Collected by E. Jensen, BE-RF 1 ATOP days RF limitations

 RF limitations:  Voltage necessary to create a certain accelerating bucket area – this becomes often a power limit  Beam loading (BL) will increase the power needs by (at least) the power transferred to the beam (good for higher efficiency)  But BL also leads to an induced voltage that interacts with the various beam and cavity control loops, which may become unstable.  High intensity beams will get closer to a number of stability limits (or instability thresholds). This is RF related since the system dealing with these are often RF systems. 2 ATOP days RF limitations

3

 Linac 2 can produce 180 mA (190 mA in TRA10 were obtained in MD’s in 1994)  It produces regularly 150 – 170 mA for all requested intensity ranges.  Rien à signaler … 4 ATOP days RF limitations M. Vretenar

5 ATOP days RF limitations

Krusche, Paoluzzi: The PSB regularly produces very high intensity beams for Isolde, (3.5 · ) not limited by the RF systems. 6 + transverse damper

 C04 power limitations (for faster cycle)  C04: “High Loss Mode” (not intensity related)  Instability at low C04 voltage and high BL  “Ring 4 problem” (transverse plane)  C02 beam loading 7 ATOP days RF limitations

Haase, Paoluzzi: 8 ATOP days RF limitations

Paoluzzi: (for completeness – not intensity related) 9 ATOP days RF limitations

Note in preparation: Blas, Findlay, Haase, Paoluzzi, Pedersen In MD’s in 2007 and 2008, a stability threshold was observed when increasing the beam-loading (BL) by lowering the C04 voltage. This leads to phase and amplitude coupling and a complex interplay between C02 and C04 control loops. 10 ATOP days RF limitations

I G /V I B /V seen by tuning loop: φ L cavity tuning angle: φ Z Y If I B /I 0 becomes large, small perturbations of I B will have large effects. I 0 /V locus of cavity admittance 11 ATOP days RF limitations

Blas, Chanel, Findlay, Hanke, Mikulec, Quatraro, Rumolo 12

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15 ATOP days RF limitations + transverse damper (2 x 6 kW)

 Phase drift at low voltages due to beam loading  Over-current at γ tr crossing with high BL  Beam losses at γ tr (partly RF related)  Insufficient transient beam-loading compensation for an asymmetrically filled machine  Coupled bunch instabilities above γ tr. (For LHC 25 and 50 ns beams). Ok up to nominal.  Bunch lengthening due to residual impedance of 40 and 80 MHz cavities. 16 ATOP days RF limitations

voltage phase radial position phase H. Damerau When reducing the voltage, the relative BL gets stronger. It leads to the slow phase drift, which the AC coupled phase loop cannot correct. An intensity dependent phase drift is observed, which in turn acts also on the radial position. beam 17 ATOP days RF limitations

 A phase switch is necessary at γ tr.  In the presence of strong BL, this fast phase change requires large power, resulting in a significant, but short increase in anode current, which made the tube protection trip.  In 2008, the tube protection circuit was modified to cope (increased lag time from 500 µs to a few ms) – should be OK now. 18 ATOP days RF limitations C. Rossi

S. Aumon, S. Giladroni, J. Belleman MRP vs. C-timing 19 ATOP days RF limitations

 Observed on LHC type beams.  At present, two C10 cavities are used as longitudinal kicker in the CB feedback; this works OK up to nominal intensity.  Most probable source: the impedance of the C10 cavities themselves. beam peak detected transition H. Damerau et al. : Beam PU signal around 5 th harmonic, down-converted 20 ATOP days RF limitations

 System dimensioned for injection error damping (6 kW per plane) – OK during the cycle.  Somewhat counter-intuitively (for me), higher brilliance (same intensity with smaller ε) will slow down incoherent betatron motion and thus leave more time for the transverse damper before filamentation smears out the transverse beam. A. Blas, G. Rumolo, E. Benedetto 21 ATOP days RF limitations

 Bunch length (4 σ Gaussian fit) vs. bunch # using 2 (blue) and 3 (red) 80 MHz cavities.  Bunches near the end of the batch are longer, due to residual impedance of 40/80 MHz systems.  This effect is more pronounced with all 3 cavities.  Bunches # 50+ are shorter due to coupled-bunch feed- back. Damerau: 22 ATOP days RF limitations

23 ATOP days RF limitations

Each line feeds one cavity 24 ATOP days RF limitations

Total voltage (2 cavities): 4.1 MV w/o BL, ≈ 3.3 MV with nominal BL ( ppb). With new tubes: 350 kW/TX Total voltage (2 cavities): 5.5 MV w/o BL, ≈ 4. 2 MV with nominal BL ( ppb). With new tubes: 400 kW/TX …… 1 line sketched 25 ATOP days RF limitations

26 ATOP days RF limitations

4 x 25 kW RF System runs stably RAS ATOP days RF limitations 27

28 ATOP days RF limitations E. Chapochnikova

V acc /MV 350 kW 450 kW 550 kW 750 kW I b /A (200 MHz component) nominal LHC ( ppb, 25 ns) Extrapolated from: G. Dôme: “The SPS Acceleration System”, CERN-SPS/ARF/ ATOP days RF limitations

# of interventions per week outside normal working hours weeks with piquet service From 2005, limited resources forced us to reduce some maintenance work. CNGS type beams result in more wear and thus reduce tube-lifetime (16! tubes broken in 2008!) This is more related to maintenance and high power than high intensity E. Montesinos 30 ATOP days RF limitations mentioned in D. Manglunki’s talk

The upgrade to more modern IOT is in full swing (white paper). IOT’s are used widely for digital TV transmitters (DVB-T). At present in the “Market Survey” state. Modular: Each line will be composed of 4 identical PA “cubicles” A cubicle can produce 60 kW, 4 cubicles will make up one transmitter, a total of 2 transmitters is needed. Present planning: 1 (test) cubicle in 2009, 4 cubicles in 2011, completion in ATOP days RF limitations

 All systems OK up to nominal LHC.  Main Issues:  PSB C04 with strong beam loading at low voltage  PSB transverse damper installed power marginal  PS C10 with strong beam loading at low voltage  PS around transition – under investigation  PS coupled bunch instability and residual impedances  SPS 200 MHz: frequent interventions, requires regular maintenance  SPS 800 MHz – renovation underway (IOT based) 32 ATOP days RF limitations