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MEIC Electron Cooler Design Concept MEIC Electron Cooler Design Concept

MEIC Electron Cooler Design Concept - PowerPoint Presentation

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MEIC Electron Cooler Design Concept - PPT Presentation

  EC potential impact to colliders Reaching a high start luminosity Very short i bunches achieved by longitudinal cooling in combination with SRF cannot be attained with stochastic cooling ID: 152083

cooling beam bunch electron beam cooling electron bunch energy erl charge kicker ccr fast circulator injector emittance ring current

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Slide1

MEIC Electron Cooler Design Concept Slide2

EC potential impact to colliders

Reaching a high start luminosity

Very short

i

-bunches

achieved by

longitudinal cooling

in combination with

SRF

(

cannot

be attained with

stochastic cooling

!)

make sense to design a

super-strong focusing (low beta) at IP

Short bunches

allow one to

employ

the crab-crossing beams, thus avoiding the parasitic b-

binteractions

Low transverse

emittance

+ high rep. rate

allow one to

minimize charge/bunch

Extending the luminosity lifetime

EC

suppresses beam heating

and

luminosity loss

caused by multiple and

Touschek

IBS Slide3

ion bunch

electron bunch

Cooling section

solenoid

HEEC basics

Magnetized e-gun

Injector

SRF

linac

Cooling time grows with

Therefore:

staged cooling

Cooling conditions:

Co-moving “cold” electron beam serves as

thermostat for a

hot ion beam

(

i

– e Coulomb collision exchange)Slide4

Parameter

(p/e)

Unit

Value

Beam energy

GeV

150/7

Energy of cooling beam

MeV

75

Bunch rep rate

GHz

1.5

Particles/bunch

10

10

0.2/1

Beam current

A

0.5/2.5

Cooling current

A

2.5

Horizontal

emittance

*

m

1/100

Vertical

emittance

*

m

0.01/1Number of interaction points

4

Total beam-beam tune shift

0.04/0.16

Laslett’s

tune shift in p-beam

0.02

Luminosity overall IP (10

35)

cm

-2

s

-1

2

Cooling/IBS time in p-beam core

min

5

Luminosity

Touschek’s lifetime

h

20

High luminosity colliding beams

Parameter

(p/e)

Unit

Value

Energy

GeV/MeV

20/10

Cooling length/ circumf.

%

1

Particles/bunch

10

10

0.2/1

Energy spread

**

10-43/1

Bunch length

**

cm

20/3

Proton emittance

, norm**

m

4

Cooling time

min

10

Equilibrium emittance, *

m

1

Equilibrium bunch length*

cm2

Laslett’s

tune shift

0.1

Initial electron cooling

** max. amplitude

* norm.

rms

* norm.

rms

Staged ECSlide5

Staged Cooling in Ion Collider Ring

Initial

after boost

Colliding

Mode

Energy

GeV

/MeV15 / 8.15

60 / 32.6760 / 32.67proton/electron b

eam currentA0.5 / 1.50.5 / 1.5

0.5 / 1.5

Particles/Bunch1010

0.416 / 2

0.416 / 2

0.416 / 2Bunch length

mm(coasted)10 / 20~30 10 /

20~30Momentum spread10-4

10 / 2

5 / 2

3 / 2Hori. & vert.

emittance, norm.µm4 / 4

0.35 / 0.07

Laslett’s tune shift (proton)0.002

0.0050.06Initial cooling after ions injected into the collider ring for reduction of

3d emittance before accelerationAfter boost & re-bunching, cooling for reaching design values of beam parameters in colliding mode

Continuous cooling during collision for suppressing IBS, maintaining luminosity lifetime Slide6

High Energy e-Cooler for Collider Ring

Design Requirements:

up to 10.8

MeV

for cooling at injection energy (20

GeV

/c)up to

54 MeV for cooling top proton energy (100 GeV/c)Cooling e-beam current :up to 1.5 A CW beam at 750 MHz repetition rate

About 2 nC bunch charge (possible space charge issue at low energy)Solution: ERL Based Circulator Cooler (ERL-CCR)

Must be an SRF Linac for accelerating electron beamMust be Energy Recovery (ERL)

to solve RF power problemMust be Circulator -cooler ring (CCR)

for reducing current from source/ERLERL-CCR is considered to

provide the required

high cooling current while consuming fairly

low RF power and reasonable current

from injector Slide7

Conceptual Design of Circulator e-Cooler

ion bunch

electron bunch

Electron circulator ring

Cooling section

solenoid

Fast beam kicker

Fast beam kicker

SRF Linac

dump

electron injector

energy recovery path

(Layout A)Slide8

ERL Circulator Electron Cooler

ion bunch

electron bunch

Cooling section

solenoid

(Fast) kicker

(Fast) kicker

SRF

Linac

dump

injector

(Layout B)Slide9

Optimized Location of Cooling Channel

10 m

Solenoid (7.5 m)

SRF

injector

dumper

Eliminating a long circulating beam-line could

cut cooling time by half, or

reduce the cooling electron current by half, or

Center of Figure-8

(Layout C)Slide10

Cooler Design Parameters

Max/min energy of e-beam

MeV

54/11

Electrons/bunch

10

10

1.25

bunch revolutions in CCR

~100

Current in CCR/ERL

A

1.5/0.015

Bunch repetition in CCR/ERL

MHz

750/7.5

CCR circumference

m

~80

Cooling section length

m

15x2

Circulation duration

s

27

RMS Bunch length

cm

1-3

Energy spread

10

-4

1-3

Solenoid field in cooling section

T

2

Beam radius in solenoid

mm

~1

Beta-function

m

0.5

Thermal cyclotron radius

m

2

Beam radius at cathode

mm

3

Solenoid field at cathode

KG

2

Laslett’s

tune shift @60

MeV

0.07

Longitudinal inter/intra beam heating

s

200

Number of turns in circulator cooler ring is determined by degradation of electron beam quality caused by inter/intra beam heating up and space charge effect.

Space charge effect could be a leading issue when electron beam energy is low.

It is estimated that beam quality (as well as cooling efficiency) is still good enough after 100 to 300 turns in circulator ring.

This leads directly to a 100 to 300 times saving of electron currents from the source/injector and ERL.Slide11

Issues

Space charge limitations in CCR

:

Coulomb interaction (non-linear

Laslett

detune)

CSRIntra- and Inter-Beam Scattering in CCRSource/Injector/ERL/CCR beam matching gymnasticsMagnetized cathode

Matching with cooling solenoids, straights and arcsBeam size at cathode and related canonical emittanceOther agendas? (space charge dominated beam in axial optics…) Fast kicker

(beam-beam or other) And more…Slide12

Backup slides Slide13

Parameter

Unit

Value

Max/min energy of e-beam

MeV

75/10

Electrons/bunch

10

10

1

Number of bunch revolutions in CR

100

1

Current in CR/current in ERL

A

2.5/0.025

Bunch rep. rate in CR

GHz

1.5

CR circumference

m

60

Cooling section length

m

15

Circulation duration

s

20

Bunch length

cm

1

Energy spread

10

-4

3-5

Solenoid field in cooling section

T

2

Beam radius in solenoid

mm

1

Cyclotron beta-function

m

0.6

Thermal cyclotron radius

m

2

Beam radius at cathode

mm

3

Solenoid field at cathode

KG

2

Laslett’s

tune shift in CR at 10

MeV

0.03

Time of longitudinal inter/

intrabeam

heating

s

200

ERL-based EC with circulator ring

Slide14

Technology: Ultra-Fast Kicker

h

v

0

v≈c

surface charge density

F

L

σ

c

D

kicking beam

A short (1~ 3 cm) target electron bunch passes through a long (15 ~ 50 cm) low-energy flat bunch at a very close distance, receiving a transverse kick

The kicking force is

integrating it over whole kicking bunching gives the total transverse momentum kick

Proof-of-principle test of this fast kicker idea can be planned. Simulation studies will be initiated.

Circulating beam energy

MeV

33

Kicking beam energy

MeV

~0.3

Repetition

frequency

MHz

5 -15

Kicking angle

mrad

0.2Kinking bunch lengthcm

15~50Kinking bunch widthcm

0.5

Bunch chargenC

2 An ultra-fast RF kicker is also under development.

V.

Shiltsev, NIM 1996Beam-beam kickerSlide15

Electron source

e-gun V 500

KeV

Pulse

duration

0.33 ns

Bunch charge 2

nC

Peak current 0.65 A

Emittance, norm 1 mm.mrad

Rep.rate

15 MHz

Average

current

30 mA

1st compressor

Prebuncher

frequency

500 MHzVoltage 0.2 MV

Energy gradient after prebuncher 2x 10%

1

st drift 2 m

Bunch length after 1st compression 1 cm

Beam radius (assumed value) 2 mm

Coulomb defocusing length 30 cm

1

st

accellerator cavity

Voltage 2 MVFrequency 500 MHz

Beam energy 2.5

MeV

2nd compressor

Buncher

frequency 1.5 GHz

Energy gradient 2 x 10% 2nd

drift 1.8 m

Bunch length, final 0.5mm

Beam radius 2 mm Coulomb defocusing length 35 cm

Estimates for Injector to ERL