ess-bilbao initiative workshop. psi experience with high power beam handling, activation and...

PAUL SCHERRER INSTITUT

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

M.Seidel, PSIESS - Bilbao Initiative Workshop, March 16-18, 2009

M.Seidel, ESS Bilbao Initiative Workshop, March 16-18 (2009)

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


Injector II Cyclotron 72 MeV

870 keV transfer channel

72 MeV transfer channelRing Cyclotron 590 MeV

SINQ transfer channel

SINQspallation source

Overview PSI Facility

2.2 mA /1.3 MW

1.5 mA /0.9 MWCW operation

isotope production(Ib <100µµµµA)

µµµµ/ππππ secondary beamlines

target M (d = 5mm)

target E (d = 4cm)

Cockcroft Walton

proton therapie center [250MeV sc. cyclotron]

SINQexperiments

[Markus Lüthy]


TASPRITA-II

TRICS POLDI MORPHEUS AMOR

FOCUS

SANS-I

SANS-II

HRPT

DMC

NEUTRA

CNR

MARS

Eiger

K. ClausenSpallation Source Experimental Area – 13 Beamlines


CW Acceleration using a Sector Cyclotron

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

- 8 Sector Magnets 1 T- Magnet weight ~250 tons- 4 Accelerator Cavities850kV (1.2MV)- Accelerator frequency: 50.63 MHz- harmonic number: 6- beam energy: 72 →→→→ 590MeV- 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]


history max. current of the PSI accelerator

license temporary operation with 2.2mA given

4 Cu Resonators complete

beam current is limited by beam losses;

upgrade path foresees constant absolute losses by improvements of the accelerator

1.3MW !


reliability and trips

duration of interruption ~30sec

duration of run period (this case: 21hours!)

� 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 ADS systemsthe frequency of interruptions is of major interest


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

hydraulic tuning devices (5x)

resonator inside


historical development of turn numbers in PSI Ring Cyclotron

Cyclotron Facility Upgrade Path• keep absolute losses constant; increase acceleration

voltage and beam quality, better turn separation at extraction

• losses ∝ [turns]3 ∝ [charge density (sector model)] × [accel. time] / [turn separation] (W.Joho)

turns Ring turns Injector

now (2.0mA)

202(Upeak≈3.0MV)

81(Upeak≈1.12MV)

inter. step(2.6mA)

~180(Upeak≈3.3MV)

~73(Upeak≈1.25MV)

upgrade(3.0mA)

~165(Upeak≈3.6MV)

~65(Upeak≈1.40MV)

planned turn numbers and voltages


critical: electrostatic elements

principle of extraction channel

injection element in Ring

Tungsten stripesbeam pattern on outer turns in Ring

parameters extraction chan.:Ek= 590MeVE = 8.8 MV/mθ = 8.2 mradρ = 115 mU = 144 kV


extraction losses reduced by faster acceleration

achieved in 2008:

gap voltage increase: 780kV → 850kV

turn number reduction: 202 → 186

figure shows absolute losses for optimized machine setup

absolute loss (nA) in Ring Cyclotron as a function of current


avoid tail generation with short bunches

-multiparticle simulations-106 macroparticles [on supercomputer simulation of all protons in bunch feasible!]

- precise field-map- bunch dimensions: σσσσz ~ 2, 6, 10 mm; σxy ~ 10 mm

→ operation with short bunches and reduced flattop voltage seems possible

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

court.: J.Yang CAEA

radial/long. bunch distribution, varying initial bunch length

after 100 turns!


“round beam” – space charge in cyclotrons

qualitative picture:

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

coordinate frame moves with bunch

→ a round beam is observed in the Injector II cyclotron


High Power Meson Production Target

p-beam

BALL BEARINGS *)Silicon nitride ballsRings and cage silver coatedLifetime 2 y*) GMN, Nürnberg, Germany

SPOKES

To enable the thermal expansion of the target cone

TARGET CONE

3.0mA o.k., limit: sublimation

Mean diameter: 450 mmGraphite density: 1.8 g/cm3

Operating Temp.: 1700 KIrrad. damage rate: 0.1 dpa/AhRotation Speed: 1 Turn/sTarget thickness: 60 / 40 mm

10 / 7 g/cm2

Beam loss: 18 / 12 %Power deposit.: 30 / 20 kW/mA

G.Heidenreich et. al.


high power beams – technical safetybeam hits material (e.g. steel vacuum chamber):

K/sec000.250]g/cm[2 2

0 =≈∆∆

pIyx cP

tT

λσσπ

beam power

beam size material specific interaction length

heat capacity

melts after 8ms !

→ fast and reliable interlock systems are necessary to avoid damage !

[even more so in pulsed machines with higher P0]

��


Diagnostics for Machine Protection

→→→→ losses outside margins are interlocked (including low values)

System based on ca. 150 interconnected very fast (<100µs) hardware CAMACand VME modules treating about 1500 signals provided by the equipment:

1. Ionisation chambers as beam loss monitors with fixed warning and interlock limits; critical ones also with limits as function of the beam current.Simple and reliable device

Permanent display of losses

Warning level

Actual losses

Dyamic window

log

scal

e


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 currentsexceeds margin


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

100 % transmission in beampipes, except for splitted beams

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 mAWindow:± 5 µA at 0 µA and ± 90 µA at 2 mA

4. Many other signals: validity window on magnet settings, cavity voltages, …

transmission monitoring through Meson production target E


practical experience: overheating of Lead filled steel tubes in spallation target because of wrong beam optics

� cause: wrong beam optics installed, caused narrow beam width →→→→ power density too high

� usual current density <=40µA/cm2, in this case: 70µA/cm2

Pb filled stainless steel tubes

Pb filled Zy-2 tubes

Target cooling

Window cooling

neutron radiography

damaged tubes

wrong beam optics (pink), matched for 6cm Meson target but accidentally applied for 4cm target

note: βγεβγεβγεβγεx = 7.5/40 mm⋅⋅⋅⋅mrad before/after 4cm graphite target


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

2d display and projection

metallic mesh (tungsten)

vertical cut through beamline and target showing installation of VIMOS camera

VIMOS, K.Thomsen


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


BEAM DUMP

shielding (2) – target / 590MeV transport chan.

side view

primary shielding

Iron !

vacuum chimneys for inserts, pumping connections

� 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.

collimators

4cm TargetBeam Dump


predicted activation at Meson production target

D.Kiselev, M.Wohlmuther

30% beam loss; target (1..3Sv/h) exchange via special flask

top view


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

measured component activation – Ring Cyclotron

EEC


overview: auxiliary expertise for High Power Operation

High Power Accelerator

Facility

Personnel Safety Systems

[access to accelerator bunkers, experimental

areas]

technical infrastructure[vacuum, cooling, RF, magnets,

power supplies, survey, diagnostics, controls etc.]

Radiative Waste Disposal

[declare nuclide inventory, predict disposal costs,

simulate temporary storage decay etc]

Facility Licensing [documentation and

paperwork, communication with legal authorities]

Radiation Safety

[personnel dose monitoring, radiation

monitoring etc.]

specific infrastructure[HotLab, mobile shielding

devices, radioanalytics etc.]

technical safety systems[interlock systems]


special infrastructure – hot cell facility

view through lead-glass window:

Meson production target wheel

irradiated SINQ spallation target, taken out of the cover


• 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]

special infrastructure – mobile shielding / exchange flask

picture: exchange flask for Meson production target E (4cm graphite wheel)


numerical modelling in the context of high power beams

particle generation/transport without/with electromagnetic fields

MCNPX, MARS

activation of components PWWMBS, MCNPX

radioactive waste disposal, declaration of nuclide inventory

PWWMBS, ISRAM

design/estimation of shielding MCNPX, ATTILA

thermo hydraulic / cooling problems ANSYS, CFD-ACE

beam dynamics codes omitted here!

Activity [Bq]

1.E+00

1.E+02

1.E+04

1.E+06

1.E+08

1.E+10

1.E+12

1.E+14

Fe-55

Co-60 H-3

Ni-63

Ti-44

Mn-54

Ni-59

Na-22

Zn-65

Ag-10

8mC-1

4Mo-

93Cl-3

6Fe-

60Be-

10

Bq

example: predicted nuclide inventory for old beam dump

M.WohlmutherS.TeichmannD.Kiselev


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!


Thank you for your attention!

ess-bilbao initiative workshop. psi experience with high power beam handling, activation and...

Technology

high power beam handling

overview psi facilityinjector

ess bilbao initiative

performance overview

interlock systems

target intensity

radiation protectionm

kev transfer channel