Demonstration of the Beam loading compensation

(Preparation status for ILC beam loading compensation experiments at ATF injector in this September)

(PoP experiment on beam loading for truly conventional positron source at ATF injector )

AWLC14 at FNAL, 12-16 May 2014KEK, Junji Urakawa

Contents : 1. Short review of conventional positron source for ILC2. 300Hz Linac Scheme for Beam Loading Compensation using TW.3. Plan for beam loading compensation experiment at ATF4. Preparation status5. Summary

1. Short review of conventional positron source for ILC

A conventional positron source for international linear collider,NIM A Volume 672, 21 April 2012, Pages 52-56

Time structure of beam0<t<264.45ns, i=0.532A264.45<t<362.85ns, 0A362.85ns<t<627.3ns, 0.532A627.3ns<t<725.7ns, 0A725.7ns<t<990.15ns, 0.532A0.532A is beam loading current.

Bunch by bunch extraction fromDamping Ringto make ILC beamtrain.

This is the model for positron target systemto confirm the generationof ILC positron beam.

Phase to Amplitude Modulation Method for Beam Loading Compensation

300Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner

50W High PowerTerminator

80MW Klystron

2. 300Hz Linac Scheme for Beam Loading Compensation

500 1000 1500 2000 2500ns

10

20

30

40

50

60

MV

300Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner 50W High Power

Terminator

80MW Klystron

3m long constant gradient travelling wave structure

We need the precise control ofthe phase shifters.

Also, I assume 10% margin as wave guide loss and so on because of the experience at ATF Linac. So, klystron output power 80MW and3ms pulse width are necessary.

3x1010 positron/bunch300Hz triplet beamLess than +/- 0.7%Beam loading current0.78A.

500 1000 1500 2000 2500ns

63

64MV

20

30

40

50

60

70

- 500 0 500 1000 1500 2000

2データ

Y [MW]

X [ns]

Detail of beam loading compensation:Less than ±0.7% is possibleFor ILC 300Hz multi-bunchbeam.

Control of input RF power by phase shifters

12.5Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner 50W High Power

Terminator

80MW Klystron

3m long constant gradient travelling wave structure3m long constant gradient travelling wave structure

Essential Beam Loading Compensation Schemefor proof-principle experiment at ATF in thisSeptember

300ns53.2ns 53.2ns 53.2ns

ATF laser system for photo-cathode RF Gun can generate triplet laser beam of 20 pulse with 2.8ns bunch spacing and about 100ns gap by minor modifications.

357MHz Laser oscillator

Pockels cell to make triplet laser

pulse train12.5Hz Amp.

4th higher harmonics generator

(crystal:BBO)

Photo-cathode RF gun(electron source)

S-band Linac

Extraction line

Damping Ring

3. Plan for beam loading compensation experiment at ATF

12.5Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner 50W High Power

Terminator

80MW Klystron

3m long constant gradient travelling wave structure

We need the precise control ofthe low level phase shifters.

Also, I assume 10% margin as wave guide loss and so on because of the experience at ATF Linac. So, klystron output power 80MW and3ms pulse width are necessary.

500 1000 1500 2000 2500ns

10

20

30

40

50

60

70MV1.4x1010 electrons/bunch

with 2.8nsec bunch spacingand 2856MHz Linacbeam loading current: 0.78A

3.6 cell RF Gun

3m long TW 3m long TW

3x1010 with 6.15nsec bunch spacing corresponds to 1.4x1010 in the case of 2.8nsec bunch spacing with same beam loadingin multi-bunch trains.ATF Triplet Beam : 3x20 bunches/train with 60nsec train gapand 2.8nsec bunch spacing. This operation is possible in thesafety of the radiation for ATF accelerator. However, since I want to make more safety margin, following doublet beamscheme is proposed.

45 degrees bending magnetto measure the energy of multi-bunch

Beam Transport

ATF Injector for 1.3 GeV ATF Linac will be modified for beam loading compensation experiment in this summer.

80MW, 4.5ms12.5Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner 50W High Power

Terminator

80MW Klystron

3m long constant gradient travelling wave structure3m long constant gradient travelling wave structure

Essential Beam Loading Compensation Schemefor proof-of-principle experiment at ATF

166.4ns53.2ns 53.2ns

~60.0ns

3.6 cell RF Gun SW 3m long TW 3m long TW

45 degrees bending magnetto measure the energy of multi-bunch

12.5Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner

50W High PowerTerminator

60MW Klystron

fast phase control

23

23.1

23.2

23.3

23.4

0 50 100 150

Mo

men

tum

[M

eV/c

]

Bunch Number

-0.3

-0.2

-0.1

0

-100 0 100 200 300 400 500 600

Inte

nsi

ty [

V]

Time [ns]

Energy spread 0.1% in rms

150 bunches/pulse with 2.8ns bunch spacing

Generation of threemini-train per pulse

12.5Hz Power Supply

2nC/bunch

Chicane

AmplitudeModulation

40MW, 1.5ms 80MW, 3ms

ATF laser system for photo-cathode RF Gun can generate doublet laser beam of 20 pulse with 2.8ns bunch spacing and about 100ns gap by two Pockels cells.

357MHz Laser oscillator

Pockels cell to make doublet

laser pulse train12.5Hz Amp.

4th higher harmonics generator

(crystal:BBO)Delay line

Present laser system,Two Pockels cells,1.6 cell RF Gun, Chicaneand BPM were usedto generate doublet pulse train and to measureenergy of each bunch.0.78 x1010 electrons perbunch.

Waveguide system should be changed to match the beam loading experiment after summer shutdown of ATF operation. Following plan was proposed and necessary componentswere ordered. We want to start the change of the waveguide system from mid. of July and willcomplete it by mid. of August.

Present waveguide for KLY#0Present waveguide for KLY#1

Present waveguide for KLY#2

KLY#0KLY#1KLY#2

KLY#0KLY#1KLY#2

Present waveguide system

New waveguide system for beam loading compensation experiment

To GunTo L0

3.6 cell RF Gun SWL03m long TW 3m long TW

45 degrees bending magnetto measure the energy of multi-bunch

Generation of twomini-train per pulse

Chicane

Several modules and function generators were ordered for the control of RF phase and amplitude which are necessary for the beam loading compensation experiment. We will install necessary control devices and monitor systemby mid. of August. Then, we will start the RF aging and test new instrumentation from end of August.

Function Generator

I-Q modulation & detection

3.6 cell RF Gun

3m long TW 3m long TW

2x1010 with 6.15nsec bunch spacing corresponds to 0.9x1010 in the case of 2.8nsec bunch spacing with same beam loadingin multi-bunch trains.

3x1010 with 6.15nsec bunch spacing corresponds to 1.4x1010 in the case of 2.8nsec bunch spacing with same beam loadingin multi-bunch trains.

45 degrees bending magnetto measure the energy of multi-bunch

Beam Transport

Injector for 1.3GeV ATF Linac will be modified for beam loading compensation experiment in this summer.Due to the lack of 2013 budget, we delayed this experiment, sorry.

5. Summary

3.6 cell RF Gun SW 3m long TW 3m long TW

45 degrees bending magnetto measure the energy of multi-bunch

80MW, 3ms12.5Hz Power Supply

Low Level RFPhase Shifterand Amp.

3dB High PowerRF Combiner

50W High PowerTerminator

60MW Klystron

23

23.1

23.2

23.3

23.4

0 50 100 150

Mo

men

tum

[M

eV/c

]

Bunch Number

-0.3

-0.2

-0.1

0

-100 0 100 200 300 400 500 600

Inte

nsi

ty [

V]

Time [ns]

Energy spread 0.1% in rms

150 bunches/pulse with 2.8ns bunch spacing

Generation of threemini-train per pulse

40MW, 1.5ms12.5Hz Power Supply

1nC/bunch

Chicane

Amplitudemodulation