Interplay of Space Charge and Intra-Beam Scattering in the LHC ion injector chain

The ion injectors of the CERN accelerator chain, in particular the Super Proton Synchrotron (SPS) and the Low Energy Ion Ring (LEIR), operate in a strong Space Charge (SC) and Intra-Beam Scattering (IBS) regime, which can degrade beam quality. Optimizing the ion beam performance requires thus to study the interplay of these two effects in tracking simulations by incorporating both SC and IBS effects interleaved with lattice non-linearities. In this respect, the kinetic theory approach of treating IBS effects has been deployed. A new, modified approach has been introduced using the formalism of the Bjorken and Mtingwa model and the complete integrals of the second kind for faster numerical evaluation. This IBS kick is implemented in PyORBIT and extensive benchmarking cases against analytical models are shown. Results of combined space charge and intra-beam scattering simulations for the SPS and LEIR are presented and compared with observations from beam measurements.Comment: 13 pages, 13 figures, to be submitted to Physical Review Accelerators and Beam

Runtime support for programming explicit communication chip multiprocessors

Τα σύγχρονα πολυεπεξεργαστικά συστήματα με διαχείριση αποκλειστικών τοπικών μνημών προσφέρουν μια αποτελεσματική πλατφόρμα ανάπτυξης παράλληλων προγραμμάτων. Η ρητή διαχείριση μνημών επιτρέπει στους προγραμματιστές να ελέγχουν άμεσα την τοπικότητα και τη μεταφορά των δεδομένων ενός προγράμματος. Η χρήση αυτού του άμεσου ελέγχου επιτρέπει τη δημιουργία εφαρμογών οι οποίες επιτυγχάνουν υψηλές επιδόσεις αφού οι μεταφορές δεδομένων βελτιστοποιούνται και τα δεδομένα διαμοιράζονται κατάλληλα ανάμεσα σε τοπικές και κοινές μνήμες. Η εκμετάλλευση, όμως, τέτοιων συστημώτων παιτεί την ύπαρξη κατάλληλων εφαρμογών οι οποίες θα είναι σε θέση να χρησιμοποιούν τους διαθέσιμους πόρους με τέτοιο τρόπο ώστε να πετύχουν την αδιάλειπτη τους χρήση. Σε αυτή την εργασία αναπτύσσουμε διάφορες εφαρμογές χρησιμοποιώντας ένα πολυεπεξεργαστικό σύστημα ανάπτυξης βασισμένο σε πολλαπλούς πυρήνες με αποκλειστικές τοπικές μνήμες οι οποίες διαχειρίζονται αίτε με σαφής είτε με έμμεσους τρόπους επικοινωνίας. Προκειμένου να επιτύχουμε τη μέγιστη επίδοση εκμεταλλευόμαστε τους μηχανισμούς ρητής επικοινωνίας που το σύστημα προσφέρει ώστε να διαχειριστούμε τις μνήμες και να ανταλλάξουμε δεδομένα επιτυγχάνοντας τη μέγιστη δυνατή χρήση των διαθέσιμων πόρων του συστήατος. Ακόμα, μετράμε και αναλύουμε τις επιδόσεις κάθε εφαρμογής για διάφορες περιπτώσεις και αναφέρουμε τις μεθόδους βελτιστοποίησης για καθε μια. Οι εφαρμογές που αναπτύσσουμε είναι ο γνωστός μετασχηματισμός Fourrier, ένας διτονικός αλγόριθμος ταξινόμησης, τρεις εφαρμογές Map-Reduce και, τέλος, μια εφαρμογή stream μέτρησης επιδόσεων της μεταφοράς δεδομένων στο σύστημα μας. Το σύστημα το οποίο χρησιμοποιούμε αναπτύχθηκε στο εργασήριο CARV (Computer Architecture and VLSI Systems) του ΙΤΕ (Ίδρυμα Τεχνολογίας και Έρευνας) και βασίζεται σε μια σύγχρονη πλατφόρμα ανάπτυξης FPGA (Field Programmable Gate Array). Σε αυτή την εργασία προσθέτουμε επιπλέον υπομονάδες στο σύστημα και λειτουργικότητες στις βιβλιοθήκες, ώστε να εκμεταλλευτούμε την ρητή επικοινωνία στα παράλληλα προγραμματιστικά μοντέλα. Επιπλέον, μεταφέρουμε και αναλύουμε τις επιδόσεις των εφαρμογών και αναφέρουμε τεχνικές εκμετάλλευσης των διαθέσιμων μηχανισμών επικοινωνίας ώστε να επιτύχουμε υψηλές επιδόσεις με τη χρήση των ρητών μεθόδων επικοινωνίας. Μετράμε την επίδοση και τον ελάχιστο κόκκο προγράμματος όπου μπορούμε να επιτύχουμε επιτάχυνση της παράλληλης εκτέλεσης μιας εφαρμογής συγκρινόμενη με τη σειριακη σε διάφορες περιπτώσεις. Τέλος, αναφέρουμε τις δυσκολίες και τους περιορισμούς της ανάπτυξης των εφαρμογών στο πρωτότυπο σύστημα. Μετράμε επιτάχυνση της παράλληλης εκτέλεσης του αλγόριθμου της διτονικής ταξινόμησης ο οποίος απαιτεί μόλις 700 κύκλους σειριακής εκτέλεσης. Στις εφαρμογές MapReduce μετράμε επιτάχυνση της εκτέλεσης μέχρι περίπου 2 και 4 για δυο και τέσσερις επεξεργστές αντίστοιχα και στην Stream εφαρμογή πιέζουμε τους μηχανισμούς επικοινωνίας του συστήματος επιτυγχάνοντας ρυθμούς μεταφοράς on-chip δεδομένων με ταχύτητες μέχρι και 3200MB/s.Modern chip multiprocessors (CMP) with explicit managed local memories offer robust and efficient developmment systems. Explicitly managed memories allow programmers to control the locality and the exchange of the data of the programs they develop. Using this immediate control of data exchange ptogrammers can develop applications that achieve high performance by optimizing data transfers and apply proper data distribution between local and global memories. Programmers have to develop applications that must be specific fir each system in order to fully exploit the availale resources and achieve high performance. In this work we develop several applications using a modern multicore development system based on multiple processors and local memories managed by explicit and imlicit communication mechanisms. In order to achieve high performance we exploit the available communication mechanisms to explicitly manage memories and apply data exchange patterns that maximize the resource utilization of the system and achieve high performance. For each application, we measure its performance for various cases and analyze their performance under various circumstances. We develop a Fast Fourrier Transform (FFT), a bitonic sort algorithm, three applications based on the MapReduce framework and a stream application that measures the communication mechanisms' performance by stressing the system. The system we use is a system that was developed at the CARV (Computer Architecture and VLSI Systems) laboratory of FORTH (Foundation of Research and Technology) and is based on a modern development platform FPGA (Field Programmable Gate Array). In this thesis we introduce modules and functionalities in system software libraries, to exploit explixit on-chip communication mechanisms in parallel programming models. Moreover, we port and analyze the performance of the applications for the development system and report techniques on how to exploit the available communications mechanisms in order to achieve high performance using explicit communication mechanisms. We measure that performance and the minimum granularity at which the parallel applications can gain speedup under various cases. And finally we identify the difficulties and the limitations of the applications' porting to the prototype system. We achieve speedup at parallel execution of the Bitonic sort application that takes even 700 cycles to be executed in sequetial execution. In MapReduce applications we achieve speedup almost up to 2 and 4 for two and four processors respectively and in Stream application we stress the communication mechanisms of the prototype system and achieve up to 3200MB/s on-chip data transfer rate

Interplay Between Space Charge, Intra-Beam Scattering, and Synchrotron Radiation Effects

The objective of this research is to study the interplay of synchrotron radiation, intra-beam scattering, and space charge in the vicinity of excited resonances. In this respect, two modules were developed to simulate intra-beam scattering and synchrotron radiation effects and plugged into pyORBIT to be used together with its space charge module. Different regimes of synchrotron motion were used to study the response of the beam to a lattice resonance when space charge, intra-beam scattering and synchrotron radiation are present

Interplay of Space Charge, Intra-Beam Scattering and Synchrotron Radiation in the CLIC Damping Rings

Future ultra-low emittance rings for electron/positron colliders requiring extremely high beam brightness can be limited by collective effects. In this paper, the interplay of effects such as synchrotron radiation, intra-beam scattering (IBS) and space charge in the vicinity of excited betatron resonances is assessed. In this respect, two algorithms were developed to simulate IBS and synchrotron radiation effects and integrated in the pyORBIT tracking code, to be combined with its widely used space charge module. The impact of these effects on the achievable beam parameters of the Compact Linear Collider (CLIC) Damping Rings was studied, showing that synchrotron radiation damping mitigates the adverse effects of IBS and space charge induced resonance crossing. The studies include also a full dynamic simulation of the CLIC damping ring cycle starting from the injection beam parameters. It is demonstrated that a careful working point choice is necessary, in order to accommodate the transition from a non-linear lattice induced detuning to a space-charge dominated one and thereby avoid excessive losses and emittance growth generated in the vicinity of strong resonances

Interplay between Space Charge and Intra-beam Scattering for the CERN Ion Injectors

The CERN ion injectors, SPS and LEIR, operate in a strong space charge and intra-beam scattering regime, which can lead to degradation of their beam performance. To optimize machine performance requires thus to study the interplay of these two effects in combined space charge and intrabeam scattering tracking simulations. In this respect, the kinetic theory approach of intra-beam scattering has been implemented in pyORBIT and benchmarked against analytical models. First results of combined space charge and intra-beam scattering simulations for SPS and LEIR are presented in this contribution. The simulation results are compared with observations from beam measurements

Detailed characterisation of the LEIR intensity limitations for a Pb ion beam

The equilibrium emittance of the Pb beam in the CERN Low Energy Ion Ring (LEIR) results from the interplay of electron cooling and heating processes, as intra-beam scattering and space charge. In this paper we present the measurements of the emittance evolution as a function of intensity, working point and resonance excitation, and compare them with the simulations of the heating processes. Optimum settings for normal and skew sextupoles have been found for the compensation of resonances excited by the lattice

A reconfigurable accelerator for quantum computations

Summarization: This paper presents a new architecture to accelerate quantum computations, using reconfigurable computing structures. It was designed post place and route, validated with standard benchmarks, and its performance has been evaluated vs. a high end computer running the same benchmarks with highly optimized code. The acceleration of arbitrary quantum circuits is very promising because it extends the kind of quantum computing problems that can be solved with reconfigurable architectures.Παρουσιάστηκε στο: International Conference on Field Programmable Logic and Application

Review of LEIR operation in 2018

During run 2 (2015-2018) the LEIR machine experienced several important improvements in terms of extracted intensity, driven by the LHC Injectors Upgrade (LIU) project requirements. In 2018 the machine not only gave another step forward in extracted intensity, but also demonstrated that it could deliver the LIU target intensity in a reproducible and reliable way. The main steps that allowed the high performance reach of the NOMINAL beam and improvements to the machine stability are detailed in this paper. This work is also intended to be a reference for the restart after the Long Shutdown 2