vacuum system design impact on cryomodulesthis presentation will focus on a few specific vacuum...

This material is based upon work supported by the U.S. Department of Energy Office of Science under Cooperative Agreement DE-SC0000661.

Michigan State University designs and establishes FRIB as a DOE Office of Science National User Facility in support of the mission of the Office of Nuclear Physics.

Paul GibsonVacuum & Installation Group Leader

Vacuum System Design Impact on Cryomodules

This presentation will focus on a few specific vacuum areas which are potential sources of gas loading on cryomodules• (1) The MEBT connection to the first cryomodule

• (2) The standard Diagnostic Box used adjacent to every cryomodule

• (3) The Charge Stripper system and its impact on adjacent matching cryomodules

• (4 – overall) The Fast Valve layout

Outline

QWR 0.041QWR 0.085

HWR 0.29 HWR 0.53

HWR 0.53

RFQ

ECR

Charge stripper 13

2

P. Gibson, March 2014 Workshop on Cryomodule Maintenance - 15, Slide 2

Requirements for vacuum systems connecting to cryomodules are defined» FRIB Driver Linac Vacuum Requirements (T31201-SP-000031)

• Warm section (between cryomodule) ready for beam: From a vacuum requirement point of view, a cryomodule and its adjacent warm section(s) are ready for beam when under cold conditions:» 1. Warm section pressure < 5.E-9 Torr with gate valves open and all cavities conditioned.

» 2. If warm section pressure > 1.E-7 Torr, gate valve should be closed

• Cold-warm transition (between cryomodule and other section) vacuum: Pressure < 1 E-8 Torr

Vacuum calculations have been done with cryomodule gate valves CLOSED• Assure there is no pumping REQUIRED from the cryomodule to meet the

requirements (highly conservative)

“SRF Standard” processing will be applied to all vacuum boxes adjacent to cryomodules (minimize particulates)• Same cleaning processes applied to all vacuum components in the accelerator

Beamline components should be capable of 125 degree C minimum bakeout• Baking done as pre-processing or in situ as needed to meet requirements

Vacuum Requirements for Cryomodules Defined


Medium Energy Beam Transport (MEBT) couples directly to first cryomodule• Ion Sources are ~ 43 m away

from the first cryomodule

MEBT Requirement: < 1E-8 Torr

Requirements met using:• Conservative outgassing value

for Radio Frequency Quadrupole (RFQ) source term; 5E-8 Torr» RFQ valve open to the MEBT

• Unbaked desorption value

• Cryomodule valve closed

• Pumps sized for MEBT bunchergas loads

MEBT Does Not Impose a Gas Load on the first Cryomodule [1]

~ 7.25 m


MEBT Does Not Impose a Gas Load on the first Cryomodule [2]

MEBT reaches required vacuum with cryomodule valve closed

RFQ Cryomodule


Cryomodule requirements dictate ultra-high vacuum handling and “particulate free” methodology (SRF Standard) on installations adjacent to cryomodules

» Cleanroom techniques for assembly / installation

» Pump down / venting using clean pump carts

Diagnostic Box used throughout accelerator» 3 3/8” Conflat flanges and 40 mm I.D. (@ cryomodules - 57)

• SRF Standard applied to these installations

» Similar box in transport regions, 47.5 mm I.D.

Diagnostic Box installations have:» 75 l/s diode ion pump

» Cold cathode gauge

» Metal sealed right angle valve

» Beam Position Monitor (BPM)

» Halo Monitor Ring

.

Diagnostic Box Does Not Impose a Gas Load on the Cryomodules [1]

Diagnostic Port(Shown for reference)

BPM

A mock-up is planned for this

system to study the accessibility

and the installation processes

required


Diagnostic Box Does Not Impose a Gas Load on the Cryomodules [2]

Diagnostic box reaches required vacuum with cryomodule valves closed

CryomoduleCryomodule


Lattice drawing layout of Charge Stripper area (upstream section)• “Optical dog-leg” prior to nearest matching cryomodules (4 – 50 magnets)

• Fast valves prior to nearest matching cryomodules

• Diagnostic box with ion pump at exit of charge stripper

• Large crosses allow substantial differential pumping capacity

Charge Stripper Does Not Impose a Gas Load on the Matching Modules [1]

~6.8 m from Charge Stripper Valves to Matching CM Valves

(similar downstream configuration)


Vacuum model• Matching Cryomodules (CMs) upstream and downstream from Charge Stripper

• Boundary conditions: CM valves closed

Outgassing sources:• Thermal desorption from walls

• Lithium vapor» Liquid lithium in vacuum chamber

» Lithium sticks to walls at room temperature

Requirements:• < 1E-8 Torr near matching CMs

• < 1E-6 Torr near Lithium (Li) stripper

Lithium diffusion model:• Li vapor pressure at the Charge Stripper cylinder set to 1E-5 Torr

» Provided by F. Marti

• Two cases considered:1. Simulation assuming Li sticks to walls outside of charge stripper module (realistic)

2. Simulation assuming Li is non-sticking, relying on pumps only (pessimistic)


Model provided by P. Guetschow



Matching CM Matching CM



Requirements



Fast Valves Protect Cryomodules

8 fast valves located in the accelerator to protect cryomodule vacuum» Baseline design is using VAT model 75 Fast Valves; 40 mm I.D.

• Fast valve can sense and close in < 10 ms (per VAT)

» Fast valve trigger will pull the fast MPS which inhibits the beam in ~ 35 us

» Multiple valves will trigger based upon a single sensor reading• Sensors in folding segments 1 and 2 will trip both entry and exit fast valves

• Sensors upstream and downstream of the charge stripper will trip both fast valves

• A fast valve trigger will close isolation valves on cryomodules in the vicinity as well as nearby beamline isolation valves via the control system

• Sensor threshold is programmable and for FRIB is planned to be 1x10-7 Torr

• Fast valve trigger is planned to be disabled via the control system when beam is off to avoid inadvertent trips


Calculations show that cryomodules do not experience gas loads from the warm / transport sections

Fast valve systems are located throughout the accelerator to protect cryomodules

Summary


Backup


Front End Vacuum Calculation Results [1]


Split into 3 vacuum models:• Pre-RFQ = Extraction Region (ER) + CSS + LEBT

• RFQ

• MEBT (from RFQ exit to first cryomodule in LS1)

RFQ

VENUS

Source

ARTEMIS

SourceCSS

LEBT

MEBT

Front End Vacuum Calculation Results [2]


Vacuum covers the entire FRIB facility but this talk focuses on ASD and vacuum in relation to cryomodule interfaces

Accelerator Vacuum Layout and Preliminary Design Complete [1]


Accelerator Vacuum Layout and Preliminary Design Complete [2]

Lattice Model

Requirements

Vacuum Model

Folding Segment 2• SC dipoles

• RT optical elements

• 1 matching module

• 1 beam dump

Molflow+ Results

Establish

Basis of

Estimate

(BOE)

Similar models provided for

vacuum calculations by:

B. Durickovic – FRIB


ASDRequirements specified

• FRIB Driver Linac Vacuum Requirements (T31201-SP-000031)» Prepared by the FRIB Accelerator Physics Group,

» Includes all systems from ion sources to the gate valve prior to the ESD target chamber

• Requirements basis• Vacuum estimates for the FRIB driver linac (T31201-TD-000157)

» Prepared by F. Marti and Y. Zhang

• Layout• Expanded Lattice File

(T31201-CM-00022)

• Design• ASD Vacuum System Design

(T31210-TD-000240)

Vacuum Requirements Defined

*Table from FRIB Driver Linac Vacuum Requirements


Cold cathode – Inverted magnetron vacuum gauge• 1x10-11 torr capability

• 2 ¾” CF connection

• At least 125o C bakeout with magnets and connectors attached• Depending upon mfg

• MKS 422 and Agilent IMG-300

Metal sealed right angle valve• UHV metal to metal seal closing, leak rate < 2x10-10 cc/sec

• Bakeable to > 250o C• Depending upon mfg

• 2 ¾” CF connection

• MDC, Agilent, VAT, Nor-Cal

Extra 2 ¾” CF port for fast valve sensor or additional gauge• Convection enhanced pirani considered

» Not installed since available on pump cart during pumpdown and qualification

Diagnostic Box Design Complete [1]


65 l/s diode ion pump initially selected• 75 l/s for diode – 65 l/s for triode

• Rated 50,000 hours at 1x10-6 torr• Equals ~ 5,000,000 hours at 1x10-8 FRIB

operating pressure > 570 yrs

• Lifetime is proportional to pump treatment

• Residuals are H2, CO, and N2

• 6” CF connection; SHV connector

• Mfgs: Gamma, Agilent, Duniway

Diagnostic Box Design Complete [2]

For Agilent

VacIon Plus

75 Diode


The plot is for an “average section” of beam transport line ~ 5.5 m long and 47.5 mm I.D. with diagnostic boxes at each end• The average pressure changes minimally with pumping speed

• Indicates that the system is heavily conductance limited

Ion Pump Pumping Speed vs. Average Pressure Analyzed


Accelerator System• Protect the superconducting accelerating and matching modules from a

beam induced vacuum event (failure)» Worst case assumption is a sonic pressure wave; 340 m/s

» Fast valve can sense and close in < 10 ms (per VAT)

» Therefore sensors must be place at least 3.4 m from fast valve or as far as possible based upon layout• This is accomplished in most areas

» Multiple valves will trigger based upon a single sensor reading• Additional sensor in the middle of the folding segments will trip both entry and exit fast valve

• Sensors upstream and downstream of stripper area will trip both fast valves to isolate system

» A fast valve trip will pull the fast MPS which inhibits the beam in < 35 us

» A fast valve trip will close slow valves on cryomodules in the vicinity as well as any nearby beamline isolation valves through the controls system

» Sensor threshold is programmable and for FRIB is 1x10-7 torr

» Fast valve trigger is disabled via the control system when beam is off

Fast Valve Requirements


vacuum system design impact on cryomodulesthis presentation will focus on a few specific vacuum...

Documents