Reliability challenges for circular ADS drivers - PowerPoint Presentation

Slide1

Reliability challenges for circular ADS drivers

Mike Seidel, PSI

Reliability Workshop CERN, June 22

1

Slide2
Outline

Suited Circular Accelerator Conceptsrequirements for ADS accelerators

cyclotrons, rapid cycling synchrotrons, FFAGGenerics on failure probability / trip ratesredundancy in accelerators; AND vs OR fault logics; failure and survival probability measured trip statistics at PSIC

omments on FFAG, J-PARC RCS, PSI cyclotronNew cyclotron ideasH2+ Daedalus, stacked/flux coupled cyclotrons, reverse bend cyc.DiscussionPro’s and Con’s of Circular concepts

Reliability Workshop CERN, June 22M.Seidel, PSI

Slide3
Requirements for ADS Accelerators

energy: flat optimum 

1.2GeV; however 0.8 .. 2.5GeV under discussion power: 2...10MW; Ptherm = P

beam  G/(1-k)low losses:  1W/m; PSI: 100W at critical locationreliability & stability: 0.01…0.1 trips per day(!)

efficiency: as best as possible, =Pbeam/Pgrid= 20…30%

cost: as low as possible; optimize for series production; modern nuclear power plant: (5B€)

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide4

High

Intensity

Accelerator Landscape

2.4mA = 1.416MW

PSI

SNS, Sep 2013

(

today

target

limits

intensity

)

Reliability Workshop CERN, June 22

M.Seidel

, PSI

J-PARC RCS

ramping

up

!

1MW

routine

operation

expected

2016

Slide5
reliability, trip performance

todays trip performance of accelerators is orders of magnitude worse than desired for ADS, e.g 10…100d

-1 achieved vs. 0.01…0.1d-1 desired by reactor expertsin recent years discussions took place and requirements were somewhat relaxed:

fatigue failure of fuel elements is not seen extremely critical anymoreshort trips (few seconds) can be accepted; shorter than thermal time constantsaccelerator and reactor developers must find compromises, my impression: reactor community in general not very flexible due to strict safety rules; e.g. studying fast reactor startup, bridging trips

IBR-2 pulsed reactor

demonstrates fast cycling

even without technical reasons,

for industrial power production (and consumption) reliability is very

important

!

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide6
Suited

Accelerator Concepts?

Linear

Accelerators

Cyclic Accelerators

normalconducting

linac

superconducting

linac

e

lectrostatic

(E limited!)

p

ulsed

CW:

very

low

gradient

CW

possible

c

ooling

power!

cost

!

Synchrotron

[rapid

cycling

]

Cyclotron

Synchro-Cyclotron

(

cycling

)

Other: Betatron,

Microtron

FFAG

CW

possible

beam

dynamics

!

extraction

!

pulsed

p

ower limited (1MW?)

compact

cycling

/ CW

questionable

no

demonstrator

exotic(laser, plasma, diel. efficiency!)

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide7
classification of circular accelerators

bending radius

bending field vs.

time

bending field vs. radius

RF frequency vs. time

operation mode

(pulsed/CW)

comment

betatron

induction

microtron

varying

h

classical cyclotron

simple,

but limited

E

k

isochronous cyclotron

suited for high power!

synchro

- cyclotron

higher

E

k

, but low P

FFAG

strong focusing!

a.g.

synchrotron

high

E

k

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide8
reliability

calculation in a nutshell

Reliability Workshop CERN, June 22M.Seidel, PSI

example: lightbulbs (MTBF=1000h)N(t) number

of surviving lightbulbsN0 original number of

funct. bulbs

(t)

fractional

failures

per time

constant

, i.e.

no

aging

/

history

(

Markov

process

)

simple, but

for

some

applications

too

simple!

mathematical

treatment

:

S

(>t)

survival probabilityF(>t) failure prob. (1-S(t))f(t) failure

density function =F‘(t)(t) hazard function

beyond

=const: Weibull

distribution

Slide9
duration

statistics for un-interrupted run

periodsReliability Workshop CERN, June 22

M.Seidel, PSI

PSI run data analyzed:integrated

distribution of

un-interrupted

beam

times

double log

scale

How many runs per day with duration longer than t.

total trips per day

Slide10
modelling with exponential and Weibull distributions

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide11
fault

topology of an accelerator

Reliability Workshop CERN, June 22M.Seidel, PSI

&

1

&

2

system

A

system

A´

system

B

system

B‘

system

C

system

C‘

system

C‘‘

system

C‘‘‘

classical

simple

redundancy

multiple

redundancy

beam on

clearly redundancy is desirable

whether redundancy is possible with major subsystems depends on the choice of accelerator concept

Slide12
reliability, concepts

numerical example:tube: MTBF=5000h; MTTR=8h

Linac with 80 tubes, accepting 0 fault: MTBF

eff = 62hLinac with 80 tubes, accepting 1(k=2) fault: MTBFeff = 1.074h

Linac with 80 tubes, accepting 2 faults: MTBFeff = 26.067h

cyclotron with 4 tubes, accepting

0 faults:

MTBF

eff

=

1.250h

binomial distribution,

B

p

= incomplete Beta Function

Reliability Workshop CERN, June 22

M.Seidel, PSI

circular

accelerator

linear

accelerator

only

few

resonators

/

magnets

redundancy

difficult

redundancy

wrt

.

resonators possible

Slide13
distribution of trip duration

D. Vandeplassche, Proc. IPAC

012

PSI analysis of trip-periods

Reliability Workshop CERN, June 22

double

logarithmic

:

power

law

is

straight

line

.

PSI

PSI

total trips per

day

Slide14
next

: circular concepts compared…

Reliability Workshop CERN, June 22

M.Seidel, PSIcomplexity

= less availability (?)

isochronous cyclotron: continuous, nothing cycles

FFAG: pulsed, RF cycling

synchrotron: pulsed, magnets + RF cycling

Slide15

[investigation towards CW operation:

S.Machida

, FFAG, EMMA, serpentine acceleration]Fixed Field Alternating

Gadient Accelerator ?Reliability Workshop CERN, June 22

M.Seidel, PSI

strong

focusing

, large E

acceptance

,

magnets

fixed

in time

RF must

be

cycled



faster

than synchrotron, but less

intensity than CW

cyclotron

not

ramping

the

magnets

should

be

an

advantage

for

reliability

otherwise same arguments as for RCS hold

cyclic injection/extraction potentially

difficulthigh intensity: not demonstrated

[EMMA]

Slide16

Reliability Workshop CERN, June 22

M.Seidel, PSI

[M.Shirakata, J-PARC]f

RF: 0.94MHz – 1.67MHz

Slide17

Outline of the J-PARC RCS

Circumference

348.333 m

Superperiodicity

3

Harmonic number

2

Number of bunches

2

Injection

Multi-turn,

Charge-exchange

Injection energy

181 MeV

Injection period

0.5 ms (307 turns)

Injection peak current

30 mA

Extraction energy

3 GeV

Repetition rate

25 Hz

Particles per pulse

5 x 10

13

Output beam power

600 kW

Transition gamma

9.14 GeV

Number of dipoles

24

quadrupoles

60 (7 families)

sextupoles

18 (3 families)

steerings

52

RF cavities

12

Now the RCS is in the final beam commissioning phase

aiming for the design output beam power of 1 MW.

Recently

t

he hardware improvement of the injector linac

has been completed.

⇒

400 MeV in 2013

⇒

8.3 x 10

13

⇒

1 MW

400 MeV H-

3GeV

proton

MLF

: Material and Life Science

E

xperimental

F

acility

MR

: 50-GeV Main

R

ing Synchrotron

⇒

50 mA

in 2014

[

H.Hotchi

, IPAC2015]

Slide18

Earthquake

300 kW

Hg-target

replacement

Incident at

Hadron Facility

532 kW

300 kW

as of 3

rd

of June 2015

〜

560 kW

～

10

months interruption

due to the earthquake

593 kW

～

1

month interruption

d

ue to

the fire in MLF

Beam Power History at MLF

Interruption due a trouble of Hg-target

500

kW

400

kW

[

T.Koseki

]

Slide19
J-PARC Rapid

Cycling Synchrotron [RCS]

1.01MW avg beampower achieved (Hotchi

, IPAC15); still high losses, not routinehigh average availability:  90% (!)drives neutron source (mercury target); i.e. ADS like application thus J-PARC RCS has demonstrated a respectable high intensity performance!

Reliability Workshop CERN, June 22M.Seidel, PSI

one would think the rapid cycling of the magnets would cause specific problems, more than in an CW accelerator; but nothing outstanding was reported and 90% was achieved, on par with SNS and PSI.

typical failures from the past (taken from

M.Shirakata

presentation

)

LINAC HV DC supply failure (2012: 59h, 2013:103h)

bending magnet supply (resonant circuit, 2014: 115h, oil pump)

radiation accident caused 23 months interruption (Au target got full charge in 5ms instead 2s)

 not specific to RCS

Japan’s great earthquake: recovered in 286 days!!

 not specific to RCS

possibly related

to cycling

Slide20

PSI Ring Cyclotron

8 Sector Magnets:

1 T

Magnet weight:

~280 tons

4 Accelerator Cavities:

860 kV (1.2 MV)

1 Flat-Top Resonator

150 MHz

Accelerator frequency:

50.63 MHz

harmonic number:

6

kinetic beam energy:

72



590 MeV

beam current max.:

2.4 mA

extraction orbit radius:

4.5 m

outer diameter:

15 m

RF efficiency Grid/Beam

0.90

0.640.55 = 32%

rel. losses @ 2.2mA:

~1..2

10

-4

transmitted power:

0.32 MW/Res.

Reliability

Workshop CERN, June 22

Slide21
Typical

Trip Causes for Cyclotrons

Reliability Workshop CERN, June 22

electrostatic elements: high voltage breakdowns due to plasma discharges; stray electrons collected on insulators; presence of intense proton beam in vicinity of electrodes and insulators; comparably poor vacuum of 10-6mbarloss tuning: depends critically on complete accelerator chain incl. source; low tail density very sensitive to all parameters

cavities & RF systems: breakdown, multipacting, MW level amplifier chains (eg. 50MHz)

 see presentation by

J.Grillenberger

on concrete examples

Slide22

critical: injection/extraction schemesdeflecting element should affect just one turn, not neighboured

turn  critical, cause of lossesoften used: electrostatic deflectors with thin electrodesalternative: charge exchange, stripping foil; accelerate H

- or H2+ to extract protons (problem: significant probability for unwanted loss of electron; Lorentz dissociation: B-field low, scattering: vacuum 10

-8mbar)

0

-

HV

foil

extraction electrode

placed between turns

extraction by charge exchange in

foil

eg

.: H

-

 H

+

H

2

+

 2H

+

binding

energies

H

-

H

2

+

0.75eV

15eV

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide23
extraction profile measured at PSI Ring Cyclotron

dynamic range:

f

actor

2.000 in

particle density

red

:

tracking

simulation

[OPAL]

black

:

measurement

position of extraction septum

d=50µm

turn

numbers

from

simulation

[

Y.Bi

et al]

Reliability Workshop CERN, June 22

M.Seidel, PSI

Slide24
proposed cyclotrons I: H

2+ Daedalus cyclotron [neutrino source]

[

L.Calabretta, A.Calanna et al]Reliability Workshop CERN, June 22M.Seidel, PSI

purpose: pulsed high power beam for neutrino production

800MeV kin. energy5MW avg. beam power

note:

complex extraction path

binding

energies

H

-

H

2

+

0.75eV

15eV

Slide25

proposed

Cycl

. II: H

2

+

AIMA Cyclotron w reverse bend and multiple 60keV injection [

P.Mandrillon

]

The reverse valley B-field concept avoids the internal loop

(cf. DAEdALUS extraction) for the stripped proton beam from H2+

.

Vacc

=150kV

Vacc

=165kV

Reliability Workshop CERN, June 22

25

Slide26

Texas A&M University

Two

Stages Cyclotron: 100 MeV SF

injector

+ 800 MeV SF booster.

Stack

of 3 Cyclotrons in //

Booster: 12 Flux

coupled

stack

of

dipole

magnet

sectors

10

Superconducting

100 MHz RF

cavities

providing

a 20 MeV

Energy

Gain/

turn

multiple power

couplers

per

cavity

Large

turn

separation

allowing

to insert SF

beam

transport

channels

made of Panofsky

Qpoles

(G=6T/m)

proposed

cycl

. III: TEXAS

A&M: 800 MeV SUPERCONDUCTING

STRONG-FOCUSING CYCLOTRON

[

P.McIntyre

, Texas A&M]

Reliability Workshop CERN, June 22

26

recently

: DOE

awards

stewardship funding for idea of strong focusing channels in cyclotrons

Slide27
Summary –

Reliability of Circular Accelerators

Reliability Workshop CERN, June 22

M.Seidel, PSI

reliability

of high intensity circular accelerators today is

around 90%

(PSI, J-PARC), on par with the

s.c.

linac

and accumulator of SNS;

trip rates are 10…100d

-1

for PSI

, at least three orders of magnitudes worse than desired for ADS

implementation of

redundancy difficult

in circular accelerators; on the upside circular acceleration is an economic concept;

injection/extraction

elements

in cyclotrons are critical devices; their reliability could be improved by certain measures when considering

ADS

cyclotrons with CW

operation should have best stability; next is FFAG with ramping of RF; rapid cycling synchrotron needs magnet ramping; nevertheless high reliability demonstrated by J-PARC

personal remark on choice of technology

:

today a

s.c.

linac

is a straightforward solution for a multi-MW facility;

however, despite of it‘s greater beam dynamics complexity and intrinsically higher susceptibility for trips, an

optimized cyclotron

, built in series can be very cost effective and could reach high availability as well.

Slide28

t

hank

you for

the

attention

!

Reliability Workshop CERN, June 22

M.Seidel, PSI