Generation of Higher Brightness Beams for LHC Needs Possibilities: Batch compression in the PS Linac 4 SPL Summary R. Garoby

Needs of various LHC luminosity upgrade scenarios * Luminosity ´1034 cm-2s-1 Comment Brightness factor** Protons in 25 ns (en=3.75 mm) Protons ejected from the PS*** (en=3 mm) Nominal 25 ns 1.0 0.58 A 285 mrad 1 1.15 ´1011 1.35 ´1011 Ultimate 2.3 0.86 A 315 mrad 1.5 1.7 ´1011 2.0 ´1011 Short bunches 12.5 ns 9.2 1.72 A 445 mrad 3 3.4 ´1011 4 ´1011 Long bunch 75 ns 8.9 1 A 430 mrad 1.74 2.4 ´1011 1 TeV inj. 3.44 A ? 5.9 6.8 ´1011 8 ´1011 Needs clarification ! * HIF05 paper ** w.r.t. nominal in LHC *** Transmission PS-> LHC= 0.85 R.G. 2

Increasing brightness in the PS Batch compression [1/5] Proposed procedure: inject 7 (4+3) or possibly 8 (4+4) bunches from two PSB batches into the PS operating on harmonic 9, accelerate this beam up to an intermediate energy where space charge is sufficiently reduced, compress the 7 (8) bunches into 7 (8)/14 of the PS circumference by adiabatically increasing from h=9 to 10,11, 12, 13, 14, accelerate the beam on harmonic 14 up to 25 GeV, triple split the bunches using rf on h=14, 28 and 42 (similar process than used at 1.4 GeV for the 25 ns bunch train), double split bunches, changing the harmonic from 42 to 84, and rotate them before ejection, as in the present 25 ns bunch train scheme. Þ Finally, a train of 42 or 48 bunches, spaced by 25 ns is sent to the SPS every 3.6 s. Best expected performance: assuming that the space-charge limit (with a 1.2 s flat porch at 1.4 GeV) is attained in the PS with 84´1.7´1011 protons over the circumference Þ 2.6´1011 ppb @ PS ejection R.G. 3

Batch compression (7 bunches case) [2/5]: Bucket Height (arb. units) Time R.G. 4

Batch compression (7 bunches case) [3/5]: Bucket parameters during the process (arb. units) Extreme edge Buckets (9 bunches) R.G. 5

Batch compression (7 bunches case) [4/5]: “Ultimate” filling scheme for 42 PS bunches P. Collier, AB/OP 2604 bunches/ring: only 7% fewer than for nominal 72 bunch scheme. 6 injections and 18 s SPS flat bottom: problems with high brightness? R.G. 6

Batch compression in the PS [5/5]: Main characteristics Stage Advantages Limitations & drawbacks Implementation Fast & “Low cost” (low level RF) Manpower intensive preparation Need for much machine time Operation Delicate operation (manpower intensive & prone to imperfection) Lower LHC filling factor (~ -7 %) Longer LHC filling time (~ ´ 1.35) Reduced availability for other users 1.2 s flat porch in the PS with high space-charge SPS capability ? Potential (ppb at PS ejection) 42 bunches every 3.6 s with 2.6´1011 ppb [DQ ~ 0.25] R.G. 7

Increasing brightness in the PSB with Linac 4 (scheme 1) [1/4] Procedure 1 (72 bunches): inject 12 (4´3) bunches from one PSB batch into the PS operating on harmonic 14, accelerate this beam on h=14 up 25 GeV, triple split the bunches using rf on h=14, 28 and 42 (similar process than used at 1.4 GeV for the 25 ns bunch train), double split bunches, changing the harmonic from 42 to 84, and rotate them before ejection, as in the present 25 ns bunch train scheme. Þ Finally, a train of 72 bunches, spaced by 25 ns is sent to the SPS every 2.4 s. Best expected performance: assuming that the PSB can deliver 3.6´1012 protons/ring within 2.5 mm emittances (bg2 x 2 at injection) and that space-charge in the PS at 1.4 GeV can be increased by 1.17 (14/12) (no flat porch) Þ 2.0´1011 ppb @ PS ejection R.G. 8

Increasing brightness in the PSB with Linac 4 (scheme 2) [2/4] Procedure 2 (48 bunches): inject 4 (4´1) bunches from one PSB batch into the PS operating on harmonic 7, accelerate this beam on h=7 up to an intermediate energy, double split bunches, changing the harmonic from 7 to 14, accelerate on h=14 up to 25 GeV, triple split the bunches using rf on h=14, 28 and 42 (similar process than used at 1.4 GeV for the 25 ns bunch train), double split bunches, changing the harmonic from 42 to 84, and rotate them before ejection, as in the present 25 ns bunch train scheme. Þ Finally, a train of 48 bunches, spaced by 25 ns is sent to the SPS every 2.4 s. Best expected performance: assuming that the PSB can deliver 3.6´1012 protons/ring within 2.5 mm emittances (bg2 x 2 at injection) and that space-charge in the PS at 1.4 GeV can be increased by 1.75 (7/4) (no flat porch) Þ 3.0´1011 ppb @ PS ejection R.G. 9

Increasing brightness in the PSB with Linac 4 (scheme 3) [3/4] Procedure 3 (24 bunches): inject 4 (4´1) bunches from one PSB batch into the PS operating on harmonic 7, accelerate this beam on h=7 up to an intermediate energy, compress the 4 bunches into 4/14 of the PS circumference by adiabatically increasing from h=7 to 9,11, 14, accelerate on h=14 up to 25 GeV, triple split the bunches using rf on h=14, 28 and 42 (similar process than used at 1.4 GeV for the 25 ns bunch train), double split bunches, changing the harmonic from 42 to 84, and rotate them before ejection, as in the present 25 ns bunch train scheme. Þ Finally, a train of 24 bunches, spaced by 25 ns is sent to the SPS every 2.4 s. Best expected performance: assuming that the PSB can deliver 3.6´1012 protons/ring within 2.5 mm emittances (bg2 x 2 at injection) and that space-charge in the PS at 1.4 GeV can be increased by 1.75 (7/4) (no flat porch) Þ 6.0´1011 ppb @ PS ejection R.G. 10

Limitations & drawbacks Increasing brightness in the PSB with Linac 4 [4/4]: Main characteristics Stage Advantages (25 ns bunch spacing) Limitations & drawbacks Implementation Cost (P+M ~ 70 MCHF) Construction time (~ 3 years) Operation Reliability (simple & robust operation for the 72 bunches scheme) Short dwelling time at high space charge Reduced LHC filling time (~ ´ 0.82 with 72 bunches) Increased beam availability for other users Need for similar RF gymnastics than today in the PS Capability to accept a DQ of 0.44 for a short duration at 1.4 GeV in the PS ? SPS capability ? Potential (ppb at PS ejection) 72 bunches every 2.4 s with 2´1011 ppb [DQ ~ 0.3] 48 bunches every 2.4 s with 3´1011 ppb [DQ ~ 0.44] 24 bunches every 2.4 s with 6´1011 ppb [DQ ~ 0.44] Safe Possibly OK To be demonstrated R.G. 11

Replacing the PSB by an SPL [1/2]: Main features Injection energy in the PS (SPL CDR-1): 3.5 GeV Þ bg2 ´ 3.9 & DQ ´ 0.26 For a given DQ, brightness can be quadrupled. Þ 8 ´ 1011 ppb at 26 GeV [with DQ ~ 0.31 at injection] Þ other limitations will be dominant (instabilities) Longitudinal bunch population can easily be tailored to the needs (number of bunches, distance between bunches) Acceleration takes place with the harmonic number used at injection (new RF system ?) No need for RF gymnastics (except “rebucketing” inside 40 or 80 MHz buckets) Cycling rate is determined by the PS magnetic cycle (~ 1.5 s) A train of 1 to 80 bunches, spaced by 25 ns (typical) can be sent to the SPS every ~ 1.5 s R.G. 12

Replacing the PSB by an SPL [2/2]: Main characteristics Stage Advantages Limitations & drawbacks Implementation Cost (P+M ~ 500 MCHF) Construction time (~ 5-6 years) Operation Renewed & modern PS injector No need for RF gymnastics in the PS Reliability (simple & robust operation) Short dwelling time at high space charge Reduced LHC filling time (~ ´ 0.82 with 80 bunches) Increased beam availability for other users SPS capability ? Potential (ppb at PS ejection with 25 ns spacing) No more space-charge limitation in the PS: train of 1-80 bunches every 1.5 s with up to 8´1011 ppb Other phenomena will certainly limit intensity at a lower level R.G. 13

Replacing the PSB by an RCS [1/2]: Main features To improve space charge in the PS, transfer energy has to be significantly above today’s value (1.4 GeV). Typically: 3.5 GeV Þ bg2 ´ 3.9 & DQ ´ 0.26 For a given DQ, brightness can be quadrupled. Þ 8 ´ 1011 ppb at 26 GeV [with DQ ~ 0.31 at injection] Þ other limitations will be dominant (instabilities) Space charge in the RCPSB must match the PS capability. Assuming it has the size of the PSB Þ bg2 ´ 7.8 w.r.t. 50 MeV Þ Injection energy = 760 MeV To minimize the duration of the PS flat porch, it must either have 4 rings or cycle fast (typically 50 Hz) and fill 6/7 of the PS in 6 pulses To match the SPL potential w.r.t. the LHC, it must deliver > 9.6´1012 protons/pulse within en=2.5 mm A train of 72 bunches (8 ´ 1011 ppb) , spaced by 25 ns (typical) can be sent to the SPS every ~1.5 s R.G. 14

Replacing the PSB by an RCS [2/2]: Main characteristics Stage Advantages Limitations & drawbacks Implementation Cost (P+M ~ xy0 MCHF) Construction time (~ 3-4 years) Operation Renewed & modern PS injector Reliability (simple & robust operation for the 72 bunches scheme) Medium dwelling time at high space charge Reduced LHC filling time (~ ´ 0.82 with 80 bunches) Increased beam availability for other users Need for similar RF gymnastics than today in the PS SPS capability ? Potential (ppb at PS ejection) No more space-charge limitation in the PS: train of 72 bunches every 1.5 s with up to 8´1011 ppb Other phenomena will certainly limit intensity at a lower level R.G. 15

Comparative summary (25 ns bunch spacing) Batch compression in PS Linac 4 SPL RCS Delay Fast 3 years 5-6 years 3-4 years Implementation MD intensive Setting-up period during start-up Operation Delicate Limited reliability Comfort + Reliability + Comfort ++ Reliability +++ Reliability ++ Number of bunches / PS pulse 42 72 (48 - 24) 1-80 72 Potential intensity per PS bunch 2.6 ´ 1011 ppb 2 ´ 1011 ppb (3 - 6 ´ 1011) 8 ? ´ 1011 ppb Repetition period 3.6 s 2.4 s 1.5 s BEST USE Exploratory tests Reliable operation + 50% of upgrades Reliable operation + all upgrades R.G. 16