Damped emittance and right time of flight

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Dhital
Posts: 14
Joined: 24 Oct 2018, 14:11
Location: NY

Damped emittance and right time of flight

Post by Dhital » 27 May 2020, 17:55

Hi Michael,

What is the right way to set up Synchrotron Radiation and Quantum Excitation effect in a ring? I m trying to estimate equilibrium damped emittance from tracking in a dual-energy storage ring. I am using the following:

&alter_elements name=*, type=CSBEND, item=N_KICKS, value=150, allow_missing_elements=1 &end
&alter_elements name=*, type=KSEXT, item=N_KICKS, value=200, allow_missing_elements=1 &end
&alter_elements name=*, type=KQUAD, item=N_KICKS, value=150, allow_missing_elements=1 &end

&alter_elements name=B*, type=CSBEND, item=SYNCH_RAD, value=1 &end
&alter_elements name=B*, type=CSBEND, item=ISR, value=1 &end
&alter_elements name=Q*, type=KQUAD, item=SYNCH_RAD, value=1 &end
&alter_elements name=Q*, type=KQUAD, item=ISR, value=1 &end
&alter_elements name=S*, type=*SEXT*, item=SYNCH_RAD, value=1 &end
&alter_elements name=S*, type=*SEXT*, item=ISR, value=1 &end

Is this the right way to set up? Does it possible to include IBS (Intra-Beam Scattering) effect during elegant tracking? I mean (Radiation damping + Quantum Excitation + IBS = Equilibrium Emittance / Energy Spread) is possible?

Next is about the right time of flight. We have two rings connected by RF structures which first accelerates the beam and in the next pass decelerates the beam.I use elegant to calculate the right time of flight. Taking single particle single turn and p_central for low energy ring I calculate the revolution time using sdds2stream file.w1 -col=Ct. I repeat the process for high energy ring taking p_central for high energy ring. Then the total revolution time is sum of revolution times for each ring. Is this the right way?

In my simulation, RF cavities lengths are zeros, i.e., l=0.0 in rfca element. I have used matrix element (EMATRIX) of zero length to reduce M56 value. I am not taking these zero elements during my calculation of revolution times thinking that these zero length elements does not affect the revolution time.

I am having some trouble with particle stability with radiation on in my system. If RF frequency is not right then that results in a momentum offset which finally leads towards instability.

Any suggestions will be appreciated.

Sincerely,
Bhawin

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Damped emittance and right time of flight

Post by michael_borland » 10 Jun 2020, 17:49

Bhawin,

You are doing the right thing for synchrotron radiation tracking. If you want to include IBS, you need to insert IBSCATTER elements in the lattice. Generally for rings a single IBSCATTER at the end should be enough.

Using the Ct parameter is also the right way to find the time of flight and set up the rf cavities. I'm not sure what more to say about the instability without seeing more details, however, with acceleration/deceleration you have to ensure that there is still phase focusing.

--Michael

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