review on interfacingunilac –sis18...

L. Groening, Report on “Review on Interfacing UNILAC – SIS18 wrt Uranium Delivery”, November 25th , 2013

Report onReview on Interfacing UNILAC – SIS18 wrt Uranium Delivery

Outline

• Motivation for review

• Committee members and charge

• Presented issues

• Recommendations of committee

• Strategy do deal with recommendations


Motivation for Review

• in 1998 the following parameters were defined as requirement for the injected beam:• 15 mA of U28+

• tot. norm. hor. emittance ε ≤ 1 mm mrad

• presentation at LINAC1998 conference (W. Barth)

• simulations done 15 years ago indicated that aim might be too ambitious

• requirements have not been updated since 1998

• best achieved (in June 2007): factor 4 too low wrt brilliance requirements

• last achieved (May 2012): factor 17 too low


Committee & Charge

• review took place at GSI on Nov. 4th , 2013

• focused on achievable linac performance (above 1.4 MeV/u) and injection into SIS18

• SIS100 & beyond has not been addressed

• committee:• Frank Gerigk, CERN• Peter Ostroumov, ANL• Chris Prior, Trinity College Oxford• Christian Carli, CERN• Yoshishige Yamazaki, MSU

• all persons asked to join the committee agreed to do so !

• charge to the committee:


Agenda

• Brief introduction: uranium delivery chain at FAIR, O. Boine-Frankenheim

• UNILAC-upgrade: high current development wrt U28+, W. Barth

• Sources: recent measurements of source performance wrt uranium, R. Hollinger

• HE-Linac: layout & (quasi) front-to-end simulations, L. Groening

• SIS18 goals & status of upgrade program, challanges from dyn. vacuum, P. Spiller

• Coffee

• SIS18-Injection: param. studies on MTI efficiency with space charge & collimationand longitudinal aspects, S. Appel

• SIS18-Injection: experimental investigation of beam collimation in the transferchannel, further optimization of injection parameters and modification of set-values

• HE-Linac: concepts for provision of flat beams, L. Groening

• Lunch

• Discussion

• first assessment of committee


Presentation (W. Barth)UNILAC-upgrade: high current development wrt U28+

• Introduction of the UNILAC & Upgrade (Wideröe → IH-DTL) 2.2 keV/u to 1.4 MeV/u

• upgrade aimed at achieving SIS18 space charge limit w/o e-cooler

• Wideröe-DTL replacement between Dec 98 & Feb 2000

• high current performance with argon achieved

FAIR requir.

! Argon !



• UNILAC upgrade program until 2007

• new RFQ rods

• increased stripper gas density, matching to Alvarez DTL with space charge



• History of performance wrt uranium until 2007

best achieved:

0,0

0,5

1,0

1,5

2,0

2,5

3,0

LEBT HSI Gasstripper Alvarez Single GapResonators

Foil Stripper

90%

-tota

l em

ittan

ce [m

m*m

rad]

horizontalvertical

U4+

U28+

U73+

horizontal SIS-acceptance

vertical SIS-acceptance



• Upgrade program beyond 2007

• further upgrade of RFQ rods (increased voltage)

• increase of transv. focusing along Alvarez DTL

0.1

0.2

0.3

0.4

30 50 70 90 110 130Transverse Zero Current Phase Advance (deg)

Nor

m. T

rans

v. rm

s-Em

itt. (

mm

mra

d)

measured at exit of 1st Alvarez tankold limit

new limit


Presentation (R. Hollinger)Sources: recent developments wrt uranium

• new dc post acceleration system

• present status for operation


Presentation (R. Hollinger)Sources: recent developments wrt uranium

• recent measurements (September 2013)

measurements being back-transformed to source exit & used for front-to-end simulations


Presentation (L. Groening I)HE-Linac: front-to-end simulations

• talk motivated upgrade of existing Alvarez DTL

• aim of f-2-e simulations: estimate what performance seems achievable with new DTL foracceleration from 1.4 to 11.4 MeV/u

• it has been stated clearly that beam dynamics optimization of existing Alvarez is much moreadvanced wrt planned IH-DTL

• term „High Energy (HE)-linac“ is misleading: final energy equal to Alvarez DTL exit energy !!



• introduction of various sections (function & parameters) of UNILAC for FAIR

gashor. slit

new dedicated U-termial & LEBT

RFQ

36 MHz IH-DTL

stripping, q-separation, freq.-trans., x→y emit.transfer, DTL matching

108 MHz IH-DTL (planned)

108 MHz Alvarez-DTL (today)



• definition of brilliance

• presentation of front-to-end simulations (tools, distributions, envelopes, emit. growths, ...)

• evaluation of brilliances behind each section



• brilliance evolution along linac simulated for IH- & Alvarez DTL:

• reminder:• more experience wrt dynamics for Alvarez DTLs• there is potential to improve IH-DTL performance• simulations aimed at estimating „what is possible with a new DTL beyond 1.4 Mev/u“

FAIR requir. (before review)


Presentation (L. Groening II)HE-Linac: concept for flat beam provision

• talk introduces the motivation & concept for emit transfer from hor to ver plane

• “proof of principle” experiment EmTEx :

• uses deuterium → no space charge, no q-separation needed, low rigidity

• currently under construction in transfer channel UNILAC-SIS18

• experiment in summer 2014


• Emittance transfer beam line for FAIR, i.e. uranium

HE-Linac108 MHz U28+



• Brilliances from round & flat beams

• reminder:• more experience wrt dynamics for Alvarez DTLs• there is potential to improve IH-DTL performance• simulations aimed at estimating „what is possible with

a new DTL beyond 1.4 Mev/u“

Summary:

• flat beams may provide significantenhancement of hor. brilliance at DTLentrance

• may open a path towards higher horbrilliance compared to round beam scheme

• flat beam acceleration is quite prone tobrilliance delution from mismatch

• DTL must provide proper periodicity incl.inter-tank transitions

FAIR requir. (prior to review)



Draft Recommendations of Committee

Linac:

• Replace Alvarez; new system with low emittance growth; preserve beam quality

• Don’t sacrifice beam quality for rf power

• IH structure - significant drop in brilliance; space charge not very high. Develop system to maintain beam emittance in this energy range

• After RFQ need to redesign whole accelerator. Replace with structure that has very regular strong focusing. Space constraint argument for IH structure no longer valid

• Recommend redesign gas stripping section: very long, not designed for high intensity beams



Linac ... :

• From source, extraction loss - redesign LEBT. Issues in getting to 3Hz; only one uranium supplier

• Build dedicated U-terminal + LEBT

• More effort in understanding beam dynamics between RFQ and stripper section

• Systematic study of beam properties along linac. Include full simulation with SINGLE code, incl. collimation upstream of SIS18. Get clear what beam is being injected



• oral comment (F. Gerigk): „is it worth to increase UNILAC brilliance by factor 5 to gainfactor 2 in SIS18 ?“


Strategy do deal with Recommendations

• revision of draft HE-Linac design:• increase focusing, long. & transv.• consider IH-cavities with long. foc. in each gap instead of KONUS (at least at low β)• more triplets, i.e. more & shorter IH-cavities• consider Alvarez-type DTL• sacrifice margin for future energy-upgrade for beam quality

• re-investigate beam dynamics between RFQ and gas stripper

• model UNILAC with BEAMPATH code

• consider emittance transfer for upgrade, not for baseline design

• suspension of optional replacement of HSI, since:• existing Alvarez is critical wrt reliable operation during FAIR commissioning• FAIR will ask beam from first day• HSI is reliable• FAIR won‘t ask design brilliances from first day• there is still potential to improve HSI performance

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