1 / 69

V. Chohan CERN

An overview of CERN Antiproton facility in the Eighties & Nineties : i.e., what was done & happened at CERN in the AA  (1980 onwards) and later on in the AA+AC era (1987 onwards) till the closure in 1996 and re-starting 3 years later in AD. V. Chohan CERN.

svea
Download Presentation

V. Chohan CERN

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. An overview of CERN Antiproton facility in the Eighties & Nineties : i.e., what was done & happened at CERN in the AA  (1980 onwards) and later on in the AA+AC era (1987 onwards) till the closure in 1996 and re-starting 3 years later in AD V. ChohanCERN Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  2. The CERN Antiproton Operation- 1980-83 Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  3. The Antiproton Machines after ISR closure but with LEAR (1983 onwards )& AAC (1987 onwards) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  4. Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  5. Some Generalities • The p-pbar Collider Physics at UA1, UA2 was the ‘raison d’etre’ • The whole Laboratory was involved in this ‘adventure’ into the unknown • From the day production started ~ end 1980, we discovered that our overall pbar yields were rather low, much lower than expected . The AA machine had many limitations including Acceptances, cooling systems’ interplay and limits ( ‘combined functionalities’ , shutters ) and so forth. • Hence the Quest was for producing & storing more Antiprotons from 1981 onwards • The talk specifically excludes issues of machine & stochastic cooling systems design because it is well documented elsewhere Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  6. Broad Outline of the Talk • AA and What it was • AC Design & AAC • Towards the AAC: Machine & Production • R & D on Collectors & Production • Conducting Target • Li lens • Improved Horn • Consolidation of Passive Target • { Plasma lens } • Constraints at Start up in 1987 & ‘ Abandoned ‘ issues • AAC Operation at Peak Performance for p-pbar Collider ( ‘89-’90) • AAC Performance Issues for a Complex of Several Machines Abandoned hopes for the top-Quark at CERN • AAC Op. for Collider Low Luminosity run ’91 ( precursor of LHC- TOTEM) • AAC Operation for steady-state LEAR runs ’92-96 • Some Issues for Operational robustness, reliability ? Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  7. Overview 1980-1987 • What was the AA – Single Ring Limitations In AA • Design of AC Ring Expectations of the AAC complex ( AA +AC concentric Rings) • Design Goals & Collector Lenses Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  8. The Antiproton Accumulator • Machine was constructed 1978-1980 as an “Experiment” • The UA1 & UA2 were the first Large collaborations and the pioneering pre-cursors to large LEP Expts. & present LHC Expts. • Machine Design was for 100π Transverse Acceptance 1.5 % in Δp Achieved only ~ 80 πin both transverse planes • Copper Target & Magnetic Horn for pbar collection first target was tungsten but was soon replaced by Cu for better yields Operational Yield ( pbars per proton) on Inj Orbit ~ 5E-7 Best Accum. Rate ~ 6 E9 /hr • Several Stochastic cooling systems ( pre-cooling, Stack tail & Core )& multi-functionality within same ring needing pulsed Shutters, interference of systems & limitations in stack Core size Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  9. 1981 First Yields and “ MISSING FACTOR “ Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  10. The AA before AC & the continued struggle for chasing the “ Missing Factor ” (1986 ) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  11. Towards the Design of the CERN AC Ring ( 1982-83-84 )& [AD+AA]@FNAL too ! Aim to Increase the Stacking Rate by a factor 10 and hence provide a bigger flux for the Collider Operation ( LEAR was only a ‘parasitic’ operation ) How? Have a Separate Ring( AC-Antiproton Collector) separate some functions ( fast pre-collect , debunch & fast pre-cool ) and use AA purely for Stack Core Accumulation Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  12. How Was the Factor 10 in Stacking Rate to be Achieved ? AC Ring Design • Transverse Acceptance Design : 240 π in both H & V • So up on the AA ( Design was 100 π both planes) by aFACTOR 4 AC design was for 240π for a simple reason, since AA only achieved 80π i.e., 20 % less than Design 100π, we DESIGNED AC for 20 % more, to achieve 200 π in REALITY ! • Longitudinal Acceptance 6 % ( AA was 1.5 %) • So up on the AA by a Factor 4 • Total Expectation of a GAIN by a factor 4 x 4 = 16 in Pbars Acceptance • For the same Production Beam Repetition rate (every 2.4s = 1500 shots per hour), this increased transverse & longitud. Phase space necessitated a re-designed Pbar production target system to provide the increased yield & to populate this phase space; this gave an expectation in increased pbar flux or an Accumulation Rate increase of at least factor 10, ie., 6 E6 → 60 E6 pbars per PS Prod. Beam Shot Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  13. Greater thanFactor of 16 in Production meant what ? • Even if we had an increased number per shot arriving on the Inj. Orbit in AC by a factor 16 , i.e., 6E6 ( as was on AA Inj orbit ) x 16 = ~ 100E6 ( in AC ) • For the whole chain from Inj in AC to final store in AA only a 50% efficiency was considered as reasonable, meaning 50E6 x 1500 cycles per hr. ( in 2.4 sec PS Production cycles), = 7.5 E10 pbars per hr. so largely meeting the physics aim of having factor 10 in stacking rate per hour from 6E9 in AA to 6E10 in the AAC complex Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  14. Factor 16 in Acceptance and its Filling • To fill 16 times bigger machine acceptance also needed at least a factor 16 in the Pbar Production at the target. • The Development of new Cylindrical ‘Magnetic lenses’ focussing in both or all planes straight after the target was started already in early 1982 after “discovering” that at least a factor 5 was missing in the AA Production &/or Accumulation rate ; Such lenses reduce the ‘collecting’ angles by at least 10 compared to normal Quadrupoles. Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  15. Quest for more pbars & Expected Yield Gains in AC over AAfor Different Targets & Collector Lenses Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  16. Development of New Targets & Collection Lenses The R & D was on various fronts: • Lab tests of a conducting target +horn assembly pulsed at 200 kA , 30 µs pulse followed by Machine Testsof theConducting Target and Yield evaluation • Further development of “wire lenses” , meaning the wire conductor is a cylindrical rod ofLithium contained inside a steel or titanium shell ( Novosibirsk & FNAL ideas & development) • Improvement of the “current-carrying” sheet CERN design(1962)Magnetic Horn used already in AA but with larger current and collection angles • ‘plasma Lens’ R & D was also envisaged • Consolidation & Improvement of Passive Targets Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  17. Pulsed Conducting Targets : ( subject seems reactivated today for neutrinos ) • Advantages: • Large Collection Angle implying Greater number of particles within a given Acceptance • Drawbacks • Larger the collection angle, stronger the collector lens needed DOWNSTREAM of the target • The field that focuses the antiprotons de-focuses the protons and this effect must be taken into account and imply putting an extra pulsed focusing lens on the proton beam BEFORE the target • Many particles forced to traverse the target & re-absorption is relatively high • Long Testing Periods in laboratory to evaluate mechanical issues • Further Durability issues to be considered under repeated ‘shocks’ of proton beams • Highly radioactive zone making repair/replace conditions very difficult Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  18. Pulsed Conducting Targets Development • Laboratory Tests : • Connecting Horn in series with Target (3 mm dia.) and pulsing at 200 kA , 30 us pulse to permit sufficient field penetration • Lab. Tests were all Destructive • Container lifetime problems & technological challenges • Machine Tests • THREE Experiments were carried out • Higher Yields ( >50 % more) were observed • Very limited lifetime of the target – few hours due to fracturing of the device • Beam Induced Effects - problems due to maximum of current (140 uA) being at the same time as proton beam releasing energy in the target ( high temperature rise), resulting stresses & shock effects • Technological problems of stress , fatigue in target containers • Thermal cooling using gas • Some Lessons from Tests & further development directions • Reduce the stresses by decrease in current or increase in target diameter, etc.. • Highly radioactive target meant very difficult repair & replacement ; if frequent target exchanges were necessary, a rapid exchange using remote-handling capability was needed for the target area ( new Target Area Design) • Separation of Pulsers – one each for horn & Conducting target • Study liquid metal targets.. [ in vogue again now (2007) …!! For neutrinos…..] Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  19. Conducting Target – first ideas 1982 Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  20. Conducting Target : Yield Expectations Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  21. Proton Pre-Focus Li Lens, pulsed Conducting Target, pulsed Magnetic Horn as pbar Collector Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  22. Development of Lithium Lens • Original Novosibirsk Development, taken further for Pbar Source at Fermilab in early eighties. • Water Cooling was used in Li lens assembly • At Fermilab, problems overcome with : • sufficient spares of targets & Li lenses, • a new, well designed target area with quick replacement , exchange possibilities ( unlike at CERN where we already had AA running with the original target area based on the concept of AA being a one-off experiment !) • Work on 20 mm Li Lens with pulser of up to 625 kA in lab and somewhat less ( 450 kA ) in the machine • Work on 36 mm Li Lens to operate at 1.3 MA with a pulser delivering up to 1.5 MA Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  23. Li Lens instead of Magnetic Horn for higher yields – First Ideas Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  24. Water cooled 36 mm Li Lens Assembly Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  25. Some Problems & Drawbacks of Lithium Lens • 36 mm lens did indeed have larger yields over 20 mm one BUT ONLY for large value of current ( > 1.1 MA ) • Water Leak problems and issues of repair in radioactive area • Life tests in lab again gave container problems with the stainless steel container and this had to be INCREASED at the expense ofREDUCING the Li diameter from 36 mm to 34 mm– however this reduced the effectiveness of cooling and consequentlylimited the max . Permissible current to about 1 MA – else Li would partially melt; however now, it meant that the yield gain over 20 mm Li lens was very small ~ 7 %and the only way was to go to Liquid Li and develop a new cooling system ! • High Current Pulsers Need and Development Costs & finally, 1989/90 runs had shown that Top Quark limit was beyond the 315 GeV on 315 GeV collisions at SPS Collider & 980-980 GeV FNAL had an open field for them - so nobody would want to finance new R&D on Li lenses - and LEP had already started!! Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  26. Yields vs Intensity : Different Collectors ( last CERN Results ) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  27. Subject not complete without talking of Robustness of Passive Targets • Problems of Target Fracturing, loss of Yield in early AA operation • Damaged but highly radioactive Targets were sliced /analysed in EIR-CH( now PSI) & in Seibersdorf – Austria • Lots of Work done on improving Targets • Final AAC start up in July 1987 used passive Irridium Targets in a unit of 3 pellets assembled together • Lots of References – Terry Eaton et al Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  28. AA Shutdown for AC installation & AAC Startup for Physics • Only Nine month shutdown to install AC ( Aug86-July87) • Competition with FNAL was still on – race for the discovery of the Top Quark & having UA1 + UA2 running with p-pbars again as fast as possible { problems in UA1 Detector + Rubbia as DG 1989 issue came after } • Difficulties in manning & funding R & D – especially to test in beam conditions and at the same time providing operational facility for physics meant that AAC started with options of : • smaller 20 mm dia. Li lens & • 60 mm Horn as a backup that is, No Conducting Target, hence no proton Focus Li lens either • No 36 mm Li Lens Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  29. AAC Startup & Injection Line Matching • However, the Injection Line from the Target+ Collector lens to the AC Ring was DESIGNED for Matching the 36mm Li lens to the AC ring with 240π Transverse Acceptance and 6 % Momentum Acceptance • So by now using a 20 mm Li lens or Horn, this Matching was no more valid to transmit 240 π acceptance ; only about 200 π Acceptance was possible, after modifying the matching conditions. The radius of beam at exit of the collector lens was used as a variable parameter such that: R-acc = 15 mm for 20mm Li lens with α =0 R-acc = 30 mm for 60mm Horn with α ≠ 0(tilted ellipse) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  30. AC Injection Line Matching & Isuues of 36 mm, 20 mm Li Lenses & 60 mm Magnetic Horn Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  31. 20 mm Li Lens permitted only 200πAcceptance Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  32. AAC Startup & Injection Line Air Scattering • Due to high level of induced radioactivity and maintenance difficulties for vacuum systems, large part of the dogleg up to the proton Dump are in the air as well as the antiproton Channel towards the AC (~15 m of beam line elements have no vacuum chamber ) • The presence of air implies multiple Coulomb scattering and consequent beam loss ; the loss in yield due to air is of the order of up to 16 % • Several Modeling & Simulation programs to estimate yields : the origin from AA days had S.van der Meer’s program later on modified by Sherwood & Hancock for AAC and finally Nick Walker using Monte Carlo techniques Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  33. Final Results for p-pbar Collider Operation (1988-1991) & later only LEAR (till 1996) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  34. Operational Yields with 1.5E13 Protons on Target ( CERN Experience) Yield defined as no. of Antiprotons on Inj Orbit in the AC Ring per Incident Proton on Target Yields & Operational Performance Comparisons Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  35. Peak Performance AAC era: SPS & LEAR both running Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  36. The interplay of multifarious systems to finally arrive at pbars stored in the stack in the AA Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  37. AAC Performance & Dependency Factors : Final Figure of Merit Note: pbars per shot: > 71 E6 Stacking rate: 53 E9/hr Accumulation Yield: ~ 44 E-7 Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  38. From AA to [AA+AC] : 1981-1991Stacking Rates & Peak Stacks Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  39. SPS Collider Peak Performnce pbar transfers – 1989 [ 6 on 6 p & pbar ] Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  40. Last Pbars sent to SPS [ Dec 1991 ] : 3 proton shots v.s 3 Antiproton shots Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  41. Sending Antiprotons both to SPS & LEAR (1991) Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  42. AAC for SPS Collider & LEAR {1987-91 } to a single -client LEAR {1992-96 } Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  43. AD Example of recent times: Uses Robust Magnetic Horn 1.4 mm thick Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  44. Some Lessons Learnt Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  45. Engineering of Passive Targets • This is vast domain in its own right • Suffice to say that at CERN we went through the whole range of issues from Initial Copper Target of 1981 to what is used in AD today • Problems of Cu Target micro cavitation / fracture & loss in Yield • documentation exists, particularly for the period leading up to the AC Ring in 1987 and why we have now (for the AD) the Irridium Target Assembly in a unit of 3 pellets assembled together Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  46. Antiproton Production & Collection Ensemble • The Collector lenses should not be disassociated from issues of antiproton production by hitting a target • Target assembly and associated issues need to be dealt with fully in a correctly engineered manner to lead to a properly designed “Target + Collector Area” • Lot of the early days of AA (1980-85) were spent in having target aspects being analyzed, consolidated, modified , improved etc to build up a store of engineering knowledge that one takes for granted today ( say, in AD running of today) . Some of these aspects were also related to AA being defined as an “experiment” only as well as due to the idea of developing ‘conducting ‘ targets. Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  47. Robustness, Reliability Issues ( Assuming that the machine and stochastic Cooling systems are all well designed from the wealth of experience at CERN & FNAL ) Production depends on what one wants in terms of Reliability and associated Robustness • Production Area is implicitly highly Radioactive • Hence, one needs minimized repair and interventions as well as to have assured uptime • One must therefore consider: • Production Targets and Target Assembly Design • Collector Lens that go with the Target • Design of the Target Area consisting of the appropriately engineered issues of Targets, Cooling , high current pulsers and the powering of the Collectors in a radiation-hard manner in most general sense of the word • Separate Water Collection possibilities for Target Cooling circuits due to radiation • Facilitated Target or Collector replacement by Spares with easy-to-change procedures &/or remote handling and “cooling down” or storage zone for highly active, removed devices Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  48. Production Yields & Suitability of Collectors We Consider Essentially the TWO types of requirements where Antiprotons are produced and the solutions chosen: • High Production Yields & high energy Collider Needs • CERN during Collider days, FNAL even now • Reliable steady state Yields and Low Energy type of needs • LEAR • AD • GSI ?? Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  49. Magnetic Horns • Horns were to become the preferred Solution for the AAC era for the single-client operation (LEAR) from 1992 onwards till the end of LEAR in 1996 • Development of robustness • Development of sufficient spares • Conical to bi-conical shape permitted independence from adjustment of target distance from horn like in li lens operation optimisation Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

  50. Target & Magnetic Horn Assembly Schematics Pbar@FAIR Workshop GSI, Darmstadt 3-4 Dec 2007

More Related