ROBUST AND COMPACT DESIGN OF A 30-MW
BEAM TRANSPORT LINE FOR AN
ACCELERATOR-DRIVEN SUBCRITICAL SYSTEM
Bruce Yee-Rendon*, Yasuhiro Kondo, Jun Tamura, Keita Nakano,Fujio Maekawa, and Shin-ichiro Meigo
Nuclear Transmutation & Accelerator Division
Japan Proton Accelerator Research Complex (J-PARC)
Japan Atomic Energy Agency (JAEA)
Acknowledgments: Hiroki Iwamoto, Takanori Sugawara, Kenji Nishihara, and the membersof the JAEA-ADS. This work was supported by ADS 補助金 .
*byee@post.j-parc.jp

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Contents• Goal
• Introduction• BTT baseline design• Error studies• Conclusions

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Goal
• Accelerator-driven system subcritical systems (ADS) are an advanced option to face
the problem of nuclear waste storage.
• The beam transport to the target (BTT) carries out the beam from the end of thelinac to the beam windows and onto the spallation target, with specified beamcharacteristics, performance, and design considerations.

Fig.1: JAEA-ADS scheme.
Fig.2: JAEA-ADS BTT requirements.
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Introduction
The BTT must transport a 30-MW with high-reliability and fulfill all therequirements of Table 1 [1-3].

Thus, we adopted a robust andcompact design to satisfy thespecifications.

[1] T. Sugawara and K. Nishihara, private communication, Nov. 2021.
[2] H. Iwamoto et al., “Radiation shielding analysis of the upper structure of an accelerator-driven system”, JAEA, Tokai, Japan, Rep. JAEA-Research 2021-012,Dec. 2021 (Japanese).
[3] T. Sugawara et al., “Conceptual Design Study of Beam Window for Accelerator-Driven System”, J. Nucl. Sci. Techol., 47, 953 (2010).
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Design considerations••

Compact:•

Decreasing the number of element, the reliability is
increased for a series configuration.

•Design reactor.

Robust:••Simple:•••Avoid complex or risky configurations that areprone to error or harmful failures.

Beam window feasibility:••

Beam stability.

Low beam peak density.

Maintenance:•

Confined the beam losses inside the reactor part.

•

Dipole aperture are set to 100 mm to allow the easy
exchange of the fuel.

Among others…

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Fig.3. Schematic view of the JAEA-ADS BTT.
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BTT beam optics•Information of the elements that composes the BTT and its envelopes.
(a)

(b)

(c)

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Fig.4. Horizontal (a), vertical (b) rms size and dispersion
function (c) along the BTT.
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BTT baseline design•

Smooth beam scraping confined in the reactor part, where it has propershielding.

•The beam profile has a lower peak and lower percentage of beam
scraping than the accepted Gaussian profile [1].
Current density limit

Fig.5. Maximum transverse envelope for the baseline
and the double error case.

Fig.6. Radial current density from the beam tracking
simulations and the accepted Gaussian profile.

[1] T. Sugawara et al., “Conceptual Design Study of Beam Window for Accelerator-Driven System”, J. Nucl. Sci. Techol., 47, 953 (2010).
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Errors•To achieve a stable beam operation, the BTT must be evaluated in thepresence of errors to improve its design.

•Errors are divided into statics (long time) and dynamics (jitters).

•Error for the components that integrate the BTT (elements errors) andfrom the beam delivered for the JAEA-ADS linac (input beam errors)•The below tables show the element errors based on the JAEA-ADS
linac [1] and other beam transport lines [2].

Fig.7. Misalignments errors. The blue
arrows show the transverse offset. The
red arrows are the phase rotation
errors.
[1] B. Yee-Rendon, et al, “Design and beam dynamic studies of a 30-MW superconducting linac for an accelerator driven subcritical system” Phys. Rev. ST.
Accel. Beams 24, 120101 (2021).
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Yee-Rendon
8[2] B. Branhas et al, “Design, manufacturing and tests of the LIPAc
high energy
beam transportB.
line”,
Nucl. Fusion 61 (2021) 015001.

Input beam errors•

To increase the reliability of the system, JAEA-ADS adopted local
compensated schemes to achieve a fast beam recovery [1].

•Compensation schemes were developed for single SRF cavity failures(SSRFC), multiple SRF cavity failures (MSRFC), and magnet failures(Magnet).

[1] B. Yee-Rendon et al., “Beam dynamics studies for fast beam trip recovery of the Japan Atomic Energy Agency accelerator driven subcritical system”, Phys.
Rev. Accel. Beams., vol. 25,080101(2022).
[2] The final normalized rms emittance growth with respect to the baseline.
[3] The final beam mismatch with respect to the baseline.
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9Error studies•The error studies consisted of 1000 independents runs with more than
9 million macroparticles.

•In each run, the amplitude for each of the errors associated with eachelement was chosen independently.

•The types of errors are divided into statics and dynamics.

•We simulated double errors: errors in the elements (misalignments,etc.) + errors in the input beam (emittance growth, mismatch).

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Error case I : Static element error + input error from compensationof single SRF cavity failures.

•This case is considered the most likely error case among all.

Power fluctuation was confined ± 0.4.

Fig.8. Beam power fluctuations to the baseline for double error
case I.

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Fig.9. Maximum transverse envelope for the baseline andthe double error case.
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11Summary of the beam stability
for double errors
(a)

(b)

(c)

(d)

The
requiredtarget stability isshowed by the redlines
inthesubplots.

Fig.10. Summary of the beam error degradation for different error cases defined in Table.
The plot (a) is the difference in kinetic energy, (b) beam power, (c) radial rms size, and (d)transverse offset. The error bars denote a 99% confidence interval.
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12Summary• The JAEA-ADS BTT efficiently transports a 30-MW beam fromthe end of the linac to the beam window while fulfilling
stringent conditions of beam stability and engineering
specifications.
• A suitable beam profile is delivered, which satisfies thefeasibility of the beam windows and small beam scraping.
• The error analysis showed that the BTT meets the stringent
beam window stability of the JAEA-ADS [1].
• In the future, beam expander methods (non-linear optics andbeam rastering) will be evaluated.
[1] B. Yee-Rendon et al., “Beam physics design of a 30-MW beam transport to the target for anaccelerator-driven subcritical system”, JINST, vol. 17, P10005 (2022).
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