RF measurements during floating MD in Week 45

5th of November 2012

LIU-SPS BD WG 22/11/2012

Participants:T. Argyropoulos, H. Bartosik, T. Bohl, J. Esteban Müller, H. Timko, E. ShaposhnikovaCCC: G. Iadarola, Y. Papaphilippou, G. Rumolo

Thanks to all SPS OP on shift

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GeneralMD title: Longitudinal set up of the 25 ns LHC beam with Q20 optics (nominal ~1.25x1011 pb and higher >1.4x1011 p/b injected intensities)

MD aim: Beam stability and acceptable (for the LHC) beam parameters on flat top

Beam conditions: 1 or 4 batches of 72 bunches Intensities at injection: Np~(1.28 -1.6) x1011 p/b

Varying parameters @SPS: RF voltage amplitudes at FB (V200 - operation always in double RF) Longitudinal emittance at PS Increase horizontal chromaticity at flat bottom

Outline Losses

Voltage programs

Stability

Bunch lengths at injection Dipole oscillations at FT Quadrupole oscillations at FT Examples

Comparing with MD@2012-10-03 Before the low level set-up

Summary

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Losses Transmission (from BCT and Larger) ~ 85-89 % for single batch 90-92 % for 3 or 4 batches continuous losses along flat bottom Big losses in the last part of the 4th batch

Larger emittance from PS - similar intensities

Losses after injectionInjected

like this

Voltage programs 200 MHz voltage program settings:

I. 2.5 to 4.5 MV - 4 dips at injections II. 4.5 MV constantIII. 3.5 to 4.5 MV – 1st injection and 2.5 to 4.5 MV – for the restIV. As in III + 500 kV at acceleration and flat top (avoid losses for

higher intensities)V. As in IV but no first dipVI. 5 MV constant (only one file)

optimal

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Stability – Bunch lengths at injection During the MD we asked to increase the longitudinal emittance of the incoming bunches in the PS change of about 100 ps

After the second increase beam was stable with good quality for intensities up to 1.3x1011 p/b

Similar bunch lengths for the operational beam of 50 ns.

εl ~ 0.31-0.33 eVs

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Stability – Dipole oscillations at FT Maximum dipole oscillation only of the first batch is shown: smaller emittance due to phase loop more unstable than the others Vertical lines indicate the long. emittance increase from the PS

Stable conditionsfor intensities Np ~ 1.3x1011 p/b on FT

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Stability – Quadrupole oscillations at FT Maximum Quadrupole oscillation for all 4 batches Vertical lines indicate the long. emittance increase from the PS Similar results as for the dipole oscillations

Stable conditionsfor intensities Np ~ 1.3x1011 p/b on FT

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Examples High intensity: Np = 1.36x1011 p/b at FT

TWC 200 MHz voltage program: case III

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Examples Iintensity: Np = 1.3x1011 p/b at FT

TWC 200 MHz voltage program: case V

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Comparing with MD@2012-10-03 The MD@2012-10-03 was before the low level set-up

Only 4 files to compare with: Similar RF voltages at FB (V200 = 4.5 MV and V800 = 0.45 MV) Longitudinal damper gains

Differences in machine conditions: V200 calculated for bucket area of 0.65 eVs (0.6 eV) Long. Emit. BUP:

Margin High: 1.1 (1.1) Margin Low: 0.85 (0.8) Scaling: 0.85 (0.83) Amp: 50 mV (30 mv)

Different chromaticity settings (both planes)

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Comparing with MD@2012-10-03 Smaller bunch lengths at injection Comparable bunch lengths on FB after capture for the cases with stable conditions Lower injected intensities compared to the stable Smaller total losses

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Summary Bad transmission:

~85-89 % with single batch ~90-92 % with 4 batches

Optimal machine conditions for Np~1.3x1011 p/b at FT Not yet for higher intensities

Significant improvement with longer incoming bunches (τinj ~4.2 ns) as in the operational 50 ns beam. more losses (1-2% ?)

It seams that for smaller bunches with higher intensities BUP is more difficult to optimize (observed also in the past) more induce voltage effect on the shape of the incoherent synchrotron frequency spread (?)

Comparison with the MD@2012-10-03 before the low level set-up (beam was unstable for Np>1.4x1011 p/b at injection):

Smaller bunch lengths at injection Similar at flat bottom after capture Beam was stable in the MD@2012-11-05

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Higher intensities (~1.45x1011 at injection) Increase ScaleBUP while keeping the same high VBUP (60 mV) improved stability Still unstable with long bunches at FT

V200 = 3 MV – V800 = 0.3 MV ScaleBUP = 0.85 – VBUP = 60 mV

V200 = 3 MV – V800 = 0.45 MV ScaleBUP = 0.9 – VBUP = 60 mV

Change of the ratio V800/V200 to 0.1 improved the situation but not significantly

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Higher intensities (~1.45x1011 at injection) Increase RF voltage at FB improved stability

Still some bunches are unstable with very long bunches at FT

V200 = 4.5 MV – V800 = 0.45 MV ScaleBUP = 0.85 – VBUP = 60 mV

V200 = 3 MV – V800 = 0.3 MV ScaleBUP = 0.85 – VBUP = 60 mV