# Presentation: 445721

## SPEAR Overview and ID Beamline Simulation

- SPEAR overview and beam line types
- ID Beam line geometry and apertures
- Safe points and justification
- Methodology
- Parameter sensitivity
- Assumptions and justifications
- Solution
- Discussion of Control Measures

## SPEAR Layout and Beamlines

**BL12**

**Insertion Device Beamlines **

**Future BL**

**Dipole Beamlines **

**Future Beamlines**

**BL 13**

## Dipole and ID beamlines in a standard cell

**Dipole and ID beamlines in a standard cell**

- 3 Dipole Beamlines
- 8 ID Beamlines
- Beamlines BL12 in the chicane section, and BL13 in the matching straight have a different geometry
- These are the only types that will be in place during 2007-08 run when top-off operations begin
- Today's presentations cover:
- 1 ID beamline (BL9)
- 1 Dipole beamline (B8)

## SPEAR  ID Beamline

- Apertures in SPEAR chamber

- Apertures in Beamline chamber

- SPEAR Tunnel Wall

**SPEAR  ID Beamline**

- What is relevant for ABC?

## Safe Point and Point Well Downstream of Injection

**Safe Point and Point Well Downstream of Injection**

**Safe point: inner side of the  tunnel wall**
- Preliminary dose simulations and approval by Radiation Physics
- Transverse dimensions +/- 136 mm defined by the lead opening

- PWDI

- Beamline hutch – an exclusion zone.
- No personnel allowed during operations

- Safe Point

## Relevant apertures (BL9)

**Relevant apertures (BL9)**

- +59/-43 mm

- +90/-43 mm

- +50/-43 mm

- Lead Opening
- In SPEAR wall
- +/-136 mm

- Fixed Mask
- +/-43.2 mm

*Beamline-specific*

## Apertures Tolerances

**In simulations we use:**
**2mm **for apertures inside SPEAR vacuum chamber
- Supported by beam base alignment
** ****5 mm** for Fixed Masks and lead shielding in the beamline
- At SSRL, documentation and verification of BL apertures is a part of PPS process

## ID Beamline: Relevant Magnets Parameters, High-Medium Probability of change

**2. QF, QD field strength contributions from**
- Main Coils
- QMS coils
- Of-axis effects
- For simulations, only the aggregate matters
- Wide range of QF, QD values is desirable to make the ABC argument valid for a range of lattices

**1. Energy of the injected beam**
- Simultaneously scales the strength of all magnets

**3. Insertion Device**
- Gap changes
- ID trims

**4. Corrector Magnets**
- Only [N 1] corrector is used
- May activate [N 2] in the future

- These parameters can (and do) change independently. (Denoted as High-Medium probability in the previous talk)

**5. Sextupole**
- In ID beamline small effect from sextupole field – crossing too far from the center

## ID Beamline: Relevant Magnets Parameters, Low Probability of change

**2. QF, QD pole failures**
- Full or partial short of 1 pole. (Does not matter, main or QMS coils)
- Scenarios (‘left wrench’ accident) when more than 1 pole shorts

**1. Dipole, loss off current (Amp-Turns) **
- Dipoles are never adjusted in operations
- Multiple user configurations with different energies  are unlikely in the future.

**3. Insertion Device**
- Pole damage. The resulting kick should be a small fraction of a kick from a single pole.

- These changes (called ‘low probability’ in previous talk) may occur in addition to any combination from  ‘High-Medium probability’ group

**ID Beamline: Relevant Magnets Parameters, Low Probability of change**

## How to account for particles with vertical offset?

**SEXTUPOLE**
- In simulations  the total range on the positive side will include **5%** from pole field amplification
- Additional kick at X=0 is **less than 0.15 [mrad]**  for
- SF(K2=17m-3,L=0.21m)  and SD(K2=20m-3,L=0.21m)
- Small, but will be included in final ‘full scan’ simulation as a thin corrector magnet next to the sextupoles

**QUADRUPOLE**
- In simulations  the total range on the positive side will include **5%** from pole field amplification

**How to account for particles with vertical offset?**

## ID Beamline: Relevant Magnets

**C.** No particles traveling *forward* from a **point well downstream of injection** and no particles launched from  the ***safe point ***traveling *backwards* can have the same position *and* angle at any intermediate point

**Backwards from ‘Safe Point’**

**Forward from ‘Well Downstream of Injection’**

**ID Beamline: Relevant Magnets**

## Explore Strongest Single-Parameter Effects: QF Strength

- QF must be limited  on the lower side to maintain ABC
- Values of QF near zero almost violate ABC
- In present lattice ΔKQF =-20% leads to beam loss  due to integer tune crossing
- It is possible to incrementally tune the machine to a state where complete QF failure does not lead to beam loss

## Qualitative explanation

- A group of rays with narrow range of x,x’ is at risk of violating AB**C**.
- They sample reduced field in the dipole
- Benefit from focusing in QF near peak
- Suffer from defocusing in QD near peak
- Any field change that bends back-propagating beam towards positive x,  contributes to AB**C** violation (Corrector, Quadrupole Trims, Insertion Device, ID trims)

- Enter Dipole

- Exit Dipole

**Center Ray**

**At Risk Ray**

## Explore Strongest Single-Parameter Effects: QD strength

- Stronger QD contributes to ABC violation
- Can rely on power supply limit to set upper bound
- Pole failures in QD are not a concern for ID beamline
- Total simulation range 0...150% is justified by
- 	1. +30% PS limit
- 	2. +5%  off-axis amplification effect
- 	3. +5%  QMS coil

## Explore Strongest Single-Parameter Effects

- Injected Beam Energy Error

- Positive energy error makes all magnets simultaneously weaker
- The net effect is towards ABC violation
- Several interlock options are currently under consideration

## Explore Strongest Single-Parameter Effects

- Dipole Field  Error (treat as low-probability chane)

## Weaker effects: Kick from ID

- Field Integral on axis
- Pole Error (Mechanical)
- Trajectory Error
- Trim Coil

- Preliminary analysis suggests pole error effect is small
- ~fraction of single pole kick

- Can estimate trajectory effect  as

- In simulations, use **+/- 3mrad kicks** at the beginning and the end to simulate all effects together

## Weaker effects: SD Sextupole strength and pole failures

- The effect is small an virtually zero where it matters

## Putting it together. Parameter Tradeoff

- At least one continuous region in the parameter space exist where ABC is satisfied
- Finding the exact shape or proving that there are no ‘holes’ is *not required*
- Need to find (or  guess) and optimize a reasonable ‘box’,  such that ABC is satisfied everywhere inside

## Summary: practical solution ‘ box’ for ID beamline

**QF  Quadrupole K value: 1.75**
**Range for simulations: -30% ... +55%**
**To ensure this range in operations **
- Current Interlock individual QF (current and at -25%)
- Voltage interlock or other means to protect against a full short
- Pole shorts OK – no interlock required
- QMS PS interlock – optional
- Redundancy in integer tune crossing

**QD  Quadrupole K value: -1.5**
**Range for simulations: -100% ... +55%**
**To ensure this range in operations **
- Rely on PS limit
- Pole shorts, full magnet OK – no interlock required
- QMS PS interlock – optional

**Correctors**
- Range for simulations: 3mrad (twice the PS full range)
- Guaranteed by the PS limits and orbit feedback trip limit

**ID Trims + ID trajectory Error**
- Range for simulations: 3mrad at the beginning
- And 3mrad at the end of device

**Dipole failure**
**Range for simulations: -10% ... +10%**
**To ensure this range in operations **
- Rely on Stored Current Interlock
- Redundancy in Orbit Interlock

## Stress test worst case tuning against dipole failure

**Dipole error no more than -10%** is ensured by the
- Stored current interlock, in present lattice
- Closed orbit interlock – may use for redundancy

**Stored Current interlock limits dipole range indirectly**
- Must prove  for a range of lattices, tunes
- Consider response of fast orbit feedback
- Add a generous safety margin

**Facts that make 10% Error margin look comfortable:**
- 10% dipole failure is makes18 mrad kick, corrector limit is  1.5 mrad
- FOFB response moves correctors in the right direction, to keep the orbit and help maintain ABC criteria.
- Additional redundancy: FOFB corrector limit

- Is this good enough? Yes!
- The separation of 2mrad, 2mm corresponds  ~25 mm at Safe Point 12.3 m away

## FOFB response to dipole failure, simulation in present lattice (sp3v82): 

- FOFB failure scenarios
- First corrector **reaches limit**, FOFB keeps going
- First corrector **reaches limit**, FOFB stops
- Unlimited corrector strength, Orbit Interlock
**10%  failure before stored beam is lost -**
**	****safe   assumption**

- Lower Orbit Interlock trip limit from 5 mm to 1.5 mm

- COR Kick [rad]

- COR Kick [rad]

- COR Kick [rad]

## Stress test the worst case against QF Pole failures

- Is this good enough? Yes
- The separation of 2mrad, 2mm corresponds  ~25 mm at Safe Point 12.3 m away

## Full scan simulation will be completed before making the interlock trip limits ‘official’.

- SPEAR ID – simple case.
- Few parameters have predictable and quasi-independent effects on ABC
- Other beamlines types require tighter energy limit on the lower side (-3%)
- In the next talk we will present dipole beamline analysis

**Full scan simulation will be completed before making the interlock trip limits ‘official’.**
- (but we expect no surprises for ID beamlines)