Summary tables
Important
An effort to classify the different noise sources into common categories has been proposed. This implies a reasonable but subjective balance between synthesis and simplification.
The presented tables should be considered as an entry point for a general overview, useful to bridge the different topics: a starting point to be improved in a collaborative approach.
Mechanism of interaction
| Noise source | Mechanism of beam interaction | Dipolar/quadrupolar |
|---|---|---|
| GM: ground motion and thermal effect | Seismic noise/thermal drift/ancillary mechanical device vibrations (mechanically coupled with the cold masses/magnets): change of the magnetic center of quadrupole (and higher multipoles). | Dipolar effect considered due to quadrupolar feed-down. |
| BS: beam screen vibrations | Induced by seismic noise and/or by turbulent He cooling flow. At high frequency the field follow the BS therefore a vibration is equivalent to dipolar kicks. | Dipolar considered (BS offset or BS radius vibration). |
| ADT: damper | Dominated by the PU noise (Lebedev model). The kicker reacts to the noise of the PU and excites the beam. | Dipolar (by construction). |
| PC: power converters | By construction, harmonics of the commuting frequency of the semiconductor device perturb the PC output and, after filtering (inductive load, vacuum chamber, beam screen), perturb the magnetic field, hence the beam. | Dipolar and quadrupolar considered. |
| CC: crab cavities | Dominated by the LLRF noise in terms of amplitude and phase of the RF kick. | Dipolar (by construction). |
| FJ: flux jump | Related to well known physics of the Nb3Sn technology (and its mild interplay with the PC). Variation of the field in the magnet. | Much more information on the dipolar noise effect. Preliminary consideration on quadrupolar effect have been made. |
| HEL: hollow electron lens | Interaction with the the beam core due to non-symmetric distribution of the electrons with respect beam orbit (at the moment no intra-bunch effect is expected/studied). S-shape HEL compensate most of the “edge” effects. | Studies concentrated on dipolar kick. |
| UPS: uninterruptible power supplies |
Potential effect on the beam
| Noise source | Potential effects on the beam | Direct observation in LHC? |
|---|---|---|
| GM: ground motion and thermal effect | Orbit effects à Instantaneous Luminosity jitter and beam losses at TCP (possible dumps) | Yes (during CE work in 2018 or earthquakes). It induced BLM dumps in LHC (10 Hz). |
| BS: beam screen vibrations | Orbit effects à Instantaneous Luminosity jitter and beam losses at TCP (possible dumps) Higher frequency (>1 kHz) can cause emittance blow-up and halo repopulation. | No for f>50 Hz. Specific test conducted in 2006. New BS will be tested (not in the STRING). |
| ADT: damper | Emittance blow-up, beam lifetime and halo repopulation à Integral luminosity and beam losses, latency in instabilities. | Yes. Lower noise PU expected in Run3. |
| PC: power converters | Emittance blow-up, beam lifetime and halo repopulation à Integral luminosity and beam losses, latency in instabilities. Tune-tracking degraded. Tune-modulation. | Yes, dipole noise (since Run1, extensive observations in 2018). No, quadrupole noise (tune modulation). |
| CC: crab cavities | Emittance blow-up, beam lifetime and halo repopulation à Integral luminosity and beam losses, latency in instabilities. | No. Extensive MD program in SPS in 2018. |
| FJ: flux jump | Orbit effects (mainly) à Instantaneous Luminosity jitter and beam losses at TCP (possible dumps) | No. More data expected in Run3 (11 T dipoles). |
| HEL: hollow electron lens | Emittance blow-up, beam lifetime and core diffusion à Instantaneous Luminosity jitter and beam losses at TCP (possible dumps) | No. MD studies in LHC during Run2. |
| UPS: uninterruptible power supplies |
The s-dependence
| Noise source | Single or multiple locations in the lattice? |
|---|---|
| GM: ground motion and thermal effect | Distributed effect (in principle). In practice dominated by the triplets (but exception for the ‘10 Hz’-event). Depending of the frequency (>3 Hz), limited spatial correlation is expected. |
| BS: beam screen vibrations | In practice dominated by the triplets. If induced by the He cooling flow, no spatial correlation expected. |
| ADT: damper | Localized at the ADT kickers. |
| PC: power converters | Distributed. Spatial correlation expected for PCs powering a long string of magnets (difficult to compute above few tens of Hz). |
| CC: crab cavities | Localized at the CC location. |
| FJ: flux jump | Localized at the Nb3Sn magnets (IR⅕ triplets and 11 T dipoles). |
| HEL: hollow electron lens | Localized at the HEL. |
| UPS: uninterruptible power supplies |
The t-dependence
| Noise source | Effects along the beam cycle |
|---|---|
| GM: ground motion and thermal effect | Despite the GM and thermal effect are always present, effect mainly optics-driven (high value of beta-function in the triplets): mainly at FLATTOP and for high tele-index. To consider evolution with Geothermie2020. |
| BS: beam screen vibrations | See GM. Mainly at FLATTOP and for high tele-index. |
| ADT: damper | During the full cycle but dependent on gain of the ADT settings and of the beam tune spread…(Lebedev model). |
| PC: power converters | Dipole component: observed during the full cycle. Quadrupole component: larger at high tele-index. |
| CC: crab cavities | Studies focus when crabbing bump is active (FLATTOP). |
| FJ: flux jump | Mainly during the first part of the ramp (<3 TeV). |
| HEL: hollow electron lens | Mainly when the HEL is powered in resonant mode (most likely a cleaning of the tail will be done after the injection and before the squeeze, tbc) |
| UPS: uninterruptible power supplies |
Frequency spectrum
| Noise source | Frequency spectrum |
|---|---|
| GM: ground motion and thermal effect | From DC to ~100 Hz, but significant contribution expected at the resonance of the triplets (~21 Hz). |
| BS: beam screen vibrations | New BS are quite massive due to the tungsten masks (~500 Kg/~10 m). First three modes resonance between 10-20 Hz. Test of vibration induced by turbulent flow planned but minor effects are expected. |
| ADT: damper | The noise is in the ATD BW, 3 kHz – 1 MHz (20 MHz in extended mode). |
| PC: power converters | Harmonics of the switching frequency. Depending on the technology (SCR, silicon-controlled rectifier, or SMPS, switched-mode power supply), the switching frequency can very different (from ~50 Hz for SCR to up to 200 kHz for the SMPS) |
| CC: crab cavities | Two very different mechanism: phase and amplitude noise. Both originated by the noise of the LLRF loops (from DC to 100 kHz). The first one will appear as a bbb kick while the second is equivalent to an intra-bunch kick (hence beyond ADT capability) |
| FJ: flux jump | Magnetic measurement show effects mainly between 10-100 Hz |
| HEL: hollow electron lens | Spectrum will depend on the powering mode. Assuming resonant excitation, one should expect noise from the first betatron line (>3 kHz). Intra-bunch kick is not considered. |
| UPS: uninterruptible power supplies |
Expected effect on the beam
| Noise | Orbit effect expected | Emittance blow-up |
|---|---|---|
| GM: ground motion and thermal effect | HL-LHC twice more sensitive than LHC. The 10-Hz noise induced 10 dumps in Run2. Triplet expected vertical motion (magnetic axis) below 0.04 μm (for f>3 Hz) and a consequent expected luminosity losses <0.1%. Monitor effect of Geothermie2020. | Negligible. |
| BS: beam screen vibrations | None additional to GM (rigid motion triplets-BS wrt the CM). | Negligible. |
| ADT: damper | Negligible. | Estimated in LHC (Lebedev model fit, gain of 50 turns) in 2%/h emittance growth in LHC. To maintain a similar level for HL-LHC, ADT PU noise needs be reduced by x4. Lebedev model implemented in the LHC luminosity model: ~0.12 um/h at injection, ~0.045 um/h in production. |
| PC: power converters | Negligible. | DIPOLES: Simulations show impact on lifetime (~15% reduction). QUADRUPOLES: Negligible. |
| CC: crab cavities | Negligible. | Expected 3.7%/h (amplitude noise) and 0.94%/h (phase noise). |
| FJ: flux jump | DIPOLE FJ: below BLM threshold. QUADRUPOLE FJ: more critical (induced dumps expected in a non negligible number of beam) but input needed. | Negligible. |
| HEL: hollow electron lens | Negligible. | MD studies report effects larger than the ones (negligible) expected from simulations. Details depend strongly on the resonance mode selected. The dipole kick assumed is 15 nrad (this equivalent to 3e-6 stability of a single main bend). |
| UPS: uninterruptible power supplies |
Assumptions and open questions
To be filled.
| Noise | Assumptions, limits of the approach and open questions |
|---|---|
| GM: ground motion and thermal effect | |
| BS: beam screen vibrations | |
| ADT: damper | |
| PC: power converters | |
| CC: crab cavities | |
| FJ: flux jump | |
| HEL: hollow electron lens | |
| UPS: uninterruptible power supplies |