ESS-Bilbao Initiative Workshop. Charge to working group: accelerator components/ beam dynamics

Charge to working group: accelerator components/beam dynamicsF. Gerigk, C. Prior

ESS-B initiative workshop, 16.-18.03.2009

“Accelerator Components”, ESS-B workshop 2009, F. Gerigk

Outline

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goals, expected results,

scope of the session,

accelerator design/beam parameters,

key questions per subject,


goals, expected results

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goal of the workshop:

bring together people working on subjects important to high-power spallation sources,

identify challenges of next generation machines,

propose necessary R&D programs,

identify common areas/interests with other projects.

expected result:

a summary document highlighting the challenges,

addressing future prospects,

define potential collaborative developments programmes,

“Accelerator Components”, ESS-B workshop 2009, F. Gerigk4

This workshop is not a design review of ESS!!


...instead, this is where we start to develop recommendations for any future high-power

(long-pulse) spallation source


scope of the session

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high-power, highly reliable front-ends,

high-intensity light ion linacs: component design, performance of existing machines, reliability,

synergies with ongoing and planned linac projects,

low-energy superconducting structures (< 100 MeV?),


beam parameter ⇔ linac designhow the basic target parameters influence the linac design


beam parameters ⇔ linac design

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target/instrument requirements

linac design

beam power ~ 5 MW ?

pulse width ~ ms ?

beam energy 1 GeV (... 3 GeV ?) ?

repetition rate ≤ 20 Hz (15,20,25 ??) ?


linac constraints (simplified..)

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peak power/coupler: Ppeak≤1 MW

average power/coupler: ~50/120 kW

(TTF type 1300 MHz/LHC 400 MHz)

space charge:

max. cavity voltage:Vacc=Ppeak/Ipulse,average

Pav=Ppeak*(tpulse*frep)

beam stability (emittance increase, beam loss, machine

activation)

examples:150 mA: 6.7 MV50 mA: 20 MV

2 ms, 20 Hz: 40 kW2 ms, 40 Hz: 80 kW

high current (150 mA)yields high probability for

loss limited machine performance and/or

need for front-end funnel

cavity gradient (+ n. of cav. families): ≤ 20 - 25 MV/m

frequency/number of cells per cavity

704 MHz: 5/6 cells1300 MHz: 9/10 cells



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1 GeV, 16.7 Hz, 2 ms, 5 MW

150 mA, Eacc = 6.7 MV, linac length = l0

first order scaling...



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1 GeV, 16.7 Hz, 2 ms, 5 MW


3 GeV, 16.7 Hz, 2 ms, 5 MW

50 mA, Eacc = 20 MV, linac length = l0




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1 GeV, 16.7 Hz, 2 ms, 5 MW


3 GeV, 16.7 Hz, 2 ms, 5 MW


2.5 GeV, 20 Hz, 2 ms, 5 MW

50 mA, Eacc = 20 MV, linac length = l0*16.7/20=0.83*l0




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1 GeV, 16.7 Hz, 2 ms, 5 MW


3 GeV, 16.7 Hz, 2 ms, 5 MW


2.5 GeV, 20 Hz, 2 ms, 5 MW


2 GeV, 25 Hz, 2 ms, 5 MW




target/instrument requirements

linac design

beam power ~ 5 MW fixed

pulse width ~ ms fixed

beam energy 1 GeV (... 3 GeV ?)high/low pulse current, length

constant

repetition rate ≤ 20 Hz (15,20,25 ??)higher rep. rate ⇒shorter linac



⇒ Questions with high impact on linac design/cost/reliability:

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1.) linac:how strict is the limit of 1 MW/coupler? how difficult are 2 couplers/cavity?are 20 - 25 MV/m realistic?source/front-end limitations (current/time structure)?

2.) beam dynamics:what are the current limits to avoid a funnel in the front-end?current limits for low-loss operation in the linac?

3.) target:how do different energies (1,2,3 GeV) and rep-rates (16, 20, 25 Hz ..) influence the target design?

4.) instruments:how hard is the limit on the repetition rate (16, 20, 25 Hz ..)?


Parameter review of CERN SPL

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RF frequency & cryogenic temperature

CERN-AB-2008-067


SPL (high-power version):

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HP-SPL (5 GeV)

H- source RFQ chopper DTL CCDTL PIMS

3 MeV 50 MeV 102 MeV

352.2 MHz

β=0.65 β=1.0

732 MeV 5 GeV

704.4 MHz

160 MeV

kinetic energy 5 GeV

beam power 3-8 MW

repetition rate 50 Hz

pulse length up to1.2 ms

average pulse current 0-40 mA

cavity gradient (β=0.65/1.0) 19/25 MV/m

protons p. pulse 1.5 1014

length (SC linac) 472 m


RF frequency review: 704 MHz

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frequency 704 MHz 1408 MHzlength 472 m +12%

Ncavities 246 +15%

Nβ-families 2 3

ε-growth (x/y/z) 5.6/8.2/6.8 6.3/7.8/12.1

long. beam loss none in simulations lossy runs for realistic RF gradient/phase variations

BBU (HOM) IBBU,704 1/(8..128)

trapped modes normal risk 2..4 higher riskRF power density limit (RF

distribution) ok problematic

klystrons comfortable: MBK difficultoverall power consumption

(RF+cryo, nom. SPL) 28 MW up to -30%

power converter more bulky saves tunnel space


cryogenic temperature review: 2K

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@ 704 MHz T [K]eq. capacity @ 4.5 K [kW]

el. power[MW]

HP SPL, 2% beam d.c. (4% cryo d.c.) 2 19.4 4.48

HP SPL, 2% beam d.c. (4% cryo d.c.) 4.5 104 26.0

LP SPL, 0.24% beam d.c. (0.32% cryo d.c.) 2 6.1 1.5

LP SPL, 0.24% beam d.c. (0.32% cryo d.c.) 4.5 11 2.75

not clear that 25 MV/m can be achieved at 4.5 K!


questions to the working group:

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has anyone done a similar analysis?is there experience with high-power RF equipment at high duty cycle (~5%) for high frequencies (≥1200 MHz): klystrons, circulators, RF loads, phase shifters, splitters,...sensitivity to higher order modes for high-current machines (50/150 mA)? Is there any relevant experience?

Dedicated workshop on HOMs in high-power linacs will take place at CERN (~June, exact date to be decided)


key questions per subject....common to many SC high-power linacs


further questions

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1.) instrumentation:

high power proton machines: how can we do profile measurements during regular operation?

ionisation detector readings disturbed by X-rays from the cavities,

neutron detectors?

halo diagnostics (loss management) 10-5 - 10-6 fractional beam?,

localised beam loss measurements in well shielded low-energy beam (<100 MeV)?,

high-energy emittance measurements?,

beam instrumentation inside accelerating structures?,

beam centre, profile, emittance to <1%?

P. Ostroumov

J. Galambos


questions II

3.) cryo-modules:how many layers of insulation?

how many cavities per module? length of cryo-modules?

warm or cold focusing magnets?

conversion of electron modules (TTF/XFEL) for protons?

parallel handling of 2K and 4K two phase circuits?

pressure vessel codes conformance issues?

interplay of module and cryo-system design?

Dedicated workshop on segmentation of cryo-modules will be organised by FNAL/CERN (~September, exact date to be decided)

2.) reliability (spare parts):

for which machine elements are spares necessary? (apart from the obvious ones..): source, RFQ, cryo-modules (how many),

P. Pierini

J-L. Biarotte: fault tolerance


questions III

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4.) power converters:

R&D effort to get a reliable, high duty cycle pulsed power supply?

can we use a DC power supply with pulsed mod-Anode power supply for RF test stands? instead of pulsed power supplies (or even for machine operation?), size? operational impact? droop? (can it be compensated by LLRF?)

how much distance can we have between a modulator and the klystrons? 1, 10, 100 m? state of the art in cables? cost comparison to housing the modulators in the tunnel?

R. Cassel


questions IV5.) low-beta cavities (<200 MeV):

optimum structures (NC or SC) for various beta regions?,

simplification/standardisation of mechanical construction/tuning?,

influence of low-loss beam dynamics on structure design?

6.) medium/high-beta SC cavities:

transition energies NC/spoke/elliptical,

how many cavity families,

realistic gradients for each structure type (and beta),

best recipes for surface treatment,

M. Vretenenar

E. Zaplatin

S. Bousson


questions V

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7.) power and HOM couplers:

peak/average power limits?

adaption/re-design of existing devices for different frequencies?

damping requirements (beam dynamics)?

power and HOM couplers for spoke cavities?

S. Belomestnykh

8.) RF power splitting:

how many cavities per klystron?

fast amplitude/phase shifters (high duty cycle)?

flexibility/reliability compared to single sources?

R. Pasquinelli


questions VI

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A. Letchford9.) Front-ends:

space charge limits?

source, LEBT (space charge compensation), RFQ?

R. Duperrier

10.) Linac modelling:

how close are simulations to reality?

code capabilities?

do we understand LEBT modelling?

J. Stovall

C. Prior

11.) machine activation:

beam loss in high-power machines

M. Seidel


questions VII

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9.) Collaborations:

Which other projects have similar questions?

A. Mosnier

ESS-Bilbao Initiative Workshop. Charge to working group: accelerator components/ beam dynamics

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