Hall B Beamline and ControlsHovanes Egiyan

Jefferson Lab

Outline

Main Hall B Beamline Components

Beam Tuning Procedure

HV System in Hall B

Temperature Sensors

Summary

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Expected g-Beam Parameters

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Vacuum through out the system on a way of primary and scattered electrons, and bremsstrahlung photons.

The target and the Si-tracker installed inside a vacuum enclosure.

Adequate beam diagnostics for beam profile, position and current measurements and monitoring.

Parameter Requirement Unit

Ee 2254,4446, 5542 MeV

Eg 0.2 – 0.95 x Ee

δEg/Eg ~10-3

g-flux 107 - 108 s-1

Flux Instability < 10 %

2 σX ~3 mm

2 σY ~3 mm

2H01Location

Magnets

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Tagger PS Torus

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2C24Location

Not to ScaleControlled by

MCC

MCC controls Hall B vacuum systems

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arp

Each magnet in Hall–B has its own power supply, controllable from the Hall B counting house. Tagger magnet is controlled by MCC.

For Frascatti magnets (chicane) we would need to use CLAS Minitorus power supply.

Power Supplies

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Beam PositionsExisting nA BPMs

Owned by the Accelerator Division, we get EPICS PVs Monitor electron beam position (precision ~20 mm) Monitor electron beam current Hall B BPMs are in three location:

o For all runs: 2C21A, 2C24A, o For electron runs only: 2H01

Harp scans for electron and photon beams Position relative to previous scans

Photon beam profiler during photon beam runs Usually it is in the shadow of the collimator.

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Beam Quality Harp scans

At 2C21 (before Moeller target) e-beam At 2C24 (@ radiator) e-beam At 2H01 (@ converter) e- and g-beams Dynamic range of 105

What to do with the HPS detectors during harp scans? Determines the X, Y and the diagonal beam profile.

Upstream and downstream beam halo counters PMTs or scintillation counters positions around the beam pipe to measure the

beam halo. Upstream counters before CLAS target, may not be used for HDICE. Downstream counters after the target.

Beam offset monitor Circular array of thin fibers around beam.

Photon collimator Collimate the photon beam to desired size before pair spectrometer (e.g. 3 mm).

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Harps

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Third wire will be added to existing Hall B beam scanner

• Two wires move into beamline at ~0.5 mm/sec speed.

• Some detector downstream see increased counting rates.

• Scalers read out and recorded together with the motor position.• Synchronization can

be important for high precision scans.

• Harp scans need to be synchronized with scalers.

Photons

Electron

Example scan at 2C21

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sx=140mm sy=43mm

Harp Scan Optimized Optics

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sx=280mm sy=18mm

Scalers

Hall B uses EPICS to monitor scalers: 16 channel 40MHz Joerger VSC16 VME scaler module

o simple hardware and sofware 32 channel 200MHz SIS3801 VME scaler module

o 64K FIFOo 2 latching bits

JLab new FPGA-based discriminator modules and FADCs also have scalers, but currently there is no EPICS interface Combines discrimination and scaler functionality. Work in progress for EPICS interface for the JLab discriminator

modules. May not have EPICS software on time for tests.

It would be nice to have “scalers” on SVTs, if they can be set up.

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Beam Intensity Synchrotron Light Monitor (SLM)

Needs to be calibrated against BPM Orbit dependent calibrations

BPMs can measure electron beam current. Main measurement for photon runs.

Faraday Cup measures the beam current during electron runs. Does not see beam during photon runs. Will probably be blocked for electron runs with high currents.

Variations in scaler rates from detectors can indicate changes is intensity or quality changes.

Hall B has application to measure “60Hz” component of the beam intensity variation using scaler or F-Cup info. We require 60Hz component be < 20%. “60Hz” has not been a problem recently.

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Main EPICS GUI

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Initially Hall-B beam always tuned by MCC first. Directed into the tagger dump using Tagger Magnet After MCC finished we verify the beam quality using Harp Scans at 2C21 and 2C24

o Halo/Peak < 10-4

o X- and Y- widths on harps less than 200 mm

For photon runs the g-beam is tuned through the collimator to the target. Centering on the target Centering the collimator

For electron runs the tagger magnet is degaussed, and the electron beam is tuned to the Faraday Cup. We may check the beam profile with 2H01 harp. We center the beam on the target (MCC does the steering).

Continuously monitor BPMs, scalers and periodically perform harp scans.

Moeller runs may be required for circularly polarized g-beam. Beam tuned into the tagger dump, Moller target is inserted into e-beam upstream of the

tagger. What is the impact on the HPS detectors? What needs to be done during Moeller runs?

Beam Tuning

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Three types of HV mainframes are currently used in Hall B LeCroy chassis were originally used for CLAS PMTs

o Currently being phased out Transitions to CAEN SY1527 chassis for CLAS is underway.

o Main choice for CLAS12 upgrade CAEN SY527 chassis are used for CLAS Drift Chambers and LAC

o EPICS interface for VxWorks over CAENET exists (Sergey B.)o Interface is relatively slow.

All PMT HV are controlled and monitored from EPICS

EPICS Alarm Handler is used for trip notifications.

HV parameters saved and restored to/from text files. No real archiving.

High Voltages

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CLAS IC colorimeter required stable temperature.

Instrumented with resistance temperature detectors (RTD).

Readout is done using NI FieldPoint network module.

LabView-to-EPICS interface was a problem sometimes, but it works with IC. It is a good idea to go to direct EPICS interface for ECAL, but

extra work.

SVT temperature monitoring in EPICS may require work. Interface between EPICS and SVT DAQ should be created. Undesirable feature of having to run DAQ for HW monitoring.

Temperature Sensors

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Krister Bruhwel, Nerses Gevorgyan and myself will work on integrating the HPS and existing Hall B control systems. We are familiar with Hall B setup, and less familiar with

HPS requirements. Involving more manpower in controls would be useful.

Need input from detector components Description of the hardware and its functionality Parameters to monitor and control, and how Existing software/firmware description Parameters that need archiving Alarm conditions Software interlocks Backup/restore requirements

Request

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Summary Hall B beamline instrumentation and procedures can accommodate HPS

during planned tests in spring. Use Frascatti magnets with Minitorus PS for chicane during electron running.

Beamline components have necessary controls and software. Minor modifications may be needed.

Having an early run plan will help identifying missing pieces. Need information on controls requirements. Try CAEN board for SVT with our EPICS driver for SY1527. Some procurement/manufacturing may be needed for controls, e.g. motors.

New controls needed for: SVT scans need controls software. Target control, may be similar to CLAS eg2-run solid target system. Scans? Temperature sensor monitoring on SVT (ECAL) need to be developed. HV and LV controls may need attention. Software interlock strategy for SVT protection is unclear.

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Thank You

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