S. Bettoni, R. Corsini, A. Vivoli(CERN)

CLIC drive beam injector design

Outline

CTF3 drive beam injector: • Design, experimental verifications

CLIC drive beam injector layout:• Optimization process and criteria • Proposed layout• Longitudinal and transverse beam dynamics

simulations• Critical view of the results and possible cures

Conclusions & outlook

Drive beam injector: CTF3 example

odd buckets

even buckets

RF deflector n0 / 2

Gap creation and combinationPhase coding

180 phase switch

Acceleration n0

Deflection n0 / 2

Sub-harmonic bunching n0 / 2

DRIVE BEAM LINAC

CLEXCLIC Experimental Area

DELAY LOOP

COMBINERRING

10 m

4 A – 1.2 ms150 Mev

32 A – 140 ns150 Mev

SHB

SHBSHB

gun

buncher 2 accelerating structures

Drive beam injector: CTF3 experienceKey parameters for the SHB system:

Time for phase switch < 10 ns Satellites (particles captured in 3 GHz RF buckets) population < 7 %

Phase switch:

Phase switch within eight 1.5 GHz periods (<6 ns).

Satellite bunch population:

Satellites bunch populationestimated to ~8 %.

Main

Satellites

CTF3 first rescaling: the SHB system• Lshb = 3*LshbCTF3 (6 cells)• Gshb = GshbCTF3/3

• Lshb = LshbCTF3 (2 cells)• Gshb = GshbCTF3

• Lshb = 2/3*LshbCTF3 (4 cells)• Gshb = 3/4*GshbCTF3

Frequency (GHz) 1.49928Number of cells 6Iris diameter (mm) 66Cell length (mm) 26Input power (kW) 40Filling time (ns) 10

SHB1 SHB2 SHB3Phase advance/cell (º) 74.82 70.21 68.23Phase velocity/c 0.63 0.67 0.69

CTF3

The Matlab driven optimization tool STARTING

DISTRIBUTION

PARMELA FILE INPUT

PARMELA RUN

0 200 400 600 800 1000 1200 1400-600

-500

-400

-300

-200

-100

0

-1*n

umer

of p

artic

les

Iteration number

ANALYSIS OF THE RESULTS

AUTOMATIC MINIMIZATIO

NPROCESS

The optimization process: some details

0 200 400 600 800 1000 1200 1400-600

-500

-400

-300

-200

-100

0

-1*n

umer

of p

artic

les

Iteration number

2 4 6 8 10 12 14 16 180.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0.11

Parameter number

L (m

)

0 2 4 6 8 10 12 14 16 183

3.5

4

4.5

5

5.5x 10

6

Parameter number

G (M

V/m

)

0 0.5 1 1.5 2 2.5 3 3.5

x 10-11

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Nor

mal

ized

inte

nsity

Bunch length (s)

During the optimization:

The code varies the parameters of the system and it does some checks on them From the output of Parmela the tool calculates the number of particles in the main of the reference particles cutting the distribution at the target bunch length The number of particles in this region is maximized

iiLiLiiGiG

GGendG

CELLCELL

CELLCELL

BuncherCELL

CELLCELL

)()1()()1(

3.0)1(

)1()(-1 0 1 2 3

x 10-10

2

4

6

8

10

12x 10

6

time (s)

p

Analysis-CLIC

-1 0 1 2 3

x 10-10

0

0.5

1

1.5

2

2.5

3x 10

-11

time (s)

bunch lengthnorm. intensitynorm. charge

CLIC drive beam injector layout

THERMIONIC GUNPREBUNCHERBUNCHER

SLIT

QUADRUPOLEBEND

ACCELERATING CAVITY

53 MeV

140 KeV 6 MeV

26 MeV

SHB

SOLENOIDS

Exit of the gun

Energy = 0.140 MeVsE= 0.00016 MeVDT= 6 nsgb ex,y= 3.48 mm rad

CLIC parameter Unit Value

Pulse duration

Repetition rate

ms

Hz

140.3

50

SHB system

Energy = 0.138 MeVsE= 0.029 MeVDT= 9.68 ns

SHB1 Unit Value

LengthN. cellsFrequencyPhase velocityVoltageAperture radius

cm

MHzckVcm

15.62499.750.9335.04.7

SHB2 Unit Value

LengthN. cellsFrequencyPhase velocityVoltageAperture radius

cm

MHzckVcm

15.62499.750.6136.54.7

SHB3 Unit Value

LengthN. cellsFrequencyPhase velocityVoltageAperture radius

cm

MHzckVcm

15.62499.750.7338.84.7

Prebuncher

Energy = 0.147 MeVsE= 0.035 MeVDT= 9.7 nsSatellites= 5.5 %

Parameter Unit Value

Length

Number of cells

Frequency

Accelerating gradient

Aperture radius

cm

MHz

MV/m

cm

6

1

999.5

1.2

4.7

Energy = 4.20 MeV; sE= 1.01 MeV; st= 55.89 ps.

BuncherParameter Unit Value

Phase velocity:

First 12 cells

Last 6 cells

Phase advance/cell

Total length

Accelerating field

Beam aperture radius

c

cp

m

MV/m

cm

0.68-0.99

1

2/3

1.681

4.2

4.7

Energy = 26.34 MeV; sE= 2.16 MeV; st= 36.58 ps.

Exit of the solenoids (E30 MeV)Accelerating cavities parameter Unit Value

Phase velocity

Number of cells

Phase advance per cell

Total length

Voltage

Beam aperture radius

c

p

m

MV

cm

1

10

2/3

0.9998

4.8

4.7

Cleaning chicane

Bend length = 15 cm; Bend angle = 14.32 deg; Reference E = 26 MeV; Slit aperture = 7 mm;Intensity decrease = 24%.

CL.V

VS

0412

CL.Q

FA 0

405

CL.B

HA 0

425

CL.B

PM 0

402

CL.W

CM 0

490

CL.D

HC 0

410

CL.D

VC 0

410

CL.Q

FA 0

420

CL.Q

DA

0415

CL.D

HC

0480

CL.D

VC 0

480

CL.B

HA

0430

CL.

BHA

045

0

CL.B

HA

0455

CL.Q

FA 0

460

CL.Q

DA

0465

CL.BHA0425-SCL.BHA0430-S

CL.S

LH 0

445

CL.

BPR

0475

CLS.

MTV

044

0

CL.V

PI 0

413

DUMP

CLS.

SDU

0442

R5,6 = 78 mm

BEFORE THE CHICANEAFTER THE CHICANE

-1 0 1 2 3 4 5x 10-10

0

5

10

15

20

25

30

Time (s)

Ene

rgy

(MeV

)

-1 0 1 2 3 4 5x 10

-10

0

1

2

3

4x 10

-11

Time (s)

rms

bunc

h le

ngth

(s)

Bunch length

Bunch chargeintensity (a.u.)

CTF3

After the cleaning chicane

Energy = 26.07 MeV; sE= 0.40 MeV; st= 17.14 ps.

BEFORE THE CHICANEAFTER THE CHICANE

Injector exit (E50 MeV)

Energy = 53.25 MeV; sE= 0.45 MeV; st= 9.45 ps. gbex= 32.92 mm rad; gbey= 28.73 mm rad.

0 2 4 6 8 10 12 14 160

0.05

0.1

0.15

0.2

0.25

z (m)

Bz (T

)

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2-3

-2

-1

0

1

2

3

X (cm)

X'

(mra

d)-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

-3

-2

-1

0

1

2

3

Y (cm)Y

' (m

rad)

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

X (cm)

Y (

cm)

CLIC drive beam injector: transverse dynamics

CLIC requests and simulation results

Parameter Unit Simulations CLIC

Energy

Bunch charge

Bunch length (rms)

Energy spread (rms)

Horizontal normalized emittance (rms)

Vertical normalized emittance (rms)

Satellites population

MeV

nC

mm

MeV

mm rad

mm rad

%

53.2

8.16

2.83

0.45 (@53 MeV)

32.9

28.7

4.9

8.4

3 (@ 50 MeV)

< 0.50 (@ 50 MeV)

100

100

As less as possible

CLIC drive beam injector design: a critical viewMore optimizations still ongoing:

Intensity decrease at the chicane = 24% (close to CTF3 20%)

Additional chicane needed(power???)

Satellites population = 4.9 %-3 -2 -1 0 1 2 3 4

x 10-9

51.5

52

52.5

53

53.5

54

54.5

55

Time (s)K

inet

ic E

nerg

y (M

eV)

Identified two approaches to minimize the satellites content: Minimize the number of particles in the time interval of the satellites

Use an additional SHB to shift the energy of the satellites

Satellites minimization: possible cures

-5 -4 -3 -2 -1 0 1 2 3 4 5

x 10-9

0

0.5

1

1.5

2

2.5

3x 10

5

-3000 -2000 -1000 0 1000 2000 3000 40000

1

2

3x 10

5

time (ps)p

After drift after extra shb

-3000 -2000 -1000 0 1000 2000 3000 40000

20

40

60

80

time (ps)

Starting from an idea by P. Urschütz (presently at Siemens)

-4000 -3000 -2000 -1000 0 1000 2000 30000

1

2

3x 10

5

time (ps)

p

After drift after PB

-3000 -2000 -1000 0 1000 2000 3000 4000 50000

20

40

60

time (ps)

CDR versionModified version

0 10 20 30 40 50 605

10

15

20

25

30

35

40

45

50

55

Par

ticle

s in

the

left

sate

llite

Iteration number

0.25*RF/2

0.5*RF/2

Efficiency: an alternative solutionRe-optimization using as a figure of merit the energy spread at a fixed bunch length and optimization of the accelerating cavities:

Intensity decrease at the chicane = 19% (24%)

Total losses from the start = 22% (30%)

Particles to be lost in the additional chicane reduced

by a factor 2

0 50 100 150 200 2500.004

0.006

0.008

0.01

0.012

0.014

0.016

iteration number

D E

/E

Cut at 10 ps rms

Particles in a more confined E-t region

0 50 100 150 200 250 300 3500

50

100

150

200

250

iteration number

Pha

ses

(from

2)

Phase2

Phase3

Phase4

Conclusions

A design of the CLIC drive beam injector based on a thermionic gun has been

studied

Parmela simulations verified that the challenging CLIC requests can be fulfilled

(longitudinal & transverse)

Identified some possible improvements (beam losses, satellites content) and

optimization already ongoing

Further studies (beam loading compensation, wakefields effects and beam

stability) to be done

Proper RF design of the elements to be done

Spare slide: space charge

Without space charge

With space charge