Add spin to ExactQuad. by cemitch99 · Pull Request #1323 · BLAST-ImpactX/impactx

cemitch99 · 2026-02-25T00:39:15Z

This PR adds spin tracking to the ExactQuad element, which requires combining the Thomas-BMT equation s-push with the orbit symplectic integration, to the correct order in stepsize h. The basic framework will be reused for the ExactMultipole and ExactCFbend elements.

add basic spin structure for ExactQuad
add Thomas-BMT precession vector evaluation
add 2nd-order symplectic integration in the presence of spin
add 4th-6th-order symplectic integration in the presence of spin
move Thomas-BMT precession vector to mixin/spin_transport class
add a benchmark (e.g. comparison against a linear Quad as a limiting case)
fix failing CI tests (all works locally)
fix inline comment on bunch charge in particle container

Follow-up: Investigate alternative 4th and 6th-order symplectic integration algorithms with spin to improve performance (by reducing the number of required map evaluations). See Issue #1341

codspeed-hq · 2026-02-25T02:56:10Z

Merging this PR will not alter performance

✅ 37 untouched benchmarks

_{Comparing cemitch99:add_spin_exact_quad (3d70b36) with development (a375136)}

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cemitch99 · 2026-03-07T00:06:26Z

I tried initializing the OpenMP / GCC w/SIMD w/o MPI w/ Python runner three times, and each time it fails to build with the error:

ninja: build stopped: interrupted by user.

ax3l · 2026-03-08T05:39:50Z

Maybe uses too many resources, try to lower from -j4 to -j3 in CI script of the GH action?

cemitch99

Corrected filename in CMakeList...

ax3l · 2026-03-20T21:42:23Z

I wonder if #1351 can help with the spike of resource usage that fails one of the builds: OpenMP / GCC w/ SIMD w/o MPI w/ Python

…ct_quad

ax3l · 2026-03-23T22:18:25Z

Great, #1351 helped to lower the peak resource usage of the compiler (by splitting over multiple translation units / .cpp files).

Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

Use some intermediate constants for common terms.

-        amrex::ParticleReal const alpha = 1_prt - std::pow(2_prt,1_prt/3_prt);
-        amrex::ParticleReal const tau2 = dz/(1_prt + alpha);
+        amrex::ParticleReal const dz = (zout - zin) / static_cast<amrex::ParticleReal>(nsteps);
+        constexpr amrex::ParticleReal alpha = -0.2599210498948732;  // C++26: 1_prt - std::pow(2_prt,1_prt/3_prt);


-        amrex::ParticleReal const dz = (zout-zin)/nsteps;
-        amrex::ParticleReal const alpha = 1_prt - std::pow(2_prt,1_prt/3_prt);
+        amrex::ParticleReal const dz = (zout - zin) / static_cast<amrex::ParticleReal>(nsteps);
+        constexpr amrex::ParticleReal alpha = -0.2599210498948732;  // C++26: 1_prt - std::pow(2_prt,1_prt/3_prt);


ax3l

🎉

Start spin addition to ExactQuad.

154058e

github-advanced-security AI found potential problems Feb 25, 2026

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Comment thread src/elements/ExactQuad.H Fixed

ax3l added this to the FY26-27 LDRD: future colliders & light sources milestone Feb 25, 2026

ax3l added component: elements Elements/maps/external fields component: spin tracking Spin tracking labels Feb 25, 2026

This was referenced Feb 25, 2026

Spin Tracking for Plasma Staging #1154

Open

Spin capability element list #1322

Open

ax3l self-requested a review February 26, 2026 21:36

cemitch99 and others added 2 commits February 26, 2026 17:26

Add integrator with spin.

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cemitch99 commented Feb 27, 2026

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Comment thread src/elements/ExactQuad.H Outdated

Comment unused variable t

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Comment thread src/elements/ExactQuad.H Fixed

cemitch99 and others added 4 commits February 27, 2026 09:20

For T_Real replace std::sqrt with sqrt.

4dcaf6c

Forgot to re-assign updated sx,sy,sz in map3.

bbc99a3

Add TBMT evaluation to mixin class in preparation for other elements.

0b2ef48

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cemitch99 requested a review from qianglbl February 27, 2026 23:38

cemitch99 and others added 9 commits March 6, 2026 11:15

Move Thomas-BMT evaluation to mixin class.

92a4451

Try modified template type for mixin tbmt function call.

4cec40f

Revert to previous template declaration.

3affc16

Add possible E dependence to TBMT precession evaluation.

8510cf2

Demote some TBMT arguments from T_Real -> amrex::ParticleReal.

454731d

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Add support for 4th and 6th-order integrators.

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Small clean-up of Integrators.H

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Comment thread src/particles/ImpactXParticleContainer.cpp Fixed

Update CMakeLists.txt

f2a7696

cemitch99 commented Mar 11, 2026

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Update analysis_exact_quad_spin_scaling.py

7b44e65

ax3l mentioned this pull request Mar 18, 2026

Release 26.03 #1358

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ax3l reviewed Mar 20, 2026

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Comment thread examples/spin_tracking/run_exact_quad_spin_scaling.py Outdated

ax3l added 2 commits March 20, 2026 16:10

MPI: Add Particles Once

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Simplify Python Slightly

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ax3l mentioned this pull request Mar 23, 2026

Elements: Compile Push in Separate Translation Units #1351

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ax3l added 2 commits March 23, 2026 14:25

Merge remote-tracking branch 'mainline/development' into add_spin_exa…

43baa07

…ct_quad

CI: 4 Cores

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ax3l reviewed Mar 23, 2026

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ax3l added 3 commits March 23, 2026 16:38

Apply suggestions from code review

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Co-authored-by: Axel Huebl <axel.huebl@plasma.ninja>

Fix Const/Constexpr

d3284fa

Formatting of tbmt_precession_vector

3542147

Use some intermediate constants for common terms.

cemitch99 commented Mar 25, 2026

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Comment thread examples/spin_tracking/run_exact_quad_spin_scaling.py Outdated

ax3l reviewed Mar 25, 2026

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Comment thread src/elements/ExactQuad.H Outdated

ax3l reviewed Mar 25, 2026

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Comment thread src/particles/integrators/Integrators.H Outdated

Cleanup

fbd4c40

ax3l force-pushed the add_spin_exact_quad branch from 4f8ae5d to fbd4c40 Compare March 25, 2026 17:44

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cemitch99 and others added 2 commits March 26, 2026 12:55

Fix Python handling of w optional argument.

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ax3l approved these changes Mar 26, 2026

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ax3l enabled auto-merge (squash) March 26, 2026 20:56

ax3l self-assigned this Mar 26, 2026

ax3l merged commit 4aadf29 into BLAST-ImpactX:development Mar 26, 2026
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cemitch99 commented Feb 25, 2026 •

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