Getting Beam to NuMI

(It’s a worry!)

Peter Kasper

The Fermilab Accelerator Components

• Preaccelerator

H- ions from 0 to 750 keV

• Linac

H- ions from 0.75 to 400 MeV

• Booster ( 474.2 m circumference )

Protons from 0.4 to 8 GeV

Linac beam is injected over multiple Booster turns

Magnets pulse resonantly at 15 Hz

• Main Injector ( 7 x 474.2 m circumference )

Protons from 8 to 120 GeV

Can be loaded with up to 6 Booster batches

Booster Injection System

ORBMP magnets

P+

• Booster

Booster intensity given by Linac current (50-55 mA), number of turns, and “acceleration efficiency”.

Typically 10-12 turns of 5.0-5.5e11 p/turn

Limit is determined by beam loss which is not linear w.r.t. number of turns

H-

Foil

P+

P+

P+

Ring magnet Ring magnet

Typical Injection System

• MI circumference is 7 Booster circumference

• MI intensity is determined by Booster Intensity

• Can fit only 6 Booster batches since a gap is needed to allow time for the injection kicker’s field to dissipate.

Slip stacking gets round this limitation

P+

P+

Ring magnet

Injection kicker

P+ Ring

magnet

Time Structure of Beam

• Time structure of the beam is defined by:-

Booster RF 37.8 MHz at injection 52.8 MHz at extraction

Booster beam energy = 0.994 at extraction

Booster circumference = 474.2 m

Booster batch = 474.2 52.8 / c = 84 bunches length = 84/52.8 = 1.6 sec

NuMI beam = 5 x Booster batches

NuMI Protons/Year with Run IIb

• Assume Booster can deliver 5e12 p/batch

• Assume MI accelerates 6 batches

1 batch is extracted to thep source

5 batches are extracted to NuMI

• NuMI intensity = 2.5e13 p/cycle

• Assume MI acceleration cycle is 22 Booster cycles

Total cycle time = ( 22 + 6 )/15 = 1.87 sec

• Assume 1 year = 2e7 seconds ( 63% up time )

NuMI gets 2.68e20 p/year

NuMI Protons/Year with CKM

• MI cycle time is increased by 1 sec due to time required for slow extraction to CKM

• Assume MI accelerates 6 batches

5 batches are extracted to NuMI

1 batch is extracted to CKM ( nop )

• NuMI intensity = 2.5e13 p/cycle

• Assume 1 year = 2e7 seconds ( 63% up time )

NuMI gets 1.74e20 p/year

CKM gets 0.35e20 p/year

Effect of Slip Stacking

• Assumed time line ( other scenarios possible )

Inject 6 Booster batches into MI

Use RF to vary velocities of individual batches

Allow batches to overlap then recapture Takes ~2 Booster cycles

Repeat process twice more to add 5 more batches.

• Intensity to NuMI = ( 11 - 2 ) 5e12 = 4.5e13

• Cycle time = ( 22 + 11 + 32 ) / 15 = 2.60 sec

• Gain = ( 4.5 / 2.5 ) ( 1.87 / 2.60 ) = 1.29

Demands on the Booster

• The Booster is the primary limit to NuMI’s intensity

• NuMI’s demands on the Booster

5e12 p/cycle

5.8e16 p/hr ( 7.5e16 p/hr with slip stacking )

4.3 Hz rep rate ( 5 Hz with slip stacking ) 2 conditioning cycles are needed prior to

each burst ( 15 Hz ) of beam cycles

• MiniBooNE: 5e12 p/cycle, 1.0e17 p/hr, and 7.2 Hz

• To date, only the per cycle requirement has been achieved.

Rep Rate Issues

• The main magnets cycle continuously at 15 Hz

• Other systems do not

Pulsed magnets and their power supplies etc. ORBMP ( injection magnets ) MP02 and MP02 ( extraction septa )

– Overheat at 2.5 Hz– Replacement MP02 magnet is currently under test

Kickers BEXBMP ( extraction magnets )

RF cavities and their power supplies etc.

Needed upgrades have been done or are in progress

Hourly Rate is Limited by Radiation

• It is permitted to accelerate up to 1.8e17 p/hr

BUT ...

Only if you can do so without tripping the safety system

The above ground areas around the Booster are protected by ~50 interlocked radiation detectors

• There are no well defined limits to the allowed activation within the tunnel ( 1 watt/m for SNS/ORNL )

BUT ...

Maintenance issues impose practical limits

Performance vs. Time

• Performance: Detector closest to its trip point

Normalized to trip its trip point

Scaled to an intensity of 1.2e16 p/hr (Run IIb)

Performance vs.. Cycle Intensity

• Surprisingly little if any dependency

• NuMI trip point would be at 0.2

• Green points represent best performance periods

Best Performance Periods

Best Performance Periods

• Worst detectors are protecting office space

• Offices can receive no more than 100 mr/yr

• Year averages is 5 < hourly limit

Problem Areas: West Towers

• Best performance is still 8 higher than allowed at NuMI intensities ( 1.5 trip point )

Contain office areas

Located above extraction region

• Situation has greatly improved over past several years

Steel shielding added above the extraction region

Beam notched (see later) to avoid extraction losses

• To do :-

Minor shielding upgrade factor 6

Collimator system to relocate losses

The Notch

• Create a gap (notch) in the beam ( 4-5 RF buckets ) at 400 MeV ( low energy less radiation )

• Fire extraction kickers so that the current rise time coincides with the gap being inside the magnets

• Avoids intolerable high energy losses on the extraction septum

• Good for MiniBooNE or single batch injection into MI

Booster uses notch position to set the timing

• Unsolved timing problems exist for multi-batch injection

MI sets timing based on location of 1st batch

Problem Areas: East Towers

• Best performance is 5.6 higher than allowed at NuMI intensities ( just over trip point )

Contain office areas

Losses are dominated by the creation of the notch

• To do :-

Minor shielding upgrade factor 6

Use “pinger” to create notch over multiple turns Works like resonant extraction Needs R&D to make efficient at high intensity

Collimator system to relocate losses

Activation in the Tunnel

• Have started systematically monitoring activation levels throughout the tunnel

• Several 100-200 mr/hr @ 1 ft locations have been noted

• Will become 10 worse at NuMI intensities!

No focussed plan as yet

Requires controlling actual losses E.g. collimator system

Argues against extreme measures to solve above ground problems

Conclusion

• Most Booster problems will (hopefully) be solved before NuMI runs

MiniBooNE sets the most stringent limits

• Some are unique to NuMI

Notch timing issues

• NuMI’s requests cannot be met without raising the cycle intensity

7.5e12 ( 6.3e12 with slip stacking ) gives 4e20 p/yr

This will require some R&D on space charge issues

• Assistance will be greatly appreciated!