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RF measurements during long MD in Week 45 7-8 & 9-10 November 2011. Faraday Cage : T. Argyropoulos , T. Bohl , H. Damerau , J. E. Muller, E. Shaposhnikova , H. Timko CCC : H. Bartosik , W. Hofle , Y. Papaphilippou , G. Rumolo , B. Salvant , SPS OP + …. SPSU-BD 24/11/2011.
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RF measurements during long MD in Week 45 7-8 & 9-10 November 2011 Faraday Cage: T. Argyropoulos, T. Bohl, H. Damerau, J. E. Muller, E. Shaposhnikova, H. Timko CCC: H. Bartosik, W. Hofle, Y. Papaphilippou, G. Rumolo, B. Salvant, SPS OP + … SPSU-BD 24/11/2011
MD aims • PS SPS transfer studies (H. Timko) • (only with 25 ns beam) • Nominal (Q26) ─ Low γt (Q20) optics threshold comparison (optimization) • 25 ns beam (1st period, 7-8 November) • 50 ns beam (2nd period, 9-10 November) • Higher intensities
Outline • 50 ns beam (2nd period) • I. Intensity : ~1.6x1011 p/b (injected) • II. Intensity : ~1.9x1011 p/b (injected) • 25 ns beam (1st period) • Intensity : nominal (~1.2x1011 p/b) • Nominal optics (Q26 - LHCMD1) optimization • ─ Phase between the two RF systems φ800 • ─ Voltage of the 800 MHz RF • Low γt optics (Q20 – LHCFAST3) optimization • ─ Voltage of the 200 MHz RF • ─ Voltage of the 800 MHz RF • ─ Gain of the Long. Damper at Flat Bottom (FB) • Threshold comparison in single RF system for similar bucket • parameters • Examples • Threshold comparison in single RF • Examples in double RF (bunch shortening mode) • 1 batch mainly • No time for controlled emittance blow-up optimization • beam was unstable at Flat Top (FT) in most cases
Q26 - Double RF - 50 ns (1.6x1011 p/b) • V800 = 0.1 V200 • Instability starts at 16 -17 s • Scan of φ800 didn’t help much • (same for whole cycle) • Losses ~ 5 %
Q26 - Double RF - 50 ns (1.6x1011 p/b) • Change voltage of TWC800 to • V800 = 0.15 V200 • More stable during ramp but not • enough V800 for FT • Quadrupole, dipole oscillations at FT • Losses ~ 5 % Controlled emittance blow-up is needed !!
Q20 - Double RF - 50 ns (1.6x1011 p/b) • V200 for the same mismatch at injection • as for Q26 • V800 = 0.1 V200 • Instability starts at16.5 -17.8 s later! • Long Damper nominal settings for Q20 • (15 dB gain at FB) • Losses ~ 5 %
Q20 - Double RF - 50 ns (1.6x1011 p/b) • Results • ─ When unstable, instability starts at the end of acceleration • ─ Quadrupole oscillations Δτ ~ (0.15 – 0.4) ns at flat top (mainly at the • end of the batch) • ─ Dipole oscillations Δt up to ~ 200 ps (~15°) for the less unstable (quadrupole) • cases (bigger at the middle of the batch) • Best settings • V200 closer to matched conditions • V800 as before (0.56 MV const at FB) • voltage ratio 0.23 at injection , 0.13 the rest of FB • and 0.1 ramp & FT • Long Damper gain 10 dB at FB • Losses ~ 4 %
Q20 - Double RF - 50 ns (1.6x1011 p/b) • Round bunches immediately after • injection • Small emittances at FT applying emittance blow-up is possible • Small bunch length spread inside the batch small dipole oscillations no quadruple oscillations
Q20 - Double RF - 4 batches - 50 ns (1.6x1011 p/b) • V200 4.5 MV const at FB • V800 0.56 MV const at FB (0.13 ratio) • Long Damper gain 10 dB at FB • 2 – 4 batches are blown-up at FB • stable at FT • Losses ~ 5 %
Q26/Q20 - Single RF thresholds - 50 ns (1.6x1011 p/b) • V200 as before • Instability starts at14.2 -14.7 s • Losses ~ 5 - 6 % Q26 • V200 as before (5.6 MV const at FB) • Long Damper nominal settings for • Q20 (15 dB gain at FB) • Instability starts at 16 -17.5 s • Beam blows-up after injection (or • FB) • Losses ~ 5 - 6 % Q20
Q20 - Single RF thresholds - 50 ns (1.6x1011 p/b) • V200 as before (5.6 MV const at FB) • Long Damper gain15 dB at FB • Blow-up at FB Instability comes later • Losses ~ 5 -6 % Q20 • V200 as before (5.6 MV const at FB) • Long Damper gain 10 dB at FB • No blow-up Instability comes earlier • (at 14.5 – 15.2 s) • Losses ~ 5 -6 % Q20
Q26/Q20 - Double RF - 50 ns (1.9x1011 p/b) • V200 nominal (2 MV inj 3 MV at FB) • V800 = 0.1 V200 • Instability starts at 15.5 -16.5 s • Bigger bunch length spread inside the • batch • Losses ~ 8 – 9 % Q26 • V200 4.5 MV const at FB • V800 0.56 MV const at FB • Instability starts at 16.8 - 17.7 s • Losses ~ 8 – 9 % Q20
Q26/Q20 - Single RF - 25 ns (1.2x1011 p/b) • V200 for constant bucket area • of 0.65 eVs (1.8 MV at FB) • + 7 MV at FT • Beam was lost Q26 • V200 for constant bucket area • of 0.65 eVs (5.25 MV at FB) • + 7 MV at FT • Instability starts later in the cycle • Blow-up of the beam at FB • Bigger bunch length spread inside • the batch before beam blows-up Q20
Q26/Q20 - Double RF - 25 ns (1.2x1011 p/b) • V200 for constant bucket area • of 0.65 eVs (1.8 MV at FB) • + 7 MV at FT • V800 = 0.1 V200 • Controlled emittance blow-up is • necessary Q26 • V200 for constant bucket area • of 0.65 eVs (5.25 MV at FB) • + 7 MV at FT • V800 = 0.1 V200 (of Q26!!) • Beam is stable at FT • Large dipole oscillations for some • bunches Q20
Summary • 50 ns beam • I. Intensity : ~1.5x1011 p/b (injected) • II. Intensity : ~1.9x1011 p/b (injected) • ─ Better for Q20 but unstable in both cycles • ─ Losses ~ 8 – 9 % • ─ Need time for emittance blow-up for both cycles • 25 ns beam • Intensity : nominal ~1.2x1011 p/b (injected) • ─ Better for Q20. Need of 800 MHz RF for both cycles • ─ Low Losses 2.5 – 3 % • Nominal optics (Q26) • ─ Big improvement by increasing the voltage ratio V800 /V200 to 0.15 • ─Emittance blow-up is still necessary. • Low γt optics (Q20) • ─ Stable (quadrupole) at FT after optimization (1 batch, 2 RF systems) • ─ Small emittances at FT and applying emittance blow-up is still possible • ─Dipole oscillations not always acceptable • ─Further optimization of the Long. Damper settings (and other LLRF?) • Q26/Q20 threshold comparison in single RF system • ─ Higher for Q20 • ─ Uncontrolled beam blow-up on FB in Q20 More MD time is needed!
