Specifications for NuMI Primary Beam Instrumentation

1. Specifications for NuMI Primary Beam Instrumentation

2. Outline • Types of beam monitoring needs covered by P. Lucas. • For each type of monitoring provide quantitative assessment of functional requirements. • From these develop specifications for each type of primary beam instrumentation • A general consideration is to utilize existing instrumentation designs - when these are compatible with requirements.

3. Beam Intensity & Spill Requirements • NuMI operational requirements are for the highest possible intensity which can be provided from the Main Injector, in parallel with targeting for Pbar production. For current machine function, the first Booster batch would be sent to AP0, with remaining 5 batches or ~ 80% of MI intensity extracted to NuMI. • For NuMI system design requirements, we utilize an intensity limit of 4x1013 protons / pulse at 120 GeV, with a 1.87 sec. cycle time. • Beam is extracted with single turn kicker extraction. Use of single turn extraction is driven by excessive unavoidable beam loss with originally planned resonant extraction. • Significantly reduced intensity is required for beam tuning, and near detector rate studies. Viable lower intensity capability is 2.5x1011 protons/ pulse with one Booster batch, or 3x109 protons / bunch.

4. Intensity Monitors • Specified are two Torroid (beam current transformer) units of standard design. Features include: • Absolute intensity measurement to ~ 3% • No material in beam • Bandwidth ~ 4 MHz • Plan also to have intensity outputs for beam position monitors (described later)

5. Beam Loss Monitoring • NuMI requirements are for a very large fraction of the available Main Injector intensity over a period of several years. For each MI accelerator cycle, 5 of 6 batches will be sent to NuMI. • Transport of this intense beam is in a tunnel located in the protected groundwater aquifer region. • Shielding of the primary beam transport, as is done for the target hall, would be cost prohibitive. • These constraints lead to a requirement for rigorous monitoring and control of beam loss during primary transport. Detailed MARS modeling of beam loss modes indicates the need to control NuMI high intensity beam loss to ~ 10-4 of the transmitted intensity.

6. Loss Monitor Requirements • The single most important NuMI primary beam instrumentation requirement is to provide complete loss monitor coverage including: • sensitivity to all possible beam loss modes • redundancy for demonstration of full loss coverage • continuous checks for loss monitor function (crate high voltage, heartbeat sensor for a comprehensive set of monitors) • calibrated response, with a means of regularly checking monitor calibrations • dynamic range over a continuous spectrum of fractional beam loss from 10-5 of the high intensity beam to a full beam loss

7. Loss Monitor Selection • Three types of loss monitor units have been in general use in our beam systems. Two of these address NuMI loss monitoring needs, and are the types specified: • Lab standard sealed units (Argon gas), with new electronics designed for MI transfer lines. Thirty-five of these units are specified.. One issue to address is the need for dynamic range over a continuous spectrum of fractional beam loss from 10-5 of the high intensity beam to a full beam loss These will provide the precision monitoring of beam loss points, with monitor mounting in a uniform manner on beam transport magnets. • Long loss monitors. These are heliax cables with ArCO2 gas flow. Use is to provide continuous total loss monitor coverage for carrier pipe and pre-target tunnels. An issue to address is continuous checks for loss monitor function (crate high voltage, heartbeat signal)

8. Beam Profile Monitoring • Beam profile monitors are essential to understand beam-line optics, emittance, momentum spread, etc. • Existing types of external beam profile monitors (SWIC’s, Multiwires) obtain a profile distribution by passage of beam through precision planes [horizontal and vertical] of wires. • For high intensity NuMI operation, beam loss from interactions in the monitor material preclude continuous use of either monitor type in the beam. Also monitor degradation from continuous beam exposure would be a concern. • The alternative is to use non-interacting beam position monitors (BPM’s) for continuous monitoring of beam centroid position. Then the profile monitor material exposed to the beam must be sufficiently thin to enable diagnostic insertion into the beam.

9. BeamProfile Monitors • Monitor wire plane spacing requirements are compatible with existing designs for either SWICS or Multiwires: • 1 mm along beam transport • 0.5 mm for targeting lineup. Beam centroid determination can be as good as 1/12 of the wire spacing for a Gaussian beam distribution. Affecting absolute accuracy are alignment and fiducialization errors, plus errors in monitor insertion into the beam • Either type of monitor uses the same 48 channel scanner for signal processing • Remote capability for controlling in/out motion of monitor is needed, as well as a robust signal indicating monitor position status. • A robust in/out motion is needed to maintain measurement accuracy. This indicates positioning reproducibility to < 50 microns.

10. SWIC’s vs Multi-wires • SWIC’s (Segmented wire ionization chambers) have been the external beam standard for beam profile / position monitoring since the mid 1970’s. • Multi-wires (Secondary emission signal output) were developed for the collider transfer lines in the 1980’s. • Each has comparable wire spacings, identical scanner readout systems, switchable gain for intensity range, and can be remotely positioned in or out of the beam. • Previous multi-wire positioning system has not been robust. New upgraded design effort (G. Tassotto, R. Ford). • Existing SWIC’s were available for use, while new multi-wires must be built.

11. Fundamental Multi-wire Advantages • For NuMI primary beam, Multi-wires have fundamental advantages over SWICS: • Material in beam. • Vacuum SWIC ~ 1.5 x 10-3 fractional beam loss • Multiwire 8 x 10-5 fractional loss The ability to put SWICS in the beam at high intensity would be severely restricted. Also, the multi-wire provides an appropriate thickness target for absolute calibration of beam loss monitors in the loss region of interest. The SWIC interacts too much beam for a credible calibration of beam loss in the < 10-4 region. • Accuracy of measurement for beam tails. SWIC profiles for tails of the beam distribution are strongly biased; multi-wire distributions are much more accurate. • Current SWICdesign is not well matched to the vacuum levels needed for NuMI - organic seals, mylar windows,etc. Multi-wires are designed for lines with better vacuum than milli-Torr levels. • Hence, the specification of multi-wires for NuMI profile monitors.

12. Beam Position Monitors • An essential feature of NuMI beam position monitors is that they must be always active and in place for measurement whenever beam is present. • Of existing detectors this feature is met only by non-interacting beam position monitors (BPM’s), as used in the accelerators. For similar reasons, these are also used in the MI to AP0 transport lines. • While not providing information re. beam profile, BPM’s give both beam intensity and position of the charge centroid of the beam. • Differences in NuMI BPM requirements beyond those used in current MI transfer lines are of two types, and are driven by the NuMI need for very good beam control. • Sub-millimeter functional accuracy (resolution plus stability) Specification is for 0.2 mm along the transport, and 0.05 mm for target line-up. • Need for reliable detector function calibration

13. BPM Specifications (continued) • For each BPM detector, beam position and intensity should be provided for each Booster batch of the extracted spill. • Provision must be made to avoid the possible use of stale BPM data. • A goal is dynamic range meeting position accuracy specifications for an intensity range of 2.5 x 1011 to an upper limit of 8 x 1012 protons / batch. • The most important requirement is maintaining accuracy needs for high intensity operation. If conflict exists between this and dynamic intensity range, priority should be given to high intensity measurement precision. As example, current log-amp electronics provides large dynamic range, but at the expense of functional measurement accuracy. • An engineering prototyping effort is underway (C. Drennan) to evaluate alternate BPM electronics designs.

14. Beam Instrumentation Stations • A total of seven beam position / profile instrumentation stations are located along the NuMI primary transport. Each station has horizontal and vertical BPM’s, and a multi-wire (H & V planes), except for the most upstream station, where limited transverse space allows only BPM’s. • Horizontal and vertical correctors are positioned in close proximity to the beam instrumentation to the extent feasible. • These locations are shown graphically, along with beam transverse size, in the following two figures. • A total of 35 sealed beam loss monitors are positioned on transport magnets to provide full geometrical coverage of beam loss conditions (confirmed with MARS runs).

15. System Function of Instrumentation • To provide the capability for the precision beam control needed for NuMI, a comprehensive system approach is needed in the use of beam instrumentation. Examples include: • The use of multi-wires as targets to provide absolute calibration of beam loss monitors for low beam loss levels. • Regular precision calibration of BPM function with use of multi-wires. • Quantitative monitoring of BPM intensities in comparison to Torroids as a functional check for both devices. • Closed loop auto-tune beam position control to enable position corrections without the typical beam losses produced in the correction process. • A comprehensive beam extraction permit system to preclude sustained high beam loss situations, and many individual beam cycle problems. • Beam loss budget monitor system to provide verification of clean primary beam transport.

16. Auto-tune Beam Control • Automatic computer controlled correction of small (few mm) beam position excursions, using MI correctors and beam position monitors. • Corrections are applied for the full beam line at one time, eliminating the beam loss during correction process which is common with manual beam tuning. • Needs always active beam position instrumentation - BPM’s. • More severe requirements on BPM function than for many applications. • In previous usage of auto-tune beam control, computer controlled tuning was initiated when positions from nominal deviated by the following amounts: • Switchyard: along beam transport - 400 microns (0.4 mm) septa lineup - 200 microns (0.2 mm) • KTeV: along beam transport - 1000 microns (1.0 mm) (used wire profile detectors) target line-up - 50 microns (0.05 mm) • NuMI (projected): along beam transport - 1000 microns (1.0 mm) target line-up -250 microns (0.25 mm)

17. Upcoming Reviews • Instrumentation - Part 2: - Aug. 14 Engineering design / construction progress Note: changed from original date of Aug. 6 • Beam Extraction Permit System - Aug. 17