Minimum emittance from PSB H- injection

E.Benedetto

Input and discussions with (so far): G.Rumolo, C.Bracco, B.Mikulec, J.B. Lallement

Outline• Minimum emittance from H- injection in PSB (is obtained

with no transverse painting) :

eL4 +Defoil +Desc +Demismatch

– Emittance from Linac4 eL4 – Scattering at the foil Defoil

– Space charge Desc – Mismatch errors & ripples Demismatch: beta, disp, trajectory, ripples

• BCMS beams• Can we measure small beams?

– Wire scanners– SEMgrids, MTVs, IPM,…

• Transfer between machines

From Linac4

• Emittance (always rms normalized)– Nominal Emittance: from source 0.25um

• Assuming some blow-up ~0.35um delivered to PSB– Maximum emittance:

• Defined by RFQ acceptance = ~0.35um ~0.4um to PSB

• Intensity (average): – Nominal: from source 80mA

• After RFQ, chopper,… 40mA to PSB– Minimum intensity (inside the 0.35um emittance)

• We can assume 20mA to PSBFrom JB Lallement and M. Vretenar’s presentation @ LIU day

Scattering at the foil• Absolute De (depends on b -function and Nh foil traversals):

• Number of passages:– 13turns injection(20mA) + ~7 turns KSW decay (remove beam from foil)

= 20passages

• cfr. B. Goddard et al., Proc. IPAC ‘10, Kyoto: Dex, y= 0.25, 0.15 um for 25 hits (carbon 200 ug/cm2)

assume Defoil <~0.20um

From Chiara

Space Charge

• No machine experience of injecting <1um beams– We should rely on simulations & scaling for the same DQSC

• Curve Emittance vs. Intensity with Linac4 – Simulation campaign ongoing– Depends on:

• Laslett tune spread• Working point (and resonance compensation)• Injection & painting schemes• Longitudinal parameters• …

EB, Chiara, Vivien, Giovanni, Bettina

Mismatch @ inj., kicker ripples, jitters

• Ripples in these elements:• Steerers in BI line• KSW painting bump• BSW (slow chicane bump) constant B field during injection

– will induce offset in injected beam (or in the closed orbit) cfr. In the production of high intensity beams with H- injection, voluntary Dy to increase vertical emittance

– or unwanted painting

• Need input from hardware• Will be considered in Chiara’s injection simulations

Discussion with Chiara and ABT started

Scraping in PSB• Preliminary consideration: reduces Emittance but also

Intensity no gain in brightness– See today production 50ns BCMS beam

• (Scraping is after inj. process i.e. independent of L2 or L4)

– Stays on the same curve Emi vs. Int.

• Issues (to be studied): – Losses at >160MeV induce higher activation– Scrapers strength at higher energy (Brho & smaller beam size)

• Ok! today <8A @65MeV (power supply can go up to 50A)

– Precision of scraping such a tiny beam (if we want to get half of ~0.5-0.6um) need studies & maybe MD with LHCPROBE after LS1?

From Bettina

• Production without scraping• Inject half # of turns

Scattering • (~7+7 foil traversals=14 Vs. 20)

Half the SC tune spread• ~same DQ as today @160MeV

– Measurements @160MeV confirm no appreciable blow-up over 150ms plateau for today LHC-type beams of 2-3um (MD 4/6/12 by V.Forte, A.Molodozhenstev)

• BUT for a smaller (~0.5-6um) beam– No experience– SpaceCharge simulations needed

Emittance BCMS beam (~half intensity)Assumption with Linac4 “half-of-the-slope” (cfr. Giovanni’s Slide2, 19/7/13), here for the BCMS curve

• IF ripples & mismatch at injection are “small”, we could keep the Linac4 emittance + scattering < 0.6um – Again, this is the open point

Can we measure small beams?

• No problem with Wire Scanners in PSB and PS– Enough resolution– May be a problem in the SPS…

PSB @ extractionLHCPROBE, I=1.2e10Verticals=1.23en=0.8um

PS @ extractionLHC50#24b_BC…, Ip=388e10Verticals=0.714en=0.65um(?)

Can we measure small beams?

• SEM grids in BTP line are at the limitLHCPROBEen,x=0.6umen,y=0.8um

Transfer between machines

• Emittance dilution due to Injection and Dispersion Mismatch are “absolute”, i.e. independent on the initial Emittance (the betatron mismatch is “relative”)

• Impact on smaller beams is higher and given by the mismatch factors:

• i.e. half the emittance, twice the blow-up in %

• Can we still consider it “zero” in our budget?

Summary• Assuming from Linac4: 20mA (min) in 0.4um (max), the emittance at the

end of H- injection is ~0.6um (no SC, no ripple, only scattering).• Space-charge and kicker ripples not taken into account in values above:

– ONGOING space-charge simulations (emi vs. Intensity curve)– Need input for ripples & mismatch to be implemented in inj simulations

• For BCMS beam, DQSC ~same as today nominal @160MeV – more confident to keep ~0.6um apart from ripples, inj. mismatch and jitters.

• Scraping at >160 MeV may be an issue because of activation, and required scraping precision need study

• No problem to measure ~0.7um with FWS in PSB & PS and enough resolution to go down, SEM grids in the line at the limit.

• Transfer between machines: – Injection &Dispersion mismatch for smaller beams have a larger impact on

emittance dilution. Can we still consider it “zero”?