vdM beam production in the injectors

H. Bartosik, G. Rumolo

LBOC, 26. November 2013

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Introduction

o 2 options for producing such bunches (large transverse emittance wrt requested intensity …)a) Low intensity INDIV bunch in the PSB with normalized emittance of about 1-2

μm and then blow-up downstream (mismatch at PS-SPS transfer, resonances in SPS, …)

b) Controlled generation of (relatively low intensity) bunch with already large transverse emittance at exit from PSB (avoid necessity of blow-up downstreams)

o Option b) used in the end of 2012 turned out to be easiest and most reproducible way, while transverse tails were obtained with option a) in the past (see vdM scans early 2012)

LBOC, 26. November 2013

Single bunch beam parameters requested by LHCIntensity 0.7-0.9x1011 p/b

Transverse emittance (norm.) ≥ 2.5 μm

Transverse distribution Gaussian

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Beam preparation in PSB and PSo PSB

• Injection of 2.5 turns and loss of 92% of intensity through slow capture (“longitudinal shaving”) longitudinal emittance around 0.25 eVs

• Adjustment of intensity with vertical shavers (good reproducibility) less than Gaussian vertical tails !!!

o PS• No specific manipulation apart from slight longitudinal emittance blow-up

εx≈3μmεy≈2.5μm (tails less populated than Gaussian)

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Beam preparation in SPSo INDIV cycle in the SPS (flat bottom of 7.2 s to allow for 4 injections)

o Small incoherent losses on flat bottom (large beam size) and capture losses

o Final adjustments of intensity and transverse distribution with scrapers close to flat top intensity around 0.9(±0.1)x1011 p/b

scrapingcapture losses

flat bottom

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Resulting beam profiles at SPS extraction (1)

o Looks pretty Gaussian on the SPS wire scanner• but hard to tell due to limited resolution and linear scale ⇒ tails were populated somewhere from PSB extraction to SPS flat top!

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Resulting beam profiles at SPS extraction (2)o Closer look on beam profiles in log-scale

o Still slightly less than Gaussian tails (apart from the noise floor) in SPS

o These bunches become almost perfectly Gaussian between SPS extraction and collision due to processes in the LHC (see presentation of W. Kozanecki, LBOC December 3rd 2013) with emittances of 2.5-3μm

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Summary and Conclusionso Single bunches for van der Meer scans successfully produced in 2012

• Starting from bunches with large transverse emittance in the PSB (instead of intentional blow-up downstream as used in the past)

o Optimized transverse beam distribution• Significantly less than Gaussian tails at exit from the PSB diffusion and

blow-up in PS and SPS• Slightly less than Gaussian tails at SPS extraction almost perfect Gaussian

distribution at LHC collision (during van der Meer scans)

o Reached beam characteristics requested by LHC• Intensity around 0.9(±0.1)x1011 p/b• emittances of 2.5-3μm• Gaussian profiles at collision in the LHC

o Summary of beam production scheme in ATS note: CERN-ACC-NOTE-2013-0008 MD

LBOC, 26. November 2013