BCC 46-alternative to the LBS line 1

Ideal location of energy spread measurements in the linac4-PSB

transfer line

Alessandra Lombardi

25/07/2013

BCC 46-alternative to the LBS line 2

introduction

• Distances involved in meters

• Reminder: 1 m in linac2 = 2 m in LINAC4 !!! • If we re-scale from linac2 we could measure

the en spread about 100m before PSB injection, let’s call this point “point F”.

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Linac4 Linac2

Accelerator-debuncher 42m 22m

Debuncher to LBS 88m 62m

LBS to BI injection 49m 49m

BCC 46-alternative to the LBS line 3

LINAC4 at PSB injection-specs

• Average energy : 160 ±??

• Energy swing over 20 µsec: 1.2 MeV

• Energy spread : min 0.120 MeV

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BCC 46-alternative to the LBS line 4

Energy…..• TOF via 3 BPM and phase pick ups • we have 3 x 28 deg + 2 X 15 deg + BHZ20 and BHZ30 : we can measure the energy from the

linac and find the zero crossing of the cavity

• Line dispersion is very sensitive to Quadrupole(s) in the first horizontal bending. There are 3 beam centre position measurements before the vertical bending.

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0.00E+00 1.00E+01 2.00E+01 3.00E+01 4.00E+01 5.00E+01 6.00E+01 7.00E+01 8.00E+01

-1.50E+00

-1.00E+00

-5.00E-01

0.00E+00

5.00E-01

1.00E+00

1.50E+00

beam centre dispersion [m]-PIMS to BHZ20

BCC 46-alternative to the LBS line 5

And energy spread…

• This varies along the line due to :

• Cavity in L4T line (L4T.ACDB.1075) :PIMS-like ; 700 kV effective voltage available.

• Space charge : peak space charge in the RF bucket, it doesn't depend on the chopping factor, it depends on the source current and the losses along the linac.

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BCC 46-alternative to the LBS line 6

What happens to energy spread along the line- effect of the cavity

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0 20 40 60 80 100 120 140 160 180 2000.00E+00

1.00E-04

2.00E-04

3.00E-04

4.00E-04

5.00E-04

6.00E-04

7.00E-04

rms energy spread in GeV - 62mA- buncher voltage 700kV

phase 90cavity offphase -90

BCC 46-alternative to the LBS line 7

Zoom in after the cavity – see effect of space charge

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40 60 80 100 120 140 160 180 2000.00E+00

2.00E-05

4.00E-05

6.00E-05

8.00E-05

1.00E-04

1.20E-04

1.40E-04 rms energy spread in GeV- evolution from cavity to PSB injection

65mA30 mA0 mA L4T.ACDB.1075point FPSB inj foil

meters

BCC 46-alternative to the LBS line 8

Comparison with LINAC2

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0 20 40 60 80 100 120 1400.00E+00

5.00E-05

1.00E-04

1.50E-04

2.00E-04

2.50E-04

evolution of rms energy spread in GeV-160 mA

Kinetic Energy RMS [GeV] linacout LBS PSB inj

meters

BCC 46-alternative to the LBS line 9

measuring≠controlling

• The quality of the beam that we deliver to the PSB depends on

• Linac4 RF settings and their control (phase and ampli jitter)• The available field in L4T.ACDB.1075

• With the present layout we can match the specs of the PSB : energy swing (±1.2 MeV over 20-40 µsec); rms energy spread variable 120keV-700 keV

• If we need to reduce the energy spread or if we want to guarantee more control under different conditions we should ask for more power in the buncher and/or a second buncher but we cannot improve the situation with a more precise measurement!

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BCC 46-alternative to the LBS line 10

Conclusion

• It is possible to measure the energy spread of the beam before the LT LTB line and deduce sound values for the energy spread delivered to the PSB

• This opens the possibility to measure the energy spread with different techniques than a bending magnet, which are more suitable for our layout and increased beam energy.

25/07/2013