Design of BNL Extended EBIS Vacuum System and Development of Compact Linear ZAO NEG Pumping Module

S. Kondrashev, E. Beebe, B. Coe, J. Ritter, T. Rodowicz,

R. Schoepfer, L. Smart, S. Trabocchi

October 2, 2020

Outline

➢Design of BNL Extended EBIS vacuum system

➢Development of compact linear ZAO NEGpumping module

➢Development and implementation of in-situ method of pumping speed measurements

➢Design of ZAO NEG linear pumping system

➢Summary

Extended EBIS Upgrade

• Increase the intensity of the Au32+ ion beams by 40%–50% to 2.1 ⋅ 109 Au32+

ions/pulse at the booster ring entrance

• Generation of intense beams of polarized 3He2+ ions with up to ∼ 5 ⋅ 1011

ions/pulse for the RHIC and the future electron–ion collider.

Extended EBIS Setup

Approach to Extended EBIS Vacuum System Design

Approach is based on common principles of UHV system design and

previous experience with Test EBIS and RHIC EBIS:

• High temperature bake (1000 ⁰C for 1 hour) of all stainless-steel parts

to drive hydrogen out of bulk material

• In-situ bake out of whole vacuum system (at least 250 ⁰C for 24 hours)

• Differential pumping between ion trap and high outgassing areas – e-

gun, collector and gas injection unit

• Backing turbo molecular pumps (TMPs) by other TMP

• Using only UHV compatible materials

• No trapped volumes

• Using new ZAO NEG modules in ion trap area and in other locations

• Using WS2 plating of all screws instead of silver-plated screws

Schematics of Extended EBIS Vacuum System

T1 backed by TP1

T2 backed by TP2

T3, T4, T5 and T7

backed by TP3

T6 and T8 backed by

scroll pumps

Combination of turbo pump and ZAO NEG cartridge everywhere

Only one cryo pump

Differential Pumping – E-gun Side

Differential pumping baffle

Differential Pumping – Gas Injection Section

Differential Pumping – Collector Side

Top view Side view

New ZAO Getter Alloy

• ZAO (Zr-V-Ti-Al) getter became commercially available from SAES Getters in the form of sintered discs about 4 years ago

• According to SAES Getters (Enrico Maccallini’spresentation, June 2017, BNL) ZAO demonstrated:

➢Larger sorption capacity for all active gases

➢Higher pumping speed

➢Ability to withstand more reactivation cycles

➢Discs are more robust (higher embrittlement limit)

➢Generate much less micro particles

Single ZAO NEG Module Activation

Pumping Speed Measurement Setup

Electromagnetic pulse valve

RGA (SRS RGA200) – Pumping Speed Measurements

RGA – NEG+TMP vs NEG Only (Hydrogen)

What Is NEG Pumping Speed at Cartridge Location?

Can One See if NEG is Saturated Using RGA?

H2

Pumping Speed – RGA vs Cold Cathode Gauge

Pumping of nitrogen by TMP (NEG was not activated)

RGA - STMP ≈ 150 l/s

Gauge - STMP ≈ 170 l/s

𝑃(𝑡) = 𝑃(𝑡 = 0) ∙ 𝑒−𝑉𝑆 ∙𝑡

P(t) – pressure vs time at RGA location,

S – pumping speed at RGA location,

V – volume of vacuum chamber

TMP specified pumping speed

for N2 – 250 l/s (pump CF port)

Pumping speed in the chamber

taking into account conductance

- 160 l/s

Good agreement with both RGA

and CC gauge measured values.

Design of ZAO NEG Linear Pumping System

ZAO NEG linear pumping system will be placed under tray supporting drift tubes

Tray supporting drift tubesHeat shield

ZAO NEG linear pumping system

Pumping System Assembly

NEG Activation Test (3 Modules)

• Two step activation process

(recommended by SAES Getters):

1-st step – pre-heating to 300 ºC

for 30 minutes

2-d step – heat to 550 ºC for 1 hour

• Above 550 ºC over whole pump length

(570-620 ºC thermocouples readings)

for 1 hour and 15 minutes

• Heating power – 1085 W (70 A/15.5 V)

Partial Pressures during NEG Pre-heating to 300 °C

H2O

Partial Pressures during NEG Activation

Temperatures in the end of activation cycle:

NEG – 540-630 °C, Heat shield – 435 °C, Drift tube tray – 290 °C

RGA Spectra Before and After NEG Activation

Pumping speed measured for hydrogen after NEG activation:

• Only NEG linear pumping system (3 modules) – 644 ± 19 l/s

• Both NEG pumping system and TMP - 815 ± 25 l/s

Dependence of Pumping Speed on NEG Temperature

Linear ZAO NEG Module for Ion Trap within First Solenoid

Summary

• Advanced vacuum system has been designed for BNL Extended EBIS upgrade

• Key elements of vacuum system are different ZAO NEG pumping modules

• ZAO NEG modules are very attractive for EBIS applications due to large sorption capacity, high pumping speed and transverse compactness

• In-situ method of pumping speed measurements has been developed and applied to ZAO NEG modules characterization

• Both RGA and ion gauge can be used for pumping speed measurements

• Developed method can be used to monitor in-situ NEG conditions in EBIS or any other UHV device

• Linear pumping system based on 2 and 3 ZAO NEG modules has been designed, build, tested and will be used for Extended EBIS Upgrade project

Acknowledgment

Thanks to:

Daniel McCafferty (retired) for excellent technical support

Anatoli Zelenski and Grigor Atoian for providing pulse gas valve