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Fix atBunchLength #585

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Fix atBunchLength #585

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f0c5c2e
blgrowth separated from BunchLength
carmignani Mar 24, 2023
c4956f5
atBunchLength uses atx in case the ring is 6D
carmignani Mar 24, 2023
fa84464
help of atBunchLength updated
carmignani Mar 24, 2023
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24 changes: 1 addition & 23 deletions atmat/atphysics/LongitudinalDynamics/BunchLength.m
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Original file line number Diff line number Diff line change
Expand Up @@ -15,7 +15,7 @@
% sigmadelta is the energy spread
% circ is the ring circumference
%
% see also: atBunchLength
% see also: atBunchLength, blgrowth

blg = abs(blgrowth(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta));
phi=pi - asin(U0./Vrf);
Expand All @@ -24,26 +24,4 @@
BL = zcBL .* blg;
end

function blg = blgrowth(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta)
% bunch lengthening factor due to the potential well effect

% Ib is the bunch current [A] (it may be a vector for multiple values)
% Zn is the longitudinal broadband impedance [Ohms]
% Vrf is the RF voltage [V] (it may be a vector for multiple values)
% U0 is the energy loss around the ring [eV]
% h is the harmonic number
% alpha is the momentum compaction factor
% sigmadelta is the energy spread

phi=pi - asin(U0./Vrf);
nus= sqrt(-(Vrf/E0).*(h * alpha)/(2*pi) .* cos(phi));

Delta = -(2*pi*Ib*Zn)./(Vrf*h.*cos(phi).*(alpha*sigdelta./nus).^3);
Q=Delta/(4*sqrt(pi));



blg = (2/3)^(1/3)./(9*Q + sqrt(3)*sqrt(-4+27*Q.^2)).^(1/3)...
+ (9*Q + sqrt(3)*sqrt(-4+27*Q.^2)).^(1/3)./(2^(1/3)*3^(2/3));
end

28 changes: 20 additions & 8 deletions atmat/atphysics/LongitudinalDynamics/atBunchLength.m
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Expand Up @@ -6,17 +6,29 @@
%
% Ib is the bunch current [A] (it may be a vector for multiple values)
% Zn is the longitudinal broadband impedance [Ohms]
% ring is the at ring without radiation
% ring is the at lattice (4D or 6D)
%
% BL is the bunch length in metres
%
% see also: BunchLength
% see also: BunchLength, blgrowth

rp=ringpara(ring);
[E0,~,Vrf,h,U0]=atenergy(ring);
alpha=rp.alphac;
sigdelta=rp.sigma_E;
is6d=check_6d(ring);
circ=findspos(ring,length(ring)+1);

BL = BunchLength(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta,circ);

if ~is6d
[E0,~,Vrf,h,U0]=atenergy(ring);
rp=ringpara(ring);
alpha=rp.alphac;
sigdelta=rp.sigma_E;
BL = BunchLength(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta,circ);
else
[~,ringdata]=atx(ring,1);
[~,~,Vrf,h]=atenergy(ring);
alpha = ringdata.alpha;
E0 = ringdata.energy;
U0 = ringdata.eloss;
sigdelta = ringdata.espread;
bl0 = ringdata.blength;
BL = bl0 * blgrowth(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta);
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@swhite2401 swhite2401 Mar 24, 2023

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There are some possible optimizations here:
alpha -> mcf(disable_6d(ring))
energy, vrf, h -> atGetRingProperties
sigdelta, bl0 -> ohmi_envelope
U0 -> atgetU0(ring, 'method', 'tracking')

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@lfarv lfarv Mar 26, 2023

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On top of @swhite2401 proposal:

is6d and alpha are also available through atGetRingProperties. Asking for is6d, Vrf, E0, h, alpha and circ in one call (before the if test) minimises the number of passes through the lattice. Be careful to use the "single cell" attributes: cell_rf_voltage, cell_harmnumber, cell_length.

You could also get both bl0 and sigdelta from ringpara and completely forget BunchLength.

end
end
27 changes: 27 additions & 0 deletions atmat/atphysics/LongitudinalDynamics/blgrowth.m
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Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
function blg = blgrowth(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta)
% blg = blgrowth(Ib,Zn,Vrf,U0,E0,h,alpha,sigdelta)
%
% bunch lengthening factor due to the potential well effect
%
% Ib is the bunch current [A] (it may be a vector for multiple values)
% Zn is the longitudinal broadband impedance [Ohms]
% Vrf is the RF voltage [V] (it may be a vector for multiple values)
% U0 is the energy loss around the ring [eV]
% h is the harmonic number
% alpha is the momentum compaction factor
% sigmadelta is the energy spread
%
% see also: atBunchLength, BunchLength
%

phi=pi - asin(U0./Vrf);
nus= sqrt(-(Vrf/E0).*(h * alpha)/(2*pi) .* cos(phi));

Delta = -(2*pi*Ib*Zn)./(Vrf*h.*cos(phi).*(alpha*sigdelta./nus).^3);
Q=Delta/(4*sqrt(pi));



blg = (2/3)^(1/3)./(9*Q + sqrt(3)*sqrt(-4+27*Q.^2)).^(1/3)...
+ (9*Q + sqrt(3)*sqrt(-4+27*Q.^2)).^(1/3)./(2^(1/3)*3^(2/3));
end