tracewin lattice for fnal drift-tube linac: status

TraceWin Lattice for FNAL Drift-Tube Linac: Status

Valery Kapin

30-Jul-2014

PIP General Meeting

V.Kapin, PIP meeting, July-2014 2

Contents• Start with the lattice file for FNAL DTLs with old PARMILA based on

MM~1968 data (not convenient interface –> command codes)

• TraceWin code (only exe, commercial) with user-friendly interface

• Existing DTL lattice (by Kim?) for TraceWin used by J.P. (~2013);My inspection -> inaccurate interpretations of “DTL_CELL” elements

• TraceWin lattice generation: old PARMILA outputs “DTL_cell” lines via post-processing of MM-data & DTL cell parameters generated by PARMILA’s GENLIN subroutine

• Beam dynamics simulations with a nominal Q-stengths: 1) mismatched input beam; 2) input beam matched to DTL acceptances

• Beam dynamics simulations with “smoothed” cell-by-cell quadrupole strengths: SG stability diagram => DTL1&2 (BNL pattern)+DTL3-5(FNAL pattern) => larger transverse acceptances (>50%)

• Needs for accurate “4-rod RFQ” & MEBT lattices => TraceWin lattice with field maps extracted from MWS for sections/cells


Previous 2013 presentation

• Review previous talks:- D.McGinnis(2011); - H.J.Kim(Jan-2012)

• New restart in Oct-2012 by VK• Optics reconstruction for accelerator model• SNS: XAL(Java) online models• PARMILA new vs old versions• A new configuration for on/off-line modeling• Overview FNAL DTL lattices • FNAL & BNL designs – history• New lattice based on MM68 data is well agree with BNL 1990 lattice

and all published design specifications• Questions on intertank distances and quad strengths• About on-line modeling DTL’s pre-injector (4-rod RFQ)

Beams-doc-4293-v1


(F)NAL & BNL DTL tank geometries are the same


BNL DTL tank had NOT been designed by PARMILA

9-DTL 200-MeV 138m Linac: L =1.3cm (~0.01%); W = 170keV (~0.1%)


Example of Messymesh data printout (~1968 for BNL DTL) for one cell

MM calculates E/M parameters of linac cell and output TTFs


Drift-tube geometry - restored

VK01 - only Messymesh data


TTFs from MM68 and might be corrected for tracking

Original Messymesh TTFs have be used for design; PARMILA should use original for design (step1 - GENLIN), and refined TTFs for tracking (step2; also for TraceWin)


Restore field tilt in DTL1C. Curtis et al, in report "fermilab-fn-0201“; HEACC-7, Yerevan, 1969, USSR, p.192-204.

The plot (left) has been digitized and normalized values from the 1969-plots had beenconverted into absolute values of the electrical field strength needed for PARMILA. The right plot shows the measured field (red circles), the design field (blue-line), the gap fields set with by PARMILA's command "CHANGE=4" (green crosses).


Start with the lattice file for FNAL DTLs based on Messymesh~1968 data with old PARMILA

OUTPROC: SUBNUM# command codes:- not convenient interface - NOT for a CASUAL (MODERN) USER!

V.Kapin, Post-processing for old Parmila (SY12): notes with examples for FNAL DTL, June-2013, 20pages

The example plot from data in <OUT1_good_bad_particles.out> for FNAL DTL1-5 (text-file => external plotting soft):


Old PARMILA: SUBNUM8 example

: SUBNUM 8 : Plots two profiles as functions of cell numberSUBNUM 8 : (34) dPhi & dW profiles: dPhiMax=180deg dWmax=1MeV ----------------OUTPUT 2 1 34 180 1. 220.11 1 204 1OPTCON 0 0

Coding Number for plotTypes and frame sizes


TraceWin code (only EXEcutable, commercial) with a user-friendly interface

What physics is inside? “DTL_CELL” ?

Source code is not available; Manual is in a laconic & briefly style (in English, but some chapters in French)

Need to communicateWith code owners !

In red box:from my E-mail communications


TraceWin code (con-ed)


V=E0*T*L, s – Must be known “a priory” – They are written into a lattice file !

Supposing A true design particle!


“Wangler’s book page 202”

Tracking according to Lapostolle & Co treatment, not PARMILA’s (Swenson’s style) – see discussion in LINAC bible (1970)In 1960-70 multi-step integration (e.g.Runge-Kutta – time&memory consuming!)TTF definitions are different from PARMILA’s ! TTFs are expanded around a given synchronous particle => still “design code” !Exact implementation in TraceWin is unknown … (e.g. at center or entrance)



Discussion from LINAC bible 1970

Tracking method in TraceWin according to Lapostolle’s Formulae is similar to one in PARMILA’s (Swenson’s style):“Drift+thin-lens+drift”


Existing TraceWin Start-to-end lattice

J.P. Carneiro, The FNAL 400 MeV Linac in TRACEWIN (from Ion Source to Stripping Foil), PIP meeting, 12-June-2013.

Start-to-end Model with TRACEWIN; (TRACEWIN and TOUTATIS;)

Citation: “How was the model built ? • LEBT (35 keV): from TRACE2D input file (CY Tan, D.

Bollinger)• RFQ (750 keV) : from PARMTEQM input file (CY Tan)• MEBT +DTL (117 MeV) + CCL (400 MeV) : from

PARMILA input file (H.J. Kim)”

Out: TraceWin lattice file “fnal_pip_linac.dat” containing “RFQ_CELL”, “DTL_CELL” (by Kim ?) etc. commands


Inspection of existing TraceWin lattice

Gap shift ignored:As for symmetrical cell

R aperture 20mm assumed everywhere in DTL1-5 Wrong by factor “-2”

Inaccurate values will affect on beam dynamics results: a) Equivalent particle trajectory – position of trajectory bend

due to the gap center position (“drift+kick+drift”);b) Particle losses – largest & constant radius of aperture

(instead of stepwise increase 1.0;1.25;1.5;2.0)c) Equivalent particle trajectory – shift value for both phase & radial position

due to wrong value of T’(k)

inaccurate interpretations of “DTL_CELL” elements


TraceWin lattice generationOld PARMILA (with specially written using FORTRAN source code) outputs “DTL_cell” lines via post-processing of MessyMesh-data & DTL cell parameters generated by PARMILA’s GENLIN subroutine

Methods for particle tracking through the gaps in PARMILA & TraceWin are different, but based on the same approach (“drift+kick+drift”). Benchmarking of results might be useful.

Several parameters are needed at the cell centers (not at the ends as in PARMILA)


Beam dynamics with a nominal Q-strengths; Finding Longitudinal Acceptance DTL1-5

Zoom

Surv. Particles At DTL1 Entry

Beam:xy-> 0; Ibeam=0

Within separatrix – non-linear oscillations


Finding Long. Acceptance DTL1-5(con-ed)

Surv. Particles At DTL1 Entry

Surv. Particles At DTL5 Exit

Particles with non-linear oscillations

TraceWin provides approx. ellipse Parameters & its shift:


Long. Accept.: small (linear) oscillations

1) drawing inscribed "small (linear oscillations)" 25%-ellipsewith a plotting soft (&=const; shifted center)2) superpose it on large accept.

Test run with 0%-loss (Beam: xy-> 0; Ibeam=0):

Figs: Entry; Exit; (z)


Beam dynamics with a nominal Q-stengths; Finding Transverse Acceptance X-X’plane

Inj. beam:

y,L-> 0;Ibeam=0

ZoomZoom

Particles At DTL1 Entry – (survived=dark):

Entry & ExitNot yet 100%


Beam dynamics with a nominal Q-stengths; Finding Trans. X-X’ Accept. (con-ed)

DTL1Entry:

DTL5Exit:

Reduce x-emittance until 100% transm. is reached


Beam dynamics with a nominal Q-stengths; Finding Transverse Acceptance: Y-Y’plane

DTL1Entry:

DTL5Exit:

Reduce y-emittance until 100% transm. is reached (as for x-x’)


Partial acceptances & unmatched input beamCalculated partial acceptances (for 0%-loss, I=0 & zero emittances in other planes)

Initial parameters of unmatched injected beam (file "pmi2tw.dst" by new PARMILA): Input 35 10000 1.269 20.18 0.0128 2.138 38.01 0.0083 50 0.05 0.0 0 0 0 0 0 0


Unmatched input beam

Blue ellipsesacceptances; red elipses:Total 5-rmsEmittances(unnorm.)

Iout(Iinp=50mA)=43.2mA (86%)

Iout(Iinp=2mA)=1.76mA (88%)

Iout(Iinp=100mA)=68mA (68%)

Imax(Iinp=140mA)=74mA (53%)

Current dependent -growthIn all 3 phase space (L~2; X~4; Y~6.5 times)!


Matched input beam

Blue ellipses - DTLs acceptances; red elipses: Total 5-rms beam Emittances (unnorm.)


Matched input beam: -growth & I-transmission

Current dependent -growthIn all 3 phase space (L~2; X~6; Y~6.5 times)!


Losses %: matched vs mismatched (Iinj=1mA& 45mA)


Ibeam mA: matched vs mismatched (Iinj=1mA & 45mA)


z,norm: matched vs mism. (Iinj=1mA & 45mA)


t,norm: matched vs mism. at Iinj=1mA & 45mA:


On emittance growth in proton linacs

References: •1972 Batchelor Emittance vs Quads BNL LINAC_p47;•1979 Jameson & Mills EmittanceGrowth in Linacs LinacConfProcs_p231•1979 Jameson Emittance Growth in Linacs HeavyIonFusionWorkshop_p84•1985 Wangler Emittance Growth of IntenseBEam PAC1985_2196•2008 Reiser Emittance Growth Ch06 in his book•2008 Wangler SpCh Multiparticle Dynamic ch09 in RF linacs book•2010 Wei Simulations of Errors JPARC Linac


Quad. Strengths and Smith-Gluckstern stability diagram

BNL linac (1990) FNAL linac (nomin. Qs)

Quads in DTL1


Simple Smoothing of quad. G(nq)Quad. gradient G vs quad number nq : for DTL1&2 use BNL’s (AK90); for DTL3-5 use FNAL’s nominal (FG01).Liner interpolation; equate adjacent Quad pairs (common power supply)Keep Quad-settings at the tank ends (matching between tanks in a future)


Q-smoothing DTL3-5


Increased acceptances for smoothed G(nq)a) blue= original; red = smoothed Quads

X-X’ plane Y-Y’ plane

X-acceptance: 1.5->2.3Y-acceptance:1.4->4.0

b) blue= original; red = smoothed (Q2-3 exactly as AK90)

X-acceptance: 1.5->2.6Y-acceptance:1.4->2.6

(w/o matching With MEBT beamat DTL1 entry)


Known & unknown DTL parametersXY ; centroidI, A

4-rodRFQ

MEBTRF cavity& Quads

~Long (PARMTEQ, tests)W-Phi Centroid DTL1:

E+, PhiS+,56 gaps;57 QuadsGrad(Qi, Qi+1)=F(I)+

DTL2:E+, PhiS+,60 gaps;61Quads

DTL3:E+, PhiS+,35 gaps;36 Qs

BPMs I, A

BPMs I, A


BPMs I, A


RF param.: Power Prf & phases between resonators dPhi are tuned for best Ibeam !?Prf & dPhi values unknown; different from design values E0 & PhiS used by TraceWin !This difference affects on both long. & transv. Tracking results!Actual E0 & PhiS must be recalculated (additional code or another code, e.g. TRACK?

Quad param.: Gradients are calculated from currents with ideal formulae ~5-10%There is no dipoles & BPMs inside => usual optics reconstruction is impossible

Initial beam: Transv. Emittances are measured (at what conditions ?); Long. Emittance – upright ellipse (ideal MEBT) via PARMTEQ (not for 4-rod RFQ)Particle Distributions (Gaussian etc) are unknown !

Intertank BPMs: for correction of coherent oscillations (ini. Beam or misalignments)


Existing 4-rod RFQ lattice with TraceWin

• RFQ (750 keV) : from PARMTEQM input file (CY Tan)• RFQ: RFQ_CELL; RFQ_GAP_RMS_FFS etc.

Analytical function for ideal RFQ with pure quad-symmetry (like 4-vane RFQ): Type: 2=>Acc. cell; 3=> Front end cell; 4=>Transcell

TraceWin manual:


Need for a correct TraceWin lattice for 4-rod RFQ

• Existing TraceWin lattice (based on PARMTEQ-M lattice)• It ignore its inherent asymmetry; it describes an ideal RFQ

with ideal Quad-symmetry like 4-vane RFQ (w/o dipoles)• Problems are in matching section and regular RFQ channel,

where additional components generated.• Experimentally 4-rod RFQ never had a high transmission as

PARMTEQ(M) predicted • Existing TraceWin lattice will not model features of 4-rod

RFQ (acceptance; emittance & shifts of beam centroid).• I had worked on 4-rod RFQ simulations in 198x-199x

(EPAC-94, Linac-94, JJAP-97) (see APCsem-2013)• Additional non-quadrupole fields in 4-rod RFQ were shown

and a new model for beam dynamics simulations was used• I guess now it is possible simulate 4-rod RFQ with TraceWin

using field maps from MWS


Conclusion

• TraceWin lattice for FNAL DTL1-5 is updated• Long. & Transv acceptances are calculated• Beam transmission and emittance growth for matched and

unmatched beam are compared • Beam transmission for matched beam ~97% at 50mA• Emittance growth depends on Ibeam (unavoidable); it is the

same for matched and unmatched beams• Simple smoothing of Grad(nq) increases accept. (>50%);

Matching at entry and in inter-tanks might be needed• Limitations for simulations of a real beam discussed;

supplementary or other code (a’la TRACK) is needed• The lattices for MEBT & 4-rod RFQ should be studied &

updated for more accurate simulations

tracewin lattice for fnal drift-tube linac: status

Documents