PAUL SCHERRER INSTITUT




PSI experience with high power beam handling,
      activation and radiation protection

      ...
Outline
    the PSI facility and its performance
[overview, cyclotrons, availability, resonators, target]
    intensity li...
Overview PSI Facility
 Injector II Cyclotron 72 MeV                                                          Cockcroft Wal...
Spallation Source Experimental Area                       K. Clausen
                               – 13 Beamlines
       ...
CW Acceleration using a
        Sector Cyclotron

590 MeV Ring Cyclotron
(magnets) in operation for 30+ years

- 8 Sector ...
history max. current of the PSI accelerator

                                        4 Cu Resonators
         license temp...
reliability and trips
typical: short (30sec) interrupts; trips of electrostatic elements; loss interlocks
average availabi...
major component: RF Resonators for Ring Cyclotron

•   the shown Cu Resonators have replaced the original Al resonators [l...
Cyclotron Facility Upgrade Path
  • keep absolute losses constant; increase acceleration
    voltage and beam quality, bet...
critical: electrostatic elements
                                                                                parameter...
extraction losses reduced by faster acceleration

absolute loss (nA) in Ring Cyclotron
as a function of current
          ...
avoid tail generation with short bunches
numerical study of beam dynamics in Ring Cyclotron
→ behavior of short bunches, g...
“round beam” – space charge in cyclotrons

qualitative picture:                    coordinate frame
                      ...
High Power Meson Production Target
     TARGET CONE
     3.0mA o.k., limit: sublimation


     Mean diameter:     450 mm
 ...
high power beams – technical safety
beam hits material (e.g. steel vacuum chamber):
                                beam p...
Diagnostics for Machine Protection
System based on ca. 150 interconnected very fast (<100µs) hardware CAMAC
and VME module...
Diagnostics (cont.)
2. Segmented Collimators measuring the balance of right and left, up and down
    scraped beam current...
Diagnostics (cont.)
3. Beam current transmission monitors compare the beam current at different
    spots for detecting lo...
practical experience: overheating of Lead filled steel
            tubes in spallation target because of wrong beam optics...
special interlock system: direct current density monitoring

beam projection on a glowing mesh observed with an optical ca...
Shielding
strategy: use standardized (mobile) concrete/iron blocks for shielding purposes
in PSI experimental hall: totall...
shielding (2) – target / 590MeV transport chan.
      elaborate shielding required
      reliability of activated componen...
predicted activation at Meson production target
30% beam loss; target (1..3Sv/h) exchange via special flask

             ...
measured component activation – Ring Cyclotron
activation level allows for necessary service/repair work
• personnel dose ...
overview: auxiliary expertise for High Power Operation

                               Facility Licensing
 Personnel Safet...
special infrastructure – hot cell facility


view through lead-glass window:
Meson production target wheel




           ...
special infrastructure – mobile shielding / exchange flask

• mobile and specifically adapted shielding devices are used f...
numerical modelling in the context of high power beams

                    particle generation/transport without/with MCN...
Summary
• the PSI accelerator delivers 1.3MW beam power
  in continuous mode; average reliability is 90%;
  ~25 trips per ...
Thank you for your attention!




             M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
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ESS-Bilbao Initiative Workshop. PSI experience with high power beam handling, activation and radiation protection.

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PSI experience with high power beam handling, activation and radiation protection.
Mike Seidel (PSI).

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ESS-Bilbao Initiative Workshop. PSI experience with high power beam handling, activation and radiation protection.

  1. 1. PAUL SCHERRER INSTITUT PSI experience with high power beam handling, activation and radiation protection M.Seidel, PSI ESS - Bilbao Initiative Workshop, March 16-18, 2009
  2. 2. Outline the PSI facility and its performance [overview, cyclotrons, availability, resonators, target] intensity limiting effects [space charge and beam blow up, scaling law for cyclotrons, round beam, beam dynamics simulations] high power related accelerator aspects [special controls/diagnostics, interlock systems, shielded beamlines, activation] specific infrastructure [rad.safety, disposal, legal requirements and all that …] conclusion M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  3. 3. Overview PSI Facility Injector II Cyclotron 72 MeV Cockcroft Walton isotope production 870 keV transfer channel µ (Ib <100µA) Ring Cyclotron 590 MeV 72 MeV transfer channel 2.2 mA /1.3 MW µ/π secondary beamlines π target M (d = 5mm) target E (d = 4cm) 1.5 mA /0.9 MW CW operation SINQ spallation source proton therapie center [250MeV sc. cyclotron] SINQ transfer channel SINQ experiments [Markus Lüthy] M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  4. 4. Spallation Source Experimental Area K. Clausen – 13 Beamlines NEUTRA TRICS HRPT POLDI MORPHEUS AMOR SANS-I CNR MARS DMC SANS-II RITA-II TASP FOCUS Eiger M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  5. 5. CW Acceleration using a Sector Cyclotron 590 MeV Ring Cyclotron (magnets) in operation for 30+ years - 8 Sector Magnets 1T - Magnet weight ~250 tons - 4 Accelerator Cavities850kV (1.2MV) - Accelerator frequency: 50.63 MHz - harmonic number: 6 72 → 590MeV - beam energy: - beam current max.: 2.2 mA - extraction orbit radius: 4.5m ⋅ - relative Losses @ 2mA: ~1..2⋅10-4 - transmitted power: 0.26-0.39 MW/Res. Pro: Con: - CW operation is inherently stable - inj./extr. difficult, interruptions, losses! - efficient power transfer with only 4 resonators - large and heavy magnets (therm. equiliblium!) - cost effective, compact - energy limited ~1GeV [- no pulsed stress in target] [- no pulsed structure for neutrons] M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  6. 6. history max. current of the PSI accelerator 4 Cu Resonators license temporary operation complete with 2.2mA given 1.3MW ! beam current is limited by beam losses; upgrade path foresees constant absolute losses by improvements of the accelerator M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  7. 7. reliability and trips typical: short (30sec) interrupts; trips of electrostatic elements; loss interlocks average availability: 90%; from June to December 2008: 94%(!) on average: 25 trips per day in the discussion on application of cyclotrons for duration of run period (this case: 21hours!) ADS systems the frequency of interruptions is of major interest duration of interruption ~30sec M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  8. 8. major component: RF Resonators for Ring Cyclotron • the shown Cu Resonators have replaced the original Al resonators [less wall losses, higher gap voltage possible, better cooling distribution, better vacuum seals] ⋅ • f = 50.6MHz; Q0 = 4⋅104; Umax=1.2MV (presently 0.85MV→186 turns in cyclotron, goal for 3mA: 165 turns) • transfer of up to 400kW power to the beam per cavity • deformation from air pressure ~20mm; hydraulic tuning devices in feedback loop → regulation precision ~10µm resonator inside hydraulic tuning devices (5x) M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  9. 9. Cyclotron Facility Upgrade Path • keep absolute losses constant; increase acceleration voltage and beam quality, better turn separation at extraction ∝ [turns]3 ∝ [charge density (sector model)] • losses × [accel. time] / [turn separation] (W.Joho) planned turn numbers and voltages turns Ring turns Injector now 202 81 (2.0mA) (Upeak≈3.0MV) (Upeak≈1.12MV) inter. step ~180 ~73 (Upeak≈3.3MV) (Upeak≈1.25MV) historical development of turn (2.6mA) numbers in PSI Ring Cyclotron upgrade ~165 ~65 (Upeak≈3.6MV) (Upeak≈1.40MV) (3.0mA) M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  10. 10. critical: electrostatic elements parameters extraction chan.: principle of extraction Ek= 590MeV channel E = 8.8 MV/m θ = 8.2 mrad ρ = 115 m U = 144 kV injection element in Ring Tungsten stripes beam pattern on outer turns in Ring M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  11. 11. extraction losses reduced by faster acceleration absolute loss (nA) in Ring Cyclotron as a function of current achieved in 2008: gap voltage increase: 780kV → 850kV turn number reduction: 202 → 186 figure shows absolute losses for optimized machine setup M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  12. 12. avoid tail generation with short bunches numerical study of beam dynamics in Ring Cyclotron → behavior of short bunches, generated by 10’th harmonic buncher → optimum parameters of flat-top cavity at these conditions after 100 turns! -multiparticle simulations -106 macroparticles [on supercomputer simulation of all protons in bunch feasible!] - precise field-map - bunch dimensions: radial/long. bunch distribution, varying initial bunch length σz ~ 2, 6, 10 mm; σxy ~ 10 mm → operation with short bunches and reduced flattop voltage seems possible court.: J.Yang CAEA M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  13. 13. “round beam” – space charge in cyclotrons qualitative picture: coordinate frame moves with bunch protons in the field of a round, short bunch + vertically oriented magnetic field (neglect relativistic effects and focusing) [Chasman & Baltz (1984)] though the force is repulsive a “bound motion” is established → for short bunches a round beam shape is formed → a round beam is observed in the Injector II cyclotron M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  14. 14. High Power Meson Production Target TARGET CONE 3.0mA o.k., limit: sublimation Mean diameter: 450 mm Graphite density: 1.8 g/cm3 Operating Temp.: 1700 K Irrad. damage rate: 0.1 dpa/Ah Rotation Speed: 1 Turn/s Target thickness: 60 / 40 mm 10 / 7 g/cm2 Beam loss: 18 / 12 % Power deposit.: 30 / 20 kW/mA SPOKES To enable the thermal expansion p-beam of the target cone BALL BEARINGS *) Silicon nitride balls Rings and cage silver coated Lifetime 2 y G.Heidenreich et. al. *) GMN, Nürnberg, Germany M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  15. 15. high power beams – technical safety beam hits material (e.g. steel vacuum chamber): beam power ∆T P0 ≈ = 250.000 K/sec ∆t 2π σ xσ y λI [g/cm ] c p 2 melts after 8ms ! heat capacity beam size material specific interaction length → fast and reliable interlock systems are necessary to avoid damage ! [even more so in pulsed machines with higher P0] M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  16. 16. Diagnostics for Machine Protection System based on ca. 150 interconnected very fast (<100µs) hardware CAMAC and VME modules treating about 1500 signals provided by the equipment: Ionisation chambers as beam loss monitors with fixed warning and 1. interlock limits; critical ones also with limits as function of the beam current. Simple and reliable device Warning level log scale Dyamic window Actual losses Permanent display of losses → losses outside margins are interlocked (including low values) M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  17. 17. Diagnostics (cont.) 2. Segmented Collimators measuring the balance of right and left, up and down scraped beam currents interlock is generated in case currents or asymmetry of currents exceeds margin M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  18. 18. Diagnostics (cont.) 3. Beam current transmission monitors compare the beam current at different spots for detecting loss of beam, normally 100% of transmission except at the targets and when beams are splitted. 100 % transmission in main cyclotron transmission monitoring 100 % transmission in beampipes, through Meson except for splitted beams production target E 97 % transmission of thin target M 70 % transmission of thick target E Integration time: 110 ms at 0 µA down to 10 ms above 1.5 mA Window: ± 5 µA at 0 µA and ± 90 µA at 2 mA 4. Many other signals: validity window on magnet settings, cavity voltages, … M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  19. 19. practical experience: overheating of Lead filled steel tubes in spallation target because of wrong beam optics cause: wrong beam optics installed, caused narrow wrong beam optics (pink), matched for beam width → power density too high 6cm Meson target but accidentally applied for 4cm target usual current density <=40µA/cm2, in this case: 70µA/cm2 note: βγεx = 7.5/40 mm⋅mrad ⋅ before/after 4cm graphite target Pb filled stainless steel tubes Window Pb filled Zy-2 cooling tubes damaged Target tubes cooling neutron radiography M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  20. 20. special interlock system: direct current density monitoring beam projection on a glowing mesh observed with an optical camera; problem: lifetime of camera; new version: glass-fiber optics to shielded camera position metallic mesh (tungsten) vertical cut through beamline and target showing installation of VIMOS camera 2d display and projection VIMOS, K.Thomsen M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  21. 21. Shielding strategy: use standardized (mobile) concrete/iron blocks for shielding purposes in PSI experimental hall: totally ~10.000 shielding blocks; in sum 32.000 tons of weight; all documented in CATIA CAD system iron is 30% fraction by the number 14 different standardized shapes 20% per the number of the blocks have special shapes with odd dimensions PSI experimental hall M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  22. 22. shielding (2) – target / 590MeV transport chan. elaborate shielding required reliability of activated components!; water cooling; few electrical connections Component activation in beamline up to ~300Sv/h! secondary shielding platform for electronics, pumps etc. 4cm Target Beam Dump collimators BEAM DUMP vacuum chimneys for inserts, primary shielding pumping connections Iron ! side view M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  23. 23. predicted activation at Meson production target 30% beam loss; target (1..3Sv/h) exchange via special flask top view D.Kiselev, M.Wohlmuther M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  24. 24. measured component activation – Ring Cyclotron activation level allows for necessary service/repair work • personnel dose for typical repair mission 50-300µSv • optimization by adapted local shielding measures; shielded service boxes for exchange of activated components • detailed planning of shutdown work activation map of Ring Cyclotron (EEC = electrostatic extraction channel) personal dose for 3 month shutdown (2008): 57mSv, 188 persons max: 2.6mSv cool down times for service: 2000 → 1700 µA for 2h 0 µA for 2h map interpolated from ~30 measured locations EEC M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  25. 25. overview: auxiliary expertise for High Power Operation Facility Licensing Personnel Safety [documentation and Systems paperwork, communication Radiation Safety [access to accelerator with legal authorities] bunkers, experimental [personnel dose areas] monitoring, radiation monitoring etc.] Radiative Waste Disposal High Power [declare nuclide technical safety systems Accelerator inventory, predict [interlock systems] disposal costs, Facility simulate temporary storage decay etc] technical infrastructure specific infrastructure [vacuum, cooling, RF, magnets, [HotLab, mobile shielding power supplies, survey, devices, radioanalytics etc.] diagnostics, controls etc.] M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  26. 26. special infrastructure – hot cell facility view through lead-glass window: Meson production target wheel irradiated SINQ spallation target, taken out of the cover M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  27. 27. special infrastructure – mobile shielding / exchange flask • mobile and specifically adapted shielding devices are used for targets and critical components as extraction elements or septum magnets • target exchange flasks are complicated and expensive devices [heavy, motors, instrumentation, SPS controls] picture: exchange flask for Meson production target E (4cm graphite wheel) M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  28. 28. numerical modelling in the context of high power beams particle generation/transport without/with MCNPX, electromagnetic fields MARS activation of components PWWMBS, MCNPX radioactive waste disposal, declaration of PWWMBS, nuclide inventory ISRAM design/estimation of shielding MCNPX, ATTILA beam dynamics codes omitted thermo hydraulic / cooling problems ANSYS, here! CFD-ACE Activity [Bq] example: 1.E+14 predicted nuclide 1.E+12 inventory for old 1.E+10 beam dump 1.E+08 Bq 1.E+06 1.E+04 M.Wohlmuther 1.E+02 S.Teichmann 1.E+00 D.Kiselev C5 3 N9 Fe 6 Be 0 60 Zn 2 54 M4 93 m -3 M4 -1 5 0 -5 -6 i-6 i-5 2 l-3 -1 -4 Ag -6 -1 08 H o- a- n- o- Fe Ti C N N C M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  29. 29. Summary • the PSI accelerator delivers 1.3MW beam power in continuous mode; average reliability is 90%; ~25 trips per day • performance is limited by uncontrolled losses → upgrade path through faster acceleration (higher resonator voltages) + bunch compression; max. acceptable activation of serviced accelerator components: ~ several mSv; total loss ~ 200W • infrastructure for dealing with activated components and formal aspects connected to safety and radiation issues are challenging and are often underestimated! M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)
  30. 30. Thank you for your attention! M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)

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