status report of the design of superconducting proton

7th ACFA-HPPA B. Yee-Rendon 1

Status report of the design of

superconducting proton linac for the

JAEA-ADS

Bruce Yee-Rendon*, Kazuo Hasegawa, Yasuhiro Kondo, FujioMaekawa, Shin-ichiro Meigo and Jun Tamura

Nuclear Transmutation & Accelerator Division Japan Proton Accelerator Research Complex (J-PARC)Japan Atomic Energy Agency (JAEA)

Acknowledgments: Y. Liu (KEK) and the members of the JAEA-ADS and J-PARC linac for their support. This work was supported by ADS 補助金.

*[email protected]

Contents

• Introduction

• SRF cavity models

▪ Low beta cavities (Half-Wave Resonator (HWR) & Single Spoke (SS) )

▪ High beta (Elliptical cavity (Ellip))

▪ Conclusions and Future work

• Beam optics

▪ Lattice design

▪ Emittance growth study

▪ Conclusions and Future work


Introduction• The detail description the JAEA-ADS project was

presented on the talk “The Concept Design of theProton Linac for the JAEA-ADS” (by J. Tamurayesterday)

• JAEA ADS in a nutshell:

▪ CW Superconducting proton linac with beam current of 20 mA and final energy of 1.5 GeV with a low beam loss

• Work to be discuss:

▪ Optimization EM design of the superconducting cavities

▪ Beam optics design with an excellent control in the beam loss (avoidemittance growth, beam halo)


SRF cavities

• The optimization in the numbers of cavities and 𝛽𝑔 were chosen to obtain

maximum voltage gain per cavity + smooth transition


SRF cavity start point model

Cavity type Freq [MHz] # of Cell

HWR 162 2

SS 324 2

Elliptical 648 5

Voltage gain was computed assuming: • Sinusoidal E fields• Synchronous phase of -30⁰

JAEA-ADS SRF cavity parameters

Cavity type Freq [MHz] βg

HWR 162 0.08

SSR1 324 0.16

SSR2 324 0.43

EllipR1 648 0.68

EllipR2 648 0.89

Low beta


Inner center conductor geometry

JAEA-ADS low beta Cavity Parameters

Cavity type Freq [MHz] βg Energy range [MeV]

HWR 162 0.08 2-10

SSR1 324 0.16 10-35

SSR2 324 0.43 35-180

SS parametrization geometryHWR parametrization geometry

Low beta criteria

• The Transit Time Factor (TTF) is given by [1,2]

𝑇𝑇𝐹 𝛽 =𝑆𝑖𝑛

𝜋𝑔𝑒𝑓𝑓

𝛽𝜆𝜋𝑔𝑒𝑓𝑓

𝛽𝜆

𝑆𝑖𝑛(2𝜋𝐼𝑇𝑍

𝛽𝜆)

Where geff is the effective gap (geff = (𝑁𝑆 − 𝐼𝑇𝑍)2+ 2𝑅𝐵𝑃 2 ),

NS-ITZ is the gap, RBP is the beam pipe radius, ITZ inner torus longitudinal distance. TTF >0.7

• Electromagnetic peaks criteria

• Epk <60 MV/m

• Hpk < 120 mT


[1] A. Facco “Tutorial on LOW BETA CAVITY DESING”[2] G. Tae Park et al “ELECTROMAGNETIC DESING OF HALF WAVE RESONATOR WITH B=0.13, F=325MHZ FOR FUTURE HIGH POWER AND HIGH INTENSITY PROTON DRIVER KEK”

HWR optimization inner centerconductor shape


HWR Inner conductor geometryin the X-Y plane

• The comparison for a torus to elliptical torus shape (ITZ1 is fixed for the TTF condition)

1 IT defined the length of the elliptical torus shape of the inner conductor, therefore, ITX, ITY and ITZ are the horizontal, vertical andlongitudinal length of the elliptical torus inner conductor shape

Spokes Optimization Inner Center conductor shape

• The comparison for a inner ring conductor shape (ITZ1 is fixed for the TTF condition)


Single spoke Inner conductor geometry in the X-Y plane

1 IT defined the length of the elliptical torus shape of the inner conductor, therefore, ITX, ITY and ITZ are the horizontal, vertical andlongitudinal length of the elliptical torus inner conductor shape

HWR summary


1 The PIP-II Reference Design Report V1.00 June 2015

Figures of merits of the HWR cavities for the projects: PIP-II1 and JAEA-ADS

PIP-II JAEA-ADS

𝛽𝑔 0.112 0.08

Freq [MHz] 162.5 162.0

Eacc [MV/m] 9.7 9.7

Epk/Eacc 4.62 4.21

Hpk/Eacc [mT/MV/m] 4.97 3.41

R/Q [ohm] 275 285.39G [ohm] 48 59.15

TTF -- 0.77

Absolute value of the longitudinal electric field for the HWR model

SS Summary

7th ACFA-HPPA B. Yee-Rendon 101 The PIP-II Reference Design Report V1.00 June 2015.2 SRF CAVITIES FOR ADS PROJECT IN CHINA. H. Ye et al , SRF2013, THIOD01

Figures of merits of the SS cavities for the projects: PIP-II1 , C-ADS2 and JAEA-ADS

PIP-II C-ADS JAEA-ADS PIP-II JAEA-ADS

𝛽𝑔 0.222 0.12 0.16 0.475 0.43

Freq [MHz] 325 325 324 325 323.99

Eacc [MV/m] 10 -- 10 11.4 11.4

Epk/Eacc 3.84 4.5 4.7 3.50 3.55

Hpk/Eacc [mT/MV/m] 5.81 6.4 6.68 5.65 5.13

R/Q [ohm] 242 142 212.72 296 285.80

G [ohm] 84 63 64.78 115 129.20

TTF --- ---- 0.75 -- 0.77

Absolute value of the longitudinal electric field for the single spoke cavities βg =0.16 on the left and βg =0.43 on the right.

Elliptical Introduction

• Design goals

▪ Lower electromagnetic peaks ratios:

o Epk/Eacc < 2.60 & Hpk/Eacc < 4.6 mT/MV/m

• Using the codes:

▪ SUPERFISH (SF)+ Python

▪ CST Microwave studio (CST)


JAEA-ADS high beta Cavity Parameters

Cavity type Freq [MHz] βg Energy range [MeV]

EllipR1 648 0.68 0.18-.050

EllipR2 648 0.89 0.5-1.5

• SUPERFISH code

• Two symmetries cell:

▪ Inside cell:

➢ The parameters 𝐿 =𝛽𝑔𝜆

4(fixed)

➢ Tune was done adjusting the cavity radius “R”

➢ A,B, a, b and 𝛼 were changed to obtain the values of the figuresmerit required

▪ End cell:

➢ Only the half end cell was modified by changing the length andwall angle to obtain the same frequency and high electric fieldflatness


Half elliptical cell parametrization

Elliptical Simulation setup

Simulations scans


The electromagnetic peaks as a function ofthe iris ratio by adjusting the ellipse domeratio (solid red line and dash orange line)and adjusting (dot blue line and dash dotgreen line) to tune the frequency

The surface plot by changing the iris and thedome ratio to select the parameters tominimize the Epk/Eacc (top) and Hpk/Eacc(bottom).

Elliptical comparisons

7th ACFA-HPPA B. Yee-Rendon 14[1] The PIP-II Reference Design Report V1.00 June 2015

𝛽𝑔 = 0.68 𝛽𝑔 = 0.89

Figures of merits of the Elliptical cavities for the projects: PIP-II1 and JAEA-ADS

PIP-II JAEA-ADS (SF) JAEA-ADS(CST) PIP-II JAEA-ADS (SF) JAEA-ADS(CST)

𝛽𝑔 0.61 0.68 0.68 0.9 0.89 0.89

Freq [MHz] 650 647.98 647.93 650 647.98 648.05

Eacc [MV/m] 15.9 15.9 15.9 17.8 17.8 17.8

Epk/Eacc 2.26 2.15 2.17 2 1.99 2.11Hpk/Eacc [mT/MV/m] 4.21 4.04 4.22 3.75 3.70 4.07

R/Q [ohm] 378 442.78 443.22 638 619.86 619.73

G [ohm] 191 208.80 208.82 255 256.11 256.17

Comparison of the absolute value of the longitudinal electric field for the elliptical cavities between SUPERFISH and CST.

SRF Cavities summary &Future work I

• The first EM design of the JAEA-ADS were develop. The modelspresent a good performance in terms of the figures of merits andtheir values are close with the ones obtained by similar projects(PIP-II and C-ADS).

• Low beta:

• The elliptical torus inner center shape was the key to achieve thedesign goal.


Parameters HWR SSR1 SSR2 Design goalMaximum electric field

[MV/m] 40.88 47.31 40.49 < 60Maximum magnetic field

[mT] 33.07 66.80 58.48 < 120TTF 0.77 0.75 0.77 > 0.7

SRF Cavities summary &Future work II

• High beta beta:

• The double scans were essential for the optimization of thegeometry.

• The difference between SF & CST was the mesh type + adifference of geometry of 0.3 and 0.5 % for EllipR1 and EllipR2,respectively

• The future work will include:

▪ HOM, Lorentz Force detuning (Static), Multipacting, etc.


ParametersEllipR1 EllipR2

Design goalSF CST SF CSTEpk/Eacc 2.15 2.17 1.99 2.11 < 2.6

Hpk/Eacc [mT/MV/m] 4.21 4.22 3.70 4.07 <4.6Flatnnes of the field 0.98 0.96 0.98 0.98 >0.9

Beam optics


• The beam optics design was developed for asuperconducting proton linac with beam current of 20 mA andfinal energy of 1.5 GeV using the programs GenLinWin andTraceWin.

• The ADS requires an excellent control in the beam loss, themain source of the beam halo, and emittance growth is animportant source of the beam halo

• To control the emittance growth in high intensity proton linacthe next conditions were applied:

▪ The phase advance (σt/l ) < 90⁰ to avoid parametric resonances

▪ The beam must satisfy the equipartition condition (𝑇⊥

𝑇∥=

𝑘⊥𝜀𝑛⊥

𝑘∥𝜀𝑛∥= 1) to

avoid emittance exchange between the planes

▪ Smooth envelope (an excellent beam matching between differentcavity sections, specially in the ones where frequency jump occurred)

JAEA-ADS models summary


Model A/B

Parameters HWR SSRI SSR2 EllipRI EllipR2 Total

NCAV 9/10 30/34 63 51 90 247/248

Period 9/10 15/17 21 17 18 80/83

N of CM 1 15/17 21 17 18 72/74

Cavities per CM 9/10 2 3 3 5 247/248

Solenoids per CM 9/10 1 1 0 0 45/48+11

Quads per CM 0 0 0 2 2 71+21

Energy final [MeV] 10.765/10.263

34.154/34.595

180.536/182.260

518.857/522.126

1530.079/ 1535.444

Len [m]2 381.919/386.613

Phase law 𝜎𝑡 = 0.83𝜎𝑙/𝜎𝑙 = 0.85𝜎𝑡

𝜀𝑡𝑛𝑜𝑟𝑚𝑟𝑚𝑠(𝜋 𝑚𝑚𝑚𝑟𝑎𝑑) 0.48/0.36

𝜀𝑙𝑛𝑜𝑟𝑚𝑟𝑚𝑠(𝜋 𝑚𝑚𝑚𝑟𝑎𝑑) 0.4

1Additional magnets were required for the matching in the section with frequency jump2The space for the matching section was took into account

• Two models were designed to study of the rms beam dynamics, thedetails are shown in the next table

Lattice configuration1


1 Not in scale

Length: 0.69 m Length: 1.9 m Length: 3.4 m

Length: 5.5 m

Length: 9.7 m

HWR SSR1 SSR2

EllipR1

EllipR2

JAEA-ADS rms envelope


HWRSSR1 SSR2 EllipR１ EllipR2

JAEA-ADS Zero phase advance& Hoffman chart


Model BModel A

Norm rms emittances evolution


Projects Distribution 𝜀𝑡/𝑙𝑛𝑜𝑟𝑚𝑟𝑚𝑠(𝜋 𝑚𝑚 𝑚𝑟𝑎𝑑) Growth (X,Y,Z) (%)

A Uniform 0.48/0.40 1/1/12

B Uniform 0.364/0.4 2.6/2.5/5.7

• The summary of the RMS normalized emittance for the JAEA-ADSmodels

Model A Model B

Beam halo development studies

• The model B was used to study the beam halo usingan uniform (6D Water bag) and Gaussian (3𝜎) densityprofile and 100,000 macro particles.


GaussianUniform

Aperture beam tracking results


▪ 6-Dimensional Gaussian distribution (3𝜎)

HWR SSR1 SSR2

ELLIPR１ELLIPR2

Emittance growth for different beam profiles


Uniform

Gaussian

Beam optics summary &Future work I


• The models operates near the equipartitioning beamregion and far from the high emittance growth areas

• Nevertheless, both models generates space-chargedominant beams, this had a large impact in the emittancegrowth at the beginning of the linac.

• The Norm. rms emittance growths are lower than 3% onthe transverse plane and 12% on the longitudinal one

• Model B was used to study the beam halo developmentinstead of the model A, the main reasons are:

▪ Large transverse emittance values of model A

▪ Some operation points of the model A (SSR1) laid in region ofemittance growth higher than zero (Hofmann chart)

Beam optics summary &Future work II


• The beam halo development studies shows a emittancegrowth is bounded between 50% to 130% in all theplanes

• To minimize the beam loss, we should reduce the beamhalo which implies the control emittance growth

• Future work:

▪ Improve the matching between HWR and SSR1 and theirenergy gain (most of emittance growth occurred in that region)

▪ The space-charge is the main contributor to the emittancegrowth at the beginning of the linac, therefore, it is required tore-designed in the optics to mitigate that effect

▪ Optimization in the lattice configuration

Reference

• BEAM OPTICS DESIGN OF THE SUPERCONDUCTINGREGION OF THE JAEA ADS (IPAC19, MOPGWO4O)

• ELECTROMAGNETIC DESIGN OF THE LOWBETA CAVITIESFOR THE JAEA ADS (IPAC19, WEPRBO28)

• DESIGN OF THE ELLIPTICAL SUPERCONDUCTING CAVITIESFOR THE JAEA ADS (IPAC19, WEPRBO29)


Thanks for your attention

status report of the design of superconducting proton

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