte

Accelerator Seminar, CERN, Oct. 7, 2010



Alex Bogacz 2

Energy Recovery Recirculating Linacs - Motivation

Future high energy (multi-GeV), high current (hundreds of milli-Amperes) beams would require gigaWatt-class RF systems in conventional linacs - a prohibitively expensive proposition. However, invoking energy recovery alleviates extreme RF power demands; required RF power becomes nearly independent of beam current, which improves linac efficiency and increases cost effectiveness.

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.).

RLAs that use superconducting RF structures can provide exceptionally fast and economical acceleration to the extent that the focusing range of the RLA quadrupoles allows each particle to pass several times through each high-gradient cavity.

GeV scale energy recovery demonstration with high ratio of accelerated-to-recovered energies (50:1) was carried out on the CEBAF RLA (2003)




Alex Bogacz 3

Recirculating Linear Accelerator (RLA) configurations

p-60, p-140 (100), erl

Existing ER RLA’s (Jlab’s FEL & CEBAF ER Exp)

Multi-pass linac Optics in ER mode

Choice of linac Optics - 1300 FODO (1300 vs 1500)

Choice of quad gradient profile in the linacs (wake-field effects)

Linear lattice: 3-pass ‘up’ + 3-pass ‘down’

Arc-to-Linac Synchronization - Momentum compaction

Quasi-isochronous lattices

Choice of Arc Optics -1350 FODO vs FMC (Flexible Momentum Compaction )

Arc Optics Choice - Emittance preserving lattices

Various flavors of FMC lattices in the second stability region (Im. t, DBA, TEM)

Emittance dilution & momentum spread due to quantum excitations

Magnet apertures

Overview - Design Choices




Alex Bogacz 4

RLA Configurations

. Accelerator Seminar, CERN, Oct. 7, 2010



Alex Bogacz 5

LHeC Recirculator with ER

10 GeV/pass

Linac 1

Linac 2

Arc1, 3, 5 Arc 2, 4 Arc 6

10 GeV/pass

LHC

IP

0.5 GeV

60.5 GeV




Alex Bogacz 6

CEBAF - ER Experiment (2003)

Modifications include the installation of:

RF/2 path length delay chicane

Dump and beamline with diagnostics




Alex Bogacz 7

“1 pass-up / 1 pass-down” Operation

55 MeV 555 MeV

55 MeV 555 MeV

555 MeV1055 MeV

555 MeV1055 MeV

North Linac

South Linac

Inject

Dump

RF/2 phase delay




Alex Bogacz 8

Phase-space degradation?

In an effort to gain a quantitative understanding of the 6D phase space, the following measurements were taken:

Measuring the transverse emittance of the beam in the injector, in each Arc and immediately before being sent to the dump

To characterize the longitudinal phase space, the momentum spread was measured in each Arc

Measure energy recovered beam profiles with a large dynamic range as a way to quantify beam loss and the effect of energy recovery on beam preservation

Measured the RF’s response to energy recovery




Alex Bogacz 9

Transverse beam profiles

Beam viewer near the exit of the South Linac

~ 55 MeV Decelerating beam

~ 1 GeV Accelerating beam

500

400

300

200

100

0353025 20 15 105 0

Arb

itra

ry U

nit

s

Distance (mm)

3-wire scanner x 2 beams = 6 peaks




Alex Bogacz 10

Beam Profiles of ER Beam

Beam profiles (55 MeV, 1mA beam) measured with a wire scanner and 3 downstream PMTs

(courtesy A. Freyberger)

Each profile (X and Y) is fit

with a function of the form:

F = Gaussian(Core) +

Gaussian(“Halo”) + Background

Quantify beam loss by:

Ratio for X-profile is 1x10-4

Beam loss for Y-profile is

below the noise level

Core

Halo

A

A

X-profileY-profile

5 orders of dynamic

range




Alex Bogacz 11

RF Response to Energy Recovery

0.20

0.15

0.10

0.05

0.00

-0.05

-0.10

-0.15

Vol

ts

350300250200150100500Time(s)

Gradient modulator drive signals with and without energy recovery in response to 250 sec beam pulse entering the RF cavity (SL20 Cavity 8)

250 s

with ERwithout ER




Alex Bogacz 12

JLAMP 2-pass FEL with ER




Alex Bogacz 13

LHeC Recirculator with ER

10 GeV/pass

Linac 1

Linac 2

Arc1, 3, 5 Arc 2, 4 Arc 6

10 GeV/pass

LHC

IP

0.5 GeV

60.5 GeV




Alex Bogacz 14

560

0.5

0P

HA

SE

_X&

Y

Q_X Q_Y560

150

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]

BETA_X BETA_Y DISP_X DISP_Y

Linac Optics 1300 FODO Cell

phase adv/cell: x,y= 1300

700 MHz RF:

Lc =100 cm

5-cell cavity

Grad = 17.361 MeV/m

E= 555.56 MV

linac quadrupoles

Lq=100 cm

GF= 0.103 Tesla/m

GD= -0.161 Tesla/m

E = 0.5 GeV

2×9 cavities 2×9 cavities




Alex Bogacz 15

Linac 1 Focusing profile

18 FODO cells (18 ×18 = 324 RF cavities)

E = 0.5 10.5 GeV

10080

200

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


quad gradient




Alex Bogacz 16

Linac 3 (Linac 1, pass 2) Optics

10080

0.5

0P

HA

SE

_X&

Y

Q_X Q_Y

betatron phase advance

10080

500

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


E = 20.5 30.5 GeV

min

1ds

L E




Alex Bogacz 17

10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


Linac 1 multi-pass + ER Optics

10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]

BETA_X BETA_Y DISP_X DISP_Y 10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_

X&

Y[m

]


10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_

X&

Y[m

]


10080

800

0

0.5

-0.5

BE

TA

_X&

Y[m

]

DIS

P_

X&

Y[m

]


30.5 GeV

40.5 GeV

20.5 GeV

10.5 GeV

0.5 GeV

10.5 GeV

30.5 GeV

40.5 GeV

50.5 GeV

60.5 GeV

50.5 GeV

20.5 GeV




Alex Bogacz 18

Linac 2 Focusing profile

18 FODO cells

E = 10.5 0.5 GeV (ER)

10080

200

0

50

BE

TA

_X&

Y[m

]

DIS

P_X

&Y

[m]


quad gradient


Linac 2 multi-pass optics with ER mirror symmetric to Linac 1 (see previous slide)



Alex Bogacz 19

52.35990

Wed Sep 29 22:50:19 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\cell_135.opt

0.5

0P

HA

SE

_X

&Y

Q_X Q_Y

Arc dipoles:

$Lb=400 cm

$B=2.2 kGauss

$ang=0.3 deg.

$rho = 764 meter

Arc quadrupoles

$Lq=100 cm

$G= 1.2 kG/cm

Arc Optics - 1350 FODO Cell

52.35990


15

00

1.5

-1.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


phase adv/cell: x,y= 1350

50.5 GeV




Alex Bogacz 20

1350 FODO Cell

52.35990


15

00

1.5

-1.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


Emittance dispersion

〈 H 〉 averaged over

bends

2 22 ' 'H D DD D

Momentum compaction

56 bend

DM ds D

2 2.2 10H m 256 3.19 10 mM




Alex Bogacz 21

132

150

5 3 20

2 2

553.8319 10 m,

32 3

2.818 10 m,

,

2 ' '

: 0,

q

L

cC

mc

r

HHds

H D DD D

total bend of the arc

6

0 5

2

3 2N

qC r

Emittance growth due to quantum excitations

60 2

2

3N

qC r H

0180 :for arc


602 2

55

48 3N r c

Hmc



Alex Bogacz 22

3 20

1,

: 0,

Lds

total bend of the arc

Momentum spread due to quantum excitations

0180 :for arc

225

2 2 30

55 1

48 3

LE c

dsE mc

225

2 2 2

55

48 3E c

E mc




Alex Bogacz 23

Quasi-isochronous condition – Arc into Linac

Momentum

compaction56

56

56

360 360

bend

cellRF cell

RF RF

DM ds D

pC M

p

C pN M

p

43 10

0.428 m

60RF

cell

p

p

N

256 3.19 10

0.5deg

FODO

RF

M m




Alex Bogacz 24

Quasi-isochronous FMC Cell

Emittance dispersion

〈 H 〉 avereged over

bends

2 22 ' 'H D DD D

Momentum compaction

56 bend

DM ds D

356 1.16 10 mM

52.35990

Wed Sep 29 23:58:12 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\cell_FMC_2.opt

15

00

0.3

-0.3

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


factor of 27 smaller than FODO factor of 2.5 smaller than FODO

3 8.8 10 H m




Alex Bogacz 25

Arc Optics – 1350 FODO vs FMC Cell

1350 FODO FMC Cell

52.35990


15

00

1.5

-1.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]BETA_X BETA_Y DISP_X DISP_Y 52.35990


15

00

1.5

-1.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


2 2.2 10 H m

256 3.19 10 mM

3 8.8 10 H m

356 1.16 10 mM




Alex Bogacz 26

Quasi-isochronous condition – Arc into Linac

Momentum

compaction56

56

56

360 360

bend

cellRF cell

RF RF

DM ds D

pC M

p

C pN M

p

factor of 27 smaller than FODO

356 1.16 10

0.018deg

FMC

RF

M m

43 10

0.428 m

60RF

cell

p

p

N

256 3.19 10

0.5deg

FODO

RF

M m




Alex Bogacz 27

Arc dipoles:

$Lb=400 cm

$B=2.2 kGauss

$ang=0.3 deg.

$rho = 764 meter

Arc quadrupoles

$G0= -1.53 kG/cm

$G1= 5.06 kG/cm

$G2= -5.32 kG/cm

$G3= 5.07 kG/cm

50.5 GeV

FMC ‘Imaginary t’ Cell

52.35990


15

00

0.3

-0.3

BE

TA_

X&

Y[m

]

DIS

P_

X&

Y[m

]

BETA_X BETA_Y DISP_X DISP_Y 52.35990


0.5

0P

HA

SE

_X

&Y

Q_X Q_Y

second stability

region:

x,y > 1800

3 8.8 10 H m 3

56 1.16 10 M m

60




Alex Bogacz 28

52.35990

Mon Oct 04 14:46:10 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\cell_FMC_4.opt

0.5

0P

HA

SE

_X

&Y

Q_X Q_Y

Arc dipoles:

$Lb=400 cm

$B=2.2 kGauss

$ang=0.3 deg.

$rho = 764 meter

Arc quadrupoles

$G0= 2.05 kG/cm

$G1= 2.90 kG/cm

$G2= -4.07 kG/cm

$G3= 2.97 kG/cm

50.5 GeV

FMC ‘Double Bend Achromat’ Cell

second stability

region:

x > 1800

52.35990


50

00

0.5

-0.5

BE

TA_

X&

Y[m

]

DIS

P_

X&

Y[m

]


3 2.2 10 H m

60

356 5.6 10 M m




Alex Bogacz 29

52.35990


0.5

0P

HA

SE

_X

&Y

Q_X Q_Y

Arc dipoles:

$Lb=400 cm

$B=2.2 kGauss

$ang=0.3 deg.

$rho = 764 meter

Arc quadrupoles

$G0= 2.92 kG/cm

$G1= 2.89 kG/cm

$G2= -4.08 kG/cm

$G3= 2.97 kG/cm

50.5 GeV

FMC ‘Theoretical Emittance Minimum’ Cell

second stability

region:

x > 1800

52.35990


50

00

0.5

-0.5

BE

TA_

X&

Y[m

]

DIS

P_

X&

Y[m

]


3 1.2 10 H m

356 5.7 10 M m

60




Alex Bogacz 30

Arc Optics – Cumulative emittance growth

total emittance increase (all 5 arcs): xN = 1.25 × 4.5 m rad =5.6 m rad

Arc 1 , Arc2

6 2 20 2

2, 2 ' '

3N

qC r H H D DD D

52.35990

Tue Oct 05 13:59:00 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\cell_FMC_2.opt

50

00

0.5

-0.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]



50

00

0.5

-0.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]



50

00

0.5

-0.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


TEM-like Optics DBA-like Optics Imaginary t Optics

Arc 3 Arc 4 , Arc5

3 1.2 10 H m 3 8.8 10 H m 3 2.2 10 H m




Alex Bogacz 31

Highest Arc Optics – Emittance growth

total emittance increase (all 6 arcs): xN = 1.25 × 4.5 m rad =5.6 m rad

50.5 GeV, = 105

2090

Mon Oct 04 03:30:56 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\Arc_FMC_5.opt

50

00

0.5

-0.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


TEM-like Optics

emittance increase (last arc): xN = 4.5 m rad

60 2

2

3N

qC r H


RMS fluctuations of E/E0 = 2.7 × 10-4

225

2 2 2

55

48 3E c

E mc



Alex Bogacz 32

Arc 5 – Beam envelopes

50.5 GeV, = 105 x

N = 50 m rad


p/p= 2.7 × 10-4

2090

Thu Oct 07 15:36:30 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\Arc_FMC_5.opt

0.0

50

0.0

50

Siz

e_

X[c

m]

Siz

e_

Y[c

m]

Ax_bet Ay_bet Ax_disp Ay_disp

TEM-like Optics



Alex Bogacz 33

Arc 1 – Beam envelopes

10.5 GeV x

N = 200 m rad


p/p= 5 × 10-4

2090

Thu Oct 07 15:43:10 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\Arc_1_FMC_2.opt

15

00

0.5

-0.5

BE

TA

_X

&Y

[m]

DIS

P_

X&

Y[m

]


2090

Thu Oct 07 15:43:50 2010 OptiM - MAIN: - C:\Users\traveluser\Documents\CERN RLA\Optics\Arcs\Arc_1_FMC_2.opt

0.1

0

0.1

0

Siz

e_

X[c

m]

Siz

e_

Y[c

m]

Ax_bet Ay_bet Ax_disp Ay_disp

Imaginary t FMC Optics



Alex Bogacz 34

Conclusions


Proof-of-existence ER RLAs: Jlab FEL, CEBAF

Solution for Multi-pass linac Optics in ER mode

Choice of linac Optics - 1300 FODO

Linear lattice: 3-pass ‘up’ + 3-pass ‘down’

Optimized quad gradient profile in the linacs (wake-field effects)

Arc-to-Linac Synchronization - Momentum compaction

Quasi-isochronous lattices

Choice of Arc Optics - Flexible Momentum Compaction

Arc Optics Choice - Emittance preserving lattices

Arcs based on variations of FMC optics (Im. t, DBA, TEM)

Acceptable level of emittance dilution & momentum spread

Magnet apertures