RF measurements during long MD in Week 45 7-8 & 9-10 November 2011
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Transcript of RF measurements during long MD in Week 45 7-8 & 9-10 November 2011
RF measurements during long MD in Week 45
7-8 & 9-10 November 2011
SPSU-BD 24/11/2011
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 + …
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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)
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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 %
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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 %
5Controlled emittance blow-up is needed !!
• 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 %
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Q20 - Double RF - 50 ns (1.6x1011 p/b)
• 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 %
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
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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
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no quadruple oscillations
small dipole oscillations
Q20 - Double RF - 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 %
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Q20 - Double RF - 4 batches - 50 ns (1.6x1011 p/b)
• V200 as before
• Instability starts at14.2 -14.7 s
• Losses ~ 5 - 6 %
• 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 %
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Q26/Q20 - Single RF thresholds - 50 ns (1.6x1011 p/b)
Q20
Q26
• 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 %
• 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 %
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Q20 - Single RF thresholds - 50 ns (1.6x1011 p/b)
Q20
Q20
• 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 %
• 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 %
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Q26/Q20 - Double RF - 50 ns (1.9x1011 p/b)
Q26
Q20
• V200 for constant bucket area of 0.65 eVs (1.8 MV at FB) + 7 MV at FT
Beam was lost
• 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
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Q26/Q20 - Single RF - 25 ns (1.2x1011 p/b)
Q26
Q20
• 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
• 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
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Q26/Q20 - Double RF - 25 ns (1.2x1011 p/b)
Q26
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
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More MD time is needed!