Loss maps of RHICLoss maps of RHIC

Guillaume Robert-Demolaize, BNL

CERN-GSI Meeting on Collective Effects, 2-3 October 2007

Beam losses, halo generation, and Collimation

OutlineOutline

IntroductionIntroduction

Required tools – a new aperture model

Measurements vs. predictions

Conclusion

IntroductionIntroduction Main objective is to try to reproduce RHIC loss mapsreproduce RHIC loss maps, using the

tracking tools developed for LHC collimation studies (extended version of the SixTrack code, see talk by S. Redaelli) for the purpose of code benchmarking. These codes can:

◦ provide longitudinal beam loss mapslongitudinal beam loss maps for the Blue and Yellow rings,

◦ predict the cleaning inefficiencycleaning inefficiency of the collimation system,

◦ give an estimate for the maximum allowed intensitymaximum allowed intensity in the machine.

By reproducing real RHIC conditionsreal RHIC conditions in the tracking code, one can then compare the predictions with “live” BLM measurements“live” BLM measurements.

Studies presented in the following focus on the code accuracy to code accuracy to predict the halo loss locations along the machinepredict the halo loss locations along the machine.

The RHIC machineThe RHIC machine

collimation regions

Au79+ - Au79+ FY07

Number of bunches

103 - 111

Ions per bunch 1.1 x 1011

Estore [GeV] 100

β* [m] 0.8

εN [µm] 17 – 35 (at store)

Lpeak [cm2.s-1] > 30.0 x 1026

p+ - p+ FY06

Number of bunches

111

Protons per bunch

1.35 x 1011

Estore [GeV] 100

β* [m] 1.0

εN [µm] > 25

Lpeak [cm2.s-1] 35.0 x 1030

Collimation at RHICCollimation at RHIC RHIC collimators only intercept one side of the beam per transverse planeone side of the beam per transverse plane

(LHC = 2 parallel jaws per plane); RHIC primary jaw is also L-shaped:

RHIC primary scraper LHC horizontal collimator

The full RHIC betatron collimation system is made of 1 primary and 3 1 primary and 3 secondary secondary collimators per beam in IR8 (LHC = 4 primary and 16 secondary collimators per beam in IR7).

RHIC collimation layout

Pin diodes are installed at least 1m downstream of each collimator to get a direct loss signal when setting their position.

An additional secondary vertical collimator is located one arc downstream for both Blue and Yellow (not used).

OutlineOutline

Introduction

Required tools – a new aperture modelRequired tools – a new aperture model

Measurements vs. predictions

Conclusion

Required toolsRequired tools

Numerical models for the RHIC lattice and beam are already already available via MAD filesavailable via MAD files. A “Teapot” aperture model was created for previous RHIC collimation studies (PhD thesis by R. Fliller).

Problem: encoding languageencoding language for that model is significantly different from the one used for LHC tools; data was also missingmissing for the latest machine changes => need for a => need for a dedicated RHIC aperture model !!dedicated RHIC aperture model !!

The L-shaped primary jaw also requires a specific treatment in specific treatment in SixTrack SixTrack to allow collimation in both planes at the same time.

CPU resources (time & disk space) should allow tracking of tracking of large particle ensembleslarge particle ensembles (at least 200k particles in parallel jobs)…

Creating the aperture Creating the aperture modelmodel

The new aperture model consists of:

◦ a spreadsheet with the transverse dimensions for all transverse dimensions for all lattice elementslattice elements,

◦ an appropriate softwareappropriate software to superimpose the recorded trajectories of scattered particles with the datasets from that spreadsheet.

Since the original aperture model was generated, some elements were either moved, removed or replaced => any => any and all modifications must be included !!and all modifications must be included !!

The various databases only list the transverse dimensions at the beginning or the end of a given element => one => one needs the complete description along that element !!needs the complete description along that element !!

From the LHC aperture From the LHC aperture model…model…

=> the idea is to generate a similar model for the two beam lines => the idea is to generate a similar model for the two beam lines of RHIC.of RHIC.

To obtain accurate beam loss maps, a detailed LHC aperture detailed LHC aperture programprogram was developed. It allows locating proton losses with a precision of 10 cm10 cm.

S. Redaelli et al.

… … to the RHIC aperture to the RHIC aperture modelmodel

Generating the new model was split into 3 steps:

◦ step 1: get all the latest files from every source of aperture database (incl. mechanical drawingsmechanical drawings).

◦ step 2: generate the new aperture database with 10 cm bins already implemented => allows to apply “real shape” of all => allows to apply “real shape” of all elementselements.

◦ step 3: run a cross-reference with MAD-X model of the machine: the aperture model MUSTMUST match the simulated lattice.

As for the LHC studies, collimator tanks are considered as drift considered as drift spacesspaces in the aperture model, since the corresponding aperture restrictions are applied in the scattering routines of the tracking.

Some elements required extra attention when modeling…

Sample case: DX magnetSample case: DX magnet

top viewtop view

side viewside view

OutlineOutline

Introduction

Required tools – a new aperture model

Measurements vs. predictionsMeasurements vs. predictions

Conclusion

Measurements vs. Measurements vs. predictionspredictions

Live measurements data come from the 2005 proton run:

Parameter Achieved value

Injection energy [GeV] 24.3

Store energy [GeV] 100

Transverse norm. emittance at store [µm]

20

Working point at store [Qx / Qy] 0.690 / 0.685

Protons per bunch 2 x 1011

Bunches per ring 111

Peak Luminosity [cm2.s-1] 10 x 1030

β* in STAR and PHENIX [m] 1.0

β* at other IPs [m] 10.0

Dedicated datasetsDedicated datasets Fill #6981, 4/28/2005, Blue beam:

Collimator movementsCollimator movements Positions and PIN diode signals once Blue beam is at store:

Loss monitors signalLoss monitors signal

horizontal jaw movement

BLM signal at the STAR BLM signal at the STAR triplettriplet

=> RHIC collimators are designed to lower beam loss induced => RHIC collimators are designed to lower beam loss induced backgroundbackground

RAMP

INJECTION

STORE

Horizontal jaw movementHorizontal jaw movement

zoom in collimation region (jaw movement from LVDT signal)

Horizontal jaw movementHorizontal jaw movement

zoom in STAR triplet area (jaw movement from LVDT signal)

Simulated loss map – horizontal Simulated loss map – horizontal jawjaw

Tracked 240000 particles, impact parameter = 5 µm, 20 turns

=> about 59%59% of impacting protons are absorbed at the collimator (blue spike)

Zoom in the collimation Zoom in the collimation regionregion

Compare loss locations with live measurements:

Notes on simulated loss Notes on simulated loss mapsmaps

Results from SixTrack simulations only list locations of direct proton losseslocations of direct proton losses, i.e. elements in which the transverse coordinates of tracked protons get larger than the available mechanical aperture

=> comparison with live BLM measurements need to take the “zero” signal take the “zero” signal into accountinto account (when collimators are out).

The aperture model allows to spot proton losses with a 10 cm resolution10 cm resolution, while in the machine loss monitors are only installed at predetermined predetermined locationslocations, mostly looking in the horizontal plane horizontal plane and are color blindcolor blind (i.e. measure and display losses coming from both beam lines at the same time)

=> for later studies with the full system, Blue and Yellow simulated losses Blue and Yellow simulated losses should be put on the same plotshould be put on the same plot to allow proper analysis and predictions

Lattice studied was generated from MAD-X model with the ideal STAR and ideal STAR and PHENIX PHENIX ββ** values (1.0 m) values (1.0 m) and measured tune values (QQXX = 28.690, Q = 28.690, QYY = = 28.68528.685). Other real machine conditions like orbit perturbations and orbit perturbations and ββ--beatingbeating can be derived from logged datasets and inserted into the tracking model.

Zoom in the STAR triplet Zoom in the STAR triplet regionregion

Compare loss locations with live measurements:

Vertical jaw movementVertical jaw movement

zoom in collimation region (jaw movement from LVDT signal)

Vertical jaw movementVertical jaw movement

zoom in STAR triplet area (jaw movement from LVDT signal)

Tracked 240000 particles, impact parameter = 5 µm, 20 turns

Simulated loss map – vertical jawSimulated loss map – vertical jaw

=> about 59%59% of impacting protons are absorbed at the collimator (blue spike)

Zoom in the collimation Zoom in the collimation regionregion

Compare loss locations with live measurements:

Zoom in the STAR triplet Zoom in the STAR triplet regionregion

Compare loss locations with live measurements:

OutlineOutline

Introduction

Required tools – a new aperture model

Measurements vs. predictions

ConclusionConclusion

ConclusionConclusion The simulated lattice features some of the magnet non-linearities and magnet non-linearities and

measured tune valuesmeasured tune values but does not include beta-beating and real beta-beating and real chromaticity values chromaticity values

=> should be included in the future.=> should be included in the future.

During the tracking in SixTrack, particles with large amplitudes (i.e. close to usual collimator openings) get lost close to the triplet magnetlost close to the triplet magnet in STAR

=> similar behavior as the one seen in live BLM signal similar behavior as the one seen in live BLM signal !!

Predicted loss locations mostly correspond to what is observed on real mostly correspond to what is observed on real time BLM signaltime BLM signal (when integrated): downstream of collimators and at the front end of the STAR triplet magnet. One might want to reconsider reconsider the precision level of the aperture model the precision level of the aperture model to get better comparisons with live measurements.

Future studies should focus on the loss levels at the collimators and the corresponding rates at the low β* insertions, using both beams and the full RHIC collimation system

=> predictions of the most efficient settings for collimator openings !!=> predictions of the most efficient settings for collimator openings !!