34
Loss Limitations and Collimation Angelika Drees , R. Fliller, W. Fu The RHIC Collimation Sytem: history and overview RHIC Loss Limitations Operational limits Beam Dumps/Quench Limits Soil Activation Exp. Background

Loss Limitations and Collimation

Embed Size (px)

DESCRIPTION

Loss Limitations and Collimation. The RHIC Collimation Sytem: history and overview RHIC Loss Limitations Operational limits Beam Dumps/Quench Limits Soil Activation Exp. Background Summary. Angelika Drees , R. Fliller, W. Fu. RHIC Collimator Configuration. - PowerPoint PPT Presentation

Citation preview

Page 1: Loss Limitations and Collimation

Loss Limitations and CollimationAngelika Drees, R. Fliller, W. Fu

The RHIC Collimation Sytem: history and overview

RHIC Loss Limitations Operational limits Beam Dumps/Quench Limits Soil Activation Exp. Background

Summary

Page 2: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

RHIC Collimator Configuration

RHIC was originally built with a 1-stage collimation system only:

1 dual plane h/v scraper with 45 cm copper jaws, linear motion in both planes, skew motion only in horizontal1 bent crystal collimator for studies in 1 ring (yellow) only

The system was upgraded after the 2003 run because of high experimental backgrounds and gap cleaning demands. Crystal approach proved non sufficient.

Page 3: Loss Limitations and Collimation

RHIC overview: collimation system 2004 and upgrade

(capped area)

New blue 2ndary vertical collimator (v2)

New yellow 2ndary vert. Collimator (v2)

2000-2003:1-stage system including bent crystal in 1 ring

2004:Traditional 2-stage system with 2 horizontal and 1 vertical secondary collimators

2005:Traditional 2-stage system with 2 horizontal and 2 vertical secondary collimators

Page 4: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimator Section Layout

In the shutdown 2003-2004 the collimation system was upgraded to a conventional 2-stage system including new individual secondary collimators for both planes. The new system was first used in the run 2004 for both, Au and protons.

Page 5: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimator Design

cross-section of the primary collimator (dual plane)

H

V

H

45 cm copper jawsOne side onlyRotatable, positioning: few m

Page 6: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Crystal Collimation Attempt during Fill 3061 (Au)

• STAR “Yellow Halo” signal during Crystal Collimation attempt scraper is closer to the beam toward the bottom of graph

crystal is at 13.6 mm from beam center and channeling

• Scraper alone is more effective than the crystal and scraper together

… If you want to know why we pulled out the crystal and installed traditional secondaries …

Page 7: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Loss Limitations

Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour

Quench limit:magnet quenches due to accidental local losses during ramp/store => BLMsmagnet quenches at beam dump due to debunched beam => gap cleaning

Soil activation (not under radiation protection), depends on integrated yearly losses

Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time)

Page 8: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Operational Limits: Monitoring of Beam Loss/hour

dirty dumpalarm level is reset

alarm level

max.

1 hour

After every dump (operational or accidental) all RHIC loss monitors are analyzed. If dump appears to be “dirty”, i.e. unmasked loss monitors register losses above a certain level, injection into RHIC will be blocked for 1 hour (see figure).

Page 9: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Loss Limitations

Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour

Quench limit:

magnet quenches due to accidental local losses during ramp/store => BLMs

magnet quenches at beam dump due to debunched beam => gap cleaning

Soil activation (not under radiation protection), depends on integrated yearly losses

Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time)

Page 10: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

• fill 4118

Accidental Local Losses: BLM thresholds

Magnet quenches can be caused by fast (ms) type losses.=> BLM trip levels (thresholds)

• fill 4198 Continuous scraping/losses cause magnet quenches as well. Trip levels don’t help. software integration or collimators

Page 11: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimators as limiting Aperture during Store

It is difficult to maintain limiting aperture position at all times – especially during ramp!

Page 12: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimator use during the Ramp

• Losses around RHIC on 2 ramps during FY01

top: beam scraping at abort kickers

center: scrapers inserted

bottom: lattice

• Using the collimators reduced losses at abort kickers by x100

Page 13: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Loss Limitations

Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour

Quench limit:

magnet quenches due to accidental local losses during ramp/store => BLMs

magnet quenches at beam dump due to debunched beam => gap cleaning

Soil activation (not under radiation protection), depends on integrated yearly losses

Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ration in experiments and keep false trigger rate small (dead time)

Page 14: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Gap Cleaning: Motivation and Method

gap cleaning is necessary due to the extensive debunching of HI beams (quenching risk)

method:debunched beam is excited transversely (continuously during the store: 1Hz) using damping kickers

the collimation system absorbs the large amplitude particles (in addition to halo)

debunched beam should be lost in collimator area, efficiency relies on collimator performance to avoid increase of exp. backgrounds

Page 15: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Excitation frequency for Cleaning

default procedure:excite around betatron tune of bunched beam (measured automatically at the end of ramp)

optional procedure:perform automated tune scan to find resonant tune of debunched beam and excite with this frequency

Page 16: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

fill 4471, Feb. 06 2004

start of cleaning

~5 109

56 x 56

Cleaning ON vs. cleaning OFF:

yellow:cleaning off, started around 3:30 to allow clean beam dump

blue:cleaning on, debunched beam is continuously excited and absorbed by collimators

Page 17: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

1 Hz excitation on standard BLMs:

Normal cleaning levels are < 1% of tripLevel => acceptable

Page 18: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Debunching rate clearly correlated with bunch current at the beginning of the store. For 4h store length, an upper limit of 1.4*109 ions per bunch results to maintain less than 5*109 debunched beam at the end of store (for safe beam dump).

Remaining debunching with Cleaning ON:

Page 19: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Loss Limitations

Operational limit: keep allowable loss budget (radiation safety), monitored hour by hour

Quench limit:

magnet quenches due to accidental local losses during ramp/store => BLMs

magnet quenches at beam dump due to debunched beam => gap cleaning

Soil activation (not under radiation protection), depends on integrated yearly losses

RHIC has to operate such that leachate (from activated soil) cannot contain concentrations of 3H or 22Na that exceed 5% of the drinking water standard

Method: either cap the collimator area (prevent leaching) or use removable soil samples inside tunnel near collimators/dumps to monitor activation level. 22Na is easily measured.

Page 20: Loss Limitations and Collimation

Fill 4581: Au ions (100 GeV), blue gap cleaning was off

The debunched beam is lost atthe collimators:deb.rate = 2*10^7 ions/min

loss rate (total beam) is:loss rate = 3*10^7 ions/min(lost anywhere: triplets, dump ...)

total: 2-5*10^7 ions/min

Page 21: Loss Limitations and Collimation

Fill 4471, Feb. 06 2004, Au ions, 100 GeV

The debunched beam is lost atthe collimators:deb.rate = 2.3*10^7 ions/min

loss rate (total beam) is:loss rate = 3*10^7 ions/min

total (at collimators): 2.5-5*10^7 ions/min

Page 22: Loss Limitations and Collimation

Fill 4870, Mar 24 2004, Au ions, 100 GeV

The debunched beam is lost atthe collimators:deb.rate = 2.4*10^7 ions/min

loss rate (total blue beam) is:3*10^7 ions/min

loss rate (total yellow beam) is:8*10^7 ions/min

total (at blue collimators): 2.5-5*10^7 ions/min

total (at yellow collimators):2.5-10*10^7 ions/min

Page 23: Loss Limitations and Collimation

Beam losses with proton beams

Typical “bad” store:

Loss rate: 10 10^11 = 5 10^9 p/min

Page 24: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Assumptions for Soil Activation Calculation

Au Operation:

total loss/min (from gap cleaning): 2*107 ions/min

assume all is lost at collimators, 10% at new V2

-> 2*106 ions/min during the store

assume average of 100 h/week at store (best week last run)

add 0-3 106 ions/min @ v2 => 2-5*106 ions/min

proton Operation:

total loss/min (from bad lifetime store during high intensity run): 5*109 p/min

assume all is lost at collimators, 10% at new v2

-> 5*108 p/min during the store

assume average of 80 h/week at store (best avg. last run)

Page 25: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Calculate Soil Activation (Na-22) from Loss Data

Calculate for v2:given the assumptions and using an estimation with the bare collimator/no shielding (there is some concrete shielding @ v2), for Na-22, assuming 15 weeks for each of the Au and proton ions (ie. 30 weeks in total) we get:

8.7 (18) pCi/l and 11.0 pCi/lfor the case of Au-ions and protons respectively. This adds up to

19.7 (29) pCi/l (after 1year), which is just the same (or x1.5 of) the 5% drinking water limit (20 pCi/l) for Na-22.

Compare with Measurement (from soil sample): activation level at primary collimator calculated: 200 pCi/l. measured: 13 pCi/l assuming 100% of all losses at primary collimator is conservative the 15+15 weeks of running is conservative the operating efficiency is overestimated distance collimator-soil is underestimated

Page 26: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Loss Limitations

Experimental backgrounds: need ‘clean’ beams to allow good signal/noise ratio in experiments and keep false trigger rate small (dead time).

Collimator positioning should be reliable and efficient for background reduction

Time at the beginning of the store is precious because this has the highest luminosity

-> Collimation and positioning of collimators should be FAST (and precise!)

Page 27: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimation during Fill 1759 (Au)

• FY01 run has low beam current intensities

• 1-stage system

• only PHENIX benefits (some) from collimation

• there is generally no/little need for collimation during the FY01 run

Page 28: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimation during Fill 3094 in FY03 (d-Au)

• All experiments but PHOBOS benefit from collimation

• vertical scraper retraction (vert. lines) clearly raises background

• reduction rates are between 2 and 5

Page 29: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Automatic Steering Algorithm

RHIC has 5 jaws per ring, most allow both, linear motion and angular motion (to parallelize with beam). Potentially time consuming!

=> 18 degrees of freedom (+ 4 more next run)

Requires automation (3 steps):1. Move to STDBY position

(based on BPM readings)2. Move Closer to beam

(based on loss monitor feedback, serial)

3. Remove Halo/Store (based on lattice functions, parallel)

Page 30: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimation during Fill 4854 (Au) in the blue ring

Serial collimator steering (mode: Move Closer), following parallel mode does not improve backgrounds.

Vertical lines denote when each collimator moves. Background improvement approx. x6.

Note: secondary vertical collimator quite efficient.

Page 31: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Collimation during Fill 4436 (Au)

Parallel collimator steering (mode: “Store”), using lattice fct. and assumed emittances.

Vertical lines denote when collimators start and stop moving simultaneously. Background improvement approx. x10.

Note: procedure stops automatically when desired background levels are reached.

Page 32: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Fill 32541-stage

Fill 48542-stage

Compare RHIC data from 1-stage and 2-stage collimation system

Page 33: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Comparison of Background Reduction Rates

Background signal

d-Au 2003

* = 3m

Au-Au 2004

*=3m

STAR Blue 5 11

STAR Yellow 1 3

PHENIX Blue 4 11

PHENIX Yellow

1 4

Average ratio of uncollimated to collimated background for the STAR and PHENIX detectors (sensitive to beam direction) over 6 stores in 2003 and 2004. In both cases PHOBOS had a * of 3m.

Page 34: Loss Limitations and Collimation

Angelika DreesICFA-HB2004 Workshop, Bensheim, Oct. 18, 2004

Summary

Operational Limitabout 1 normal ‘fill’ /hour in uncontrolled areas

Magnet Quenchesstore/ramps: BLM thresholds pull permit (fast and slow modes)

beam dump: continuous gap cleaningSoil activation

maintain 5% of DWS (i.e. 20 pCi/l 22Na) by caps or soil sample monitoring in uncapped areas

Exp. Backgroundtraditional 2-stage collimation system achieves average background reduction of x10