# Presentation: 801321

## LHC Injector ChainSimulations & Experiments

- _J.-F Ostiguy_ and M. Popovic
- Fermilab

## People     

**CERN: G. Arduini**, **C. Carli**, M. Chanel, F. Gerigk,               M. Martini, G. Rumolo, E. Shaposhnikova
**FNAL: M. Popovic**, **J.-F. Ostiguy**,              C. Ankenbrandt,   E. Prebys, A. Burov
**SNS:  **S. Cousineau
- Others are welcome !

## The CERN LHC Injector Complex

## Linac upgrade

-  The current LHC injector chain, based on the existing 50 MeV    proton linac,should be sufficient to deliver the beam intensity    required by the LHC to meet its design luminosity.
-   There is little margin remaining, if any, to increase beam brightness     beyond the nominal design. Luminosity improvements will depend     on the ability of injector chain to deliver higher intensities.
-   At the moment, the bottleneck is presumed to be beam    instabilities and/or emittance degradation in the booster associated    with space-charge. To alleviate the problems, the currently favored     upgrade path would entail replacing the 50 MeV proton linac with    a 160 MeV H- linac.
-   If space charge is the main culprit, it is reasonable to expect the     upgrade to be successful; however, other bottlenecks may be lurking.

## Aims

**Common Interest:**
- Characterization and simulation of space charge effects,  mitigation strategies.  The expectation is that  baseline designs for both the CERN LHC and the FNAL injector upgrade(s)  can be validated  or, if  necessary,  design modifications can be identified.
- Space charge codes benchmarking, instabilities
**Specific  Interest for CERN**:Assistance with the use of ORBIT, including code modifications and improvements, if necessary.
**Specific Interest for FNAL**:
- Operational experience and experiments with multiple RF systems
- Resonance mitigation strategies in the CERN PSB

## Priority

-    Priority will be given to simulation of the CERN injector. We expect collaboration with existing, on-going efforts at FNAL to understand injection issues and intensity limitations in proposed upgrades (e.g. Project “X”)

## Experiments

- Experiments in CERN Booster at 50MeV and 160MeV, possibly taking advantage of the dual harmonic RF system to observe signature space-charge effects.
- Possible experiments in the FNAL Booster at 400MeV coordinated with on-going efforts.

## Tasks

- Common
**Simulations (ORBIT) of CERN Booster at 50MeV and 160MeV**
- Experimental validation of ORBIT simulations, especially its ability to correctly simulate space-charge effects both at injection and during acceleration.
***The CERN Booster offers interesting experimental conditions in that regard: slow ramping and a second harmonic system. Using the RF system to vary the bunch longitudinal profile may allow more direct observation of “signature” space-charge effects****.*
- Working point studies
- Identification of possible beam instabilities
-      **FNAL specific:**
- Evaluation of  a second RF harmonic system
- Evaluation of dual-harmonic magnetic ramp
- Evaluation of  bunch-to-bucket transfer process
- Coordination with on-going simulations efforts at FNAL: Booster at 400MeV,  MI  and Recycler at 8 GeV

## Workshop

-      CARE-HHH BEAM'07
-     Mini-Workshop on LHC+ Beam    Performance: 1-2   October
-    Mini-Workshop on Upgrades of LHC   Injector Complex: 4-5 October

## There is interest ... 

- -----Original Message-----
- From: Gianluigi Arduini [mailto:Gianluigi.Arduini@cern.ch]
- Sent: Thursday, August 16, 2007 11:33 AM
- To: Milorad Popovic
- Subject: Beam 07 WS
- Hi Milorad,
- Please find attached the latest version of the BEAM07 workshop on the LHC
- Injector upgrade from 1 to 5/10.
- Do you (and/or Francois) intend to come?
- It would be great as this would give us the opportunity to discuss about the
- simulations and experimental data as mentioned to you by Chruistian in his
- last e-mail
- Looking forward for your reply
- Cheers
- Gianluigi

## Current Performance

- The first two accelerators (Linac2 and PSB) almost meet the ultimate beam characteristics. Three out of the 4 PSB rings are able to deliver 2.04×1012 protons within transverse emittances of 2.5 mm.mrad. In the absence of beam loss, this converts precisely into 12 bunches of 1.7×1011 protons, which is the ultimate goal.
- The sophisticated beam manipulations in the PS are well adjusted and reproducible. However, because of beam loss at multiple places in the cycle, the maximum intensity at ejection to the SPS has never exceeded 1.4×1011 p/b (within transverse emittances of 3 mm.mrad).
- Also because of beam loss, the SPS, after scrubbing to reduce the secondary electron yield of the vacuum chamber, is only able to bring up to 450 GeV the nominal type of beam made up of 4×72 bunches with 1.15×1011 p/b (within transverse emittances of 3.5 mm.mrad).

## Bottlenecks

- Space charge at injection in the PSB and in the PS. The present solution of pulsing the PSB twice just allows meeting the LHC ultimate requirements out of the PSB, _**but it forces the PS to keep the first injected beam for the duration of a full PSB cycle (1.2 s) in the presence of a very large space charge**_. Other known difficulties are linked to electron clouds and impedance in the PS and SPS. Moreover, the fact that the maximum beam energy of the PS is uncomfortably close to transition in the SPS is a suspected source of troubles.
- Another important observation, especially obvious in 2006, is _**that the reliability of the accelerators is degrading**_, mostly because of the age of large and expensive hardware (examples of problems encountered in 2006: aggravation of vacuum leak in the Linac2 tanks, isolation of main PS dipoles, rotor failure in the PS generatrix, water leaks on the main SPS dipoles...).