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feat: off-momentum RDT #1074

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Merged
lfarv merged 2 commits into from
May 13, 2026
+36 −6
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feat: off-momentum RDT #1074

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2a33a26
feat: off-momentum RDT
wei0852 Apr 11, 2026
1d6443c
rename the variable dpp to dp
wei0852 May 9, 2026
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42 changes: 36 additions & 6 deletions atmat/atphysics/NonLinearDynamics/computeRDTfluctuation.m
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Original file line number Diff line number Diff line change
Expand Up @@ -25,17 +25,21 @@
% absolute values of one-period RDTs observed at different
% longitudinal starting position.
% same as s_dependent_driving_terms in ELEGANT.
%
%
% Bingfeng WEI, NSRL, USTC
%
% REFERENCES
% [1] Johan Bengtsson, SLS Note 09/97, (1997)
% [2] S. C. Leemann, A. Streun, Phys. Rev. ST Accel. Beams 14, 030701 (2011)
% [3] A. Franchi, L. Farvacque, F. Ewald, G. Le Bec, and K. B. Scheidt, Phys. Rev. ST Accel. Beams 17, 074001 (2014)
% [4] B. Wei, Z. Bai, J. Tan, L. Wang, and G. Feng, Phys. Rev. Accel. Beams 26, 084001 (2023)
% [5] B. Wei, Z. Bai, G. Feng, A. Loulergue, L. S. Nadolski and R. Nagaoka, Phys. Rev. Accel. Beams 27, 104001 (2024)
%

% Validates the input arguements.
[nslices,varargs]=getoption(varargin,'nslices',4);
[nperiods,varargs]=getoption(varargs,'nperiods',1);
[dp,varargs]=getoption(varargs,'dp',0.00);
if ~ isempty(varargs)
throw(MException('RDTFluctuation:parameterError', ...
['Unsupported parameter: ' varargs{1}]))
Expand Down Expand Up @@ -65,7 +69,7 @@
% same as computeRDT().
indDQSO=findcells(splitring,'Class','Bend','Quadrupole','Sextupole','Octupole','Multipole');

[~,AVEBETA,AVEMU,AVEDISP,nu,~]=atavedata(splitring,0,1:length(splitring));
[LINDATA,AVEBETA,AVEMU,AVEDISP,nu,~]=atavedata(splitring,dp,1:length(splitring));

s=[0,findspos(splitring,indDQSO)];
betax=AVEBETA(indDQSO,1);
Expand All @@ -78,12 +82,28 @@
throw(MException('RDTFluctuation:Unfinished', ...
'The coupling case cannot be handled in the current version.'))
end
b2L=getcellstruct(splitring,'PolynomB',indDQSO,1,2).*getcellstruct(splitring,'Length',indDQSO);
b2L(isnan(b2L))=0;
b3L=getcellstruct(splitring,'PolynomB',indDQSO,1,3).*getcellstruct(splitring,'Length',indDQSO);
b3L(isnan(b3L))=0;
b4L=getcellstruct(splitring,'PolynomB',indDQSO,1,4).*getcellstruct(splitring,'Length',indDQSO);
b4L(isnan(b4L))=0;
b3L=getcellstruct(splitring,'PolynomB',indDQSO,1,3).*getcellstruct(splitring,'Length',indDQSO);
b3L(isnan(b3L))=0;
b2L=getcellstruct(splitring,'PolynomB',indDQSO,1,2).*getcellstruct(splitring,'Length',indDQSO);
b2L(isnan(b2L))=0;

if dp ~= 0
closed_orbit = cat(2,LINDATA.ClosedOrbit);

if any(closed_orbit(3,:))
throw(MException('RDTFluctuation:Unfinished', ...
'The coupling case cannot be handled in the current version.'))
end

b2L = (b2L + b3L .* closed_orbit(1,indDQSO)' .* 2 + b4L .* closed_orbit(1,indDQSO)' .* closed_orbit(1,indDQSO)' .* 3);
b3L = (b3L + b4L .* closed_orbit(1,indDQSO)' .* 3);
b4L = b4L;

end


nData=length(indDQSO) + 1;

% calculate the build-up fluctuation of RDTs.
Expand Down Expand Up @@ -236,6 +256,16 @@
'dnux_dJx', -4*real(buildup_fluctuation.h22000(end))/pi, 'dnux_dJy', -2*real(buildup_fluctuation.h11110(end))/pi, 'dnuy_dJy',-4*real(buildup_fluctuation.h00220(end))/pi);
end

if dp ~= 0
% remove misleading information.
% the off-momentum RDTs directly describe the nonlinear dynamics for
% the given dp case. So we don't use the chromatic terms which
% describe the deviation from the on-momentum case.
natural_fluctuation = rmfield(natural_fluctuation, {'f20001', 'f00201', 'f10002'});
RDT = rmfield(RDT, {'h20001', 'h00201', 'h10002'});
buildup_fluctuation = rmfield(buildup_fluctuation, {'h20001', 'h00201', 'h10002'});
end

function newelems=splitelem(elem)
if isfield(elem,'Length') && elem.Length > 0 ...
&& ~strcmp(elem.PassMethod, 'IdTablePass')...
Expand Down