CLIC ACE 2-4 September 2008

Drive Beam Generation ComplexCLIC ACE2-4 September 2008 R. Corsini, J.B. Jeanneret, F. StulleR. Corsini, J.B. Jeanneret, F. Stulle

CLIC ACE 2-4 September 2008 R. Corsini, J.B.Jeanneret, F. Stulle

Drive Beam Generation ComplexDrive Beam Generation Complex

Will talk about:

• The concept

• Previous work

• Critical issues

• Status of present activities


Electron beam manipulation

Long RF PulsesP0 , n0 , 0

650 Klystrons

low frequencyhigh efficiency

Power stored inelectron beam

Short RF PulsesPA = P0 N1

A = t0 / N2 A = 0 N3

143000 Accelerating Structures

high frequency high gradient

Power extracted from beamin resonant structures

The CLIC RF power source can be described as a “black box”, combining very long RF pulses, and transforming them in many short pulses, with higher power and with higher frequency

What does the RF Power Source do ?


Drive Beam Acceleratorefficient acceleration in fully loaded linac

140 s total length - 24 24 sub-pulses - 4.2 A2.4 GeV - 60 cm between bunches

240 ns

Drive beam time structure - initial

24 pulses – 100 A – 2.5 cm between bunches

240 ns5.8 s

Drive beam time structure - final

Power Extraction

Drive Beam Decelerator Sector (24 in total)

Combiner ring 3

Combiner ring 4pulse compression &

frequency multiplication

pulse compression & frequency multiplication

Delay loop 2gap creation, pulse

compression & frequency multiplication

Transverse RF Deflectors

RF Power Source Layout


Full beam-loading acceleration in TW sections

RF in

“short” structure - low Ohmic losses

RF Power Source “building blocks”

RF to load

most of RF power (≥ 95%) to the

beam

High currentbeam

No

No beam


P0 , 0

P0 , 0

Beam combination/separation

by transverse RF deflectors

RF Deflector,

Deflecting

Field

Transverse

02 P

0 , 2

0



Counter propagation from central complex

Instead of using a single drive beam pulse for the whole main linac, several (NS = 24) short ones are used.

Each one feed a 800 m long sector of TBA.

(DLDS-like system)

Counter-flow distribution allows to power different sectors of the main linac with different time bins of a single long electron pulse. The distance between pulses is 2 LS = 2 Lmain/NS. The initial drive beam pulse length is equal to 2 Lmain= 140 s/c.


pulse 2 pulse 1

main linacdecelerator sector

main beampulse

From central complex

12


odd buckets

even buckets Delay

Loop

RF deflector

Combination scheme

Gap creation & first multiplication 2

Ldelay = n 0 = c Tsub-

pulse

Phase coding

180 phase switch

Acceleration 0

Deflection 0 / 2

Sub-Harmonic Bunching 0 / 2

How to “code” the sub-pulses


666 ps

1 8

Fast phase switch from SHB system (CTF3)

8.5 · 666 ps = 5.7 ns

Streak camera – 500 ps/mm

… or use a laser + photo-injector

satellite

main

3 TW Sub-harmonic bunchers,each fed by a wide-band TWT


RF injection in combiner ring (factor 4 for simplicity)

3rd

o/4

4rd

2nd

Cring = (n + ¼)

injection line

septum

localinner orbits

1st deflector 2nd deflector

1st turn

o RF deflector field


A complete zero-order conceptual design on the drive beam complex has been published in ’99 (Yellow report CERN 99-06). Since then, the parameters changed (in general in a favorable direction) and some of the concepts evolved and/or were tested in CTF3.

It is now time to fully review all components.

•Some conceptual work on overall drive beam complex layout remains to be done

- drive beam phase stability, see later

•Drive beam injector

- CTF3 a good example, RF injector preferred (no satellites) – to be tested in CTF3 as well

•Drive beam accelerator

- design existed for previous parameter set, needs to be redone (no major problems)

•Delay loop and combiner rings

- design needs to be revisited, modified and evaluated

- this is a critical item

•Bends into long transfer line

- does not exist but should be relatively easier than other bends

•Transfer lines and turn-around into decelerator and compressor/feedback

- baseline exists

•Drive beam decelerator

- design exists, some improvements, cost driver

Status (derived from Daniel`s talk)


1404.27.8

L. RinolfiLC ’99 Workshop

Injector

Scaling from CTF3 & new parameters reassuring, but satellites problem, stability…


• Smaller transverse emittance

• Shorter bunches, no energy tails

• No satellites

• Issues (to be tested in CTF3)

• High charge, long pulse laser…• Stability

Injector – RF gun option

PHIN test stand in former CTF II

PHIN RF gun

CTF3 thermionic injector

RF gun implementation in CTF3


Accelerator

CTF3 basically OK

In CTF3~ 1mm from

injector

Need full study (phase stability)

R. CorsiniLC ’99 Workshop No big problems expected, but design needed for realistic start-to-end

simulations (especially longitudinal gymnastics/phase stability)


R. CorsiniLC ’99 Workshop

favorable param. scaling

CTF3

CTF3

Delay Loop & Combiner Rings

to be checked


B. Jeanneretwork-in-progress

~ +/- 0.2 mm /arc at +/- 2%

~ +/- 0.3 mm /arc at +/- 2%

lattices, 2nd order isochronicity, chrom. control

R. CorsiniCERN 99-06


6 4 2 0 2 4 61.12

1.14

1.16

1.18

1.2

c t (mm)

U (G

eV)

1 1.5 2 2.5 3 3.51 10

6

1 105

1 104

1 103

0.01

Beam Energy (GeV)

Tota

l Rel

ativ

e E

nerg

y L

oss

Energy loss from SR and CSR

Both rings - = 10 m - 27 m

= 2 mm, Qb = 7.8 nC

CSRShielded (h=20mm)

SR

total

NB: I have kept the same in the rings as the old parameter set – now we need only a factor 2 in final compression

can accept more longitudinal phase space distortion will be less sensitive to energy variation for drive beam phase stability

6 4 2 0 2 4 61.12

1.14

1.16

1.18

1.2

c t (mm)

U (

GeV

)

‘99 parameters


Another ring issue – transverse stability in the RF deflectors

Optimum ring tune

D. Schulte – R. Corsini

‘99 parameters

OK in CTF3, but vertical polarity (trapped) critical – should be OK with damping or couplers


Old & last 30 GHz parameters

Drive beam current initial 5.7 A 4.2 A

Drive beam current final 181 A 100 A

DB bunch charge 12.1 nC 8.4 Nc

Drive beam energy 2.4 GeV ( 240 MeV) 2.4 GeV ( 240 MeV)

DB acceleration frequency 0.937 GHz 1 GHz

DB bunch frequency initial 0.46 GHz 0.5 GHz

DB bunch frequency final 15 GHz 12 GHz

DB pulse length initial 94 s 140 s

DB pulse length final 70 ns 240 ns

Combination factor 2 4 4 = 32 2 3 4 = 24

Number of sectors/linac 21 24

Sector length 670 m 868 m

Length delay loop/line 21 m 72 m

Length combiner ring 1 84 m 145 m

Length combiner ring 2 334 m 434 m

Rms bunch length final 400 m 1 mm

Power per PETS 640 MW 136 MW

2005 - CLIC Note 627 August 2008


1) INJECTION LINAC

a. RF Structures

b. Linear optics

c. Collective effects

d. dE/dz correlation for later compression

2) BUNCH STRUCTURE to build trains (rise time / flat section / Fall time)

3) DELAY LOOP

a. Isochronous & achromatic optics, beta-beating control

4) COMBINER RINGS

a. Isochronous & achromatic optics, beta-beating control

5) RF DEFLECTORS FOR DL, CR1, CR2

6) TRANSFER LINE DOWN TO TUNNEL

a. Optics

b. layout

7) FINALIZE THE LONG TRANSFER LINE

a. Optics & layout

b. Kick-out and matching to turnarounds

c. Beam-based alignment

8) TURN-AROUND TO DECELERATOR

a. Matching

b. Layout & compatibility with other beam lines

9) EXTRACTION OF SPENT BEAM after decelerator

a. Optics

b. Compatibility with other beam lines

10) DUMP CONCEPTUAL DESIGN

11) TIMING Drive Beam / Main Beam

12) ALL THE ABOVE

a. Transverse feed-back

b. Longitudinal feed-back

c. Magnet specification and inventory (at least for cost)

d. Specification for vacuum

e. Specification for instrumentation

f. Machine protection

g. Collimation

Task list B. Jeanneret


• Optics

• Parasitic dispersion + |dp|=2% => emittance dilution

• Logistics

• Beam line suspended to the ceiling

• Light & transversely thin magnets preferred

• Cost & power

• Weak magnets preferred

• Collective effects

• Trains : 100 A , 73 m long

• Strong transverse multi-bunch resistive wake-fields

• Ions => detuning & instabilities

Deserves global optimisation

Issues :

DB long transfer line : simple optics but 21 km long

B. Jeanneret


B. Jeanneret


B. Jeanneret


B. Jeanneret


B. Jeanneret


B. Jeanneret


B. Jeanneret


B. Jeanneret


Bunch Compressor Chicane 10 m

Turn Around Loop 77 m = 1x 60deg arc + matching + 3x 80deg arc

Bunch Compressor Chicane 20 m

1m 2.5m 1m

10.02 deg

10m

0.75m 8m 1m

5.53deg

20m

R56=−0.2 m

R56=−0.16 m

Phase measurements

Layout of final BCs & turn-around loop

F. Stulle


Bunch Compressors BC1 and BC2:

BC1 is not only a bunch compressor, but is also used to convert an incoming

energy jitter into a measurable phase jitter

for the energy jitter measurement its R56 should not be too small:

the phase error measured in front of the loop is corrected in BC2 by changing

the path length of the bunches

its R56, i.e. the bending angles, should be large enough

to allow the usage of weak correction kickers:

the influence of ISR is small due to the huge beam emittance

and the rather low electron energy

CSR (transverse) is also rather easy to control due to the huge beam emittance

Design Considerations / Constraints - BCsF. Stulle


Turn Around Loop:

the turn around loop has to be achromatic and should be isochronous

it has to be compact and simple since 2 x 24 loops are required

the R56(s) should stay close to zero, since the bunch has an energy chirp

it might be compressed to short lengths, i.e. it might radiate a lot CSR

this is the main complication for the lattice design,

a trade-off has to be made between R56(s), T566(s) and chromaticity

the influence of ISR is small due to the huge beam emittance

and the rather low electron energy

CSR (transverse) is also rather easy to control due to the huge beam emittance

Design Considerations / Constraints - TALsF. Stulle


Turn Around Loop latticeF. Stulle


longitudinal

phase space

transverse, hor

phase space

initial final

CSR in Loop

T566 in Loop

Simulation Results, 1D CSR

F. Stulle


• The last extensive and coherent study of the drive beam complex has been completed in ’99 (Yellow report CERN 99-06).

• Since then, the parameters changed (many times).

• New parameters are in most respects much more favorable than old ones.

• Still, it is now time to fully re-design and assess all components, including the ones neglected at the time. Work just started.

• The experience accumulated since then in CTF3 extremely useful. It relieved many worries we had, and raised a few new ones. Past and future studies in CTF3 are a valuable input to steer the new studies.

• Some of the critical issues (beam power and losses management, machine protection, stability...) need strong effort – scarce at present. This is especially important since they are addressed only partially in CTF3.

CONCLUSIONS


Reserve slides



Since the power per sector is fixed, the product Ibeam Ebeam is constant

For: is good to have

Transverse beam stability in decelerator high current, large aperture, long PETS

Drive beam combination in rings small current, high energy (but below about 2.5 GeV)

Drive beam current & energy trade-off


Several issues can put an upper limit to the beam energy in the combiner rings:

•Too high field in magnets not an issue (long rings – long RF pulse length)

•Synchrotron radiation:

•Energy loss not limiting

•Power loss in vacuum chamber potential limit

•Energy spread & emittance increase negligible

•Coherent synchrotron radiation

•Beneficial effect

•Deflectors

•Higher power for given angle

•Constant power from damping of real emittance → neutral

Drive beam energy limits


DRIVE BEAM LINAC

CLEXCLIC Experimental Area

DELAY LOOP

COMBINERRING

CTF3 – Layout

10 m

4 A – 1.2 s150 Mev

30 A – 140 ns150 Mev


CTF3 – R&D Issues - where

fully loaded acceleration

recombination x 2

phase-coding

bunch length control

recombination x 4

bunch compression

PETS on-off

two-beamacceleration

structures 12 GHz

structures 30 GHz

deceleration stability

R1.1 – structures

R1.2 – DB generation

R1.3 – PETS on-off

R 2.1 – structure materials

R 2.2 – DB decelerator

R 2.3 – CLIC sub-unit


CTF3 – R&D Issues - when

structures 12 GHz

fully loaded acceleration

recombination x 2

phase-coding

bunch length control

recombination x 4

bunch compression

PETS on-off

two-beamacceleration

structures 30 GHz

deceleration stability

2008

2009

2010


MKS03 MKS07MKS06MKS05

Spectrometer 10Spectrometer 4

Measured RF-to-beam efficiency

95.3 %

Theory 96% (~ 4 % ohmic losses)

RF pulse at structure output

RF pulse at structure input

analog signal

1.5 µs beam pulse

SiC load

damping slot

Dipole modes suppressed by slotted iris damping (first dipole’s Q factor < 20)and HOM frequency detuning

Full beam loading acceleration stability - efficiency


666 ps

1 8

8.5 · 666 ps = 5.7 ns3 TW Sub-harmonic bunchers,each fed by a wide-band TWT

Streak camera image

mainsatelliteFast phase switch from SHB system

phase coding


Satellite control, RF gun option

• Better emittance

• Shorter bunches

• No satellites

• Lower current


longitudinal

phase space

transverse

phase spaceinitial final

CSR in Loop

T566 in Loop

Simulation Results, 1D CSRF. Stulle

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CLIC ACE 2-4 September 2008

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