Progress ofbunch compressor simulations

for PITZ

Transparencies presented by A.Oppelt

at the LAOLA-Workshop in Wismar

8.6.2012

Running ASTRA with more longitudinal bins compared to the results presented end Nov. 2011 → no visible differences

1. Update of ASTRA simulations

Longitudinal phase space at z = 5 m(Gun +10 deg / Booster +40 deg)

40 bins 280 bins

2. Slight modification of the dogleg design

Use first approach BC layout with some changes

• dogleg with compression factor C = 4 (from RB)• R56 = (-)0.044 (from C and momentum chirp)

and some other BC parameters adjusted

D1

D2

Q1

Q2

Q3

S1

S2

L=1m

• use optimized dogleg setup from Nov. 2011 (with the problem of unrealistic quad settings)

• use ASTRA particle distribution as inputfor elegant tracking

• no re-optimization of quad settings• no matching into dogleg applied yet

3. Elegant simulation results

Longitudinal phase space distributions(elegant tracking results) in the dogleg and at the end of the dogleg

@ dogleg entrance (elegant input generated from ASTRA output):

3. Elegant simulation results (ctd.)

Conclusion from the elegant tracking results:• first simulation of dogleg was performed with elegant• bunch compression works• non-uniform compression of the bunchlets due to slightly non-linear chirp

at dogleg entrance

Remaining issues and possible solutions1. re-optimize dogleg layout (dipole parameters, drift lengthes) → open2. reduce compression in dogleg to 50% and apply two of them → open

(setup can be used as ‘normal D-shape chicane’ when switching off the quads)3. run ASTRA for 5 different single beamlets (to be combined later) → done4. optimize dogleg for each beamlet seperately (cross-check dogleg capability) → open5. invert chirp of the bunch by choosing inverse accelerating phases

and try to use a normal D-shape chicane (4 dipoles) → done

1st bunchlet: 10 pC (40 long. bins)

Comparison of long. phase spaces at z=5m (after booster, start of matching section)

Autophasing vs. fixed phase(relative to on-crest phase) (defined by optimum phase(Gun +10 deg, Booster +40 deg) of 5 bunchlet pulses)

→ only small differences in chirp, energy spread, …

4. Single bunchlet ASTRA simulation results

2nd bunchlet: 30 pC (100 long. bins)

4. Single bunchlet ASTRA simulation results (ctd.)

3rd bunchlet: 50 pC (160 long. bins)

4. Single bunchlet ASTRA simulation results (ctd.)

4th bunchlet: 70 pC (220 long. bins)

4. Single bunchlet ASTRA simulation results (ctd.)

5th bunchlet (probe pulse): 10 pC (280 long. bins)

4. Single bunchlet ASTRA simulation results (ctd.)

Idea of RB: use inverted chirp and compress bunch in D-shape chicane (4 dipoles)

Problem: space charge destroys bunchlet structure already in the gun

5. Bunch compression in a chicane

Longitudinal phase space at z = 3 m (booster entrance) from ASTRA

Gun +10 deg Gun -10 deg

→ chirp generation has to happen in the boosterBut: non-linear phase space will induce problems during the compression

→ to test: on-crest acceleration in the gun

Longitudinal phase space at z = 5 m from ASTRA

Gun +10 deg Gun + 10 deg Gun -10 degBooster +40 deg Booster -40 deg Booster -40 deg

5. Bunch compression in a chicane (ctd.)

Design of the 4-dipole D-shape chicane: R56 = 0.058, α=76.5 deg, …

5. Bunch compression in a chicane (ctd.)

Conclusion from the elegant tracking results:• very first parameter setup realized and

tracking with elegant performed• bunch compression works• non-uniform compression of the bunchlets due to

non-linear chirp at chicane entrance

6. Elegant simulation results

Longitudinal phase space distributions(elegant tracking results) in the chicane and at the end of the chicane

@ chicane entrance (elegant input generated from ASTRA output):

7. Conclusions

• at a first look compressing of a 5-bunchlet pulse while keeping its desired pulse structure seems to be complicated to impossible

• optimized compression (no over-compression) may lead to acceptable results• a number of open tasks has to be studied

→ work will continue !