Getting Beam to NuMI (It’s a worry!) Peter Kasper

The Fermilab Accelerator Components Preaccelerator êH- ions from 0 to 750 keV Linac êH- ions from 0.75 to 400 MeV Booster ( m circumference ) êProtons from 0.4 to 8 GeV êLinac beam is injected over multiple Booster turns êMagnets pulse resonantly at 15 Hz Main Injector ( 7 x m circumference ) êProtons from 8 to 120 GeV êCan be loaded with up to 6 Booster batches

Booster Injection System ORBMP magnets P+P+ Booster êBooster intensity given by Linac current (50-55 mA), number of turns, and “acceleration efficiency”. êTypically turns of e11 p/turn êLimit is determined by beam loss which is not linear w.r.t. number of turns H-H- Foil P+P+ P+P+ P+P+ 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. êSlip stacking gets round this limitation P+P+ P+P+ Ring magnet Injection kicker P+P+ Ring magnet

Time Structure of Beam Time structure of the beam is defined by:- ê Booster RF Ô 37.8 MHz at injection Ô 52.8 MHz at extraction ê Booster beam energy   = at extraction ê Booster circumference = m  Booster batch =  52.8 /  c = 84 bunches  length = 84/52.8 = 1.6  sec ê 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 the  p source ê5 batches are extracted to NuMI NuMI intensity = 2.5e13 p/cycle Assume MI acceleration cycle is 22 Booster cycles êTotal cycle time = ( )/15 = 1.87 sec Assume 1 year = 2e7 seconds ( 63% up time ) ê 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 ê 5 batches are extracted to NuMI  1 batch is extracted to CKM ( no  p ) NuMI intensity = 2.5e13 p/cycle Assume 1 year = 2e7 seconds ( 63% up time ) ê NuMI gets 1.74e20 p/year ê CKM gets 0.35e20 p/year

Effect of Slip Stacking Assumed time line ( other scenarios possible ) ê Inject 6 Booster batches into MI ê Use RF to vary velocities of individual batches ê Allow batches to overlap then recapture Ô Takes ~2 Booster cycles ê Repeat process twice more to add 5 more batches. Intensity to NuMI = ( )  5e12 = 4.5e13 Cycle time = (  2 ) / 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 ê5e12 p/cycle ê5.8e16 p/hr ( 7.5e16 p/hr with slip stacking ) ê4.3 Hz rep rate ( 5 Hz with slip stacking ) Ô 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 ê Pulsed magnets and their power supplies etc. Ô ORBMP ( injection magnets ) Ô MP02 and MP02 ( extraction septa ) –Overheat at 2.5 Hz –Replacement MP02 magnet is currently under test Ô Kickers Ô BEXBMP ( extraction magnets ) ê RF cavities and their power supplies etc. ê 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... êOnly if you can do so without tripping the safety system êThe 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... êMaintenance issues impose practical limits

Performance vs. Time Performance: Detector closest to its trip point êNormalized to trip its trip point êScaled 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

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 ) ê Contain office areas ê Located above extraction region Situation has greatly improved over past several years ê Steel shielding added above the extraction region ê Beam notched (see later) to avoid extraction losses To do :- ê Minor shielding upgrade  factor 6 ê 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 ê Booster uses notch position to set the timing Unsolved timing problems exist for multi-batch injection ê 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 ) ê Contain office areas ê Losses are dominated by the creation of the notch To do :- ê Minor shielding upgrade  factor 6 ê Use “pinger” to create notch over multiple turns Ô Works like resonant extraction Ô Needs R&D to make efficient at high intensity ê Collimator system to relocate losses

Activation in the Tunnel Have started systematically monitoring activation levels throughout the tunnel Several ft locations have been noted Will become 10  worse at NuMI intensities! ê No focussed plan as yet ê Requires controlling actual losses Ô E.g. collimator system ê Argues against extreme measures to solve above ground problems

Conclusion Most Booster problems will (hopefully) be solved before NuMI runs ê MiniBooNE sets the most stringent limits Some are unique to NuMI ê Notch timing issues NuMI’s requests cannot be met without raising the cycle intensity ê 7.5e12 ( 6.3e12 with slip stacking ) gives 4e20 p/yr ê This will require some R&D on space charge issues Assistance will be greatly appreciated!