# Presentation: 578072

## MULTI-BUNCH INTEGRATED ILC SIMULATIONS

**Glen White, SLAC/QMUL**
**Snowmass 2005**

## Multi-Bunch ILC Simulations

**Generate a representation of the ILC bunch train at a ‘snapshot’ in time to study the ILC machine Luminosity performance with ground motion and other error sources for different machine parameters.**
**Track 600 bunches through Linac, BDS and IP to observe dynamics of fast feedback correction (IP position and angle) + Lumi feedback and determine estimate of train luminosity.**
**Use PLACET for Linac simulation and MatMerlin for BDS (GUINEA-PIG used for IP collision).**
**Model case of tuned lattice + 1 pulse of GM (Linac + BDS).**
**TESLA TDR & ILC IR-1 (20mrad IP x-ing) BDS currently implemented.**
**Typical simulation times 60 hours+ depending on simulation parameters (per seed).**
**To gauge performance for a variety of parameters/simulation environments/machines need many CPU hours.**

## QMUL High-Throughput Cluster

**QMUL Test GRID cluster-  **_[http://194.36.10.1/cluster](http://194.36.10.1/cluster)_
**QMUL high-throughput cluster: GRID cluster development. Currently 348 CPUs (****128 dual 2.8 GHz Intel Xeon nodes with 2 GB RAM and 32 dual 2.0 GHz AMD Athlon nodes with 1 GB RAM)** . **Total available storage of 40TB. 1 Gb internal networking and 1Gb bandwidth to London MAN.**
**Will upgrade by 2007 to ~ 600CPUs and 100TB storage which will be mainly used for LHC computing needs.**

## Parallel Computing Infrastructure

- MySQL
- Database

- PHP-Web Interface

- http://hepwww.qmul.ac.uk/lcdata

- ......

## Linac Simulation

**PLACET:**
**Train enters linac with 20nm vertical emittance.**
**Structure Misalignment: 0.5mm RMS y, 0.3mrad y’ error.**
**Long- and short-range transverse and longitudinal wakefield functions included.**
**BPM misalignment: 25um (y).**
**Apply 1-1 steering algorithm.**
**Pick random seed which gives 50% emittance growth .**
**Apply y, y’ RMS Injection error.**
**Apply Inter-Train Ground Motion (K-Model).**
**Generate 600 bunches (multiple random seeds).**

**Long-range wakes have strong effect on bunch train.**
**Need to perform steering on **_**plateau**_** not first bunch.**

## BDS/IP Simulation

**MATMERLIN:**
**Inter-Train Ground motion applied (K-model).**
**Add 1.4ppm energy jitter on e****-**** bunches (simulates passage of e****-****’s through undulator).**
**Track 80,000 macro-particles per bunch.**
**Feedback (Simulink model in Matlab):**
**BPM Resolution:**** ****2********m**** ****(ANG FB)**** ****5********m (IP FB)**
**Kicker errors: 0.1% RMS bunch-bunch.**
**IP (Guinea-Pig):**
**Input macro-beam from MatMerlin BDS (non-gaussian).**
**Calculates Lumi & Beam-Beam kick.**
**Produces e****+****e****-**** pairs -> track through solenoid field and count number hitting LCAL first layer for Lumi FB signal.**

## IP Fast Feedback System

**Detect beam-beam kick with BPM(s) either side of IP.**
**Feed signal through digital feedback controller to fast strip-line kickers either side of IP.**
**Digital PI control algorithm is used for feedback algorithm.**

## IP-Angle Feedback System

**Place kicker at point with relatively high ******** function and at IP phase.**
**BPM at phase 90****0**** downstream from kicker.**
**To cancel angular offset at IP to 0.1********y’ ****level :**
**BPM required resolution ~ 2um**
**FB latency = 4 bunches.**
**Other FB locations possible:**
**Start of BDS to act as a pulse-flattener to reduce orbit error**
**Requires ~100nm BPM resolution with these optics.**

## Banana Bunches

**Short-range wakefields in accelerating cavities acting back on bunches cause systematic shape distortions:**
**Z-Y plane of a sample bunch:**

**Only small increase in vertical emittance, but large loss in luminosity performance with head-on collisions due to strong, non-linear beam-beam interaction.**
**Change in beam-beam dynamics from Gaussian bunches.**

## Banana-Bunch Dynamics

**Luminosity of a sample bunch over range of position and angle offsets.**
**Feedback strategy: wait for IP and ANG FB systems to ‘zero’ (coloured ellipse in figure)– then fine tune by stepping in y then y’ using LUMI monitor (count e****+****e****-**** hits in first layer of BeamCal) to find optimum collision conditions.**

## IP Feedback

**Single example seed shown.**
**Corrects < 10 bunches.**
**Corrects to finite ********y due to banana bunch effect.**
**Vertical Beam-Beam scan @ bunch 150.**

**5 Bunch e****+****e****-**** Int. Signal**

## Angle Feedback

**Single example seed shown.**
**Angle scan after 250 bunches when position scan complete.**
**Noisy for first ~100 bunches (HOM’s).**
**FB corrects to <0.1 ********y’**

## Luminosity

**Luminosity through example seed bunch train showing effects of position/angle scans.**
**Total luminosity estimate: L(1-600) + L(550-600)*(2820-600)/50**

## Luminosity – 100 Seeds

**ILC-IR1 350 GeV (left) 500 GeV (right) CME.**
**No improvement seen with addition of upstream FFB system.**

## Luminosity vs. IP Beam Size

**350 GeV CME**

**500 GeV CME**

**Lumi not directly proportional to IP beam spot size due to banana-beam effect.**

## Effect of Lumi-Scan (350 GeV)

**Effect of Pos & Ang Lumi scans compared with start of pulse with FB only.**
**Angle feedback gives some improvement.**

**After position scan**

**After position and angle scan**

## Effect of Lumi-Scan (500 GeV)

**Effect of Pos & Ang Lumi scans compared with start of pulse with FB only.**
**Angle feedback gives only small improvement.**

**After position scan**

**After position and angle scan**

## ILC Simulation Web Page

**Store all beam data from simulation runs online**
**http://hepwww.ph.qmul.ac.uk/lcdata**

## Summary and Plans

**Facility for parallel processing of accelerator codes set-up.**
**Shown here to test ILC performance with Fast-Feedback. **
**Final luminosity performance appears to be limited by banana-bunch shape.**
**Add full Linac + BDS alignment and inter-pulse feedback to provide full time-evolved simulation.**
**Add Crab Cavities to study crossing angle stability (requires addition of x-feedback)**
**Other lattices + Beam Parameters (@350, 500 & 1000 GeV).**
**Add Collimator Wakes.**