Transverse shaving on the Window Beam Scope in the PSB Magdalena Cieslak - Kowalska BE/ABP/HSI with precious help from E. Benedetto, J-M. de Cravero, B. Mikulec, A. Newborough, J-L. Sanchez Alvarez 31 January 2015 HIS Section Meeting

Outline: 1.Introduction 2.Comparison between two shaving schemes 3.Measurements results 4.Implementation 5.Studies of the future case (160 MeV HI beam) 6.Summary

- Circumference of ~158 m (divided into 16 periods) - Composed of 4 rings - Injection energy 50 MeV - Extraction energy 1.4 GeV Booster produces proton beams (intensity range e10 p+) for the entire CERN complex: low intensity beams and high intensity beams. 3/27 PS Booster

PS Booster Upgrade 4/27 Current multiturn injection will be upgraded to H- injection with the possibility of the transverse (horizontal painting). Injection energy will be raised to 160 MeV and extraction energy to 2 GeV. A special attention should be drawn to the mechanisms which drive particle losses, to mitigation measures and to improvement of the tools in order to analyse them.

Transverse shaving Shaving is presently the main method to control the beam emittance and beam intensity for low intensity beams in the PS Booster by scraping the beam - (ideally) at the PS Booster aperture restriction – Window Beam Scope (WBS). BCT vs Ctime WBS is a 40 mm thick carbon absorber, located in period 8. It’s dimensions are +/- 50 mm and +/ mm in horizontal and vertical plane respectively, which makes it the main PS Booster aperture restriction.

Old shaving vs new shaving It was proved that the current shaving method, which consists in inducing closed orbit oscillations by a single kick, causes losses around the machine. In order to localize the losses at the PS Booster aperture restriction - WBS, a new shaving scheme based on a closed bump was proposed and tested.

Studies from 2014 Measurements taken in 2014 & 2015 Planned implementation in 2016 Studies are documented in IPAC 2015 proceedings THPF087.

Global oscillation produced Beam in vertical plane while shaving Losses at multiple elements Old shaving scheme One corrector per plane Beam loss location strongly dependant on the working point and on machine errors

Proposal of a new scheme to better localize losses during the “shaving” process Beam in vertical plane while shaving Local orbit distortion Global orbit distortion can be suppressed to the negligible values Localize the losses at one location Two correctors per plane More robust wrt the working point

We have good candidates for this role: “beam scope bumpers” - DBSV7 and DBSV9

Measured and simulated orbit around the ring Simulated (continuous line) and measured (points) vertical closed orbit distortion excited during the shaving process: operational shaving is marked in blue and the proposed new shaving scheme in red MDs from 2014

Measured orbit during the cycle Operational shaving is marked in blue and the proposed new shaving scheme in red

Flexibility in final intensity By playing with the current of DBSV07 and DBSV09, one is able to scrape the beam to the desired level in terms of the intensity.

Measured beam loss while shaving with the old scheme Maximum dose rate = 8.5 mGy/s Total beam energy deposited in period 14 = 49.1 μGy integrated between C300 and C320

Measured beam loss while shaving with the new scheme Maximum dose rate = 7.2 mGy/s Total beam energy deposited in period 8 = 27.5 μGy integrated between C300 and C320

Possible reduction of the total energy deposited Ekin [MeV] Max dose rate in period 8 [mGy/s] Total energy deposited in period 8 [μGy] total Energy deposited in period 8 [μGy] total while shaving C C C C Ekin [MeV] Max dose rate in period 14 [mGy/s] Total energy deposited in period 14 [μGy] total Energy deposited in period 14 [μGy] total while shaving OP turn injectedEAST BEAM R3 Dedicated measurements concerning advancing the shaving in the super cycle is foreseen after the commissioning period. Shaving early in the cycle (once the beam is captured) was proved to be beneficial in terms of the reduction of the total energy deposited without influencing beam stability.

Implementation Two beam scope bumpers DBSV(H)7 & DBSV(H)9 will be powered (in series) in order to create closed bump. Since the phase advance between them is around 180 degrees, I (DBSV07) ~= I (DBSV09) independently of the tune and steering errors. The new shaving scheme will require some modifications for the PS Booster: re-cabling (YETS 2015) and shielding the bumpers.

Commissioning 2016 Hardware commissioning is planned to take place in February. Tests with the beam are expected to take place in March. During the commissioning, we would like to test: -Feasibility of the new shaving scheme -Benefits from advancing the shaving in the super cycle in order to lower the total energy deposited -Shielding efficiency (if time allows)

What will happen with the “old” shavers? DSHAV4L4 and DSHAH10L4 are planned to be connected to the patch panel and starting from ~June 2016 will be used as a regular orbit correctors. However until June, BR2.DSHAV4L4 and BR2.DSHAH10L4 will serve as second pair of available shavers in order to perform some dedicated measurements concerning the tails repopulation in PS Booster.

MD: tails repopulation involving shaving with two schemes Energy vs time First shaving Second shaving Possibility to profit from the availability of both systems until June. Goal of the MD: better understanding of the halo formation mecanism – essential to design future PSB absorber.

Future PSB absorber teaser … absorber region Simulations in pyORBIT of the high intensity beams (160 MeV, 1.6e13 p+). 13 cm carbon absorber was implemented into PSB lattice. Acceleration and transverse + longitudinal painting is included in the model. Lattice without errors. Red – transverse losses at the collimator Green – longitudinal losses at the collimator Blue – losses elsewhere

PBS upgrade to 160 MeV We might use shaving in the future – mostly for stability reason in order to tailor the micron emittance beams if needed. Current WBSFuture planned PSB absorber New shaving scheme is compatible with the proposal of the new PS Booster absorber (marked with the thick line on the plot below).

Summary: The new shaving scheme is planned to be implemented in PS Booster operation in The new shaving scheme was proved robust with respect the WP and machine errors. It will localize the losses at the PSB aperture restriction in period 8. Higher activation in this region is expected, however the total amount of beam loss is expected to remain the same. After the commissioning, dedicated measurements are planned in order to profit better from the new scheme.

Appendix:

Shielding DSAH10L4 horizontal “old” shaver Copper shielding to reduce the crosstalk between the rings DBSV7 vertical “new” shaver The DBSV7 and DBSV9 are not shielded against the crosstalk between the rings. New copper plates has been ordered and are planned to be installed soon.

Extreme vertical tune: Qv = 4.49

Extreme vertical tune: Qv = 4.20

Comparison of the beam trajectories (operational shaving)

Comparison of the beam trajectories (new shaving scheme)

Booster Absorber Studies Appendix 2:

Motivations: As part of the LHC Injector Upgrade Project, the PSB injection energy will increase from 50 MeV to 160 MeV and a new H- charge-exchange injection scheme will be implemented. Beam losses are a concern due to the increased injection energy, and mitigation scenarios are under investigation. It was proved that the current Window Beam Scope (WBS), which is physically a 40 mm thick carbon absorber located in period 8, will not be able to stop the beam at 160 MeV. Therefore an idea of studying a new device came. Main goal of this study is to design the device, which will allow us to control the losses in PS Booster and localize them.

Status of the studies: 1)Definition of aperture, position and thickness 2)Simulations with PTC – pyOrbit 3)Planned studies 4)Interactions with EN/STI (in appendix)

Minimum required length of an absorber 50 Mev160 MeV2 GeV[% of collimated] carbon25 mm mm cm cm cm cm cm m m99.58 Simulations in pyORBIT with the particle – matter interaction routines: Study of a stand-alone absorber Beam sent through the block of the material of assumed thickness. We are limited by free space in the lattice FLUKA simulations confirmed that an absorber made of 13 cm of carbon shows a good performance at 160 MeV and will not stop a 2 GeV beam – losses expected to occur downstream and mostly due to the accident scenario. Assumed carbon density - 2 g/cm3

PS Booster Period 8 Layout By removing the DBSV8 kicker, one can gain 0.65 m of liberated space in Booster lattice Current position of the WBS

Window Beam Scope: position place in PSB nameLS P2 LS1DRIFT_ P2 LS1DRIFT_ P3 LS1DRIFT_ P4 LS1DRIFT_ P4 LS1DRIFT_ P6 LS1DRIFT_ P7 LS1DRIFT_ P8LS1WBS P8LS1DBSV P9 LS1DRIFT_ P11 LS1DRIFT_ P11 LS1DRIFT_ P16 LS1DRIFT_ P16 LS1DRIFT_ We defined a new position for the WBS due to the PSB space constraints. From now, we will be studying the new scenario, keeping Mattias' one as a backup in case we find a showstopper. Old positionNew position ++++ Alpha almost at its minimum in both planes Possibility of shaving More liberated space (0.65 m) Possibility of shaving - Less liberated space (0.36 m) Large Alpha functions S-position [m]Betx [m]Alfx [rad]Dispx [m]Bety [m]Alfy [rad]Dispy [m] Entry Centre Exit WBS

Aperture The current dimensions of the WBS are 50mm x 28.6mm in horizontal and vertical plane respectively. With injection energy upgrade, current physical size of WBS should be scaled as sqrt(bgam160/bgam50) ~= Taking into account 5 mm of closed orbit distortion the new WBS aperture was calculated to be 38.18mm x 22.40mm* This aperture is expected to accommodate 3 sigma of the beam. Taking into account different optics at the new position, the corresponding aperture of a new absorber should be ~ 31mm x 31mm. * Matthias Scholz “Simulationen zur H- Charge Exchange Injection in den CERN Proton Synchrotron Booster mit Linac4”

Constraints in terms of the beam dynamics: TE/ABP/BTP team did the injection simulations taking into account the beam scope design proposed by M.Scholz. They found that it injection and the recombination septum impose the constraint on the vertical emittance, which limits it to 6 mm mrad normalized for HI beams. It was also agreed to limit the number of losses to 3% during the chicane fall (5ms) and this was one constraint when defining the aperture of the absorber. It turn out that if we want to keep the losses at such a low level, we need to assume a larger aperture of 37mm x 37mm, which will accommodate more than 3.5 sigma of the beam in each plane. An absorber with an aperture of 37mm x 37mm was used for the studies presented at the next slides.

Expected loss pattern: absorber region AbsorberQuad Bend Bend Simulations in pyORBIT of the high intensity beams (160 MeV, 1.6e13 p+). 13 cm carbon absorber was implemented into PSB lattice. Acceleration and transverse + longitudinal painting is included in the model. Lattice without errors. Sketch of the region:

Loss pattern at 160 MeV (13 cm of carbon 37 mm of aperture): Position [m][%] of lost particles % of total loss during first 5 ms (19489 of the macro-particles) including the injection with transverse painting Where do we lose: % of particles lost at the collimator 9 % of particles lost at the QFO82 Almost 83 % of losses will be localized in P08 CollimatorQuad Bend Bend Absorber s = BR.QFO82 s = BR.BHZ82 s = BR.BHZ91 s =

Loss pattern at 160 MeV (black body with 37 mm of aperture): Position [m][%] of lost particles % of total loss during first 5 ms (19280 of the macro-particles) including the injection with transverse painting Where do we lose: % of particles lost at the collimator 0 % of particles lost at the QFO82 Almost 83 % of losses will be localized in P08 CollimatorQuad Bend Bend Crosscheck

Losses (the aperture plot) Red – transverse losses at the collimatorGreen – longitudinal losses at the collimator Blue – losses elsewhere % of the longitudinal losses

Intensity and emittance evolution Horizontal and vertical emittance stay under control and intensity reaches steady state after 5 ms.

Conclusions (1): We presented the proposal of the thickness, position and aperture of a new absorber. Thickness of the device was defined in order to allow stopping 160 MeV impacting beam. The position of the device was chosen taking into account very tight PS Booster space constraints. The aperture was adjusted to keep the losses during the chicane fall at the 3% level. 13 cm of a carbon absorber, suits PS Booster future needs in terms of the losses control. It is expected to localize more than 80% of the losses in period 8.

Conclusions (2): It was proved that the new absorber should also serve as a future possible scraper to shave the beam (mostly for stability reasons).

Future planned studies: Simulations: Investigate the robustness of the absorber in terms of the working point and field errors and based on the output of the studies, to optimize the final parameters of the device. Ongoing measurements concern the tails repopulations (data taken in autumn 2015) and derivation of the time constant of this process and will help to understand the mechanisms of the halo formation.

Appendix:

3 critical assumed scenarios: For the EN/STI studies, we needed to define the scenarios when the beam will impact the absorber: First: "collimation the ISOLDE beam“ We assume scraping 6% of the ISOLDE beam, deposited on one jaw at the injection energy and the beginning of the ramp. Concern: intensity Second: "full beam impact at extraction energy“ We assume loosing the full beam at the extraction energy. The most critical, according to FLUKA simulations, will be ISOLDE beam at 1.4 GeV. Third: "tailoring the LHC beam“ We assume to scrape 15% of the LHC-type beam, deposited on one jaw at the injection energy and the beginning of the ramp. Concern: brightness EDMS document under preparation

Proposal of the mechanical design A set of two masks, one large and one small, is planned to be implemented per ring. The large mask should always stay in the vacuum pipe whereas the small mask is movable and can be inserted/removed. Small mask movements consist in moving from position “IN” to position “OUT” and “OUT” to “IN”, without any possible intermediate position. There are ideally four independent axis, allowing an independent control of each small mask. It has been not yet decided whether the small masks shall be inserted upstream or downstream form the large mask.

Expected loss pattern (log scale):