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Outline

Title
Abstract
Figures
Executive Summary
Safety Objectives
Introduction and Present Operational Performance
Characterization of Leir Performance Limitations
Conceptual Design
Beam Dynamics and Measurement Results
Introduction
References
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Engineering

Technical Design Report Vol. II: Ions

Profile image of R. GarobyR. Garoby

2016

Abstract
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The Technical Design Report outlines the necessary upgrades to meet the HL-LHC's requirements for integrated luminosity with Pb-Pb collisions in the post-LS2 era. It details baseline and alternative upgrade options to enhance beam parameters at the SPS extraction, with a focus on achieving high luminosity and operational performance through strategic improvements. Key findings indicate that specific upgrades can potentially exceed performance metrics initially set by HL-LHC.

Figures (51)
Table 1.1 Pb ion beam parameters at SPS extraction for the HL-LHC project.
Table 1.1 Pb ion beam parameters at SPS extraction for the HL-LHC project.
Table 1.2 Estimated performance reach for the different scenarios. Compared to the HL-LHC request, the baseline LIU-ions scenario gives 20% lower bunch intensities at he SPS extraction and 8% fewer bunches in LHC, leading to ~15% lower integrated luminosity [3]. The LIU-ions 25 ns scenario Option | compensates the 20% lower bunch intensities with up to 35% more bunches in LHC, resulting in a ~20% higher integrated luminosity than the requested value estimation based on a simple scaling with the total number of bunches). This preliminary estimate suggests that this option has the potential to meet the final requirement of integrated luminosity during he post-LS2 era and even allows for some margin against the main risks of the project (mitigation of osses throughout the injector chain, SPS slip stacking, and preservation of high LHC performance efficiency).
Table 1.2 Estimated performance reach for the different scenarios. Compared to the HL-LHC request, the baseline LIU-ions scenario gives 20% lower bunch intensities at he SPS extraction and 8% fewer bunches in LHC, leading to ~15% lower integrated luminosity [3]. The LIU-ions 25 ns scenario Option | compensates the 20% lower bunch intensities with up to 35% more bunches in LHC, resulting in a ~20% higher integrated luminosity than the requested value estimation based on a simple scaling with the total number of bunches). This preliminary estimate suggests that this option has the potential to meet the final requirement of integrated luminosity during he post-LS2 era and even allows for some margin against the main risks of the project (mitigation of osses throughout the injector chain, SPS slip stacking, and preservation of high LHC performance efficiency).
Table 2.1 Condensed summary of the experiments’ requirements. Since only four Pb-Pb runs will take place between LS2 and LS4, and one of them will be conducted with reduced magnetic field, the resulting request for yearly integrated luminosity was estimated to be about 2.85 nb’/year. In brief, the simplified model described in [1] translates this requirement into the desired Pb ion beam parameters at the SPS extraction specified in Table 2.2.
Table 2.1 Condensed summary of the experiments’ requirements. Since only four Pb-Pb runs will take place between LS2 and LS4, and one of them will be conducted with reduced magnetic field, the resulting request for yearly integrated luminosity was estimated to be about 2.85 nb’/year. In brief, the simplified model described in [1] translates this requirement into the desired Pb ion beam parameters at the SPS extraction specified in Table 2.2.
Table 2.2 Pb ion beam parameters at SPS extraction for the HL-LHC project. In present operation and after few significant improvements implemented during the 2015 run, the Pb ion beam parameters achieved at the SPS extraction [3] are summarized in Table 2.3.
Table 2.2 Pb ion beam parameters at SPS extraction for the HL-LHC project. In present operation and after few significant improvements implemented during the 2015 run, the Pb ion beam parameters achieved at the SPS extraction [3] are summarized in Table 2.3.
Table 2.3 Achieved Pb ion beam parameters at SPS extraction (2015). Comparing Table 2.2 and Table 2.3, we conclude that the HL-LHC target is roughly the same intensity per bunch within a 10% lower transverse emittance, but notably a 2.4 times larger number of bunches in the LHC.
Table 2.3 Achieved Pb ion beam parameters at SPS extraction (2015). Comparing Table 2.2 and Table 2.3, we conclude that the HL-LHC target is roughly the same intensity per bunch within a 10% lower transverse emittance, but notably a 2.4 times larger number of bunches in the LHC.
Figure 2.2 Bunch intensity at the different stages of the LHC ion injection chain. Figure 2.2 shows the evolution of the Pb ion bunch intensity (in ions/bunch) along the injector chain after all the LIU upgrades, based on all the assumptions summarized above.
Figure 2.2 Bunch intensity at the different stages of the LHC ion injection chain. Figure 2.2 shows the evolution of the Pb ion bunch intensity (in ions/bunch) along the injector chain after all the LIU upgrades, based on all the assumptions summarized above.
Table 2.4 Beam parameters at the different stages of the LHC ion injector chain for the three scenarios: Achieved 2015, during the post-LS2 LIU era (LIU-ions) and from the HL-LHC request (HL-LHC). The yearly integrated luminosity estimated with the LIU beam parame he method described in [1] and found to be about 2.5 nb”'/year [6]. In or 7 Z TeV operation and B*=0.5 m for each experiment, giving haring between the experiments (ALICE, ATLAS, CMS). The tota ers was also calculated following particular, the estimate was made approximately equal luminosity number of bunches in collision vas assumed to be 1056, lower than the theoretical maximum value of 1152, because it was calculated or a realistic filling pattern for physics, with the constraint of equal uminosity sharing, together with he delivery of a lower luminosity to LHCb. The LHC performance efficiency [8] assumed in the LIU cenario was also chosen to be 62%, which is the value achieved in 20 5 and is significantly higher than hat achieved for proton operation and assumed for the HL-LHC upgrade (i.e. 50%) [1].
Table 2.4 Beam parameters at the different stages of the LHC ion injector chain for the three scenarios: Achieved 2015, during the post-LS2 LIU era (LIU-ions) and from the HL-LHC request (HL-LHC). The yearly integrated luminosity estimated with the LIU beam parame he method described in [1] and found to be about 2.5 nb”'/year [6]. In or 7 Z TeV operation and B*=0.5 m for each experiment, giving haring between the experiments (ALICE, ATLAS, CMS). The tota ers was also calculated following particular, the estimate was made approximately equal luminosity number of bunches in collision vas assumed to be 1056, lower than the theoretical maximum value of 1152, because it was calculated or a realistic filling pattern for physics, with the constraint of equal uminosity sharing, together with he delivery of a lower luminosity to LHCb. The LHC performance efficiency [8] assumed in the LIU cenario was also chosen to be 62%, which is the value achieved in 20 5 and is significantly higher than hat achieved for proton operation and assumed for the HL-LHC upgrade (i.e. 50%) [1].
Figure 2.3 LIU Project Safety structure.
Figure 2.3 LIU Project Safety structure.
The heavy ions for the CERN ion accelerator chain are delivered from Linac3 (see Figure 3.1) and the GTS-LHC ion source [1]. Isotopically enriched *°°Pb with a purity of 99.6% is used to create the Pb-ion beam. After the separation of the charge states, Pb?** is accelerated in the Linac3 and sent through a stripper foil. From all resulting charge states, Pb*** ions are selected by the filter line before sending the beam to LEIR. Up to now, the following record values have been achieved: 215 uA of Pb’”* after the charge state separation in the spectrometer (measured with the Faraday Cup FC2) and 31 pA of Pb*** at the end of the Linac3 (ITF.BCT25, with 120-130 pA of Pb** in FC3). However, both values were not achieved at the same time, neither is it possible to produce them for long term operation, or even on demand. Maximizing the ion current at the output of the spectrometer very often leads to a poor transmission in the rest of the Linac3. This issue is part of an ongoing study. For routine operation, 100 — 120 pA of Pb*** out of the RFQ (measured with the Faraday Cup FC3) and 20-25 pA of Pb*** at the end of the Linac3 (TF.BCT25) are available. The current at the end of the Linac3 corresponds to less than 50 % of the design value.
The heavy ions for the CERN ion accelerator chain are delivered from Linac3 (see Figure 3.1) and the GTS-LHC ion source [1]. Isotopically enriched *°°Pb with a purity of 99.6% is used to create the Pb-ion beam. After the separation of the charge states, Pb?** is accelerated in the Linac3 and sent through a stripper foil. From all resulting charge states, Pb*** ions are selected by the filter line before sending the beam to LEIR. Up to now, the following record values have been achieved: 215 uA of Pb’”* after the charge state separation in the spectrometer (measured with the Faraday Cup FC2) and 31 pA of Pb*** at the end of the Linac3 (ITF.BCT25, with 120-130 pA of Pb** in FC3). However, both values were not achieved at the same time, neither is it possible to produce them for long term operation, or even on demand. Maximizing the ion current at the output of the spectrometer very often leads to a poor transmission in the rest of the Linac3. This issue is part of an ongoing study. For routine operation, 100 — 120 pA of Pb*** out of the RFQ (measured with the Faraday Cup FC3) and 20-25 pA of Pb*** at the end of the Linac3 (TF.BCT25) are available. The current at the end of the Linac3 corresponds to less than 50 % of the design value.
Figure 3.2 Tip of an oven after two weeks of operation. At the end of its lifetime, the tip of the oven is usually blocked (see Figure 3.2). An oven refill takes around 8 hours from beam to beam, with the source requiring regular tuning for the next 24 hours. This is down time for the whole Pb-ion accelerator chain.
Figure 3.2 Tip of an oven after two weeks of operation. At the end of its lifetime, the tip of the oven is usually blocked (see Figure 3.2). An oven refill takes around 8 hours from beam to beam, with the source requiring regular tuning for the next 24 hours. This is down time for the whole Pb-ion accelerator chain.
Figure 3.3 Extraction of the ion beam from the Linac3 GTS ion source, simulations performed with IBSimu. Blue: Electrodes; Green: Equipotential lines; Yellow/Red: Ion density. As illustrated in Figure 3.3, the beam extracted from the ECR source operated in afterglow mode has a very strong divergence, causing significant beam collimation on the first element encountered downstream (the magnetic solenoid ITL.SOLO1), due to the present aperture restrictions of the vacuum chamber (65 mm diameter). PATH simulations show that the transmission of ?°°Pb?** beam through this region and the following spectrometer dipoles to the slit varies between 50 and 60%. This result compares well to beam transmission measurements during operation: typical readings on the first available transformer at the end of the LEBT (ITL.BCTO05) show an average current of around 150 pA in good operation, to be compared to an estimated beam current at source extraction of approximately 5 mA (5% of which is the 7°°Pb?** component).
Figure 3.3 Extraction of the ion beam from the Linac3 GTS ion source, simulations performed with IBSimu. Blue: Electrodes; Green: Equipotential lines; Yellow/Red: Ion density. As illustrated in Figure 3.3, the beam extracted from the ECR source operated in afterglow mode has a very strong divergence, causing significant beam collimation on the first element encountered downstream (the magnetic solenoid ITL.SOLO1), due to the present aperture restrictions of the vacuum chamber (65 mm diameter). PATH simulations show that the transmission of ?°°Pb?** beam through this region and the following spectrometer dipoles to the slit varies between 50 and 60%. This result compares well to beam transmission measurements during operation: typical readings on the first available transformer at the end of the LEBT (ITL.BCTO05) show an average current of around 150 pA in good operation, to be compared to an estimated beam current at source extraction of approximately 5 mA (5% of which is the 7°°Pb?** component).
Figure 3.4 Simulated 7°°Pb?** beam distribution at the GTS-LHC source extraction. From top left clock-wise: horizontal, vertical and longitudinal phase space, and transverse cross-sectional cut x-y.
Figure 3.4 Simulated 7°°Pb?** beam distribution at the GTS-LHC source extraction. From top left clock-wise: horizontal, vertical and longitudinal phase space, and transverse cross-sectional cut x-y.
Figure 3.5 Einzel lens mechanical design.
Figure 3.5 Einzel lens mechanical design.
Figure 3.6 Transmission of ?°8Pb?** through the LEBT to the RFQ entrance with the existing (blue line) and upgraded (red) extraction system with 15kV applied Einzel lens voltage.
Figure 3.6 Transmission of ?°8Pb?** through the LEBT to the RFQ entrance with the existing (blue line) and upgraded (red) extraction system with 15kV applied Einzel lens voltage.
Figure 3.7 Comparison of Pb transmission through the LEBT between the existing (baseline) and upgraded systems for different Einzel lens voltage values. The 7°8Pb*** emittance, at the solenoid exit, is here normalised to the baseline value (~50 mm mrad rms.).
Figure 3.7 Comparison of Pb transmission through the LEBT between the existing (baseline) and upgraded systems for different Einzel lens voltage values. The 7°8Pb*** emittance, at the solenoid exit, is here normalised to the baseline value (~50 mm mrad rms.).
Figure 3.8 Location of the LBS line and the spectrometer magnet LBS.BVT10.
Figure 3.8 Location of the LBS line and the spectrometer magnet LBS.BVT10.
Figure 4.2 Comparison of losses for different longitudinal line densities. Vertical lines indicate the moments when the e-cooler is switched off, the RF is switched on, the start of the ramp and beam extraction. The bunching factor (BF) for each case is indicated in the legend.
Figure 4.2 Comparison of losses for different longitudinal line densities. Vertical lines indicate the moments when the e-cooler is switched off, the RF is switched on, the start of the ramp and beam extraction. The bunching factor (BF) for each case is indicated in the legend.
Figure 4.3 Losses on the injection plateau with advanced RF capture (indicated by the red vertical line).
Figure 4.3 Losses on the injection plateau with advanced RF capture (indicated by the red vertical line).
Figure 4.4 Normalized transverse emittances and intensity along the LEIR cycle (left). For the cycle times marked by the coloured vertical lines, the markers with the same colour code indicate the corresponding maximum space charge tune shift relative to the bare working point, which is marked by a cross (right). Solid lines in the tune diagram correspond to normal resonances, dashed lines to skew resonances. Direct space charge tune spread: The Beam Ionization Profile Monitors (BIPM) installed in LEIR allow to measure the transverse beam sizes along the cycle. The normalized emittances can be reconstructed using the optics functions of the MADX model and the rms momentum spread measured with the longitudinal Schottky monitor (typically around 0.1% after cooling). Figure 4.4 shows the normalized transverse emittances, the intensity along the cycle, and the calculated maximum transverse direct space charge tune shift relative to the bare working point.
Figure 4.4 Normalized transverse emittances and intensity along the LEIR cycle (left). For the cycle times marked by the coloured vertical lines, the markers with the same colour code indicate the corresponding maximum space charge tune shift relative to the bare working point, which is marked by a cross (right). Solid lines in the tune diagram correspond to normal resonances, dashed lines to skew resonances. Direct space charge tune spread: The Beam Ionization Profile Monitors (BIPM) installed in LEIR allow to measure the transverse beam sizes along the cycle. The normalized emittances can be reconstructed using the optics functions of the MADX model and the rms momentum spread measured with the longitudinal Schottky monitor (typically around 0.1% after cooling). Figure 4.4 shows the normalized transverse emittances, the intensity along the cycle, and the calculated maximum transverse direct space charge tune shift relative to the bare working point.
Figure 4.5 Losses during a tune scan with a low intensity coasting beam. Intensity evolution plotted as function of the vertical tune (left) and plotted in the tune diagram (right). Solid lines in the tune diagram correspond to normal resonances, dashed lines to skew resonances. Losses during tune scan with low intensity beam: Dynamic variation of the tunes along the injection plateau showed significant losses in the vicinity of low order resonances. In order to minimize the tune spread due to space charge, these tune scans were performed with low beam intensity (only one injection from Linac3). Figure 4.5 shows an example, where the vertical tune was moved from the nominal working point with Qy = 2.72 downwards by about 0.05 within a few hundred ms. Only small losses are observed close to the fourth order 2Qx + 2Qy = 9 resonance. However, significant losses are observed when the vertical tune approaches the skew third order resonance 3Qy = 8. Similar measurements where performed to probe other low order resonances. Significant losses could also be observed close to the Qx + 2 Qy =7 normal sextupole resonance.
Figure 4.5 Losses during a tune scan with a low intensity coasting beam. Intensity evolution plotted as function of the vertical tune (left) and plotted in the tune diagram (right). Solid lines in the tune diagram correspond to normal resonances, dashed lines to skew resonances. Losses during tune scan with low intensity beam: Dynamic variation of the tunes along the injection plateau showed significant losses in the vicinity of low order resonances. In order to minimize the tune spread due to space charge, these tune scans were performed with low beam intensity (only one injection from Linac3). Figure 4.5 shows an example, where the vertical tune was moved from the nominal working point with Qy = 2.72 downwards by about 0.05 within a few hundred ms. Only small losses are observed close to the fourth order 2Qx + 2Qy = 9 resonance. However, significant losses are observed when the vertical tune approaches the skew third order resonance 3Qy = 8. Similar measurements where performed to probe other low order resonances. Significant losses could also be observed close to the Qx + 2 Qy =7 normal sextupole resonance.
Figure 4.6 LEIR intensity with and without harmonic sextupoles powered. The red and black dashed lines indicate the maximum achieved intensity at RF capture and extraction, respectively.
Figure 4.6 LEIR intensity with and without harmonic sextupoles powered. The red and black dashed lines indicate the maximum achieved intensity at RF capture and extraction, respectively.
Figure 4.7 Intensity evolution for the "Nominal" LEIR cycle used for LHC filling in December 2015. The operational performance of the lead ion beams for the LHC profited from the efforts during the LEIR machine development sessions described above. Figure 4.7 shows the evolution of the total intensity after accumulation in LEIR, the intensity extracted out of LEIR and, for comparison, also the intensity of the first injection from Linac3 throughout December 2015. The intensity in LEIR is strongly correlated with the current provided by Linac3. However, it should also be stressed that the first attempt of resonance compensation using the existing harmonic sextupole correctors of LEIR yielded a clear improvement of the transmission in the last week of the run.
Figure 4.7 Intensity evolution for the "Nominal" LEIR cycle used for LHC filling in December 2015. The operational performance of the lead ion beams for the LHC profited from the efforts during the LEIR machine development sessions described above. Figure 4.7 shows the evolution of the total intensity after accumulation in LEIR, the intensity extracted out of LEIR and, for comparison, also the intensity of the first injection from Linac3 throughout December 2015. The intensity in LEIR is strongly correlated with the current provided by Linac3. However, it should also be stressed that the first attempt of resonance compensation using the existing harmonic sextupole correctors of LEIR yielded a clear improvement of the transmission in the last week of the run.
Figure 4.8 Correlation between accumulated and extracted intensity.
Figure 4.8 Correlation between accumulated and extracted intensity.
ETL.BHN10 is operated by a function generator, which dispatches for each user the two different values respectively for injection and extraction. At extraction, it normally bends the beam trajectory by 336.75 mrad towards the PS. In order to send the beam to the dump, the magnet will have to be powered by a smaller current. However, for hysteresis reasons, the nominal current will always be sent first (see Figure 4.11) [4]. The vacuum chamber inside ETL.BHN10 will be replaced by a “Y” chamber with the dump at its end. The exact geometry is still being finalized.
ETL.BHN10 is operated by a function generator, which dispatches for each user the two different values respectively for injection and extraction. At extraction, it normally bends the beam trajectory by 336.75 mrad towards the PS. In order to send the beam to the dump, the magnet will have to be powered by a smaller current. However, for hysteresis reasons, the nominal current will always be sent first (see Figure 4.11) [4]. The vacuum chamber inside ETL.BHN10 will be replaced by a “Y” chamber with the dump at its end. The exact geometry is still being finalized.
Figure 4.10 ETL.BHN10 implementation (from PS_LMETLO0002).
Figure 4.10 ETL.BHN10 implementation (from PS_LMETLO0002).
Table 4.1 Beam parameters relevant for the design of the beam dump.
Table 4.1 Beam parameters relevant for the design of the beam dump.
Figure 4.11 ETL.GSBHN10 function adapted for LEIR dump.
Figure 4.11 ETL.GSBHN10 function adapted for LEIR dump.
Stainless Steel Flange and Gasket Figure 4.12 LEIR Dump — Conceptual design.
Stainless Steel Flange and Gasket Figure 4.12 LEIR Dump — Conceptual design.
Table 5.1 RF manipulation schemes for lead ion LHC-type beams in the PS.
Table 5.1 RF manipulation schemes for lead ion LHC-type beams in the PS.
Table 5.2 Parameters of the single-bunch and nominal lead ion beams at PS extraction after the upgrades [5]. | | Qinola hunch | A kuanrhec INN nc |
Table 5.2 Parameters of the single-bunch and nominal lead ion beams at PS extraction after the upgrades [5]. | | Qinola hunch | A kuanrhec INN nc |
Figure 5.1 Voltage program during the RF manipulation on the intermediate flat-top for the generation of four bunches spaced 100 ns.
Figure 5.1 Voltage program during the RF manipulation on the intermediate flat-top for the generation of four bunches spaced 100 ns.
Figure 5.2 Evolution of the bunch profile during the RF manipulation at the intermediate flat-top for the nominal four-bunch beam with 100 ns spacing. The longitudinal parameters of the lead ion beam at PS extraction are summarized in Table 5.2. Single and multi-bunch beams have the same longitudinal characteristics and intensity.
Figure 5.2 Evolution of the bunch profile during the RF manipulation at the intermediate flat-top for the nominal four-bunch beam with 100 ns spacing. The longitudinal parameters of the lead ion beam at PS extraction are summarized in Table 5.2. Single and multi-bunch beams have the same longitudinal characteristics and intensity.
Figure 6.1 Intensity at 450 GeV proton equivalent as a function of injected bunch population, showing a strongly non-linear dependence on intensity.
Figure 6.1 Intensity at 450 GeV proton equivalent as a function of injected bunch population, showing a strongly non-linear dependence on intensity.
Figure 6.2 Intensity at 450 GeV proton equivalent as a function of bunch population at the beginning of the accelerating ramp, showing a rather linear dependence on intensity.
Figure 6.2 Intensity at 450 GeV proton equivalent as a function of bunch population at the beginning of the accelerating ramp, showing a rather linear dependence on intensity.
Figure 6.3 Bunch length as a function of time over the SPS cycle, revealing a longitudinal instability after transition crossing (left), which can be improved with controlled emittance blow-up in the PS (right). The observations from 2015 also showed that the beam is unstable in the longitudinal plane after transition crossing, see Figure 6.3 (left). A controlled longitudinal emittance blow-up was tried in the PS, Figure 6.3 (right), which improved the situation. Controlled longitudinal emittance blow-up was also tried using the SPS in the single 200 MHz RF system, but could not be made to work. No effect of the batch spacing (150 ns and 175 ns) was seen on the longitudinal bunch parameters.
Figure 6.3 Bunch length as a function of time over the SPS cycle, revealing a longitudinal instability after transition crossing (left), which can be improved with controlled emittance blow-up in the PS (right). The observations from 2015 also showed that the beam is unstable in the longitudinal plane after transition crossing, see Figure 6.3 (left). A controlled longitudinal emittance blow-up was tried in the PS, Figure 6.3 (right), which improved the situation. Controlled longitudinal emittance blow-up was also tried using the SPS in the single 200 MHz RF system, but could not be made to work. No effect of the batch spacing (150 ns and 175 ns) was seen on the longitudinal bunch parameters.
The beam tail population is expected to increase with 150 ns batch spacing, due to the larger injection offset from the residual kick on both injected and circulating bunches, combined with the finite damping time. To characterise the expected tail population, the detuning with amplitude was measured, by kicking the beam at the Flat Bottom with the tune kickers MKQH/V and using the LHC BPM turn-by- turn data to calculate the action. A linear fit to the data for different amplitudes gives the detuning coefficients, Figure 5, which were measured at cxx = 394.2 m'! and cyy = 1453.1 m'!. This data will be used for simulating the expected tail population.
The beam tail population is expected to increase with 150 ns batch spacing, due to the larger injection offset from the residual kick on both injected and circulating bunches, combined with the finite damping time. To characterise the expected tail population, the detuning with amplitude was measured, by kicking the beam at the Flat Bottom with the tune kickers MKQH/V and using the LHC BPM turn-by- turn data to calculate the action. A linear fit to the data for different amplitudes gives the detuning coefficients, Figure 5, which were measured at cxx = 394.2 m'! and cyy = 1453.1 m'!. This data will be used for simulating the expected tail population.
Figure 6.5 Measured horizontal (left) and vertical (right) detuning with amplitude at injection energy. cxx = 394.2 m! and cyy = 1453.1 m1.
Figure 6.5 Measured horizontal (left) and vertical (right) detuning with amplitude at injection energy. cxx = 394.2 m! and cyy = 1453.1 m1.
Figure 6.6 Measured MKP rise time after system improvements in 2015, with 150 ns 5-95% achieved. deployed in 2015 and is now considered as operational. This was done by reducing the kick angle through the use of an injection bump, which allows operation only with the fastest MKP1-3 generators at the ion injection energy. The synchronisation of the individual thyratrons was also improved with an upgrade of a timing module, and replacement of the worst tubes, gaining over 30 ns in the jitter. As a result, the residual kick for the injected/circulating bunches with 150 ns batch spacing is now less than 5%, as illustrated in Figure 6.6, which was compatible with the performance of the transverse damper and allowed injection without significant emittance growth. To improve further to 100 ns spacing between trains (giving a uniform 50 ns between bunches in the LHC) would require a major redesign of the injection system, the option for which is described in Chapter 7.
Figure 6.6 Measured MKP rise time after system improvements in 2015, with 150 ns 5-95% achieved. deployed in 2015 and is now considered as operational. This was done by reducing the kick angle through the use of an injection bump, which allows operation only with the fastest MKP1-3 generators at the ion injection energy. The synchronisation of the individual thyratrons was also improved with an upgrade of a timing module, and replacement of the worst tubes, gaining over 30 ns in the jitter. As a result, the residual kick for the injected/circulating bunches with 150 ns batch spacing is now less than 5%, as illustrated in Figure 6.6, which was compatible with the performance of the transverse damper and allowed injection without significant emittance growth. To improve further to 100 ns spacing between trains (giving a uniform 50 ns between bunches in the LHC) would require a major redesign of the injection system, the option for which is described in Chapter 7.
Table 6.1 Initial conditions used in simulations of slip-stacking.
Table 6.1 Initial conditions used in simulations of slip-stacking.
Figure 6.7 Schematic representation of momentum slip-stacking for halving the bunch spacing.
Figure 6.7 Schematic representation of momentum slip-stacking for halving the bunch spacing.
Figure 6.8 RF voltage (left) and frequency (right) programmes used in simulations for slip-stacking. The RF programmes applied for separating the two batches in momentum (RF frequency) and then bringing them back, close to the central orbit, are presented in Figure 6.8. For calculating the RF voltage programme, a constant filling factor in momentum of 0.9 was assumed to avoid particle losses during he procedure. In this case the duration of the slip-stacking process is 200 ms, fast compared to the cycle ime (about 50 s), but slow enough to avoid particle losses. However this does not take into account the ime of batch slippage after separation, which is determined by initial distance between batches (see below) and possible radial displacement. The final value of the RF frequency was selected such that the ratio Afpr/fs9 = 4, which corresponds to the case where the final hypothetical buckets have tangent boundaries. In fact, that condition gives a lower limit for stable motion [12], but tracking simulations show that there is a rapid effective emittance growth and that a larger value is needed for stable motion [13].
Figure 6.8 RF voltage (left) and frequency (right) programmes used in simulations for slip-stacking. The RF programmes applied for separating the two batches in momentum (RF frequency) and then bringing them back, close to the central orbit, are presented in Figure 6.8. For calculating the RF voltage programme, a constant filling factor in momentum of 0.9 was assumed to avoid particle losses during he procedure. In this case the duration of the slip-stacking process is 200 ms, fast compared to the cycle ime (about 50 s), but slow enough to avoid particle losses. However this does not take into account the ime of batch slippage after separation, which is determined by initial distance between batches (see below) and possible radial displacement. The final value of the RF frequency was selected such that the ratio Afpr/fs9 = 4, which corresponds to the case where the final hypothetical buckets have tangent boundaries. In fact, that condition gives a lower limit for stable motion [12], but tracking simulations show that there is a rapid effective emittance growth and that a larger value is needed for stable motion [13].
Table 6.2 Slippage, RF and beam parameters after recapture. The slipping distance corresponds to a batch spacing of 2.7 ps.
Table 6.2 Slippage, RF and beam parameters after recapture. The slipping distance corresponds to a batch spacing of 2.7 ps.
Table 6.3 Summary of results of the slip-stacking simulations and beam parameters at extraction.
Table 6.3 Summary of results of the slip-stacking simulations and beam parameters at extraction.
Figure 6.9 Present SPS ions-for-LHC Beam Control for Fixed Frequency Acceleration (FFA).
Figure 6.9 Present SPS ions-for-LHC Beam Control for Fixed Frequency Acceleration (FFA).
Figure 6.10 Proposed modification to existing system. Master DDS without phase loop correction and New Slave DDS generating two Master RFs, with individual phase loop error signals.
Figure 6.10 Proposed modification to existing system. Master DDS without phase loop correction and New Slave DDS generating two Master RFs, with individual phase loop error signals.
Figure 6.12 Damping of injection oscillation of 6 mm in presence of amplitude detuning with a damping time of 20 turns (left) and 200 turns (right). No blow-up for the 20 turns case and a small blow-up visible for the 200 turns case.
Figure 6.12 Damping of injection oscillation of 6 mm in presence of amplitude detuning with a damping time of 20 turns (left) and 200 turns (right). No blow-up for the 20 turns case and a small blow-up visible for the 200 turns case.
Figure 7.1 +/- 5 o ion beam envelope following the foreseen injection trajectory. To inject with 100 ns rise time only the MKP-S type injection kicker magnets would be used, powered by new PFLs in parallel to the present PFN system. Additional septa, MSI-V, are needed to compensate for the reduced MKP kick strength. A new dedicated ion injection dump is also required.
Figure 7.1 +/- 5 o ion beam envelope following the foreseen injection trajectory. To inject with 100 ns rise time only the MKP-S type injection kicker magnets would be used, powered by new PFLs in parallel to the present PFN system. Additional septa, MSI-V, are needed to compensate for the reduced MKP kick strength. A new dedicated ion injection dump is also required.
Table 7.2 Summary of the ion beam parameters in different scenarios.
Table 7.2 Summary of the ion beam parameters in different scenarios.

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How to Maximize the HL-LHC Performance *
Oliver Brüning

2014

This contribution presents an overview of the parameter space for the HL-LHC [1] upgrade options that would maximize the LHC performance after LS3. The analysis is assuming the baseline HL-LHC upgrade options including among others, 25ns spacing, LIU [2] parameters, large aperture triplet and matching-section magnets, as well as crab cavities. The analysis then focuses on illustrations of the transmission efficiency of the LIU beam parameters from the injection process to stable conditions for physics, the minimization of the luminous region volume while preserving at the same time the separation of multiple vertices, the luminosity control mechanisms to extend the duration of the most efficient data taking conditions together with the associated concerns (machine efficiency, beam instabilities, halo population, cryogenic load, and beam dump frequency) and risks (failure scenarios, and radiation damage). In conclusion the expected integrated luminosity per fill and year is presented.

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Performance of the LHC Pre-Injectors
M. Giovannozzi

The LHC pre-injector complex, comprising Linac 2, the PS Booster (PSB) and the PS, has undergone a major upgrade in order to meet the very stringent requirements of the LHC. Whereas bunches with the nominal spacing and transverse beam brightness were already available from the PS in 1999 [1], their length proved to be outside tolerance due to a debunching procedure plagued by microwave instabilities. An alternative scenario was then proposed, based on a series of bunch-splitting steps in the PS. The entire process has recently been implemented successfully, and beams whose longitudinal characteristics are safely inside LHC specifications are now routinely available. Variants of the method also enable bunch trains with gaps of different lengths to be generated. These are of interest for the study and possible cure of electron cloud effects in both the SPS and LHC. The paper summarizes the beam dynamics issues that had to be addressed to produce beams with all the requisite qualities for the LHC.

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Scenarios for upgrading the LHC injectors
Roland Garoby

2006

The presence of a powerful accelerator complex that could serve as injector has been instrumental in the decision to build the LHC at CERN. This existing complex has now confirmed its capability, having demonstrated that it is able to deliver beam with the nominal characteristics as well as numerous other types of beams which will be essential for tuning-in, commissioning and operating the future collider for physics in its first years. However it is also clear that the existing LHC injectors will not be able to deliver beam with the ultimate characteristics and that they suffer from reliability problems due to their age. An analysis has therefore been done by the working group in charge of "Proton Accelerators of the Future" (PAF) to determine a logical evolution of the accelerator complex, considering the needs of LHC and of the other potential future physics experiments at CERN. As a result, scenarios for a staged upgrade have been proposed, involving the progressive replacement of all the low energy accelerators [1].

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Parameter Space for the LHC High-Luminosity Upgrade
Oliver Brüning

2012

We review the parameter space for the high-luminosity upgrade of the LHC (HL-LHC). Starting from the luminosity targets and the primary limitations, e.g., event pile up, turnaround time, injector limits, and intrabeam scattering, we determine compatible beam parameters such as the beam intensity, bunch spacing, transverse and longitudinal emittances, bunch length, and IP beta functions required to meet the HL-LHC goals. Possible HL-LHC parameter sets together with their expected performance reach are presented for comparison and discussion.

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CERN Upgrade Plans for the LHC and its Injectors
Frank Zimmermann

Proceedings of European Physical Society Europhysics Conference on High Energy Physics — PoS(EPS-HEP 2009), 2010

The primary goal of CERN and the Large Hadron Collider (LHC) community is to ensure that LHC is operated efficiently, that it achieves nominal performance in the shortest term, and that its performance steadily improves. Since several years the community has been discussing the directions for maximizing the physics reach of the LHC by upgrading the experiments, in particular ATLAS and CMS, the LHC machine and the CERN proton injectors, in a phased approach. The first phase comprises construction of a new proton linac, LINAC4 and an LHC interaction-region (IR) upgrade, with the goal of increasing the LHC luminosity to 2 − 3 × 10 34 cm −2 s −1 , while maximizing the use of mature magnet technologies and of the existing infrastructure. These two projects were approved by the CERN Council in December 2007 and are scheduled for completion in 2014. The second phase foresees further substantial improvements in the injector chain, with a proposed replacement of the aging PS and its booster, by a superconducting proton linac (SPL) and a new higher-energy storage ring, PS2, complemented by modifications in the existing SPS, together with major upgrades of the ATLAS and CMS detectors, and, possibly, including another upgrade of the interaction regions based on a different magnet technology, as well as complementary measures such as crab cavities, or a new beam structure. Completion of this second phase around 2018-2020 should allow further increasing the luminosity of the LHC towards 10 35 cm −2 s −1. On an even longer time scale, the magnet technology developed for the second phase could provide the route towards an ultimate energy upgrade of the LHC. In this report, I first recall a few key challenges inherent in the LHC baseline design, and then describe phased upgrade scenarios for the LHC and its injectors which overcome the design limitations and may ultimately lead to a 10-fold luminosity increase.

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IONS FOR LHC:STATUS OF THE INJECTOR CHAIN
Stephane vandorpe

2007

The LHC will, in addition to proton runs, be operated with Pb ions and provide collisions at energies of 5.5 TeV per nucleon pair, i.e. more than 1.1 PeV per event, to experiments. The transformation of CERN's ion injector complex (Linac3-LEIR-PS-SPS) to allow collision of ions in LHC in 2008 is well under way. The status of these modifications and the latest results of commissioning will be presented. The remaining challenges are reviewed.

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Operational beams for the LHC
Yannis Papaphilippou

The variety of beams, needed to set-up in the injectors as requested in the LHC, are reviewed, in terms of priority but also performance expectations and reach during 2015. This includes the single bunch beams for machine commissioning and measurements (probe, Indiv) but also the standard physics beams with 50 ns and 25 ns bunch spacing and their high brightness variants using the Bunch Compression Merging and Splitting (BCMS) scheme. The required parameters and target performance of special beams like the doublet for electron cloud enhancement and the more exotic 8b$\oplus$4e beam, compatible with some post-scrubbing scenarios are also described. The progress and plans for the LHC ion production beams during 2014-2015 are detailed. Highlights on the current progress of the setting up of the various beams are finally presented with special emphasis on potential performance issues across the proton and ion injector chain.

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Preliminary accelerator plans for maximizing the integrated LHC luminosity
Roland Garoby
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The demanding beam performance requirements of the High Luminosity (HL-) LHC project translate into a set of requirements and upgrade paths for the LHC injector complex. In this paper the performance requirements for the SPS and the known limitations are reviewed in the light of the 2012 operational experience. The various SPS upgrades in progress and still under consideration are described, in addition to the machine studies and simulations performed in 2012. The expected machine performance reach is estimated on the basis of the present knowledge, and the remaining decisions that still need to be made concerning upgrade options are detailed.

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The first LHC Pb ion run took place at 1.38 A TeV/c per beam in autumn 2010. After a short period of runningin, the injector chain was able to fill the collider with up to 137 bunches per ring, with an intensity of 108 Pb82+ ions/bunch, about 50% higher than the design value. This yielded a luminosity of 3×1025 Hz/cm2, allowing the experiments to accumulate just under 10 b-1 each during the four week run. We review the performance of the individual links of the injector chain, and address the main issues limiting the LHC luminosity, in view of reaching 1026 Hz/cm2 in 2011, and substantially beyond when the LHC energy increases after the long shutdown in 2013-14.

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Challenging beams with much higher brightness than today are required for the LHC to achieve its high luminosity objective after the year 2020. It is the purpose of the LHC Injectors Upgrade (LIU) project to achieve this result, consolidating and upgrading the existing set of synchrotrons (PSB, PS and SPS), and using the new linac presently in construction (Linac4). The anticipated beam characteristics are described and compared to the known limitations in the different accelerators. The foreseen solutions are outlined as well as the planning for their implementation.

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