High Intensity Accelerators - SRF Group Site · High Intensity Accelerators 4th Lecture The Driver...

Carlo Pagani FJOH School 2002 Alex C. Mueller 1

High Intensity Accelerators

4th LectureThe Driver Accelerator for an ADS

By Carlo Pagani

ADS requirements and status of the artPresent reference for a linac-based ADSTRASCO, IPHI-ASH, PDS-XADS

R&D effort: Italy, France and rest of the worldComments on the reliability issueGeneral Remarks


ADS proton beam requirements

Very high duty cycle, possibly CW Energy of the order of 1 GeV, determined by

neutron production rate per GeV and per proton

(optimum value reached at ~1 GeV)energy dissipated in the input window

(rapidly decreasing with energy, when E<few GeV)

beam power from several MW up to tensof MW

few MW for a “demo” plant of ~100 MWth~30 MW for an industrial burner of ~1500 MWth

Very few beam trips per year accepted if longer then 1 secondNo limitation for very short beam trips: << 1 second

new challenges in the overall design of the accelerator

0

10

20

30

40

50

0 0.5 1 1.5 2 2.5

yiel

d / E

p (n

eutro

ns/G

eV)

proton energy, E_p (GeV)


Most powerful proton accelerators

LinacsLAMPF/LANSCE (~1970)

800 MeV1 mA H+ average current Peak H+ current 16.5 mA @ 100 Hz and 625 µs pulse lengthNC accelerator

CyclotronsPSI – separated sector (1974)

Original design was for 100 µAFrom 72 to 590 MeV1.8 mA average currentBeam losses at extraction < 1 µAPlans for further upgrade (new cavities)

Both linac and cyclotrons were considered as possible ADS driversNo fundamental obstacles have been found so far for a linac to deliver ~100 mA at 1 GeV or more1 GeV and few mA are considered as limiting values for a cyclotron(multistage): possible for the demonstrator, not for the burner


The ADS Linac

Linac benefits of impressive progresses in the field of SC elliptical RF cavities (CEBAF, LEP2, TRISTAN and KEK2, TTF-TESLA and now also SNS)R&D going on from several years demonstrated that this technology can be extended to proton linac down to β ~ 0.5Intrinsic modularity simplify reliability issues

Redundant design strategy based on the “spare-on-line” conceptStrong focusing and large beam aperture produce negligible losses

The scheme generally considered consists of four (three) different sections (the two first are often grouped and called injector)

The proton source: (proton energy ≈ 80-100 keV)The Radio Frequency Quadrupole (RFQ): (up to ≈ 5 MeV )A medium energy section, either NC or SC (up to ≈ 100 MeV )A high energy section made of SC elliptical rf cavities (up to final energy ≈ 1 GeV) most of the linac is here!


Reference Linac Design

80 keV 5 MeV ~100 MeV 200 MeV 500 MeV >1000 MeV

3 section linac:85/100 - 200 MeV, β=0.47200 - 500 MeV, β=0.65500 – 1000/2000 MeV, β=0.85

Five(six) cell elliptical cavitiesQuadrupole doublet focussing: multi-cavity cryostats between doublets

704.4 MHz

5 - 85/100 MeV SC linac

Spoke cavities (352 MHz)Lambda/4 cavities (176 MHz)Reentrant cavities (352 MHz)

orNC Drift Tube Linac (DTL)

8βλ focusing

High transm

ission 90%30 m

A, 5 M

eV(352 M

Hz)

Microwave

RF SourceH

igh current (35m

A)

80keV

High Energy SC LinacISCLRFQSource

3 sections high energy SC linacProton Source RFQ Medium energy ISCL linac


Injector: LEDA at LANL

130 mATotal Beam current

75 kVOperating voltage

0.2 π mm mradBeam emittance

110 mAProton Beam current

LEDA Source:

1.8 KilpatrickPeak Field

1.2 MW (structure)

670 kW (beam)RF Power

8 m (4 sections)Length


6.7 MeVFinal Energy

0.17 π deg MeV

100 mA (95 %)Beam current

LEDA RFQ:Source & RFQ fully operational since 1999

RFQ Concept

magelLorentz FF)BvE(qdtpdF

rrrrrrr+=×+⋅==

One Section of LEDA-RFQ

The LEDA-RFQ fully installed

Beam halo tests have been performed on the LEDA HEBT to compare simulation codes with experimental results


Injector: SILHI at Saclay

1.2 %2 %Beam noise (rms)

95 kV

0.11 π mm mrad

157 mA (~83 % p.f.)

Achievements

95 kVOperating voltage


110 mA (90 % p.f.)Beam current

SILHI Goals: The SILHI source is fully operationl

ECR type: 110 mA, 95 keV

Several reliability tests were performed on the source

3 before extraction system changes: 99.96% availability (1 stop in 104 hours of operation)

2 with new extraction system:99.8% availability (8 stops in 162 hours, automatic restarting in 2.5 min, MTBF=23.1 hours)


Injector: IPHI RFQ at Saclay

IPHI RFQ under fabrication

Two 1.3 Mw klystrons required

First RFQ beam expected in 2004

Picture of the first IPHI RFQ section ready for brasing

View of the vanes from the low energy side

1.7 KilpatrickPeak field

1.2 MW (structure)

500 kW (beam)RF Power

8 m (3 sections)Length

0.2 π mm mrad TBeam emittance

5 MeVFinal Energ

0.2 π deg MeV L

100 mA (99.2%)Beam current

IPHI RFQ parameters:


Linac Injector: TRASCO at INFN

RFQ e.m. simulations

TRIPS, similar to SILHI with some extraction improvement and overdesign for reliabilityECR source: 35 mA, 80 keV (operating)

Different optimization w/respect to LEDALimit to 1 klystron (1.3 MW CERN)Lower design current: 30 mAPeak field limited to 33 MV/mLower power dissipation: ~ 600 kW

RFQ short models to set technology RFQ Ansys simulationsRFQ cross section

Cooling channels

Main brasings


Medium Energy Section

The intermediate energy section, from 5 to ≈ 100 MeV, is the most controversial one: two basic solutions are possible:

Well proven NC structures (DTL or similar): as chosen for SNSNo realistic “spare-on-line” strategyHuge power dissipation in CW operation Rather small beam bore higher beam losses

Independently phased SC cavities: as chose for RIA and EURISOLWider energy acceptance “spare-on-line”Linac design can tolerate loose of few cavitiesLarger beam bore lower beam losses

The 0-order refernce deign being implemented for PDS-XADSNC DTL section up to ≈ 25 MeV2 sections of “Spoke” cavities (2 or 3 gaps) up to ≈ 100 MeVThe first part could be superconducting (e.g. the Frankfurt proposal)


R&D in Italy and France

DTL at Saclay in the framework of the IPHI programDesign finalized up to 20 MeVFew electrode prototypes builtQuadrupoles inside the electrodesFirst tank in construction

Spoke cavity prototypes constructed and to be tested soonAt Orsay one β = 0.35 cavity done with CERCA2 β = 0.175 cavities done at ZANON for LANLin collaboration with INFN Milano

Other cavity geometries under study and test at INFN Legnaro

λ/4 and λ/2 structuresat 88 MHz and 176 MHz

respectively

“Reentrant” cavityat 352 MHzalready built and tested


Linac High Energy Part

All designs are based on the technology of SC RF elliptical cavities(developed for electron accelerators)

very good efficiencyrelatively high field gradients (shorter length of the accelerator)large bore radius that is negligible beam losses lower operating costs with respect to NC for CW operation

The low velocity of protons, varying from β=0.43 at 100 MeV to β=0.88 at 1 GeV, imposes a variable length of cavities

3 sections, matched at three β values, are required for energies above ≈ 500 MeV.

A 2 section scheme is inefficientThe third section, with higher β, is the easiest and most efficient one

The same 3 sections allow an efficient energy upgrade up to ~2 GeV. The chosen energy sets the # of last section cryomodules


Franco-Italian Design up to 1 GeV

655# cells/cavity

1 GeV500 MeV200 MeV

12.3 MV/m10.2 MV/m8.5 MV/mMax. Eacc (MV/m)

525440# cavities in section

13

8.5 m

500 MeV

110 m

0.85

27

4.6 m

200 MeV

124 m

0.65

20# periods

4.2 mDoublet period

85 MeVInitial/Final Energy

0.47Section β

84 mLength

704.4 MHzRF

TRASCO High Energy Linac:

0 50 100 150 200 250 3000.00

0.20

0.25

0.30

0.35

Tran

s. rm

s em

ittan

ces

[ π m

m m

rad]

Position along the linac [m]

εnx [mm mrad] εny [mm mrad] εz [deg MeV]

0.00

0.20

0.25

0.30

0.35

0.40

Lon

g. rm

s em

ittan

ce [π

deg

MeV

]

-2%

0%

2%

4%

6%

%

varia

tion

1

2

3

4

5

6

7

8

9

10

11

12

0 200 400 600 800 1000 1200 1400 1600 1800 2000Energy [MeV]

∆Ecav

∆Emax[MeV]

1 GeV

Design may be extended to ~ 2 GeV by only adding periods of the highest βsection

Maximum ∆E at conservative peak surface fields (50 mT)

Cavity ∆E in the design

Beam Dynamics calculations (fully 3D) predict small emittance variations due to nonlinear space charge

Approximately 320 m of linac are needed from 85 MeV to 1 GeV. <240 m to 600 MeV

Designed with high current beam dynamics criteria to avoid emittance growth (smoothness, tune resonances, ...)


R&D Activities on SC Cavities

β=0.47

In the framework of the Franco-Italian collaboration for ADS, various reduced-β 700 MHz single cell cavities (bulk Nb) have been built and tested, yielding excellent performances, well above the design specifications:

β = 0.47 cavities from INFN/ZANON, tested at TJNAFβ = 0.65 cavities from CEA/CERCA tested at CEA/SaclayMulticell cavities under fabrication for both programs

1E+09

1E+10

1E+11

0 5 10 15 20 25 30

Test #3T = 2 K

TRASCO goal

Q0

Eacc [MV/m]

INFN/MI β=0.47 cavity

T = 2 K

1,E+09

1,E+10

1,E+11

0 5 10 15 20 25 30

ASH goal

Q0

Eacc [MV/m]

CEA/Saclay β=0.65 cavity

T = 1.5 K


The SNS Example

Multicell structures have been built for the SNS project, for both the β=0.61 and the β=0.81 cavities

All tests reached the design goals with good marginsIndustrial fabrication for all the SNS cavities is in progessThe actual RIA linac proposed design uses the SNS cavities adding a

β=0.47 6-cell cavity section, as inthe European scheme

Prototype of β = 0.61 SNS cavity

1,E+08

1,E+09

1,E+10

1,E+11

0 2 4 6 8 10 12 14 16 18 20 22Eacc [MV/m]

Q0

Test #1

Design Goal

β = 0.61 SNS 6-cell cavity result

1,E+08

1,E+09

1,E+10

1,E+11

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19Eacc [MV/m]

Q0

Test #1

Design goal

β = 0.81 SNS 6-cell cavity result


The 0-order Design for PDS-XADS

Section number 1 2 3 4 5 Input Energy [MeV] 5 17 95 200 490 Output Energy [MeV] 17 95 200 490 600 Cavity Technology Spoke Elliptical Structure βg 0.135 0.314 0.47 0.65 0.85 Number of cavity cells 2 2 5 5 6 Number of cavities 34 64 28 48 12 Focusing type SC quad doublet NC quad doublet Cavities/Lattice 1 2 2 3 4 Synch Phase [deg] -65 to -30 -30 -25 Lattice length [m] 1.3 1.9 4.2 5.8 8.5 Number of lattices 34 31 14 16 3 Section Length [m] 44.2 59.9 60.8 92.8 25.5 <gradient> [MV/m] 0.3 1.3 1.8 3.1 4.3

EzEyEx

TRACE_WIN - CEA/DSM/DAPNIA/SACM

Position ( m )25020015010050

Nor

m. r

ms

emitt

ance

s ( P

i.mm

.mra

d )

0.41

0.4

0.39

0.38

0.37

0.36

0.35

0.34

0.33

0.32

0.31

0.3

0.29

0.28

0.27

0.26

rms emittances in the whole linac

rms beam size along the linac

TRACE_WIN - CEA/DSM/DAPNIA/SACM

Position ( m )25020015010050

Ener

gy g

ain

per m

eter

( M

eV/m

)

5

4

3

2

1

0

Real Estate ∆E/m along the linac

Spokeβ=0.135

Spokeβ=0.315

5-cellβ=0.47

5-cellβ=0.65

6-cellβ=0.85

Output beam with 30% mismatch

SC Linac Section Parameters


Reliability Example - CEBAF

0

240

480

720

960

1200

1440

Guns

8.1

%RF

6.1

%M

ag 5

.5%

Sft 4

.4%

Cryo

2.8

%Co

ntro

l Net

2.5

%FS

D Tr

ips 2

.1%

Vacu

um 1

.4%

Plan

t 1.4

%Ot

her 1

.2%

PSS

1.1%

MPS

0.8

%Di

ag 0

.6%

RAD

0.5%

SRF

0.3%

RF Problems

FSD Faults

SRF

0

120

240

360

480

600

Gun

s 11

.6%

FSD

Trip

s 4.

2%R

F 3.

4%M

ag 2

.7%

Ops

UT

1.6%

Cry

o 1.

5%O

ther

1.4

%Sf

t 1.4

%O

psST

1.4

%Va

cuum

1.1

%Pl

ant 0

.7%

Ops

0.6

%R

AD 0

.6%

PSS

0.5%

Con

trol N

et 0

.4%

MPS

0.3

%D

iag

0.1%

SRF

0.0%

PGun3 Valve/RF feedthru failure, Injector instabilities, Injector Setups

Klystrons & Tap ChangeFSD

Magnet Cooling

Lost Time Totals June'97-May'01 Lost Time Totals FY 2001

Reliability must be improved for ADS applicationsThe SC linac is modular and allows: overdesign, redundancy and “spare-on-line”Fast dedicated control electronics is crucialBeam can stay “on” when the linac is resetting itself to use spere-on lineSC cavity technology proved to be the minor concern


Remarks on Linac Reliability

In order to meet the # of stops > 1 sThe beam startup procedure for a multi MW beam will be certainly > 1 s, so whenever is possible, operation with faulty components needs to be achieved

Linac must tolerate single failures of most of componentsProcedures for “adjusting” beam transport and repairing of components without interrupting the beam while marinating acceptable losses

As a consequence:Components and subsystems divided in two major categories if they lead to:

Failures requiring a beam stopFailures that can be repaired while the beam is on, or later…

As general rulesComponents falling in the first category should have the highest reliability

Typically passive components overdesigned and overtested with respect to operating parametersCabling, piping and connections

Components falling in the second category should have the highest accessibility for repairing or substitution

For example, this suggest the choice of a double tunnel design, with most of ancillaries situated in a free-access tunnel

Power supplies, RF generators, Control electronics, etc.


Rules for Reliability Analysis From a Deliverable of the PDS-XADS Program

The small number (few per year) of beam trips allowed during the accelerator operation, requires a detailed analysis of the accelerator availability and reliability, much deeper that in the past applications

The reliability analysis of a complex system is an iterative process, which starts from a preliminary design of the whole system and its components and is followed by the development of the Reliability Block Diagram (RBD).

This top-down approach needs to be complemented with the bottom-up approach of the FMEA/FMECA (Failure Modes and Effects Analysis, Failure Modes and Effects Criticality Analysis), that, on a particular system design, tries to identify the system failures (and failure modes) from the failure modes of the single components. This path should be used iteratively.


General Remarks - 1From the conclusions of the Accelerator WG at the NEA Workshop

Technology options for a high power proton driver: cyclotron and linacCyclotron

the only suitable reference machine is the PSI accelerator complex, delivering a 1.2 MW proton beam at 600 MeV. No remarkable R&D programs are under way to sensibly extend these limits. A part the complexity its cost scales quadratically with the output energy. The reliability and availability obtained at PSI are very high, but their further improvement looks very difficult. The machine concept does not allow the application of the concepts of redundancy and spare on line.

Linear AcceleratorA worldwide R&D effort is in progress since a few years and the high potentiality of these machines has been proven. Sources and RFQs up to 100 mA have been built and successfully operated. SRF technology is chosen above 100 MeV. For the intermediate energy NC and SC solutions are considered. The cost per MeV is decreasing with energy.A part from the front end, which can be duplicated, the linac has an intrinsic high modularity, which increases with energy. This machine can be designed on the basis of a properly set redundancy to allow the use of the spares on line concept.

Cyclotrons of the PSI type should be considered as the natural and cost effective choice for preliminary low power experiments, where availability and reliability requirements are less stringent.CW Linear accelerators must be chosen for demonstrators and full-scale

plants, because of their potentiality, once properly designed, in term of availability, reliability and power upgrading capability.


General Remarks - 2From the conclusions of the Accelerator WG at the NEA Workshop

Beam trip handlingSparks on high voltage components drive most of the beam trips. They can generally be handled in a small fraction of a millisecond and the beam can stay on. They are not counted.In principle a fast procedure to switch on the beam can be implemented to allow the use of redundancy and spares on line. Whenever losses are acceptable, beam will stay on during the linac re-tuning to compensate for a component failure.The chosen degree for over design and redundancy is a direct function of the duration and frequency of the scheduled shutdown for reactor maintenance.The number of some redundant components could be reduced if allocated in a different building or tunnel. General cost analysis will define the details.

Optimized DesignBecause slightly different designs are being studied at present, they should be compared in term of their potential degree of modularity, reliability of the used technology and cost. The final linac design has to be based on reliability and availability considerations, as defined for ADS application.

Control ElectronicsAd hoc fast digital electronics must be implementedRedundant fast electronics will be designed to avoid, in principle, the intervention of the last beam protection.

Safety IssuesThe safety rules for the accelerator and the reactor have to stay separate. The accelerator protections will be based on redundant active systems.The beam handling, in the reactor building will follow the reactor safety rules.

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