# Presentation: 862991

## Radiation Safety

- Rick Donahue

- (Hiroshi Nishimura, Dave Robin, Christoph Steier, Bob Mueller, Brian Fairchild)

## Radiation Safety - Outline

- Current Radiation Practice and Results
- Description of monitoring systems
- Characterize stray radiation fields
- Issues With Top-off mode
- Injected beam loss
- Stored beam loss
- Rf trips
- Future Plan
- Further simulations/measurements
- Radiation Safety Review

## Radiation Monitoring

- Description of monitoring systems:
- 	ACTIVE
- Interlocked neutron/gamma monitors ~12  (24/7)
- Beamline 1st optics gamma monitors ~25  (24/7)
- PASSIVE
- In-close dosimeters ~50       (24/7)
- Peripheral dosimeters ~12   (24/7)
- Badged staff (not required, change in 1996) ~50

## Slide 4

## Slide 5

## Slide 6

## Slide 7

## Slide 8

## 1. In-close Dosimeters

- Gamma - 6 wks
- Neutron - 3-4 mo
- Includes Accelerator
- Physics Shifts

- B/L3.1

- B/L 4.0

## In-close Dosimeters

## In-close Dosimeters

- 4.0

- 3.1

- Sec 1 Vac nook

## Other dosimetry results

- 12 peripheral neutron/gamma monitors:
- 		nothing above background in 10+ years 		      	operation.
- 50 badged permanent staff:
- 		nothing above background (directly related to 		ALS operations) in 10+ years operation.

## Top-off Radiation Issues/challenges

**Injected Beam** – PSS now open
- Injected e- go down beamline?
- Injected e- strike the storage ring vacuum chamber near the beamlines inside ring?
**Stored Beam** - (1440 mA/shft)/(200 mA/shft) ~ _10X_
**Rf Trips **- average I from 250 to 500 mA, so ~ _2X_
**	****	****	***First is unique to top-off.*
*          **	**	**Second and third are important, *
*	**	**	**known, but not unique.*

## Inject down beamline - how bad?

## Injected e- Down Beamline?

- Simulations: backwards tracking from the beam line towards the injector (H Nishimura) - same approach taken at APS and ESRF :
- Assume stored beam(!)
- Using apertures in the beamline front end, determine the available phase space of the beamline relative to the storage ring. This determines actual starting pt.
- Beginning at the beamline, track particles backwards towards the injector covering complete beamline phase space and vary the e- energy.
- See if e- can reach the injection point
- If no condition can reach the injection point then              injected e- can not reach the beamline.

## Worst case – Beamline 2.1

- Worst case should be beamline 2.1 (being designed). No ID’s in SR01, SR02, SR03.
- Sampled phase space of b/l 2.1 exit port set by apertures up-stream and down-stream.
- Tracking done with
- realistic field representations
- Wide range of magnetic settings (quad +/-20%, etc)
- Track backwards and plot maximum distance a particle reaches as a function of energy P/P0 (injected/stored).

## “Inject” here

- “Inject” here

- Calculate here

## BL6.1 - identical to BL2.1

| Line | T(rad) | T(deg) | dT(rad) | Point | Xo(m) | dX(m) | Z(m) |
| --- | --- | --- | --- | --- | --- | --- | --- |
| N | 0.240517 | 13.780577 | 0.000000 | 0 | 0.334870 | 0.000000 | -0.000790 |
| A | 0.326554 | 18.710122 | 0.086037 | 3 | 0.392060 | 0.057190 | 0.000960 |
| B | 0.242500 | 13.894194 | 0.001983 | 1 | 0.320070 | -0.014800 | 0.000010 |
| C | 0.236502 | 13.550535 | -0.004015 | 4 | 0.284490 | -0.050380 | 0.000010 |
| D | 0.200081 | 11.463770 | -0.040436 | 2 | 0.278820 | -0.056050 | 0.000010 |

## Tracking - starting point

## Slide 20

## Slide 22

## Superbends – Unique to the ALS

- Of the 36 dipoles, there are three Superbend magnets that have individual supplies.
- Could a magnet fail (quench) shortly before injection causing electrons to pass down the beam pipe?
- Stored beam loss occurs when Superbend reaches 99% of nominal field.
- Field must be 80% nominal to go down beamline (100% = 10o, 80% = 8o).
- Time for the Superbend to go from 99% to 80% of its field after a quench is > 0.5 seconds.
**Plenty of time to halt the next injection pulse**
- Conclusion – Not an issue

## Changes to Radiation Safety System (RSS)

## Summary - e- down beamline

- Summary: cannot inject e- down b/l assuming:
- Redundant interlock on stored current (≥*10* mA).
- Redundant interlock on energy match (< *10 *%).
- Future Plans:
- Analyses assume 2.1 worst case. Need to prove this with more simulations
- Begun forward tracking studies.
- Tracking study results are convincing but not always intuitive. Need independent study to verify results.

## Top-off Radiation Issues/challenges

**Injected Beam** – PSS now open
- Injected e- go down beamline?
- Injected e- strike the storage ring vacuum chamber near the beamlines inside ring?
**Stored Beam** - (1440 mA/shft)/(200 mA/shft) ~ _10X_
**Rf Trips **- average I from 250 to 500 mA, so ~ _2X_
**	****	****	***First is unique to top-off.*
*          **	**	**Second and third are important, *
*	**	**	**known, but not unique.*

## Increased Bremsstrahlung from Injected Electrons

- Difficult to calculate. Requesting permission from DOE for PSS-open tests. Measure under abnormal injection conditions.
- Horizontal scrapers in BTS line.
- Booster area well shielded
- Limit/localize lost injected particles
- Vertical scrapers (next section) in the Storage Ring
- Consider interlocking beamline ion chambers.
- All beamline gas bremsstrahlung Pb shields (ID and BM) are 10” thick.

## BTS Injection

- Scrapers

## Stored Beam Losses and rf Trips

**Stored Beam** - (1440 mA/shft)/(200 mA/shft) ~ _10X_
**Rf Trips **- average I from 250 to 500 mA, so ~ _2X_
- _Approach:_
- Simulate particle loss when rf trips. Predict where losses occur. Compare w/ reality/history.
- Investigate losses at “Jackson Holes”  as a function of fixed aperture heights.
- Consider installation of “semi-fixed” scrapers at optimum JH locations.
- Locally shield JH scrapers.

## Slide 30

## Modified Henderson Plug in Jackson Hole

##  Stored Beam Losses & rf Trips

- Simulation Studies (H. Nishimura): Can e- beam losses be localized/controlled?
- Lattice errors are assumed to produce realistic orbit errors.
- While the beam is circulating normally, the RF tripped instantly.
- The beam keeps circulating by loosing energy due to synchrotron radiation.
-  The 6-dim routine is used to calculate the radiation loss properly.
-  The interactions between the beam and the unpowered cavities are neglected.
- During the tracking, apertures are checked at each JH location and also at both ends of each straight section chamber.
- This process was repeated for 100 random seeds.

## Tracking with apertures

- Beam gets lost vertically on the narrow gap chamber

- 4

- 8

- 12

## Slide 35

## JH Scrapers

- Sector 1

- Sector 3

## Jackson Hole Scraper

## Storage Ring and rf Trip Losses

- Summary -
- JH scrapers can be used to localize losses.
- Complete simulations to determine optimum JH scraper locations. Determine effect on lifetime.
- Consider scraper design where position can be “changed” but then “fixed”.
- Provide local shielding close to JH scrapers.
- If all else fails...

## ... add local shielding.

- ... add local shielding.

## Future Plans

- Monitor radiation when injecting with PSS opened on Beamline 4.0 (Early 2005).
- Install BTS and JH scrapers. Show they can be used to localize losses (Early 2005).
- Radiation safety review (Mid 2005)
- Installation of RSS interlock systems (Before top-off operations)

## Slide 41