Search

The presented document if the Letter of Intent for the Gamma Factory Proof-of-Principle Experiment.

This contribution discusses the possibility of broadening the present CERN research programme making use of a novel concept of light source. The proposed, Partially Stripped Ion beam driven, light source is the backbone of the Gamma Factory (GF) initiative. It could be realized at CERN by using the infrastructure of the already existing accelerators. It could push the intensity limits of the presently operating light-sources by up to 7 orders of magnitude, reaching fluxes of 10¹⁷ photons/s in the interesting gamma-ray energy domain between 1 MeV and 400 MeV. The GF light-source cannot be replaced, in this energy domain, by a FEL source as long as the multi TeV electron beams are not available. Its intensity is beyond the reach of the Inverse Compton Scattering sources. The unprecedented-intensity, energy-tuned gamma beams, together with the gamma-beams-driven secondary beams of polarized leptons, neutrinos, neutrons and radioactive ions are the basic research tools of the proposed Gamma Factory. A broad spectrum of new opportunities, in a vast domain of uncharted fundamental and applied physics territories, could be opened by the Gamma Factory research programme., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

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., Comment: Submitted for publication in a CERN Yellow Report (YR)

For the 2013 LHC ion run the anticipated request for batches from the PS Complex comprising four ion bunches spaced by 100 ns was changed to batches of two bunches spaced by 200 ns. This modified demand was met by suppressing a splitting step in the PS machine, but with the consequence of halving the longitudinal emittance required from LEIR. Thus NOMINAL Pb54+ beams from LEIR had to be delivered inside ~9 eVs to provide sufficient blow-up margin in the PS. Machine Development (MD) sessions were carried out in LEIR to investigate methods to satisfy these stricter requirements. Two main ingredients were found to reduce longitudinal emittance. The first and most important was to adjust carefully the frequency offset at capture in order to align the RF with the position where the beam is deposited by the electron cooling system prior to acceleration. The second ingredient was to reduce the final bucket area in order to reduce any residual filamentation during capture. This note documents the results obtained in several MD sessions carried out in January 2013 and provides guidelines on how to set up similar beams.

We review the performance of the ion injector chain at the light of the improvements which will take place during LS1, and we derive the expected luminosity gain for Pb-Pb and p-Pb collisions in the LHC. We suggest a baseline plan of upgrades that will allow the requirements of the ALICE experiment after LS2 to be reached. An alternative plan is also presented. Finally, we examine the possibility for different ions species for which some of the other experiments have expressed an interest. The main outcomes of the presentation ‘Work effort in the injector complex (including the Linac4 connection)’ will be reminded with emphasis on their consequences on the ion operations.

In the light of different running scenarios potential source improvements will be discussed (e.g. one month every year versus two month every other year and impact of the different running options [e.g. an extended ion run] on the source). As the oven refills cause most of the down time the oven design and refilling strategies will be presented. A test stand for off-line developments will be taken into account. Also the implications on the necessary manpower for extended runs will be discussed.

NA61/SHINE (SPS Heavy Ion and Neutrino Experiment) is a multi-purpose experimental facility to study hadron production in hadron-proton, hadron-nucleus and nucleus-nucleus collisions at the CERN Super Proton Synchrotron. It recorded the first physics data with hadron beams in 2009 and with ion beams (secondary 7Be beams) in 2011. NA61/SHINE has greatly profited from the long development of the CERN proton and ion sources and the accelerator chain as well as the H2 beamline of the CERN North Area. The latter has recently been modified to also serve as a fragment separator as needed to produce the Be beams for NA61/SHINE. Numerous components of the NA61/SHINE set-up were inherited from its predecessors, in particular, the last one, the NA49 experiment. Important new detectors and upgrades of the legacy equipment were introduced by the NA61/SHINE Collaboration. This paper describes the state of the NA61/SHINE facility - the beams and the detector system - before the CERN Long Shutdown I, which started in March 2013. © CERN 2014 for the benefit of the NA61/SHINE collaboration..

The LHC High Luminosity upgrade project includes a performance upgrade for heavy ions. One of the present performance limitations is the rise time of the SPS injection kicker system, which imposes a spacing of at least 220 ns between injected bunch trains at the operational rigidity. A reduction of this rise time to 50 ns for lead ions is requested as part of the suite of measures needed to increase the present design performance by a factor three. A new injection system based on a fast pulsed septum and a fast kicker has been proposed to fulfil this rise time requirement, and to meet all the constraints associated with the existing high intensity proton injection in the same region. This paper describes the concept and the required equipment parameters, and explores the implications of such a system for SPS operation.

An optics with low transition energy has been developed in the SPS for removing intensity limitations of the LHC proton beam and has become operational towards the second part of the 2012 LHC proton run. The impact of this optics in the performance of the LHC ion beam is studied here, especially with respect to collective effects, at the SPS injection energy, based both on modelling and beam measurements. In particular, the potential gain of the increased beam sizes provided by this optics, with respect to losses and emittance blow up due to space-charge and Intrabeam Scattering (IBS) is evaluated. The measured lifetime is compared with the one provided by the Touschek effect and its interplay with RF noise is studied.

The plans for preparing the LHC injectors to fulfil the needs of the LHC during the next decade have significantly progressed in 2012. Linac4 construction has passed major steps of pre-series fabrication. Hardware developments and beam studies have allowed refining the baseline actions to implement and the beam characteristics achievable at injection into the collider for protons as well as for Lead ions. These achievements are described in this paper, together with the updated project planning matched to the new schedule of the LHC.

LEIR, CERN's Low Energy Ion Ring, is an essential part of the LHC ion injection chain. In addition, since 2010 the accelerator complex is also delivering ions to the fixed target programme of the SPS North Area. We review the operation of the machine during the recent runs, and we detail the plans for the coming years with Pb and other species.

During the night of 12-13 September 2012 the LHC collided protons with lead nuclei for the first time, demonstrating the feasibility of hybrid collisions despite the basic two-in-one magnet design. The centre-of-mass energy was 5 TeV per colliding nucleon pair, "Stable Beams" were declared 9 hours after the first injection of Pb beams in 2012. The integrated luminosity delivered to the four large LHC experiments was sufficient to yield new physics results. Within the same fill, stable beams were declared twice more, with the collision points displaced longitudinally by ±0.5 m from their usual locations. We provide a general overview of this p-Pb pilot physics fill before focusing on beam data at injection energy and at flat-top, before stable beams for physics were declared. We monitored the beam parameters throughout the fill and present an analysis of their evolution based on a simulation of intra-beam scattering (IBS), synchrotron radiation and the consumption of the beam intensity by collisions ("luminosity burn-off"). We also present some considerations on beam-beam effects with unequal beam sizes and the pilot run is compared, in this respect, to expectations for the forthcoming physics run in January. This pilot run was a major step in the preparation of the physics run. However it was not possible to perform an additional feasibility test designed to clarify the limits to the intensity of two beams injected and ramped with unequal revolution frequencies. We describe the plan for this test and discuss the reasons why it could not be carried out.

The first part of the feasibility test of p-Pb operation of the LHC successfully demonstrated the possibility of injecting Pb bunches in the presence of many proton bunches without apparent harmful effects from moving long-range beam-beam encounters. Two bunches in each beam were accelerated to top energy where the RF frequencies of the two rings could be locked together. Finally an RF-rephasing operation to move the collision points some 9 km, back to their proper places succeeded on the first attempt. This note also provides documentation of the many changes made to the LHC operational sequence and interlocking in order to implement this completely new mode of collider operation.

The external crossing-angle bump in IR2 of LHC partly compensates the crossing angle created by the ALICE spectrometer. In view of the spectrometer polarity reversal requested by ALICE during the 2011 Pb-Pb run, a fast procedure consisting in reversing IP2 external crossing angle after ramp and squeeze of beams was envisaged. This requires a passage through zero external crossing angle, exposing beams to beam-beam interactions at parasitic encounters where normalized separation is less than one sigma. A test of the reversal at the end of physics fill no. 2319 showed that beam sizes are large enough at these locations not to have significant effects on intensity or emittance. Consequently, the fast polarity reversal procedure was validated and the full operational cycle was tested with a few bunches before adoption in the future physics fills.

On request of Radio protection, this internal note details the ion species, energies, and intensities in the LHC injector chain from 2012 to LS2, as they are currently foreseen at the time of writing (January 2012). Since the aim is to estimate radiological doses, whenever the intensities or number of bunches are uncertain, we chose to round up to an upper limit. Hence these figures are not appropriate for luminosity measurements for instance.

At the start of the 2011 physics run quite some margin in the performance of the injectors was available and identified. Following the fast increase of the performance of the LHC itself during 2011, these margins have very much been exploited and some have even been pushed further. In view of further increase in the LHC luminosity, the 2012 performance reach of the injectors will be reviewed. One of the arising topics is satellite bunches from the injectors. Until now concerted effort went into supressing satellite bunches to a minimum, but a recent successful test with "controlled" satellites might make their routine production and characterisation an important topic in 2012.

The heavy ion beams required during the HL-LHC era will imply significant modifications to the existing injector chain. We review the various options, highlighting the importance of an early definition of the future needs and keeping in mind the compatibility with the rest of the future CERN physics programme.

The NA61 experiment, aims to study the properties of the onset of deconfinement at low SPS energies and to find signatures of the critical point of strongly interacting matter. A broad range in T-μB phase diagram will be covered by performing an energy (13A-158AGeV/c) and system size (p+p, Be+Be, Ar+Ca, Xe+La) scan. In a first phase, fragmented ion beams of 7Be or 11C produced as secondaries with the same momentum per nucleon when the incident primary Pb-ion beam hits a thin Be target will be used. The H2 beam line that transports the beam to the experiment acts as a double spectrometer which combined with a new thin target (degrader) where fragments loose energy proportional to the square of their charge allows the separation of the wanted A/Z fragments. Thin scintillators and TOF measurement for the low energy points are used as particle identification devices. In this paper results from the first test of the fragmented ion beam done in 2010 will be presented showing that a pure Be beam can be obtained satisfying the needs of the experiment.

Some of the upgrade scenarios of the high-luminosity LHC require large intensity per bunch from the injector chain. Single bunch beams with intensities of up to 3.5 to 4e11 p/b and nominal emittances were successfully produced in the PS Complex and delivered to the SPS in 2010. This contribution presents results of studies with this new intense beam in the SPS to probe single bunch intensity limitations with nominal gamma transition. In particular, the vertical Transverse Mode Coupling Instability (TMCI) threshold with low chromaticity was observed at 1.6e11 p/b for single nominal LHC bunches in the SPS. With increased vertical chromaticity, larger intensities could be injected, stored along the flat bottom and accelerated up to 450 GeV/c. However, significant losses and/or transverse emittance blow up were then observed. Longitudinal and transverse optimization efforts in the PSB, PS and SPS were put in place to minimize this beam degradation and succeeded to obtain single 2.5e11 p/b LHC type bunches with satisfying parameters at extraction of the SPS.

Now that ions are available for collisions in the LHC, several experiments have expressed interest in fixed-target heavy and light ions in the North Area of the SPS. Taking into account the demands of the LHC and other scheduling constraints, this document details the various possibilities for planning fixed target ion runs in the coming years, and the resources needed to achieve them.

For several years, a large variety of beams have been prepared in the LHC injectors, such as single-bunch and multi-bunch beams, with 25 ns, 50 ns and 75 ns bunch spacings, nominal and intermediate intensities per bunch. As compared to the nominal LHC beam (i.e. with nominal bunch intensity and 25 ns spacing) the other beams can be produced with lower transverse emittances. Beams of low transverse emittances are of interest during the commissioning phase for aperture considerations and because of the reduced long-range beam-beam effects. On the other hand machine protection considerations might lead to prefer nominal transverse emittances for safe machine operations. The purpose of this paper is to present the results of controlled transverse emittance blow-ups using the transverse feedback and octupoles. The procedures tested in the SPS in 2008 allow to tune the transverse emittances up to nominal values at SPS extraction.

The commissioning of CERN's ion injector complex [1] to allow 1.1 PeV collisions of ions in LHC is well under way. After the Low Energy Ion Ring (LEIR) in 2005 [2] and the Proton Synchrotron (PS) in 2006 [3], the Super Proton Synchrotron (SPS) has now been commissioned with the 'Early' ion beam, which should give a luminosity of $5×10^{25}cm^{-2}s^{-1}$ in the LHC. This paper summarizes the operation in 2007 of all the machines involved in the ion injection chain.

The communication and coordination between the CERN accelerator and technical control rooms will be a critical issue for an efficient operation of the LHC and its injectors, which are expected to provide also beams for fixed target experiments, for detector component tests and for other activities including machine development. Early detection of faults in the accelerator and technical infrastructure (electricity, cooling, etc.) and their possible consequences on operation are useful not only to prevent major breakdowns but also to recover from them and to reschedule efficiently machine operation to satisfy the overall beam time requests from the different and concurrent users. To meet these requirements a method to define and provide common monitoring tools for all the actors involved in machine operation has been established. This method has been applied to the SPS accelerator and is being implemented in the PS complex and in the SPS experimental areas.

The performance of the CERN LHC will depend heavily on the high-brightness beam delivered by the injector chain. In 1999, after completion of the programme of hardware upgrades of the PS Complex, a major effort was devoted to producing a proton beam with the nominal transverse characteristics foreseen for LHC operation. This paper focuses on the different beam dynamics issues encountered during the setting up of such a beam, in the Linac2, the PS-Booster (PSB), the PS and the TT2 transfer line to the SPS. During the setting-up, single-particle issues, like stop-band compensation, correction of injection oscillations during the double-batch injection process, and the correction of the high-energy closed orbit in the PS, were addressed. Furthermore, collective effects, such as high-order head-tail instabilities induced by the resistive-wall impedance, were observed and cured. The compensation of these harmful phenomena permitted to achieve the goal, namely the generation of small transverse beam emittances and their conservation along the chain of different machines.

A new optics for the FTA transfer line, delivering high energy proton beam onto the p-bar production target, is presented and discussed in details. It allows to have the same optical configuration in the TT2 transfer line as that used for the other 26 GeV/c beams.

The standard approach to measure the optical parameters and the emittance in a transfer line is based on the analysis of the profiles measured by three monitors. This is feasible, provided the dispers ion function is known a priori. In this paper we propose to measure the complete set of five parameters (the two independent Twiss parameters, the emittance, the dispersion function and its derivative ) by using five monitors with one bending magnet interleaved. The results of some measurements carried out in the transfer line connecting the CERN PS and SPS rings are presented.

In the Lead Ion Facility at CERN [1] Pb53+ ion beams are accelerated up to a kinetic energy of 4.2 GeV/u in the CERN PS, extracted and stripped to Pb82+ in the transfer line from PS to SPS where they are injected and accelerated up to 157 GeV/u. The stripping efficiency, emittance growth and energy loss in Al strippers of different thicknesses have been measured and they are in good agreement with the theoretical values. The results of these measurements and considerations on the PS-SPS transmission efficiency are presented. [1] D. Warner, ed., ŒCERN Heavy-Ion Facility Design Report¹, CERN 93-01.