Notes

Outline

Diagnostics in the Fermilab Proton Source (Linac + Booster) Eric Prebys FNAL Beams Division

Outline Description of the Fermilab Proton Source New Challenges which we face Current Diagnostic Tools *Injected Energy Bunch Shape Orbit Transverse Beam Profile *Coupled Bunch Oscillation Detector *Tune Measurement *Beam Loss Future Tools Ramp Monitor

The Fermilab Accelerator Complex

Preac(cellerator) and Linac

Booster

Primary Consumers of Protons “stacking” (last 2 years):  Proton source provides protons to Main Injector, where they are accelerated to 120 GeV for antiproton production – typically 7E15 p/hr max. MiniBooNE (last 2 months): 8 GeV protons delivered directly to neutrino production target – typically 1.5E16 p/hr max, but baseline is 7 times that!!! NUMI (2004?): protons delivered to Main Injector, which will accelerate them to 120 GeV for neutrino production – wants at least 5E16 p/hr while MiniBooNE and stacking are running.

Proton Timelines Everything measured in 15 Hz “clicks” Minimum Main Injector Ramp = 22 clicks = 1.4 s MiniBoone batches “don’t count”. Cycle times of interest Min. Stack cycle: 1 inj + 22 MI ramp = 23 clicks = 1.5 s Min. NuMI cycle: 6 inj + 22 MI ramp = 28 clicks = 1.9 s Full “Slipstack” cycle (total 11 batches):         6 inject + 2 capture (6 -> 3) + 2 inject + 2 capture (2 -> 1) + 2 inject + 2 capture (2 -> 1) + 1 inject + 22 M.I. Ramp ---------------------- 39 clicks = 2.6 s

Summary of Proton Ecomomics

What Limits Total Proton Intensity? Maximum number of Protons the Booster can stably accelerate: 5E12 Maximum average Booster rep. Rate:  formerly 2.5Hz, currently 2 Hz, soon 7.5 Hz (NUMI only) Maximum number of booster batches the Main Injector can hold: currently 6, possibly go to 11 (NUMI only) Minimum Main Injector ramp cycle time (NUMI only): 1.4s+loading time Losses in the Booster: Above ground radiation Damage and/or activation of tunnel components

Fundamental Change in Focus During collider operation (“stack and store”), fairly long periods of reduced proton source performance could be tolerated with no significant impact on the physics. Proton source has not been a limiting factor in the Fermilab physics program in a very long time. For the new generation of neutrino experiments, physics is directly related to the total number of protons delivered.

One Year Ago… The only real measure of Proton Source Performance was the delivered flux.  In particular, No measurement of energy or phase of beam going from Linac to Booster. No way to measure Booster tune without dedicated study time. No systematic way of studying losses.

Typical Booster Cycle

Injected Energy and Phase

Injected Bunch Shape Resistive Wall Monitor ¾ of the way around the ring. Problem: not yet used in a systematic way.

Orbit System of 48H+48V BPM’s, which can be read out as a function of time for the whole ring each cycle.

Beam Profile: Ionization Profile Monitor

Injected Beam Profile (“Flying Beam”) Beam sweeps over fixed wire as it returns from injection “bump”. Use secondary emission signal vs. time to get beam profile. Use to calibrate IPM (in progress)

Coupled Bunch Detection Individual Mode Lines (typically ~80 MHz) mixed down and monitored through the acceleration cycle. Problem: No automated alarm. System being redesigned.

Tune Measurement (first time in many years!) Horizontal plane pinged at 2 ms intervals. Do FFT on one of the BPM’s For the moment, coupling to vertical plane is sufficient to measure that too!!

Measured Beam Energy Loss ~ 60 “Tevatron-style” ionization monitors: 100 second running average now our primary figure of merit for Booster performance. Part of Booster permit system. Differential proton loss is measured using toroids.  Weighted by energy to produce a “Beam Energy Lost”.  Loss rate in Watts calculated using a 5 minute running average updated every minute. Part of Booster permit system (current limit 400 W).

Tunnel Loss Limits

Differential Loss Monitor Example: Collimators in – Collimators Out

Summary of Booster Limits

Above Ground Radiation Main worry are the high occupancy areas in the Booster towers. Shielding has been added both in the tunnel and to the first floor of the Booster towers. Offices have been moved to reclassify some worrisome areas. Radiation is monitored by a system of “chipmunks” positioned around the Booster. Part of the Booster permit system.

Best Performance + Shielding + BooNE Intensities

Problems with Fast Cycle Time Existing Fermilab alarms and limits system works only with DC values. There are several hundred important proton source measurements which vary over small time scales (usec to msec). At present, the only way to monitor these is either examining them by hand or using discrete samples in the alarms and limits system. -> Usually, problems can only be found indirectly by looking at performance. E.g. recently it took about a week to track down a low level RF problem which would have been obvious if we were looking at the right thing. People who should be working to improve Booster performance spend all their time keeping it running.

Ramp Monitor Program A dedicated task which will loop over all the ramping devices. For each device, it will calculate a running average curve for each type of Booster cycle (pbar production, MiniBooNE, etc), and calculate an RMS. Deviations from this curve will be logged, and possibly set alarms. It’s envisioned that this program will greatly aid in debugging problems, and may well migrate to other parts of the accelerator.

Ramp Monitor Progress

Summary Proton source performance has become important after many years of station keeping. We have made great progress in the last year or so in improving and automating diagnostics. Much work remains to be done!!!