R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 1 MEBT Lattice Optimization Ryoichi Miyamoto (ESS) For Beam Physics Group, Beam Instrumentation Group, and Collaborators in ESS-Bilbao July 4 th, 2012 ESS AD Beam Physics Internal Review

Outline MEBT lattice and beam dynamics – Short (2011) vs. long (May 2012) MEBTs – Modification of the May 2012 MEBT – End-to-end simulation with the modified MBET MEBT collimation – How to decide collimator locations – An idea of the collimator locations – End-to-end simulation with the collimators R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 2

Input distribution We use an input distribution from an RFQ simulation where the input to the RFQ is 5σ Gaussian (pessimistic). Fluctuation of the emittance and Twiss parameters important? R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 3 5σ KV

Comments on the un-captured particles The RFQ simulation actually includes the un-captured particles. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 4

Loss w/ and w/o the cut Most of the un-captured particles seem lost by the end of the DTL. No loss in the SC part for both case but some difference in the HEBT. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 5 w/o cut w/ cut

Distributions out of the DTL w/ and w/o the cut Distributions become quite similar by the end of the DTL. The computation accurate for the un-captured particles? R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 6 w/o cut w/ cut

MEBT lattice and beam dynamics R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 7

From a short to long MEBT R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 8 In CDR From the May 2012 baseline, the MEBT was extended to include Fast chopper Beam instrumentation Collimation Buncher Chopper Chopper target

Short vs. long MEBTs: envelope The envelopes of the whole beam. The RFQ and DTL are also different. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 9

Short vs. long MEBTs: output distribution The long MEBT has visibly large transverse halos. The short MEBT has a large “arm” in the longitudinal plane (due to the strong space charge?). R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 10 ShortLong

Short vs. long MEBTs: emittance and halo For the long MEBT, emittances and halos are spoiled in some planes but the overall situation doesn’t look so bad. The ugly output distribution is still a concern -> try to make a modification. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 11 Short Long

MEBT modification Goals – Improve the longitudinal distribution. – Improve the transverse distributions (taking into account the collimation). – Reduce the emittance and halo growths (if possible). – Reduce the beam loss (if possible). Strategy – Add one more buncher cavity. (4 cavity case was also considered but a good solutions hasn’t been found.) – Maintain reasonable beam sizes to avoid the strong space- charge effect and too large beam losses. – Trial and error! R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 12

New vs. old long MEBTs: envelope and loss R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 13 Old New

New vs. old long MEBTs: output distribution Quadrupolar modes smaller in all 3 planes! R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 14 OldNew

New vs. old long MEBTs: emittances and halos Sensitivity to the mismatch and lattice errors?? R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 15 OldNew

New vs. old long MEBTs: distribution out of the DTL The distribution going into SC sections is better with the new MEBT. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 16 OldNew

New vs. old long MEBTs: distribution out of the HB The distribution out of the MEBT affects the one out of the linac. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 17 OldNew

New vs. old long MEBTs: emittances and halos Loss in the DTL is also improved but no loss in the SC sections in both cases. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 18 Old New

MEBT collimation R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 19

How to decide collimator locations Sample particles in the normalized phase space: – 0.5σ, 1.0σ, …, 4.0σ – 30°, 60°, …, 360° Space charge deforms the distribution R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 20 Into MEBTOut of MEBT Into MEBT Out of MEBT Samples particles of 3σ and above at the end of the MEBT are left. Not all samples above 3σ at the entrance ends at above 3σ at the end. An effective collimation requires weights on specific angles even for a Gaussian distribution.

How to decide collimator locations (2) For the short MEBT, one collimator per plane was good enough. A pair separated by 90 deg is not always idea. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 21

“Phase advances” of each sample particle (H) R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 22

“Phase advances” of each sample particle (V) The difference among particles is larger on the vertical plane in this specific case. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 23

An idea of the collimator locations for the new MEBT Good locations found in the second space for BI. 6kW × 0.25% (~3σ) = 15 W. (Feasible ??) The influence hardly seen on the halo if placed as far as ~4σ. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 24 Between quads possible?

Output distribution and halos w/ and w/o collimators R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 25 w/ow/

Transverse emittances are slightly improved as well. The influence on the loss in the SC sections haven’t been studied yet. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 26 w/o w/ Distribution out of the linac and halos w/ and w/o collimators

Conclusions In the May 2012 baseline, the MEBT was extended from ~1.2 m to ~3.5 m to include the fast chopper, diagnostic devices, and collimators. Due to concern with the shape of the output distribution, the MEBT has been modified and one configuration with better beam dynamics property was found. It was seen that the modified MEBT improves the beam dynamics throughout the linac. (Compatibility with the mechanical constraints shall be checked by the collaborators in the ESS-Bilbao.) Following the SNS experience, the MEBT collimation scheme has been studied. It is observed that the collimators could reduce the halo throughout the linac but their influence on the loss in the SC section haven’t been clarified yet. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 27

Plans and open questions Study the sensitivity of parameters in the MEBT to the mismatch and lattice errors. Perform the beam loss study to understand how the performance of the MEBT and collimator influence the loss in the SC sections. Criterion for the collimation design ?? Tuning scheme of the MEBT ?? R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 28

Halo definition (Wangler’s) The spatial profile parameter (Kurtosis): The halo intensity parameter (extension to 2D) The normalization “2” to make the “KV” = 0 and “Gaussian” = 1. R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 29 Distribution into the DTL (from a simulation of the RFQ by A. Ponton)

Distribution evolution in the MEBT (V) The same analysis for the vertical plane R. Miyamoto, MEBT Lattice Optimization, ESS AD Beam Physics Internal Review 30 Into MEBTOut of MEBT Into MEBT Out of MEBT